Production of a milk oligosaccharide mixture

Abstract

Production of a milk oligosaccharide mixture The present invention is in the technical field of synthetic biology, metabolic engineering and cell cultivation. The present invention relates to methods for the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as well as the purification of said milk oligosaccharide mixture. The present invention also provides a cell for production of said milk oligosaccharide mixture and the use of said cell in a cultivation or incubation.

Description

[0001]Production of a milk oligosaccharide mixtureField of the invention The present invention is in the technical field of synthetic biology, metabolic engineering and cellcultivation. The present invention relates to methods for the production of a mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as well as the purification of said milk oligosaccharide mixture. The present inventionalso provides a cell for production of said milk oligosaccharide mixture and the use of said cell in acultivation or incubation. Background Milk oligosaccharides, present as unconjugated glycans in mammalian milk, like e.g. human milk, areinvolved in important developmental and immunological processes. Many structurally distinct milkoligosaccharides have been identified to date. Milk oligosaccharides constitute an elaborated groupcomprising sialylated oligosaccharides as well as non-sialylated oligosaccharides. Sialylated milkoligosaccharides are a group of negatively charged oligosaccharides comprising at least one sialic acidresidue like e.g. Neu5Ac, comprising 3’sialylated oligosaccharides like e.g. 3’-sialyllactose, sialyllacto-N-tetraose a (LSTa) and sialyllacto-N-tetraose d (LSTd) as well as 6’sialylated oligosaccharides like e.g. 6’sialyllactose, sialyllacto-N-tetraose b (LSTb), sialyllacto-N-tetraose c (LSTc), disialyllacto-N-tetraose(DSLNT) and disialyllacto-N-neotetraose (DSLNnT) as important members. Non-sialylated milkoligosaccharides are oligosaccharides that have no sialic acid residue. Non-sialylated milk oligosaccharidescomprise both non-charged (neutral) milk oligosaccharides and negatively charged milk oligosaccharides.Examples of non-sialylated milk oligosaccharides comprise fucosylated oligosaccharides comprising atleast one fucose residue like e.g. 2'-fucosyllactose (2’FL), 3-fucosyllactose (3FL), 2', 3-difucosyllactose (diFL), lacto-N-fucopentaose I (LNFP I), lacto-N-neofucopentaose I (LNnFP I), lacto-N-fucopentaose II (LNFP II), lacto-N-fucopentaose III (LNFP III), lacto-N-fucopentaose V (LNFP V), lacto-N-fucopentaose VI, lacto-N- neofucopentaose V (LNnFP V), lacto-N-difucohexaose I (LNDFH I), lacto-N-difucohexaose II (LNDFH II).Additional examples of non-sialylated milk oligosaccharides comprise non-fucosylated oligosaccharidescomprising a galactose (Gal) residue, an N-acetylglucosamine (GlcNAc) residue, an N-acetylgalactosamine(GalNAc) residue, an N-acetyllactosamine (LacNAc, Gal-^1,4-GlcNAc) epitope and / or a lacto-N-biose (LNB, Gal-^1,3-GlcNAc) epitope, like e.g. lacto-N-triose II (LN3), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), 6'-galactosyllactose, 3'-galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose and para-lacto-N-neohexaose as important members. Additional examples of non-sialylated milkoligosaccharides comprise sulphated milk oligosaccharides comprising a SO3-group and which are anexample of negatively charged non-sialylated oligosaccharides. Although milk oligosaccharides represent only a minor amount of total milk nutrients, their beneficialeffects on the development of newborns became evident over the past decades. Both sialylated milkoligosaccharides as well as non-sialylated milk oligosaccharides were observed to support severalbeneficial effects as described in the art. There is large scientific and commercial interest in the productionof a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharideand at least one non-sialylated milk oligosaccharide due to the wide functional spectrum of theseoligosaccharides. Yet, the availability of such a milk oligosaccharide mixture is limited as production relieson chemical or chemo-enzymatic synthesis or on purification from natural sources such as e.g. animalmilk. Chemical and enzymatic synthesis methods are laborious, time-consuming and because of the largenumber of steps involved they are difficult to scale-up. Enzymatic approaches using glycosyltransferasesare advantageous above chemical synthesis. Glycosyltransferases catalyze the transfer of a sugar moietyfrom an activated nucleotide-sugar donor onto saccharide or non-saccharide acceptors. These glycosyltransferases are the source for biotechnologists to synthesize oligosaccharides. However, stereospecificity and regioselectivity of glycosyltransferases are still a formidable challenge. In addition, chemo-enzymatic approaches need to regenerate in situ nucleotide-sugar donors.Cell-based production of oligosaccharides and of oligosaccharide mixtures also makes use ofglycosyltransferases and although preferred over chemo-enzymatic synthesis, cell-based methods alsoneed tight control of spatiotemporal synthesis of nucleotide-sugar donors and / or availability of adequate levels of nucleotide-sugar donors in proximity of complementary glycosyltransferases. Description Summary of the invention It is an object of the present invention to provide for tools and methods by means of which a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least onenon-sialylated milk oligosaccharide can be produced with a determined production of said at least onesialylated milk oligosaccharide in said mixture, preferably in an efficient, time and cost-effective way and which yields high amounts of the desired mixture. According to the invention, this and other objects are achieved by providing methods and a cell for production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milkoligosaccharide and at least one non-sialylated milk oligosaccharide as described herein. The presentinvention also provides methods for the purification of said mixture. Furthermore, the present inventionprovides a cell which is metabolically engineered as described herein. This invention also provides apurified mixture of at least two milk oligosaccharides comprising at least one sialylated milkoligosaccharide and at least one non-sialylated milk oligosaccharide by the above-referenced process.Further benefits of the teachings of this invention will be apparent to one skilled in the art from reading this invention. Definitions The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definitionin this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus,if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself.The various aspects and embodiments of the invention disclosed herein are to be understood not only inthe order and context specifically described in this specification, but to include any order and any combination thereof. Each embodiment as identified herein may be combined together unless otherwise indicated. All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference in its entirety. Whenever the context requires, unless specifically stated otherwise, all words used in the singular numbershall be deemed to include the plural and vice versa. Unless defined otherwise, all technical and scientificterms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Generally, the nomenclature used herein and the laboratoryprocedures in cell culture, molecular genetics, organic chemistry and nucleic acid chemistry andhybridization described herein are those well-known and commonly employed in the art. Standard techniques are used for nucleic acid and peptide synthesis. Generally, enzymatic reactions and purification steps are performed according to the manufacturer's specifications. In the specification, there have been disclosed embodiments of the invention, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims. It must be understood that the illustrated embodiments have been set forth only for the purposes of example and that it should not be taken as limiting the invention. It will be apparent to those skilled in the art that alterations, other embodiments, improvements, details and uses can be made consistent with the letter and spirit of the disclosure herein and within the scope of this disclosure, which is limited only by the claims, construed in accordance with the patent law, including the doctrine of equivalents. In the claims that follow, reference characters usedto designate claim steps are provided for convenience of description only, and are not intended to implyany particular order for performing the steps, unless specifically stated otherwise. Throughout the application, unless explicitly stated otherwise, the features "synthesize", "synthesized" and "synthesis" are interchangeably used with the features "produce", "produced" and "production", respectively. Throughout the application, unless explicitly stated otherwise, the expressions “capable of…<verb>” and “capable to…<verb>” are preferably replaced with the active voice of said verb and vice versa. For example, the expression “capable of expressing” is preferably replaced with “expresses” and vice versa, i.e., “expresses” is preferably replaced with “capable of expressing”. In this document and in its claims, the verb "to comprise", “to have” and “to contain” and their conjugations are used in their non- limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. Throughout the application, the verb “to comprise” may be replaced by “to consist” or “to consist essentially of” and vice versa. In addition, the verb “to consist” may be replaced by “to consist essentially of” meaning that a composition as defined herein may comprise additional component(s) than the ones specifically identified, said additional component(s) not altering the unique characteristic of theinvention. In this document and in its claims, unless specifically stated otherwise, the verbs "to comprise",“to have” and “to contain”, and their conjugations, may be replaced by “to consist of” (and itsconjugations) or “to consist essentially of” (and its conjugations) and vice versa. In addition, reference toan element by the indefinite article "a" or "an" does not exclude the possibility that more than one of theelements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one". Throughout the application, unless explicitly stated otherwise, the articles “a” and “an” are preferably replaced by “at least two”, more preferably by “at least three”, even more preferably by “at least four”, even more preferably by “at least five”, even more preferably by “at least six”, most preferably by “atleast two”. The word “about” or “approximately” when used in association with a numerical value (e.g.,“about 10”) or with a range (e.g., “about x to approximately y”) preferably means that the value or range is interpreted as being as accurate as the method used to measure it. If no error margins are specified, the expression “about” or “approximately” when used in association with a numerical value is interpreted as having the same round-off as the given value. Throughout this document and its claims, unless otherwise stated, the expression "from x to y", wherein x and y represent numerical values, refers to a range of numerical values wherein x is the lower value of the range and y is the upper value of the range. Herein, x and y are also included in the range. According to the present invention, the term "polynucleotide(s)" generally refers to any polyribonucleotide or polydeoxyribonucleotide, which may be unmodified RNA or DNA or modified RNAor DNA. "Polynucleotide(s)" include, without limitation, single- and double-stranded DNA, DNA that is amixture of single- and double-stranded regions or single-, double- and triple-stranded regions, single- anddouble-stranded RNA, and RNA that is mixture of single- and double-stranded regions, hybrid moleculescomprising DNA and RNA that may be single-stranded or, more typically, double-stranded, or triple-stranded regions, or a mixture of single- and double-stranded regions. In addition, "polynucleotide" asused herein refers to triple-stranded regions comprising RNA or DNA or both RNA and DNA. The strands in such regions may be from the same molecule or from different molecules. The regions may include all of one or more of the molecules, but more typically involve only a region of some of the molecules. One of the molecules of a triple-helical region often is an oligonucleotide. As used herein, the term "polynucleotide(s)" also includes DNAs or RNAs as described above that contain one or more modified bases. Thus, DNAs or RNAs with backbones modified for stability or for other reasons are "polynucleotide(s)" according to the present invention. Moreover, DNAs or RNAs comprising unusual bases, such as inosine, or modified bases, such as tritylated bases, are to be understood to be covered by the term “polynucleotides”. It will be appreciated that a great variety of modifications have been made to DNA and RNA that serve many useful purposes known to those of skill in the art. The term "polynucleotide(s)" as it is employed herein embraces such chemically, enzymatically or metabolically modified forms of polynucleotides, as well as the chemical forms of DNA and RNA characteristic of viruses and cells, including, for example, simple and complex cells. The term "polynucleotide(s)" also embraces short polynucleotides often referred to as oligonucleotide(s). "Polypeptide(s)" refers to any peptide or protein comprising two or more amino acids joined to each other by peptide bonds or modified peptide bonds. "Polypeptide(s)" refers to both short chains, commonly referred to as peptides, oligopeptides and oligomers and to longer chains generally referred to as proteins. Polypeptides may contain amino acids other than the 20 gene encoded amino acids. "Polypeptide(s)" include those modified either by natural processes, such as processing and other post-translational modifications, but also by chemical modification techniques. Such modifications are well described in basic texts and in more detailed monographs, as well as in a voluminous research literature, and they are well known to the skilled person. The same type of modification may be present in the same or varying degree at several sites in a given polypeptide. Furthermore, a given polypeptide may contain many types of modifications. Modifications can occur anywhere in a polypeptide, including the peptide backbone, the amino acid sidechains, and the amino or carboxyl termini. Modifications include, for example, acetylation, acylation, ADP-ribosylation, amidation, covalent attachment of flavin, covalent attachment of a heme moiety, covalent attachment of a nucleotide or nucleotide derivative, covalent attachment of a lipid or lipid derivative, covalent attachment of phosphatidylinositol, cross-linking, cyclization, disulphide bond formation, demethylation, formation of covalent cross-links, formation of pyroglutamate, formylation, gamma-carboxylation, glycosylation, GPI anchor formation, hydroxylation, iodination, methylation, myristoylation, oxidation, proteolytic processing, phosphorylation, prenylation, racemization, lipid attachment, sulfation, gamma-carboxylation of glutamic acid residues, hydroxylation and ADP- ribosylation, selenoylation, transfer-RNA mediated addition of amino acids to proteins, such as arginylation, and ubiquitination. Polypeptides may be branched or cyclic, with or without branching. Cyclic, branched and branched circular polypeptides may result from post-translational natural processes and may be made by entirely synthetic methods, as well. The term "polynucleotide encoding a polypeptide" as used herein encompasses polynucleotides that include a sequence encoding a polypeptide of the invention. The term also encompasses polynucleotides that include a single continuous region or discontinuous regions encoding the polypeptide (for example, interrupted by integrated phage or an insertion sequence or editing) together with additional regions that also may contain coding and / or non-coding sequences. "Isolated" means altered "by the hand of man" from its natural state, i.e., if it occurs in nature, it has been changed or removed from its original environment, or both. For example, a polynucleotide or apolypeptide naturally present in a living organism is not "isolated," but the same polynucleotide orpolypeptide separated from the coexisting materials of its natural state is "isolated", as the term is employed herein. Similarly, a "synthetic" sequence, as the term is used herein, means any sequence that has been generated synthetically and not directly isolated from a natural source. “Synthesized”, as the term is used herein, means any synthetically generated sequence and not directly isolated from a natural source. "Recombinant" means genetically engineered DNA prepared by transplanting or splicing genes from one species into the cells of a host organism of a different species. Such DNA becomes part of the host's genetic makeup and is replicated.The terms "recombinant" or “transgenic” or “metabolically engineered” or “genetically engineered” asused herein with reference to a cell or host cell are used interchangeably and indicates that the cell replicates a heterologous nucleic acid, or expresses a peptide or protein encoded by a heterologous nucleic acid (i.e., a sequence "foreign to said cell" or a sequence “foreign to said location or environment in said cell”). Such cells are described to be transformed with at least one heterologous or exogenous gene or are described to be transformed by the introduction of at least one heterologous or exogenous gene. Recombinant or metabolically engineered or genetically engineered or transgenic cells can contain genes that are not found within the native (non-recombinant) form of the cell. Recombinant cells can also contain genes found in the native form of the cell wherein the genes are modified and re-introduced into the cell by artificial means. The terms also encompass cells that contain a nucleic acid endogenous to the cell that has been modified or its expression or activity has been modified without removing the nucleic acid from the cell; such modifications include those obtained by gene replacement, replacement of a promoter; site-specific mutation; CrispR; riboswitch; recombineering; ssDNA mutagenesis; transposonmutagenesis and related techniques as known to a person skilled in the art. Accordingly, a "recombinantpolypeptide" is one which has been produced by a recombinant cell. The terms also encompass cells that have been modified by removing a nucleic acid endogenous to the cell by means of common well-known technologies for a skilled person (like e.g. knocking-out genes). A "heterologous sequence" or a "heterologous nucleic acid", as used herein, is one that originates from a source foreign to the particular cell (e.g., from a different species), or, if from the same source, is modified from its original form or place in the genome. Thus, a heterologous nucleic acid operably linked to a promoter is from a source different from that from which the promoter was derived, or, if from the same source, is modified from its original form or place in the genome. The heterologous sequence may be stably introduced, e.g., by transfection, transformation, conjugation or transduction, into the genome of the host microorganism cell, wherein techniques may be applied which will depend on the cell and the sequence that is to be introduced. Various techniques are known to a person skilled in the art and are, e.g., disclosed in Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989). The term “mutant” or “engineered” cell or microorganism as used within the context of the present invention refers to a cell or microorganism which is genetically engineered. The term "endogenous" within the context of the present disclosure refers to any polynucleotide,polypeptide or protein sequence that is a natural part of a cell and is occurring at its natural location inthe cell chromosome and of which the control of expression has not been altered compared to the naturalcontrol mechanism acting on its expression. The term “exogenous” refers to any polynucleotide,polypeptide or protein sequence which originates from outside the cell under study and not a natural part of the cell or which is not occurring at its natural location in the cell chromosome or plasmid. The term "heterologous" when used in reference to a polynucleotide, gene, nucleic acid, polypeptide, or enzyme refers to a polynucleotide, gene, nucleic acid, polypeptide, or enzyme that is from a source or derived from a source other than the host organism species. In contrast a "homologous" polynucleotide, gene, nucleic acid, polypeptide, or enzyme is used herein to denote a polynucleotide, gene, nucleic acid, polypeptide, or enzyme that is derived from the host organism species. When referring to a gene regulatory sequence or to an auxiliary nucleic acid sequence used for maintaining or manipulating a gene sequence (e.g. a promoter, a 5' untranslated region, 3' untranslated region, poly A addition sequence, intron sequence, splice site, ribosome binding site, internal ribosome entry sequence, genome homology region, recombination site, etc.), "heterologous" means that the regulatory sequence or auxiliary sequence is not naturally associated with the gene with which the regulatory or auxiliary nucleic acid sequence is juxtaposed in a construct, genome, chromosome, or episome. Thus, a promoter operably linked to a gene to which it is not operably linked to in its natural state (i.e. in the genome of a non-genetically engineered organism) is referred to herein as a "heterologous promoter," even though thepromoter may be derived from the same species (or, in some cases, the same organism) as the gene to which it is linked. The term “modified expression” of a gene relates to a change in expression compared to the wild-typeexpression of said gene in any phase of the production process of the desired mixture of at least two milkoligosaccharides as described herein. Said modified expression is either a lower or higher expressioncompared to the wild-type, wherein the term “higher expression” is also defined as “overexpression” ofsaid gene in the case of an endogenous gene or “expression” in the case of a heterologous gene that isnot present in the wild-type strain. Lower expression is obtained by means of common well-known technologies for a skilled person (such as the usage of siRNA, CrispR, CrispRi, riboswitch, recombineering, homologous recombination, ssDNA mutagenesis, RNAi, miRNA, asRNA, mutating genes, knocking-outgenes, transposon mutagenesis, etc.) which are used to change the genes in such a way that they are“less-able” (i.e., statistically significantly ‘less-able’ compared to a functional wild-type gene) orcompletely unable (such as knocked-out genes) to produce functional final products. The term “riboswitch” as used herein is defined to be part of the messenger RNA that folds into intricate structures that block expression by interfering with translation. Binding of an effector molecule induces conformational change(s) permitting regulated expression post-transcriptionally. Next to changing the gene of interest in such a way that lower expression is obtained as described above, lower expression can also be obtained by changing the transcription unit, the promoter, an untranslated region, the ribosome binding site, the Shine Dalgarno sequence or the transcription terminator. Lower expression or reduced expression can for instance be obtained by mutating one or more base pairs in the promoter sequence or changing the promoter sequence fully to a constitutive promoter with a lower expression strength compared to the wild-type or an inducible promoter which result in regulated expression or a repressible promoter which results in regulated expression. Overexpression or expression is obtained by means ofcommon well-known technologies for a skilled person (such as the usage of artificial transcription factors,de novo design of a promoter sequence, ribosome engineering, introduction or re-introduction of an expression module at euchromatin, usage of high-copy-number plasmids), wherein said gene is part of an“expression cassette” that relates to any sequence in which a promoter sequence, untranslated regionsequence (containing either a ribosome binding sequence, Shine Dalgarno or Kozak sequence), a codingsequence and optionally a transcription terminator is present, and leading to the expression of a functional active protein. Said expression is either constitutive or conditional or regulated or tuneable. The term “constitutive expression” is defined as expression that is not regulated by transcription factorsother than the subunits of RNA polymerase (e.g., the bacterial sigma factors like s70, s54, or related s-factors and the yeast mitochondrial RNA polymerase specificity factor MTF1 that co-associate with the RNA polymerase core enzyme) under certain growth conditions. Non-limiting examples of such transcription factors are CRP, LacI, ArcA, Cra, IclR in E. coli, or, Aft2p, Crz1p, Skn7 in Saccharomyces cerevisiae, or, DeoR, GntR, Fur in B. subtilis. These transcription factors bind on a specific sequence and may block or enhance expression in certain growth conditions. The RNA polymerase is the catalyticmachinery for the synthesis of RNA from a DNA template. RNA polymerase binds a specific DNA sequenceto initiate transcription, for instance via a sigma factor in prokaryotic hosts or via MTF1 in yeasts.Constitutive expression offers a constant level of expression with no need for induction or repression. The term “regulated expression” is defined as expression that is regulated by transcription factors other than the subunits of RNA polymerase (e.g. bacterial sigma factors) under certain growth conditions. Examples of such transcription factors are described above. Commonly expression regulation is obtained by means of an inducer, such as but not limited to IPTG, arabinose, rhamnose, fucose, allo-lactose or pH shifts, or temperature shifts or carbon depletion or substrates or the produced product. The term “control sequences” refers to sequences recognized by the cells transcriptional and translational systems, allowing transcription and translation of a polynucleotide sequence to a polypeptide. Such DNA sequences are thus necessary for the expression of an operably linked coding sequence in a particularhost cell, cell or organism. Such control sequences can be, but are not limited to, promoter sequences, ribosome binding sequences, Shine Dalgarno sequences, Kozak sequences, transcription terminator sequences. The control sequences that are suitable for prokaryotes, for example, include a promoter, optionally an operator sequence, and a ribosome binding site. Eukaryotic cells are known to utilize promoters, polyadenylation signals, and enhancers. DNA for a presequence or secretory leader may be operably linked to DNA for a polypeptide if it is expressed as a preprotein that participates in the secretion of the polypeptide; a promoter or enhancer is operably linked to a coding sequence if it affects the transcription of the sequence; or a ribosome binding site is operably linked to a coding sequence if it affects the transcription of the sequence; or a ribosome binding site is operably linked to a coding sequence if it is positioned so as to facilitate translation. Said control sequences can furthermore be controlled with external chemicals, such as, but not limited to, IPTG, arabinose, lactose, allo-lactose, rhamnose or fucose via an inducible promoter or via a genetic circuit that either induces or represses the transcription or translation of said polynucleotide to a polypeptide. Generally, "operably linked" means that the DNA sequences being linked are contiguous, and, in the case of a secretory leader, contiguous and in reading phase. However, enhancers do not have to be contiguous. The term “wildtype” refers to the commonly known genetic or phenotypical situation as it occurs in nature. The term “modified expression of a protein” as used herein refers to i) higher expression oroverexpression of an endogenous protein, ii) expression of a heterologous protein, iii) expression and / oroverexpression of a variant protein that has a higher activity compared to the wild-type (i.e. native in theexpression host) protein, iv) reduced expression of an endogenous protein or v) expression and / or overexpression of a variant protein that has a reduced activity compared to the wild-type (i.e. native in the expression host) protein. The term “modified activity” of a protein relates to a non-native activity of the protein in any phase of theproduction process of the desired mixture of at least two milk oligosaccharides as described herein. Theterm “non-native”, as used herein with reference to the activity of a protein indicates that the protein has been modified to have an abolished, impaired, reduced, delayed, higher, accelerated or improved activity compared to the native activity of said protein. A modified activity of a protein is obtained by modified expression of said protein or is obtained by expression of a modified, i.e., mutant form of the protein. A mutant form of the protein can be obtained by expression of a mutant form of the gene encoding theprotein, e.g., comprising a deletion, an insertion and / or a mutation of one or more nucleotides comparedto the native gene sequence. A mutant form of a gene can be obtained by techniques well-known to a person skilled in the art, such as but not limited to site-specific mutation; CrispR; riboswitch; recombineering; ssDNA mutagenesis; transposon mutagenesis. The term “non-native”, as used herein with reference to a cell producing a mixture of at least two milkoligosaccharides as described herein, indicates that said mixture is i) not naturally produced or ii) whennaturally produced not in the same amounts by the cell; and that the cell has been genetically engineeredto be able to produce said mixture or to have a higher production of the mixture.As used herein, the term “mammary cell(s)” generally refers to mammalian mammary epithelial cell(s),mammalian mammary-epithelial luminal cell(s), or mammalian epithelial alveolar cell(s), or any combination thereof. As used herein, the term “mammary-like cell(s)” generally refers to mammalian cell(s) having a phenotype / genotype similar (or substantially similar) to natural mammalian mammary cell(s) but is / are derived from mammalian non-mammary cell source(s). Such mammalian mammary-like cell(s) may be engineered to remove at least one undesired genetic component and / or to include at least one predetermined genetic construct that is typical of a mammalian mammary cell. Non-limiting examples of mammalian mammary-like cell(s) may include mammalian mammary epithelial-like cell(s), mammalian mammary epithelial luminal-like cell(s), mammalian non-mammary cell(s) that exhibits one or more characteristics of a cell of a mammalian mammary cell lineage, or any combination thereof. Further non- limiting examples of mammalian mammary-like cell(s) may include mammalian cell(s) having a phenotype similar (or substantially similar) to natural mammalian mammary cell(s), or more particularly a phenotype similar (or substantially similar) to natural mammalian mammary epithelial cell(s). A mammalian cell with a phenotype or that exhibits at least one characteristic similar to (or substantially similar to) a natural mammalian mammary cell or a mammalian mammary epithelial cell may comprise a mammalian cell (e.g., derived from a mammary cell lineage or a non-mammary cell lineage) that exhibits either naturally, or has been engineered to, be capable of expressing at least one milk component. As used herein, the term “non-mammary cell(s)” may generally include any mammalian cell of non- mammary lineage. In the context of the invention, a non-mammary cell can be any mammalian cell capable of being engineered to express at least one milk component. Non-limiting examples of such non- mammary cell(s) include hepatocyte(s), blood cell(s), kidney cell(s), cord blood cell(s), epithelial cell(s), epidermal cell(s), myocyte(s), fibroblast(s), mesenchymal cell(s), or any combination thereof. In some instances, molecular biology and genome editing techniques can be engineered to eliminate, silence, or attenuate myriad genes simultaneously. "Variant(s)" as the term is used herein, is a polynucleotide or polypeptide that differs from a reference polynucleotide or polypeptide respectively but retains essential properties. A typical variant of apolynucleotide differs in nucleotide sequence from another, reference polynucleotide. Changes in thenucleotide sequence of the variant may or may not alter the amino acid sequence of a polypeptide encoded by the reference polynucleotide. Nucleotide changes may result in amino acid substitutions, additions, deletions, fusions and truncations in the polypeptide encoded by the reference sequence, as discussed below. A typical variant of a polypeptide differs in amino acid sequence from another, reference polypeptide. Generally, differences are limited so that the sequences of the reference polypeptide and the variant are closely similar overall and, in many regions, identical. A variant and reference polypeptide may differ in amino acid sequence by one or more substitutions, additions, deletions in any combination. A substituted or inserted amino acid residue may or may not be one encoded by the genetic code. A variant of a polynucleotide or polypeptide may be a naturally occurring such as an allelic variant, or it may be a variant that is not known to occur naturally. Non-naturally occurring variants of polynucleotides andpolypeptides may be made by mutagenesis techniques, by direct synthesis, and by other recombinantmethods known to the persons skilled in the art. In some embodiments, the present invention contemplates making functional variants by modifying the structure of an enzyme, like e.g. a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N- acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase, as used in the present invention. Variants can be produced by amino acid substitution, deletion, addition, or combinations thereof. For instance, a variant can be produced as a fusion protein comprising at least one portion of anenzyme, like e.g. a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthaseand / or N-acylneuraminate cytidylyltransferase, of present invention fused to at least one portion comprising a peptide tag. Said peptide tag may be used to assist protein folding of said enzyme, assist post expression purification, protect the enzyme from the action of degradative enzymes, and / or assist the enzyme in passing through the cell membrane. Examples of said peptide tag comprise, e.g., a SUMO tag, an MBP tag, a His tag, a FLAG tag, a Strep-II tag, a Halo-tag, a NusA tag, thioredoxin, GST and / or a Fh8-tag. The fusion protein may be designed to include at least one cleavable peptide linker so that the enzyme of interest can be subsequently recovered from the fusion protein. The fusion protein may be designed to include a plurality of inclusion body tags, cleavable peptide linkers, and regions encoding the enzyme of interest.In case of amino acid substitution, it is reasonable to expect that an isolated replacement of a leucine withan isoleucine or valine, an aspartate with a glutamate, a threonine with a serine, or a similar replacement of an amino acid with a structurally related amino acid (e.g., conservative mutations) will not have a major effect on the biological activity of the resulting molecule. Conservative replacements are those that take place within a family of amino acids that are related in their side chains. Whether a change in the amino acid sequence of a polypeptide of the invention results in a functional homolog can be readily determined by assessing the ability of the variant polypeptide to produce a response in cells in a fashion similar to the wild-type polypeptide. "Fragment", with respect to a polynucleotide, refers to a clone or any part of a polynucleotide molecule, particularly a part of a polynucleotide that retains a usable, functional characteristic of the full-length polynucleotide molecule. Useful fragments include oligonucleotides and polynucleotides that may be used in hybridization or amplification technologies or in the regulation of replication, transcription or translation. A "polynucleotide fragment" refers to any subsequence of a polynucleotide SEQ ID NO, typically, comprising or consisting of at least about 9, 10, 11, 12 consecutive nucleotides from said polynucleotide SEQ ID NO, for example at least about 30 nucleotides or at least about 50 nucleotides of any of the polynucleotide sequences provided herein. Exemplary fragments can additionally or alternatively include fragments that comprise, consist essentially of, or consist of a region that encodes a conserved family domain of a polypeptide. Exemplary fragments can additionally or alternatively include fragments that comprise a conserved domain of a polypeptide. As such, a fragment of a polynucleotide SEQ ID NO preferably means a nucleotide sequence which comprises or consists of said polynucleotideSEQ ID NO wherein no more than about 200, 150, 100, 50 or 25 consecutive nucleotides are missing,preferably no more than about 50 consecutive nucleotides are missing, and which retains a usable, functional characteristic (e.g. activity) of the full-length polynucleotide molecule which can be assessed by the skilled person through routine experimentation. Alternatively, a fragment of a polynucleotide SEQID NO preferably means a nucleotide sequence which comprises or consists of an amount of consecutivenucleotides from said polynucleotide SEQ ID NO and wherein said amount of consecutive nucleotides is at least 45.0 %, 50.0 %, 60.0 %, 70.0 %, 80.0 %, 81.0 %, 82.0 %, 83.0 %, 84.0 %, 85.0 %, 86.0 %, 87.0 %, 88.0 %, 89.0 %, 90.0 %, 91.0 %, 92.0 %, 93.0 %, 94.0 %, 95.0 %, 95.5%, 96.0 %, 96.5 %, 97.0 %, 97.5 %, 98.0 %, 98.5 %, 99.0 %, 99.5 %, 100 %, preferably at least 80.0 %, more preferably at least 85.0 %, even morepreferably at least 87.0 %, even more preferably at least 90.0 %, even more preferably at least 95.0 %,most preferably at least 97.0 %, of the full-length of said polynucleotide SEQ ID NO and retains a usable,functional characteristic (e.g. activity) of the full-length polynucleotide molecule which can be routinelyassessed by the skilled person. As such, a fragment of a polynucleotide SEQ ID NO preferably means a nucleotide sequence which comprises or consists of said polynucleotide SEQ ID NO, wherein an amount of consecutive nucleotides is missing and wherein said amount is no more than 50.0 %, 40.0 %, 30.0 % of the full-length of said polynucleotide SEQ ID NO, preferably no more than 20.0 %, 15.0 %, 10.0 %, 9.0 %, 8.0 %, 7.0 %, 6.0 %, 5.0 %, 4.5 %, 4.0 %, 3.5 %, 3.0 %, 2.5 %, 2.0 %, 1.5 %, 1.0 %, 0.5 %, more preferably no more than 15.0 %, even more preferably no more than 10.0 %, even more preferably no more than 5.0 %, most preferably no more than 2.5 %, of the full-length of said polynucleotide SEQ ID NO and wherein said fragment retains a usable, functional characteristic (e.g. activity) of the full-length polynucleotide molecule which can be routinely assessed by the skilled person. “Fragment”, with respect to a polypeptide, refers to a subsequence of the polypeptide which performs at least one biological function of the intact polypeptide in substantially the same manner, or to a similarextent, as does the intact polypeptide. A “subsequence of the polypeptide” or “a stretch of amino acidresidues” as described herein refers to a sequence of contiguous amino acid residues derived from thepolypeptide. For example, a polypeptide fragment can comprise a recognizable structural motif or functional domain such as a DNA-binding site or domain that binds to a DNA promoter region, an activation domain, or a domain for protein-protein interactions, and may initiate transcription. Fragments can vary in size from as few as 3 amino acid residues to the full length of the intact polypeptide, forexample at least about 10 amino acid residues in length, for example at least about 20 amino acid residuesin length, for example at least about 30 amino acid residues in length, for example at least about 100 amino acid residues in length, for example at least about 150 amino acid residues in length, for example at least about 200 amino acid residues in length. As such, a fragment of a polypeptide SEQ ID NO (or UniProt ID) preferably means a polypeptide sequence which comprises or consists of said polypeptide SEQ ID NO (or UniProt ID) wherein no more than about 200, 150, 125, 100, 80, 60, 50, 40, 30, 20 or 15 consecutive amino acid residues are missing, preferably no more than about 100 consecutive amino acid residues are missing, more preferably no more than about 50 consecutive amino acid residues are missing, even more preferably no more than about 40 consecutive amino acid residues are missing, and performs at least one biological function of the intact polypeptide in substantially the same manner, preferably to a similar or greater extent, as does the intact polypeptide which can be routinely assessed by the skilled person. Alternatively, a fragment of a polypeptide SEQ ID NO (or UniProt ID) preferably means a polypeptide sequence which comprises or consists of an amount of consecutive amino acid residues from said polypeptide SEQ ID NO (or UniProt ID) and wherein said amount of consecutive amino acid residues is at least 45.0 %, 50.0 %, 55.0 %, 60.0 %, 65.0 %, 70.0 %, 75.0 %, 80.0 %, 81.0 %, 82.0 %, 83.0 %, 84.0 %, 85.0 %, 86.0 %, 87.0 %, 88.0 %, 89.0 %, 90.0 %, 91.0 %, 92.0 %, 93.0 %, 94.0 %, 95.0 %, 95.5%, 96.0 %, 96.5 %, 97.0 %, 97.5 %, 98.0 %, 98.5 %, 99.0 %, 99.5 %, 100 %, preferably at least 80.0 %, more preferably at least 85.0 %, even more preferably at least 87.0%, even more preferably at least 90.0 %, even more preferably at least 95.0 %, most preferably at least 97.0 % of the full-length of said polypeptide SEQ ID NO (or UniProt ID) and which performs at least one biological function of the intact polypeptide in substantially the same manner, preferably to a similar or greater extent, as does the intact polypeptidewhich can be routinely assessed by the skilled person. As such, a fragment of a polypeptide SEQ ID NO (orUniProt ID) preferably means a polypeptide sequence which comprises or consists of said polypeptide SEQ ID NO (or UniProt ID), wherein an amount of consecutive amino acid residues is missing and wherein said amount is no more than 50.0 %, 40.0 %, 30.0 % of the full-length of said polypeptide SEQ ID NO (or UniProt ID), preferably no more than 20.0 %, 15.0 %, 10.0 %, 9.0 %, 8.0 %, 7.0 %, 6.0 %, 5.0 %, 4.5 %, 4.0 %, 3.5 %, 3.0 %, 2.5 %, 2.0 %, 1.5 %, 1.0 %, 0.5 %, more preferably no more than 15.0 %, even more preferably no more than 10.0 %, even more preferably no more than 5.0 %, most preferably no more than 2.5 %, of the full-length of said polypeptide SEQ ID NO (or UniProt ID) and which performs at least one biological function of the intact polypeptide in substantially the same manner, preferably to a similar or greater extent, as does the intact polypeptide which can be routinely assessed by the skilled person. Throughout the application, the sequence of a polypeptide can be represented by a SEQ ID NO or alternatively by an UniProt ID. Therefore, the terms “polypeptide SEQ ID NO” and “polypeptide UniProt ID” can be interchangeably used, unless explicitly stated otherwise. A “functional fragment” of a polypeptide has at least one property or activity of the polypeptide from which it is derived, preferably to a similar or greater extent. A functional fragment can, for example, include a functional domain or conserved domain of a polypeptide. It is understood that a polypeptide or a fragment thereof may have conservative amino acid substitutions which have substantially no effect on the polypeptide's activity. By conservative substitutions is intended substitutions of one hydrophobic amino acid for another or substitution of one polar amino acid for another or substitution of one acidic amino acid for another or substitution of one basic amino acid for another etc. Preferably, by conservative substitutions is intended combinations such as glycine by alanine and vice versa; valine, isoleucine and leucine by methionine and vice versa; aspartate by glutamate and vice versa; asparagine by glutamine andvice versa; serine by threonine and vice versa; lysine by arginine and vice versa; cysteine by methionineand vice versa; and phenylalanine and tyrosine by tryptophan and vice versa. Homologous sequences as used herein describes those nucleotide sequences that have sequence similarity and encode polypeptides that share at least one functional characteristic such as a biochemical activity. More specifically, the term "functional homolog" as used herein describes those polypeptides that have sequence similarity (in other words, homology) and at the same time have at least onefunctional similarity such as a biochemical activity (Altenhoff et al., PLoS Comput. Biol. 8 (2012)e1002514). Homologs can be identified by analysis of nucleotide and polypeptide sequence alignments. For example, performing a query on a database of nucleotide or polypeptide sequences can identify homologs of the nucleotides or polypeptides of interest. Sequence analysis can involve BLAST, Reciprocal BLAST, or PSI- BLAST analysis of non-redundant databases using the amino acid sequence of a reference polypeptide sequence. The amino acid sequence is, in some instances, deduced from the nucleotide sequence.Typically, those polypeptides in the database that have greater than 40 % sequence identity to apolypeptide of interest are candidates for further evaluation for suitability as a homologous polypeptide. Amino acid sequence similarity allows for conservative amino acid substitutions, such as substitution ofone hydrophobic residue for another or substitution of one polar residue for another or substitution ofone acidic amino acid for another or substitution of one basic amino acid for another etc. Preferably, by conservative substitutions is intended combinations such as glycine by alanine and vice versa; valine, isoleucine and leucine by methionine and vice versa; aspartate by glutamate and vice versa; asparagineby glutamine and vice versa; serine by threonine and vice versa; lysine by arginine and vice versa; cysteineby methionine and vice versa; and phenylalanine and tyrosine by tryptophan and vice versa. If desired, manual inspection of such candidates can be carried out in order to narrow the number of candidates to be further evaluated. Protein or polypeptide sequence information and functional information can be provided by acomprehensive resource for protein sequence and annotation data like e.g., the Universal ProteinResource (UniProt) (www.uniprot.org) (Nucleic Acids Res.2021, 49(D1), D480-D489). UniProt comprises the expertly and richly curated protein database called the UniProt Knowledgebase (UniProtKB), together with the UniProt Reference Clusters (UniRef) and the UniProt Archive (UniParc). The UniProt identifiers(UniProt ID) are unique for each protein present in the database. Throughout the application, thesequence of a polypeptide is represented by a SEQ ID NO or an UniProt ID. Unless stated otherwise, the UniProt IDs of the proteins described correspond to their sequence version 01 as present in the UniProt Database (www.uniprot.org) version release 2021_03 and consulted on 09 June 2021. It should be understood for those skilled in the art that for the databases used herein, the content of each database is fixed at each release and is not to be changed. When the content of a specific database is changed, this specific database receives a new release version with a new release date. All release versions for each database with their corresponding release dates and specific content as annotated at these specific release dates are available and known to those skilled in the art. The terms "identical" or “percent identity" or “% identity” in the context of two or more nucleic acid or polypeptide sequences, refer to two or more sequences or subsequences that are the same or have a specified percentage of nucleotides or amino acid residues that are the same, when compared and aligned for maximum correspondence, as measured using sequence comparison algorithms or by visual inspection. For sequence comparison, one sequence acts as a reference sequence, to which test sequences are compared. When using a sequence comparison algorithm, test and reference sequences are inputted into a computer, subsequence coordinates are designated, if necessary, and sequence algorithm program parameters are designated. The sequence comparison algorithm then calculates the% sequence identity for the test sequence(s) relative to the reference sequence, based on the designatedprogram parameters. The percentage of sequence identity can be, preferably is, determined by alignment of the two sequences and identification of the number of positions with identical residues divided by thenumber of residues in the shorter of the sequences x 100. Percent identity may be calculated globally overthe full-length sequence of a given SEQ ID NO, i.e. the reference sequence, resulting in a global % identityscore. Alternatively, % identity may be calculated over a partial sequence of the reference sequence,resulting in a local percent identity score. A partial sequence preferably means at least about 25 %, 30 %, 35 %, 40 %, 45 %, 50 %, 55 %, 60 %, 65 %, 70 %, 75 %, 80 %, 85%, 87.5 %, 90 %, 91 %, 92 %, 93 %, 94 % or95 % of the full-length reference sequence. In another preferred embodiment, a partial sequence of areference polypeptide sequence means a stretch of at least 150 amino acid residues up to the total number of amino acid residues of a reference polypeptide sequence. In another more preferred embodiment, a partial sequence of a reference polypeptide sequence means a stretch of at least 200 amino acid residues up to the total number of amino acid residues of a reference polypeptide sequence. Using the full-length of the reference sequence in a local sequence alignment results in a global percent identity score between the test and the reference sequence. Percent identity can be determined using different algorithms like for example BLAST and PSI-BLAST(Altschul et al., 1990, J Mol Biol 215:3, 403- 410; Altschul et al., 1997, Nucleic Acids Res 25: 17, 3389-402),the Clustal Omega method (Sievers et al., 2011, Mol. Syst. Biol.7:539), the MatGAT method (Campanella et al., 2003, BMC Bioinformatics, 4:29) or EMBOSS Needle. As used herein, a polypeptide comprising, consisting of or consisting essentially of an amino acid sequence having 80 % or more sequence identity over a stretch of at least 150 amino acid residues of a reference polypeptide sequence is to be understood as that the amino acid sequence has 80.0 %, 81.0 %, 82.0 %, 83.0 %, 84.0 %, 85.0 %, 86.0 %, 87.0 %, 88.0 %, 89.0 %, 90.0 %, 91.0 %, 91.50 %, 92.00 %, 92.50 %, 93.00 %, 93.50 %, 94.00 %, 94.50 %, 95.00 %, 95.50 %, 96.00 %, 96.50 %, 97.00 %, 97.50 %, 98.00 %, 98.50 %, 99.00 %, 99.50 %, 99.60 %, 99.70 %, 99.80 %, 99.90 %, 100 % sequence identity over a stretch of at least 150 amino acid residues of the reference polypeptide sequence. A polypeptide comprising, consisting ofor consisting essentially of an amino acid sequence having 80 % or more sequence identity over a stretchof at least 200 amino acid residues of a reference polypeptide sequence is to be understood as that the amino acid sequence has 80.0 %, 81.0 %, 82.0 %, 83.0 %, 84.0 %, 85.0 %, 86.0 %, 87.0 %, 88.0 %, 89.0 %, 90.0 %, 91.0 %, 91.50 %, 92.00 %, 92.50 %, 93.00 %, 93.50 %, 94.00 %, 94.50 %, 95.00 %, 95.50 %, 96.00 %, 96.50 %, 97.00 %, 97.50 %, 98.00 %, 98.50 %, 99.00 %, 99.50 %, 99.60 %, 99.70 %, 99.80 %, 99.90 %, 100 % sequence identity over a stretch of at least 200 amino acid residues of the reference polypeptide sequence. As used herein, a polypeptide comprising, consisting of or consisting essentially of an amino acid sequencehaving 80 % or more sequence identity to the full-length sequence of a reference polypeptide sequenceis to be understood as that the amino acid sequence has 80.0 %, 81.0 %, 82.0 %, 83.0 %, 84.0 %, 85.0 %,86.0 %, 87.0 %, 88.0 %, 89.0 %, 90.0 %, 91.0 %, 91.50 %, 92.00 %, 92.50 %, 93.00 %, 93.50 %, 94.00 %,94.50 %, 95.00 %, 95.50 %, 96.00 %, 96.50 %, 97.00 %, 97.50 %, 98.00 %, 98.50 %, 99.00 %, 99.50 %, 99.60%, 99.70 %, 99.80 %, 99.90 %, 100 % sequence identity to the full-length of the amino acid sequence ofthe reference polypeptide sequence. Throughout the application, unless explicitly specified otherwise, a polypeptide comprising, consisting ofor having an amino acid sequence having 80 % or more sequence identity to the full-length amino acidsequence of a reference polypeptide, usually indicated with a SEQ ID NO or UniProt ID, preferably 80.0 %,81.0 %, 82.0 %, 83.0 %, 84.0 %, 85.0 %, 86.0 %, 87.0 %, 88.0 %, 89.0 %, 90.0 %, 91.0 %, 91.50 %, 92.00 %,92.50 %, 93.00 %, 93.50 %, 94.00 %, 94.50 %, 95.00 %, 95.50 %, 96.00 %, 96.50 %, 97.00 %, 97.50 %, 98.00%, 98.50 %, 99.00 %, 99.50 %, 99.60 %, 99.70 %, 99.80 % or 99.90 %, more preferably at least 85.0 %, evenmore preferably at least 87.50 %, even more preferably at least 90.0 % sequence identity to the full length reference sequence. Additionally, unless explicitly specified otherwise, a polynucleotide sequence comprising, consisting of orhaving a nucleotide sequence having 80 % or more sequence identity to the full-length nucleotidesequence of a reference polynucleotide sequence, usually indicated with a SEQ ID NO, preferably has 80.0%, 85.0%, 90.0%, 91.0%, 92.0%, 93.0%, 94.0%, 95.0%, 96.0%, 97.0%, 98.0% or 99.0%, more preferably has at least 85.0%, even more preferably has at least 87.50%, even more preferably has at least 90.0% sequence identity to the full-length reference polynucleotide sequence. For the purposes of this invention, percent identity is determined using MatGAT2.01 (Campanella et al., 2003, BMC Bioinformatics 4:29). The following default parameters for protein are employed: (1) Gap costExistence: 12 and Extension: 2; (2) The Matrix employed was BLOSUM50. In a preferred embodiment,sequence identity is calculated based on the full-length sequence of a given SEQ ID NO, i.e. the reference sequence, or a part thereof. Part thereof preferably means at least 50 %, 60 %, 70 %, 80 %, 90 % or 95 % of the complete reference sequence. The terms “sialic acid”, “N-acetylneuraminate”, “N-acylneuraminate”, “N-acetylneuraminic acid” are usedinterchangeably and refer to an acidic sugar comprising but not limited to Neu4Ac; Neu5Ac; Neu4,5Ac2;Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4;Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO). The term “freesialic acid” as used herein refers to unbound sialic acid, i.e. a sialic acid residue that is not bound to another molecule or that is not present as part of a disaccharide, an oligosaccharide, a polysaccharide or a glycan. The term “sialic acid residue” as used herein refers to a sialic acid molecule that is bound to another molecule or that is present as part of a disaccharide, an oligosaccharide, a polysaccharide or a glycan. The term “glycosyltransferase” as used herein refers to an enzyme capable to catalyse the transfer of asugar moiety of a donor to a specific acceptor, forming glycosidic bonds. Said donor can be a precursor asdefined herein. A classification of glycosyltransferases using nucleotide diphospho-sugar, nucleotide monophospho-sugar and sugar phosphates and related proteins into distinct sequence-based families has been described (Campbell et al., Biochem. J. 326, 929-939 (1997)) and is available on the CAZy (CArbohydrate-Active EnZymes) website (www.cazy.org). As used herein the glycosyltransferase can be selected from the list comprising but not limited to: fucosyltransferases, sialyltransferases, galactosyltransferases, glucosyltransferases, mannosyltransferases, N-acetylglucosaminyltransferases, N-acetylgalactosaminyltransferases, N- acetylmannosaminyltransferases, xylosyltransferases, glucuronyltransferases, galacturonyltransferases, glucosaminyltransferases, N-glycolylneuraminyltransferases, rhamnosyltransferases, N- acetylrhamnosyltransferases, UDP-4-amino-4,6-dideoxy-N-acetyl-beta-L-altrosamine transaminases,UDP-N-acetylglucosamine enolpyruvyl transferases and fucosaminyltransferases.Sialyltransferases are glycosyltransferases that transfer a sialic acid (like Neu5Ac) from a donor (like CMP-Neu5Ac) onto an acceptor. Sialyltransferases comprise alpha-2,3-sialyltransferases, alpha-2,6-sialyltransferases and alpha-2,8-sialyltransferases that catalyse the transfer of a sialic acid onto anacceptor via alpha-glycosidic bonds. Sialyltransferases can be found but are not limited to the GT29, GT42,GT52, GT80, GT97 and GT100 CAZy families.The term “monosaccharide” as used herein refers to a sugar that is not decomposable into simpler sugars by hydrolysis, is classed either an aldose or ketose, and contains one or more hydroxyl groups per molecule. Monosaccharides are saccharides containing only one simple sugar.The term “phosphorylated monosaccharide” as used herein refers to a monosaccharide that isphosphorylated. Examples of phosphorylated monosaccharides include but are not limited to glucose-1- phosphate, glucose-6-phosphate, glucose-1,6-bisphosphate, galactose-1-phosphate, fructose-6- phosphate, fructose-1,6-bisphosphate, fructose-1-phosphate, glucosamine-1-phosphate, glucosamine-6- phosphate, N-acetylglucosamine-1-phosphate, mannose-1-phosphate, mannose-6-phosphate or fucose- 1-phosphate. Some, but not all, of these phosphorylated monosaccharides are precursors or intermediates for the production of activated monosaccharide. The terms “activated monosaccharide”, “nucleotide-activated sugar”, “nucleotide-sugar”, “activated sugar”, “nucleoside” or “nucleotide donor” are used herein interchangeably and refer to activated forms of monosaccharides. Examples of activated monosaccharides include but are not limited to UDP-N- acetylglucosamine (UDP-GlcNAc), UDP-N-acetylgalactosamine (UDP-GalNAc), UDP-N-acetylmannosamine (UDP-ManNAc), UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal), GDP-mannose (GDP-Man), UDP- glucuronate, UDP-galacturonate, UDP-2-acetamido-2,6-dideoxy--L-arabino-4-hexulose, UDP-2- acetamido-2,6-dideoxy--L-lyxo-4-hexulose, UDP-N-acetyl-L-rhamnosamine (UDP-L-RhaNAc or UDP-2- acetamido-2,6-dideoxy-L-mannose), dTDP-N-acetylfucosamine, UDP-N-acetylfucosamine (UDP-L-FucNAc or UDP-2-acetamido-2,6-dideoxy-L-galactose), UDP-N-acetyl-L-pneumosamine (UDP-L-PneNAC or UDP-2- acetamido-2,6-dideoxy-L-talose), UDP-N-acetylmuramic acid, UDP-N-acetyl-L-quinovosamine (UDP-L- QuiNAc or UDP-2-acetamido-2,6-dideoxy-L-glucose), GDP-L-quinovose, CMP-sialic acid, GDP-fucose (GDP- Fuc), GDP-rhamnose and UDP-xylose. Nucleotide-sugars act as glycosyl donors in glycosylation reactions. Glycosylation reactions are reactions that are catalysed by glycosyltransferases. The term “CMP-sialic acid” as used herein refers to a nucleotide-activated form of sialic acid comprising but not limited to CMP-Neu5Ac, CMP-Neu4Ac, CMP-Neu5Ac9N3, CMP-Neu4,5Ac2, CMP-Neu5,7Ac2, CMP- Neu5,9Ac2, CMP-Neu5,7(8,9)Ac2, CMP-N-glycolylneuraminic acid (CMP-Neu5Gc) and CMP-KDO. The term “disaccharide” as used herein refers to a saccharide polymer containing two simple sugars, i.e. monosaccharides. Examples of disaccharides comprise lactose (Gal-^1,4-Glc), lacto-N-biose (Gal-^1,3- GlcNAc), N-acetyllactosamine (Gal-^1,4-GlcNAc), LacDiNAc (GalNAc-^1,4-GlcNAc), N-acetylgalactosaminylglucose (GalNAc-^1,4-Glc), Neu5Ac-^2,3-Gal, Neu5Ac-^2,6-Gal, fucopyranosyl- (1-4)-N-glycolylneuraminic acid (Fuc-(1-4)-Neu5Gc), sucrose (Glc-^1,2-Fru), maltose (Glc-^1,4-Glc) and melibiose (Gal-^1,6-Glc). "Oligosaccharide" as the term is used herein and as generally understood in the state of the art, refers to a saccharide polymer containing a small number, typically three to twenty, preferably three to ten, ofsimple sugars, i.e., monosaccharides. The oligosaccharide as used in the present invention can be a linearstructure or can include branches. The linkage (e.g., glycosidic linkage, galactosidic linkage, glucosidiclinkage, etc.) between two sugar units can be expressed, for example, as 1,4, 1->4, or (1-4), used interchangeably herein. For example, the terms “Gal-b1,4-Glc”, “Gal-^1,4-Glc”, “b-Gal-(1->4)-Glc”, “^-Gal- (1->4)-Glc”, “Galbeta1-4-Glc”, “Gal-b(1-4)-Glc” and “Gal-^(1-4)-Glc” have the same meaning, i.e. a beta- glycosidic bond links carbon-1 of galactose (Gal) with the carbon-4 of glucose (Glc). Each monosaccharidecan be in the cyclic form (e.g., pyranose or furanose form). Linkages between the individualmonosaccharide units may include alpha 1->2, alpha 1->3, alpha 1->4, alpha 1->6, alpha 2->1, alpha 2->3, alpha 2->4, alpha 2->6, beta 1->2, beta 1->3, beta 1->4, beta 1->6, beta 2->1, beta 2->3, beta 2->4, andbeta 2->6. An oligosaccharide can contain both alpha- and beta-glycosidic bonds or can contain only alpha-glycosidic or only beta-glycosidic bonds. The term “polysaccharide” refers to a compound consisting of alarge number, typically more than twenty, of monosaccharides linked glycosidically.As used herein, a ‘sialylated milk oligosaccharide’ is to be understood as a negatively charged sialic acidcontaining milk oligosaccharide, i.e., a milk oligosaccharide having a sialic acid residue as defined herein.It has an acidic nature. Such sialylated milk oligosaccharide is a saccharide structure comprising at least three monosaccharide subunits linked to each other via glycosidic bonds, wherein at least one of said monosaccharide subunit is a sialic acid residue. Said sialylated milk oligosaccharide may further comprise a monosaccharide subunit selected from the list comprising, con fucose, galactose, glucose, GlcNAc, GalNAc, mannose, ManNAc, xylose, rhamnose, arabinose, fructose. A sialylated milk oligosaccharide cancontain more than one sialic acid residue, e.g., two, three or more. Said more than one sialic acid residuecan be two, three or more identical sialic acid residues. Said more than one sialic acid residue can also be two, three or more different sialic acid residues. For example, a sialylated milk oligosaccharide can contain one or more Neu5Ac residues and one or more KDO residues. Said one or more sialic acid residues can be present in said sialylated milk oligosaccharide in an alpha-2,3 glycosidic linkage, in an alpha-2,6 glycosidiclinkage and / or in an alpha-2,8 glycosidic linkage. Some examples are 3-SL (3ʹ-sialyllactose or 3’SL orNeu5Ac-^2,3-Gal-^1,4-Glc), 3'-sialyllactosamine, 6-SL (6’sialyllactose, 6ʹ-sialyllactose or 6’SL or Neu5Ac-^2,6-Gal-^1,4-Glc), 3,6-disialyllactose (Neu5Ac-^2,3-(Neu5Ac-^2,6)-Gal-^1,4-Glc), 6,6’-disialyllactose (Neu5Ac-^2,6-Gal-^1,4-(Neu5Ac-^2,6)-Glc), 8,3-disialyllactose (Neu5Ac-^2,8-Neu5Ac-^2,3-Gal-^1,4-Glc), 6'-sialyllactosamine, oligosaccharides comprising 6'sialyllactose (also known as 6’sialyllactose, 6’SLand 6’-SL), oligosaccharide comprising 6’-sialyllactosamine, oligosaccharide comprising 6’-sialyllacto-N- biose, SGG hexasaccharide (Neu5Acα-2,3Galβ -1,3GalNacβ-1,3Galα-1,4Galβ-1,4Gal), sialylated tetrasaccharide (Neu5Ac-α2,3-Gal-β1,4-GlcNAc-β1,4-GlcNAc), sialylated lacto-N-triose, sialylated lacto-N- tetraose, sialyllacto-N-neotetraose, LSTa (Neu5Ac-^2,3-Gal-^1,3-GlcNAc-^1,3-Gal-^1,4-Glc, sialyllacto-N- tetraose a), LSTb (Gal-^1,3-[Neu5Ac-^2,6]-GlcNAc-^1,3-Gal-^1,4-Glc, sialyllacto-N-tetraose b), LSTc (Neu5Ac-^2,6-Gal-^1,4-GlcNAc-^1,3-Gal-^1,4-Glc, sialyllacto-N-tetraose c), LSTd (Neu5Ac-α2,3-Gal-β1,4- GlcNAc-β1,3-Gal-β1,4-Glc, sialyllacto-N-tetraose d), Neu5Ac-^2,6-(Neu5Ac-^2,3-Gal-^1,3)-GlcNAc-^1,3- Gal-^1,4-Glc (DSLNT, disialyllacto-N-tetraose), Neu5Ac-^2,6-Gal-^1,4-GlcNAc-^1,3-[Neu5Ac-^2,6]-Gal- ^1,4-Glc (DSLNnT, disialyllacto-N-neotetraose), monosialyllacto-N-hexaose, disialyllacto-N-hexaose I, monosialyllacto-N-neohexaose I, monosialyllacto-N-neohexaose II, disialyllacto-N-neohexaose, disialyllacto-N-tetraose, disialyllacto-N-hexaose II, 3'-sialyl-3-fucosyllactose, disialomonofucosyllacto-N- neohexaose, monofucosylmonosialyllacto-N-octaose (sialyl Lea), sialyllacto-N-fucohexaose II, disialyllacto-N-fucopentaose II, monofucosyldisialyllacto-N-tetraose, 3’-KDO-lactose, 3’-KDO-lactosamine, 3’-KDO-6’sialyllactose, 3’KDO-8-sialyllactose, KDO-2,3Galβ-1,3GalNAcβ-1,3Galα-1,4Galβ-1,4Gal, KDO-2,3Galβ-1,3GlcNAcβ-1,3Galβ-1,4Glc, KDO-2,3Galβ-1,4GlcNAcβ-1,3Galβ-1,4Glc, 3’-KDO-3- fucosyllactose and oligosaccharides bearing one or several sialic acid residue(s).A non-sialylated milk oligosaccharide as used herein refers to a milk oligosaccharide that has no sialic acidresidue as defined herein. A non-sialylated milk oligosaccharide can be a negatively charged milkoligosaccharide or can be a neutral milk oligosaccharide as described herein. Examples of non-sialylatednegatively charged milk oligosaccharides comprise sulphated milk oligosaccharides like e.g. 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,4-Glc; 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,4-Glc; 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,4-Glc; Gal-^1,4-GlcNAc-^1,6-[3-SO3-Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; 3-SO3-Gal-^1,4-GlcNAc-^1,6-[Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; Gal-^1,4-GlcNAc-^1,6-[3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; 3-SO3-Gal-^1,4-GlcNAc-^1,6-[Gal-^1,3-Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc. Examples ofnon-sialylated neutral milk oligosaccharide comprise neutral fucosylated milk oligosaccharides and neutral non-fucosylated milk oligosaccharides as described herein.The terms ‘neutral oligosaccharide’ and ‘non-charged’ milk oligosaccharide as used herein are usedinterchangeably and refer, as generally understood in the state of the art, to a milk oligosaccharide thathas no negative charge originating from a carboxylic acid group. Examples of such neutral milk oligosaccharide are 2'-fucosyllactose (2’FL), 3-fucosyllactose (3FL), 4-fucosyllactose (4FL), 6-fucosyllactose (6FL), 2',3-difucosyllactose (diFL), lacto-N-triose II (LN3, GlcNAcβ1-3Galβ1-4Glc), lacto-N-tetraose (LNT, Galβ1-3GlcNAcβ1-3Galβ1-4Glc), lacto-N-neotetraose (LNnT, Galβ1-4GlcNAcβ1-3Galβ1-4Glc), lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, Fuc-a1,2-Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal-b1,4-GlcNAc-b1,3- Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-Glc, Gal-b1,4-(Fuc-a1,3- )GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc,Fuc-a1,4-(Fuc-a1,2-Gal-b1,3-)GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, monofucosyllacto-N-hexaose-III,difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'-galactosyllactose, lacto-N-hexaose, lacto-N- neohexaose, para-lacto-N-hexaose, para-lacto-N-neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto- N-neohexaose, trifucosyllacto-N-hexaose, a1,3-galactosyl-3-fucosyllactose, Gal-a1,3-(Fuc-a1,2-)Gal-b1,4- (Fuc-a1,3-)Glc, GalNAc-a1,3-(Fuc-a1,2-)Gal-b1,4-(Fuc-a1,3-)Glc, 2-fucosyllactulose, 3-fucosyl-N- acetyllactosamine, 2'-fucosyl-N-acetyllactosamine, difucosyl-N-acetyllactosamine, 4-fucosyllacto-N-biose, 2'-fucosyllacto-N-biose, difucosyllacto-N-biose, GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, GlcNAc-b1,6-(GlcNAc-b1,3-)Gal-b1,4-Glc, lacto-N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N-novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto- N-neoheptaose, para lacto-N-heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto- N-decaose, novo lacto-N-decaose, lacto-N-neodecaose, para lacto-N-neodecaose (pLNnD), a1,3-galactosyllacto-N-neotetraose, GlcNAc-b1,3-Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc, GlcNAc-b1,6-(Gal-b1,4-GlcNAc-b1,3-)Gal-b1,4-Glc and GlcNAc-b1,6-(Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc. A ‘fucosylated milk oligosaccharide’ as used herein and as generally understood in the state of the art is amilk oligosaccharide that is carrying a fucose-residue. Such fucosylated milk oligosaccharide is a saccharide structure comprising at least three monosaccharide subunits linked to each other via glycosidic bonds, wherein at least one of said monosaccharide subunit is a fucose. A fucosylated milk oligosaccharide can contain more than one fucose residue, e.g., two, three or more. A fucosylated milk oligosaccharide can be a neutral milk oligosaccharide or can comprise one or more sialic acid residues. Fucose can be linked to other monosaccharide subunits comprising glucose, galactose, GlcNAc via alpha-glycosidic bonds comprising alpha-1,2 alpha-1,3, alpha-1,4, alpha-1,6 linkages. Examples comprise 2'-fucosyllactose (2’FL), 3-fucosyllactose (3FL), 4-fucosyllactose (4FL), 6-fucosyllactose (6FL), difucosyllactose (diFL), Lacto-N- fucopentaose I (LNFP I), Gal-a1,3-(Fuc-a1,2-)Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc (Gal-LNFP I), GalNAc-a1,3- (Fuc-a1,2-)Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc (GalNAc-LNFP I), Lacto-N-fucopentaose II (LNFP II), Lacto- N-fucopentaose III (LNFP III), lacto-N-fucopentaose V (LNFP V), lacto-N-fucopentaose VI (LNFP VI), lacto- N-neofucopentaose I, lacto-N-difucohexaose I (LDFH I), lacto-N-difucohexaose II (LDFH II), Monofucosyllacto-N-hexaose III (MFLNH III), difucosyllacto-N-hexaose (a), Difucosyllacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, a1,3-galactosyl-3-fucosyllactose, Gal-a1,3-(Fuc- a1,2-)Gal-b1,4-(Fuc-a1,3-)Glc, GalNAc-a1,3-(Fuc-a1,2-)Gal-b1,4-(Fuc-a1,3-)Glc, 2-fucosyllactulose, 3- fucosyl-N-acetyllactosamine, 2'-fucosyl-N-acetyllactosamine, difucosyl-N-acetyllactosamine, 4- fucosyllacto-N-biose, 2'-fucosyllacto-N-biose, difucosyllacto-N-biose and GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3- )Glc, 3'-Sialyl-2'-fucosyllactose, 6'-Sialyl-2'-fucosyllactose, 6'-Sialyl-3-fucosyllactose, 3'-sialyl-3- fucosyllactose, disialomonofucosyllacto-N-neohexaose, monofucosylmonosialyllacto-N-octaose (sialyl Lea), sialyllacto-N-fucohexaose II, disialyllacto-N-fucopentaose II, monofucosyldisialyllacto-N-tetraose. Examples of neutral fucosylated milk oligosaccharides comprise 2'-fucosyllactose (2’FL), 3-fucosyllactose (3FL), 4-fucosyllactose (4FL), 6-fucosyllactose (6FL), difucosyllactose (diFL), Lacto-N-fucopentaose I (LNFP I), Gal-a1,3-(Fuc-a1,2-)Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc (Gal-LNFP I), GalNAc-a1,3-(Fuc-a1,2-)Gal-b1,3- GlcNAc-b1,3-Gal-b1,4-Glc (GalNAc-LNFP I), Lacto-N-fucopentaose II (LNFP II), Lacto-N-fucopentaose III (LNFP III), lacto-N-fucopentaose V (LNFP V), lacto-N-fucopentaose VI (LNFP VI), lacto-N-neofucopentaose I, lacto-N-difucohexaose I (LDFH I), lacto-N-difucohexaose II (LDFH II), Monofucosyllacto-N-hexaose III (MFLNH III), difucosyllacto-N-hexaose (a), Difucosyllacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, a1,3-galactosyl-3-fucosyllactose, Gal-a1,3-(Fuc-a1,2-)Gal-b1,4-(Fuc-a1,3-)Glc, GalNAc-a1,3-(Fuc-a1,2-)Gal-b1,4-(Fuc-a1,3-)Glc, 2-fucosyllactulose, 3-fucosyl-N-acetyllactosamine, 2'- fucosyl-N-acetyllactosamine, difucosyl-N-acetyllactosamine, 4-fucosyllacto-N-biose, 2'-fucosyllacto-N- biose, difucosyllacto-N-biose and GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc.A ‘neutral non-fucosylated milk oligosaccharide’ as used herein refers to a milk oligosaccharide that hasno negative charge and that does not comprise a sialic acid residue nor a fucose residue. Examples of neutral non-fucosylated milk oligosaccharides comprise lacto-N-triose II (LN3, GlcNAcβ1-3Galβ1-4Glc), lacto-N-tetraose (LNT, Galβ1-3GlcNAcβ1-3Galβ1-4Glc), lacto-N-neotetraose (LNnT, Galβ1-4GlcNAcβ1- 3Galβ1-4Glc), 6'-galactosyllactose, 3'-galactosyllactose, GlcNAc-b1,6-(GlcNAc-b1,3-)Gal-b1,4-Glc, lacto-N- pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N-neohexaose, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N-heptaose, lacto- N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N-decaose, lacto-N-neodecaose, para lacto-N-neodecaose (pLNnD), a1,3-galactosyllacto-N-neotetraose, GlcNAc-b1,3-Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc, GlcNAc-b1,6-(Gal-b1,4-GlcNAc-b1,3-)Gal-b1,4-Glc and GlcNAc-b1,6-(Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc. The terms “a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide”, “an oligosaccharide mixture”, “ amixture of milk oligosaccharides”, “a milk oligosaccharide mixture”, “a mixture” and “a mixture of at leasttwo milk oligosaccharides” as used herein are used interchangeably and refer to a mixture of at least twomilk oligosaccharides comprising at least one sialylated milk oligosaccharide as described herein and at least one non-sialylated milk oligosaccharide as described herein. Milk oligosaccharides or MOs comprise oligosaccharides present in milk found in any phase duringlactation, including colostrum milk, from humans (i.e. human milk oligosaccharides or HMOs) andmammals (i.e. mammalian milk oligosaccharides or MMOs) including but not limited to cows (Bos Taurus),sheep (Ovis aries), goats (Capra aegagrus hircus), bactrian camels (Camelus bactrianus), horses (Equusferus caballus), pigs (Sus scropha), dogs (Canis lupus familiaris), ezo brown bears (Ursus arctos yesoensis), polar bear (Ursus maritimus), Japanese black bears (Ursus thibetanus japonicus), striped skunks (Mephitis mephitis), hooded seals (Cystophora cristata), Asian elephants (Elephas maximus), African elephant (Loxodonta africana), giant anteater (Myrmecophaga tridactyla), common bottlenose dolphins (Tursiops truncates), northern minke whales (Balaenoptera acutorostrata), tammar wallabies (Macropus eugenii), red kangaroos (Macropus rufus), common brushtail possum (Trichosurus Vulpecula), koalas(Phascolarctos cinereus), eastern quolls (Dasyurus viverrinus), platypus (Ornithorhynchus anatinus). Asused herein, MMOs refer to oligosaccharides such as but not limited to 3-fucosyllactose, 2ʹ-fucosyllactose,6-fucosyllactose, 2’,3-difucosyllactose, 2’,2-difucosyllactose, 3,4-difucosyllactose, 6ʹ-sialyllactose, 3ʹ- sialyllactose, 3,6-disialyllactose, 6,6’-disialyllactose, 8,3-disialyllactose, 3,6-disialyllacto-N-tetraose, lactodifucotetraose, lacto-N-tetraose, lacto-N-neotetraose, lacto-N-fucopentaose II, lacto-N- fucopentaose I, lacto-N-fucopentaose III, lacto-N-fucopentaose V, lacto-N-fucopentaose VI, sialyllacto-N- tetraose c, sialyllacto-N-tetraose b, sialyllacto-N-tetraose a, lacto-N-difucohexaose I, lacto-N- difucohexaose II, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, monofucosylmonosialyllacto-N-tetraose c, monofucosyl para-lacto-N-hexaose, monofucosyllacto-N- hexaose III, isomeric fucosylated lacto-N-hexaose III, isomeric fucosylated lacto-N-hexaose I, sialyllacto- N-hexaose, sialyllacto-N-neohexaose II, difucosyl-para-lacto-N-hexaose, difucosyllacto-N-hexaose, difucosyllacto-N-hexaose a, difucosyllacto-N-hexaose c, galactosylated chitosan, fucosylated oligosaccharides, neutral oligosaccharide and / or sialylated oligosaccharides. As used herein, HMOs refer to oligosaccharides such as but not limited to 3-fucosyllactose, 2ʹ-fucosyllactose, 6-fucosyllactose, 2’,3- difucosyllactose, 2’,2-difucosyllactose, 3,4-difucosyllactose, 6ʹ-sialyllactose, 3ʹ-sialyllactose, 3,6- disialyllactose, 6,6’-disialyllactose, 8,3-disialyllactose, 3,6-disialyllacto-N-tetraose, lactodifucotetraose, lacto-N-tetraose, lacto-N-neotetraose, lacto-N-fucopentaose II, lacto-N-fucopentaose I, lacto-N- fucopentaose III, lacto-N-fucopentaose V, lacto-N-fucopentaose VI, sialyllacto-N-tetraose c, sialyllacto-N- tetraose b, sialyllacto-N-tetraose a, lacto-N-difucohexaose I, lacto-N-difucohexaose II, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, monofucosylmonosialyllacto-N-tetraose c, monofucosyl para-lacto-N-hexaose, monofucosyllacto-N-hexaose III, isomeric fucosylated lacto-N-hexaose III, isomeric fucosylated lacto-N-hexaose I, sialyllacto-N-hexaose, sialyllacto-N-neohexaose II, difucosyl-para-lacto-N- hexaose, difucosyllacto-N-hexaose, difucosyllacto-N-hexaose a, difucosyllacto-N-hexaose c, galactosylated chitosan, fucosylated oligosaccharides, neutral oligosaccharide and / or sialylated oligosaccharides. The terms “LNT II”, “LNT-II”, “LN3”, “lacto-N-triose II”, “lacto-N-triose II”, “lacto-N-triose”, “lacto-N-triose” or “GlcNAcβ1-3Galβ1-4Glc” as used in the present invention, are used interchangeably. The terms “LNT”, “lacto-N-tetraose”, “lacto-N-tetraose” or “Galβ1-3GlcNAcβ1-3Galβ1-4Glc” as used in the presentinvention, are used interchangeably. The terms “LNnT”, “lacto-N-neotetraose”, “lacto-N-neotetraose”,“neo-LNT” or “Galβ1-4GlcNAcβ1-3Galβ1-4Glc” as used in the present invention, are used interchangeably. The terms “LSTa”, “LS-Tetrasaccharide a”, “Sialyl-lacto-N-tetraose a”, “sialyllacto-N-tetraose a” or “Neu5Ac-^2,3-Gal-^1,3-GlcNAc-^1,3-Gal-^1,4-Glc” as used in the present invention, are usedinterchangeably. The terms “LSTb”, “LS-Tetrasaccharide b”, “Sialyl-lacto-N-tetraose b”, “sialyllacto-N-tetraose b” or “Gal-^1,3-(Neu5Ac-^2,6)-GlcNAc-^1,3-Gal-^1,4-Glc” as used in the present invention, areused interchangeably. The terms “LSTc”, “LS-Tetrasaccharide c”, “Sialyl-lacto-N-tetraose c”, “sialyllacto-N-tetraose c”, “sialyllacto-N-neotetraose c” or “Neu5Ac-^2,6-Gal-^1,4-GlcNAc-^1,3-Gal-^1,4-Glc” as usedin the present invention, are used interchangeably. The terms “LSTd”, “LS-Tetrasaccharide d”, “Sialyl-lacto-N-tetraose d”, “sialyllacto-N-tetraose d”, “sialyllacto-N-neotetraose d” or “Neu5Ac-^2,3-Gal-^1,4-GlcNAc-^1,3-Gal-^1,4-Glc” as used in the present invention, are used interchangeably. The terms“DSLNnT” and “Disialyllacto-N-neotetraose” are used interchangeably and refer to Neu5Ac-^2,6-Gal- ^1,4-GlcNAc-^1,3-[Neu5Ac-^2,6]-Gal-^1,4-Glc. The terms “DSLNT”, “DS-LNT” and “Disialyllacto-N- tetraose” are used interchangeably and refer to Neu5Ac-^2,6-(Neu5Ac-^2,3-Gal-^1,3)-GlcNAc-^1,3-Gal- ^1,4-Glc. The term “membrane transporter proteins” as used herein refers to proteins that are part of or interact with the cell membrane and control the flow of molecules and information across the cell. The membraneproteins are thus involved in transport, be it import into or export out of the cell. Such membranetransporter proteins can be but are not limited to porters, P-P-bond-hydrolysis-driven transporters, β- Barrel Porins, auxiliary transport proteins and phosphotransfer-driven group translocators (Forrest et al., Biochim. Biophys. Acta 1807 (2011) 167-188; Lengeler, J. Mol. Microbiol. Biotechnol. 25 (2015) 79-93; Moraes and Reithmeier, Biochim. Biophys. Acta 1818 (2012), 2687-2706; Saier et al., Nucleic Acids Res. 44 (2016) D372-D379).The term “pathway for production of at least one sialylated milk oligosaccharide” as used herein is abiochemical pathway consisting of the enzymes and their respective genes involved in the synthesis of atleast one sialylated milk oligosaccharide as defined herein. Said pathway for production of at least onesialylated milk oligosaccharide can comprise but is not limited to pathways involved in the synthesis of anucleotide-activated sugar and the transfer of said nucleotide-activated sugar to an acceptor to create at least one sialylated milk oligosaccharide of the present invention. An example of such pathway is a sialylation pathway. Further examples of such pathway comprise but are not limited to a fucosylation, galactosylation, N-acetylglucosaminylation, N-acetylgalactosaminylation, mannosylation, N- acetylmannosaminylation pathway. A ‘sialylation pathway’ is a biochemical pathway consisting of at least one of the enzymes and theirrespective genes selected from the list comprising, consisting of or consisting essentially of an L-glutamine—D-fructose-6-phosphate aminotransferase, a phosphoglucosamine mutase, an N- acetylglucosamine-6-P deacetylase, an N-acylglucosamine 2-epimerase, a hydrolyzing UDP-N- acetylglucosamine 2-epimerase, an N-acetylmannosamine-6-phosphate 2-epimerase, a UDP-GlcNAc 2- epimerase / kinase, a glucosamine 6-phosphate N-acetyltransferase, an N-acetylglucosamine-6-phosphate phosphatase, a phosphoacetylglucosamine mutase, an N-acetylglucosamine 1-phosphate uridylyltransferase, a glucosamine-1-phosphate acetyltransferase, an Neu5Ac synthase, an N- acetylneuraminate lyase, an N-acylneuraminate-9-phosphate synthase, an N-acylneuraminate-9-phosphatase, a sialic acid transporter, a CMP-sialic acid synthase, d-arabinose 5-phosphate isomerase, aKDO-8P synthase, a KDO 8-phosphate phosphatase and a CMP-KDO synthetase combined with asialyltransferase leading to α 2,3; α 2,6 and / or α 2,8 sialylated oligosaccharides. The terms “hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase”, “hydrolyzing UDP-N-acylglucosamine 2-epimerase”, “hydrolyzing UDP-GlcNAc-2-epimerase”, “hydrolyzing UDP-N-acetyl-D-glucosamine 2- epimerase”, “hydrolyzing UDP-N-acetylglucosamine-2-epimerase”, “hydrolyzing UDP-N- acetylglucosamine 2-epimerase”, “hydrolyzing uridine diphosphate-N-acetylglucosamine-2’-epimerase” and “hydrolyzing uridine diphosphoacetylglucosamine 2’-epimerase” are used interchangeably and refer to an enzyme that catalyses the reaction UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) = N-acetylmannosamine (ManNAc). The nnaA and the neuC polypeptide are examples of hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerases. The term “non-hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase” refers to an enzyme that catalyses the reaction UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) = UDP-N-acetylmannosamine (UDP-ManNAc). The terms “N-acetylneuraminate synthase”, “N-acetylneuraminic acid synthase”, “N-acetylneuraminic acid synthetase”, “sialic acid synthase”, “sialic acid synthetase” and “neuB” are used interchangeably and refer to an enzyme that catalyses the conversion of N-acetylmannosamine (ManNAc) to N- acetylneuraminate (or sialic acid, Neu5Ac). The term “N-acylneuraminate cytidylyltransferase”, “CMP-N-acetylneuraminic acid synthase”, “CMP- NeuNAc synthase”, “CMP-NeuNAc synthetase”, “CMP-sialic acid synthase”, “CMP-sialic acid synthetase” and “neuA” are used interchangeably and refer to an enzyme that catalyses the conversion of sialic acid into CMP-sialic acid. The term “reductive pathway” as used herein is a biochemical pathway that results in the cytoplasmic environment of the cell to be reducing, wherein said reducing environment negatively influences proper protein folding and blocks disulfide bond formation. Examples of a reductive pathway comprise but are not limited to the reductive acetyl-CoA-pathway, the reductive pyrimidine catabolic pathway, thereductive citric acid cycle, the thiol-redox pathway and the reductive glycine pathway. A reducingcytoplasm means e.g. that the NADP+:NADPH ratio in said cytoplasmic environment is low and / or thatthe glutathione (GSH) levels are high (e.g., 10 mM). Reducing environments may affect the oxidation state of a molecule, thereby altering its solubility. The terms “glutathione reductase”, “glutathione reductase (NADPH)”, “glutathione S-reductase”, “GSH reductase”, “GSSG reductase”, “NADPH:oxidized-glutathione oxidoreductase” “NADPH-glutathionereductase”, “NADPH-GSSG reductase”, “gor”, “GR” and “GRase” are used interchangeably and refer to anenzyme that catalyses the reaction 2 glutathione + NADP+ = glutathione disulfide + H+ + NADPH.The terms “thioredoxin reductase”, "thioredoxin-disulfide reductase”, “NADPH:oxidized thioredoxin oxidoreductase”, “NADPH—thioredoxin reductase”, “NADP—thioredoxin reductase”, “thioredoxinreductase (NADPH)”, “trxB” and “TRXR”, are used interchangeably and refer to an enzyme that catalysesthe reaction [thioredoxin]-dithiol + NADP+ = [thioredoxin]-disulfide + H++ NADPH.The terms “disulfide bond isomerase”, “protein disulfide-isomerase”, “S-S rearrangase” and “PDI” areused interchangeably and refer to an enzyme that catalyses the rearrangement of disulfide bonds in proteins. The terms “disulfide oxidoreductase”, “disulfide oxidoreductase 2”, “thiol:disulfide oxidoreductase”,“dsbC” and “xprA” are used interchangeably and refer to an enzyme that is reported to be involved inprotein disulfide bond rearrangement and / or formation.The terms “thiol oxidase” and “sulfhydryl oxidase” are used interchangeably and refer to an enzyme thatcatalyses the reaction O2 + 2R’C(R)SH = H2O2 + R’C(R)S-S(R)CR’.The term “chaperone” refers to an enzyme that assist in protein folding. Examples are PDI, SecB, ERp57,heat shock proteins or Hsps, such as e.g., Hsp10, Hsp60, Hsp70, Hsp90. The terms “pyruvatedehydrogenase”, “pyruvate oxidase”, “POX”, “poxB” and “pyruvate:ubiquinone-8 oxidoreductase” are used interchangeably and refer to an enzyme that catalyses the oxidative decarboxylation of pyruvate to produce acetate and CO2. The terms “lactate dehydrogenase”, “D-lactate dehydrogenase”, “ldhA”, “hslI”, “htpH”, “D-LDH”, “fermentative lactate dehydrogenase” and “D-specific 2-hydroxyacid dehydrogenase” are used interchangeably and refer to an enzyme that catalyses the conversion of lactate into pyruvate hereby generating NADH. The term “enabled efflux” means to introduce the activity of transport of a solute over the cytoplasm membrane and / or the cell wall. Said transport may be enabled by introducing and / or increasing the expression of a membrane transporter protein as described in the present invention. The term “enhanced efflux” means to improve the activity of transport of a solute over the cytoplasm membrane and / or thecell wall. Transport of a solute over the cytoplasm membrane and / or cell wall may be enhanced byintroducing and / or increasing the expression of a membrane transporter protein as described in the present invention. “Expression” of a membrane transporter protein is defined as “overexpression” of the gene encoding said membrane transporter protein in the case said gene is an endogenous gene or “expression” in the case the gene encoding said membrane transporter protein is a heterologous gene that is not present in the wild-type strain or cell. The term "purified" refers to material that is substantially or essentially free from components that interfere with the activity of the biological molecule. For cells, saccharides, nucleic acids, and polypeptides, the term "purified" refers to material that is substantially or essentially free fromcomponents that normally accompany the material as found in its native state. Typically, purifiedsaccharides, oligosaccharides, proteins or nucleic acids of the invention are at least about 50 %, 55 %, 60%, 65 %, 70 %, 75 %, 80 % or 85 % pure, usually at least about 90 %, 91 %, 92 %, 93 %, 94 %, 95 %, 96 %,97 %, 98 %, or 99.0 % pure as measured by band intensity on a silver-stained gel or other method fordetermining purity. Purity or homogeneity can be indicated by a number of means well known in the art, such as polyacrylamide gel electrophoresis of a protein or nucleic acid sample, followed by visualization upon staining. For certain purposes high resolution will be needed and HPLC or a similar means forpurification utilized. For di- and oligosaccharides, purity can be determined using methods such as but notlimited to thin layer chromatography, gas chromatography, NMR, HPLC, capillary electrophoresis or massspectroscopy. Further herein, the terms "contaminants" and "impurities" preferably mean particulates,cells, cell components, metabolites, cell debris, proteins, peptides, amino acids, nucleic acids, glycolipids and / or endotoxins which can be present in an aqueous medium like e.g., a cultivation or an incubation. The term "clarifying" as used herein refers to the act of treating an aqueous medium like e.g., a cultivation or an incubation, to remove suspended particulates and contaminants from the production process, like e.g., cells, cell components, insoluble metabolites and debris, that could interfere with the eventual purification of the mixture of at least two milk oligosaccharides as described herein. Such treatment can be carried out in a conventional manner by centrifugation, flocculation, flocculation with optional ultrasonic treatment, gravity filtration, microfiltration, foam separation or vacuum filtration (e.g., througha ceramic filter which can include a Celite™ filter aid).The term “cultivation” refers to the culture medium wherein the cell is cultivated, or fermented, the cellitself, and a mixture of at least two milk oligosaccharides as described herein that is produced by the cellin whole broth, i.e. inside (intracellularly) as well as outside (extracellularly) of the cell. The terms “culture medium” and “cultivation medium” as used herein are used interchangeably and refer to the medium wherein the cell is cultivated.The term “incubation” refers to a mixture wherein a mixture of at least two milk oligosaccharides asdescribed herein is produced. Said incubation can comprise one or more enzyme(s), one or moreprecursor(s) and one or more acceptor(s) as defined herein present in a buffered solution and incubatedfor a certain time at a certain temperature enabling production of a mixture of at least two milkoligosaccharides as described herein, catalysed by said one or more enzyme(s) using said one or moreprecursor(s) and said one or more acceptor(s) in said incubation. Said incubation can also comprise i) thecell obtained after cultivation or incubation, optionally said cell is subjected to cell lysis, ii) a bufferedsolution or the cultivation or incubation medium wherein the cell was cultivated or fermented, and iii) amixture of at least two milk oligosaccharides as described herein that is produced by the cell in wholebroth, i.e. inside (intracellularly) as well as outside (extracellularly) of the cell. Said incubation can also be the cultivation as defined herein.The terms “reactor” and “incubator” refer to the recipient filled with the cultivation or incubation.Examples of reactors and incubators comprise but are not limited to microfluidic devices, well plates, tubes, shake flasks, fermenters, bioreactors, process vessels, cell culture incubators, CO2 incubators. As used herein, the term "cell productivity index (CPI)" refers to the mass of the sialylated milk oligosaccharide produced by the cells divided by the mass of the cells produced in the culture. Alternatively, the term "cell productivity index (CPI)" refers to the mass of the non-sialylated milk oligosaccharide produced by the cells divided by the mass of the cells produced in the culture. The term “precursor” as used herein refers to substances which are taken up or synthetized by the cellfor the specific production of a sialylated milk oligosaccharide and / or a non-sialylated milk oligosaccharideof said mixture of at least two milk oligosaccharides according to the present invention. In this sense a precursor can be an acceptor as defined herein, but can also be another substance, metabolite, which isfirst modified within the cell as part of the biochemical synthesis route of a sialylated milk oligosaccharideand / or a non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides. Theterm “precursor” as used herein is also to be understood as a chemical compound that participates in achemical or enzymatic reaction to produce another compound like e.g. an intermediate or an acceptor asdefined herein, as part in the metabolic pathway of a sialylated milk oligosaccharide and / or a non- sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides. The term “precursor”as used herein is also to be understood as a donor that is used by a glycosyltransferase to modify anacceptor as defined herein with a sugar moiety in a glycosidic bond, as part in the metabolic pathway ofa sialylated milk oligosaccharide and / or a non-sialylated milk oligosaccharide of said mixture of at leasttwo milk oligosaccharides. Examples of such precursors comprise the acceptors as defined herein, and / or a sialic acid residue, sialic acid, dihydroxyacetone, glucose, galactose, glucosamine, N-acetylglucosamine, N-acetylmannosamine, galactosamine, N-acetylgalactosamine, galactosyllactose, phosphorylated sugarsor sugar phosphates like e.g. but not limited to glucose-1-phosphate, galactose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-bisphosphate, mannose-6-phosphate, mannose-1- phosphate, glycerol-3-phosphate, glyceraldehyde-3-phosphate, dihydroxyacetone-phosphate, glucosamine-6-phosphate, N-acetylglucosamine-6-phosphate, N-acetylmannosamine-6-phosphate, N- acetylglucosamine-1-phosphate, N-acetylneuraminic acid-9-phosphate and nucleotide-activated sugarslike nucleotide diphospho-sugars and nucleotide monophospho-sugars as defined herein like e.g. UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal), UDP-N-acetylglucosamine (UDP-GlcNAc), UDP-N-acetylgalactosamine (UDP-GalNAc), CMP-sialic acid, CMP-Neu5Ac, GDP-mannose, GDP-4-dehydro-6-deoxy-α-D-mannose, GDP-fucose.Optionally, the cell is transformed to comprise and to express at least one nucleic acid sequence encodinga protein selected from the list consisting of lactose transporter, N-acetylneuraminic acid transporter,fucose transporter, glucose transporter, galactose transporter, transporter for a nucleotide-activatedsugar wherein said transporter internalizes a to the medium added precursor for the synthesis of the6’sialylated oligosaccharide of present invention.The term “acceptor” as used herein refers to a mono-, di- or oligosaccharide, which can be modified by aglycosyltransferase. Examples of such acceptors comprise glucose, galactose, fructose, glycerol, sialic acid,fucose, mannose, maltose, sucrose, lactose, lacto-N-triose (LN3), lacto-N-tetraose (LNT), lacto-N-neotetraose (LNnT), lacto-N-pentaose (LNP), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N- neopentaose, lacto-N-novopentaose I, lacto-N-hexaose (LNH), lacto-N-neohexaose (LNnH), para lacto-N- neohexaose (pLNnH), para lacto-N-hexaose (pLNH), lacto-N-heptaose, lacto-N-neoheptaose, para lacto- N-neoheptaose, para lacto-N-heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose, iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose, lacto-N-decaose, iso lacto-N-decaose, novo lacto-N-decaose, lacto-N-neodecaose, LSTa, LSTc, and oligosaccharide containing 1 or more N- acetyllactosamine units and / or 1 or more lacto-N-biose units or an intermediate into oligosaccharide, fucosylated and sialylated versions thereof. Detailed description of the inventionIt was found by the present inventors that two important nucleotide-sugar donors in the production of amixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide, are CMP-sialic acid, like e.g. CMP-Neu5Ac, and UDP- GlcNAc. CMP-sialic acid is used in the production of the sialylated milk oligosaccharide, providing the at least one sialic acid residue that is present in the sialylated milk oligosaccharide. UDP-GlcNAc can be used both in the production of the sialylated milk oligosaccharide and in the production of the non-sialylated milk oligosaccharide. UDP-GlcNAc may, in the pathway towards the production of a sialylated milk oligosaccharide, act as a precursor in the synthesis of CMP-sialic acid: a hydrolyzing UDP-N-acetyl-D- glucosamine-2-epimerase first converts UDP-GlcNAc into N-acetylmannosamine (ManNAc), followed by synthesis of CMP-sialic acid out of ManNAc via consecutive action of an N-acetylneuraminate synthase and an N-acylneuraminate cytidylyltransferase enzyme. Additionally, UDP-GlcNAc may, in the pathway towards the production of a sialylated milk oligosaccharide, be directly used by an appropriate glycosyltransferase as a donor for addition of a GlcNAc residue in the growing oligosaccharide chain of a sialylated milk oligosaccharide. Additionally, and / or alternatively, UDP-GlcNAc can be used as nucleotide- sugar donor for appropriate glycosyltransferases in the pathway towards the production of a non- sialylated milk oligosaccharide, by providing a GlcNAc residue that can be added to a growing oligosaccharide chain of a non-sialylated milk oligosaccharide. Based on the above, UDP-GlcNAc is a central molecule both in the production of the at least one sialylated milk oligosaccharide and the at least one non-sialylated milk oligosaccharide in the mixture of at least two milk oligosaccharides as described herein. The usage of UDP-GlcNAc for production of CMP-sialic acid and / or as donor for a GlcNAc residue impacts the production and thus the concentration of the at least one sialylated milk oligosaccharide in said mixture of at least two milk oligosaccharides. Also, usage of UDP-GlcNAc impacts the production of the at least one non-sialylated oligosaccharide in said mixture. To limit and / or exclude the usage of UDP-GlcNAc in the pathway towards cellular CMP-sialic acid synthesis and to have more UDP-GlcNAc available as donor for GlcNAc of an appropriate glycosyltransferase, one could synthesize ManNAc via a pathway generating unconjugated (i.e. free) GlcNAc wherein said GlcNAc is converted into ManNAc via an N-acylglucosamine 2-epimerase. However, synthesis of free GlcNAc in the context of a cellular system for production of a human milk oligosaccharide mixture is not preferred due to the unwanted side-production of unconjugated, i.e. free, N-acetyllactosamine (LacNAc, Gal-^1,4- GlcNAc) and / or unconjugated, i.e. free, lacto-N-biose (LNB, Gal-^1,3-GlcNAc) that can be formed out of said free GlcNAc by compatible glycosyltransferases. Thus, the use of an N-acylglucosamine 2-epimerase is not desired when designing a cellular production system for the production of a mixture of at least two human milk oligosaccharides comprising at least one sialylated human milk oligosaccharide and at leastone non-sialylated human milk oligosaccharide. Said side-production of LacNAc and / or LNB is less and / ornot problematic when producing a mixture of at least two mammalian non-human milk oligosaccharides comprising at least one sialylated mammalian non-human milk oligosaccharide and at least one non- sialylated mammalian non-human milk oligosaccharide. Increasing the availability of the UDP-GlcNAc pool in the cell by enhancing UDP-GlcNAc synthesis is also not an appropriate solution, as this will not result in cellular production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide either, but will result in the production of a single milk oligosaccharide and not in a milk oligosaccharide mixture comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide like is e.g. described in WO 2014 / 153253. Altogether, tight control of UDP-GlcNAc consumption in the cell is of utmost importance to finetune the desired production levels of the at least one sialylated milk oligosaccharide in said mixture of at least two milk oligosaccharides. According to a first aspect, the present invention provides a cell metabolically engineered for the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide, said cell comprising: -a pathway for production of said at least one sialylated milk oligosaccharide, wherein saidpathway comprises production of UDP-N-acetylglucosamine (UDP-GlcNAc), conversion of said UDP-GlcNAc into N-acetylmannosamine (ManNAc) by action of a hydrolyzing UDP-N-acetyl-D- glucosamine-2-epimerase, and conversion of said ManNAc into CMP-sialic acid by consecutive action of an N-acetylneuraminate synthase and an N-acylneuraminate cytidylyltransferase, and -a pathway for production of said at least one non-sialylated milk oligosaccharide,characterized in that the amount of said at least one sialylated milk oligosaccharide produced in said mixture of at least two milk oligosaccharides is determined by: -choice of said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminatesynthase and / or N-acylneuraminate cytidylyltransferase, -swapping the native promoter of any one of the genes encoding said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase with a promoter of interest, -swapping the native 5’untranslated region (5’UTR) of any one of the genes encoding saidhydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N- acylneuraminate cytidylyltransferase with a 5’UTR of interest, -modifying the copy number of any one of the genes encoding said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase, and / or -expressing any one of the genes encoding said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase from a different locus on the chromosome and / or from a vector that is used to transform said cell.In a second aspect, the present invention provides a method for the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide by a cell, the method comprising cultivating and / or incubating a cell as described herein in cultivation and / or incubation medium under conditions permissive to produce said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide. Optionally, the method further comprises separation and / or purification of said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide from said cultivation and / or incubation. In a specific embodiment, the cell of present invention comprises a pathway for production of the at least one sialylated milk oligosaccharide that is present in said mixture of at least two milk oligosaccharides as described herein. In a preferred embodiment, said pathway for production of said at least one sialylated milk oligosaccharide is a sialylation pathway. In another preferred embodiment, the cell is genetically engineered to comprise a sialylation pathway. In another and / or additional preferred embodiment, the cell comprises a sialylation pathway wherein said sialylation pathway has been genetically engineered. In another and / or additional preferred embodiment, the cell is genetically engineered for production of a sialic acid residue as described herein. Examples of such pathways comprise but are not limited to pathways involved in the synthesis of monosaccharide, phosphorylated monosaccharide, nucleotide- activated sugar, and / or glycosylation pathways like e.g., a fucosylation, sialylation, galactosylation, N- acetylglucosaminylation, N-acetylgalactosaminylation, mannosylation and / or N-acetylmannosaminylation pathway. Said pathway for production of the at least one sialylated milkoligosaccharide that is present in said mixture of at least two milk oligosaccharides as described herein preferably comprises at least one sialyltransferase. Said cell may further comprise and express at leastone further glycosyltransferase that is involved in the production of said at least one sialylated milkoligosaccharide. In an alternative preferred embodiment, the cell is genetically engineered to comprise a pathway for production of the at least one sialylated milk oligosaccharide that is present in said mixture of at least two milk oligosaccharides as described herein, and to have modified expression or activity of a sialyltransferase. Preferably, the cell as described herein comprises a sialylation pathway comprising at least one enzymeselected from the list comprising, consisting of or consisting essentially of L-glutamine—D-fructose-6-phosphate aminotransferase, phosphoglucosamine mutase, N-acetylglucosamine-6-P deacetylase, N- acylglucosamine 2-epimerase, UDP-N-acetylglucosamine 2-epimerase, N-acetylmannosamine-6- phosphate 2-epimerase, UDP-GlcNAc 2-epimerase / kinase, glucosamine 6-phosphate N-acetyltransferase, N-acetylglucosamine-6-phosphate phosphatase, phosphoacetylglucosamine mutase, N- acetylglucosamine 1-phosphate uridylyltransferase, glucosamine-1-phosphate acetyltransferase, Neu5Ac synthase, N-acetylneuraminate lyase, N-acylneuraminate-9-phosphate synthase, N-acylneuraminate-9-phosphatase, sialic acid transporter, CMP-sialic acid synthase, d-arabinose 5-phosphate isomerase, aKDO-8P synthase, a KDO 8-phosphate phosphatase and a CMP-KDO synthetase, and sialyltransferase.In another specific embodiment, the cell of present invention comprises a pathway for production of the at least one sialylated milk oligosaccharide that is present in said mixture of at least two milk oligosaccharides as described herein, wherein said pathway comprises production of UDP-N- acetylglucosamine (UDP-GlcNAc), conversion of said UDP-GlcNAc into N-acetylmannosamine (ManNAc) by action of a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, and conversion of said ManNAc into CMP-sialic acid by consecutive action of an N-acetylneuraminate synthase and an N-acylneuraminatecytidylyltransferase. The cell used herein is optionally genetically engineered to express the de novosynthesis of UDP-GlcNAc. UDP-GlcNAc can be provided by an enzyme expressed in the cell or by the metabolism of the cell. Such cell producing an UDP-GlcNAc can express enzymes converting, e.g. GlcNAc, which is to be added to the cell, to UDP-GlcNAc. These enzymes may be any one or more of the list comprising, consisting of or consisting essentially of an N-acetyl-D-glucosamine kinase, an N- acetylglucosamine-6-phosphate deacetylase, a phosphoglucosamine mutase, and an N- acetylglucosamine-1-phosphate uridylyltransferase / glucosamine-1-phosphate acetyltransferase from several species including Homo sapiens, Escherichia coli. Preferably, the cell is modified to produce UDP- GlcNAc. More preferably, the cell is modified for enhanced UDP-GlcNAc production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knock-out of an N-acetylglucosamine-6-phosphate deacetylase, over-expression of an L-glutamine—D-fructose-6- phosphate aminotransferase, over-expression of a phosphoglucosamine mutase, and over-expression of an N-acetylglucosamine-1-phosphate uridylyltransferase / glucosamine-1-phosphate acetyltransferase. In an additional specific embodiment, the cell of present invention comprises a pathway for production of the at least one non-sialylated milk oligosaccharide that is present in said mixture of at least two milk oligosaccharides as described herein. In a preferred embodiment, said pathway for production of said at least one non-sialylated milk oligosaccharide is selected from the list comprising, consisting of or consisting essentially of fucosylation pathway, galactosylation pathway, N-acetylglucosaminylation pathway, N-acetylgalactosaminylation pathway, mannosylation pathway and N- acetylmannosaminylation pathway. According to present invention, the amount of the at least one sialylated milk oligosaccharide that is produced by the cell of present invention in said mixture of at least two milk oligosaccharides is determined by: -choice of the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminatesynthase and / or N-acylneuraminate cytidylyltransferase, -swapping the native promoter of any one of the genes encoding the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase with a promoter of interest, -swapping the native 5’untranslated region (5’UTR) of any one of the genes encoding thehydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N- acylneuraminate cytidylyltransferase with a 5’UTR of interest,- modifying the copy number of any one of the genes encoding the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase, and / or -expressing any one of the genes encoding the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase from a different locus on the chromosome and / or from a vector that is used to transform said cell. In other words, it is to be understood that the amount of the at least one sialylated milk oligosaccharide that is produced by the cell of present invention in said mixture of at least two milk oligosaccharides is determined by the activity and / or expression levels of any one of the hydrolyzing UDP-N-acetyl-D- glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferasethat is / are expressed in said pathway for production of said at least one sialylated milk oligosaccharide insaid cell, since said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthaseand / or N-acylneuraminate cytidylyltransferase are involved in conversion of UDP-GlcNAc into CMP-sialicacid. Specifically, a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase is able to convert and / orconverts UDP-GlcNAc into ManNAc; an N-acetylneuraminate synthase is able to convert and / or converts ManNAc into sialic acid; an N-acylneuraminate cytidylyltransferase is able to convert and / or converts sialic acid into CMP-sialic acid. The hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase thus orchestrate (1) the useof the UDP-GlcNAc pool that is available in the cell towards synthesis of CMP-sialic acid and (2) the production and / or availability of CMP-sialic acid to be used in the production of said at least one sialylatedmilk oligosaccharide. The hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminatesynthase and / or N-acylneuraminate cytidylyltransferase also affects the UDP-GlcNAc pool that is available for compatible glycosyltransferases, like e.g. N-acetylglucosaminyltransferases, that transfer GlcNAc from said UDP-GlcNAc to a growing oligosaccharide chain of a sialylated milk oligosaccharide and / or a non-sialylated milk oligosaccharide. As such, the activity and / or expression levels of any one of hydrolyzingUDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and N-acylneuraminatecytidylyltransferase affects production of said at least one sialylated milk oligosaccharide and possiblyproduction of said at least one non-sialylated milk oligosaccharide. The amount of the at least one sialylated milk oligosaccharide that is produced by the cell of present invention in said mixture of at least two milk oligosaccharides can be increased or decreased based on the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N- acylneuraminate cytidylyltransferase that is selected to be expressed in the cell wherein the selected hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase can have a higher or lower enzymatic activity compared to theenzymatic activity of the native hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase, respectively, expressed in the cell. The cell of present invention may also have no native genes encoding a hydrolyzing UDP-N-acetyl- D-glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase and may be modified to express a recombinant gene encoding a hydrolyzing UDP-N- acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase. Additionally, and or alternatively, the amount of the at least one sialylated milk oligosaccharide that is produced by the cell of present invention in said mixture of at least two milk oligosaccharides can be increased or decreased by amending the expression levels of the genes encoding the selected hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase. The term “amending” as used herein is to be understood as “increasing” or “decreasing”. Expression levels of a gene can be amended by swapping the native promoter of the gene with a promoterof interest, wherein said promoter of interest has a different, increased or decreased activity to controlexpression of the gene compared to the native promoter of said gene. In a preferred embodiment ofpresent invention, said promoter of interest is selected from the list consisting of SEQ ID NO 15, 16 and 17. Additionally, and / or alternatively, the expression levels of a gene can be amended by swapping the native5’untranslated region (5’UTR) of the gene with a 5’UTR of interest, wherein said 5’UTR of interest has adifferent, increased or decreased activity to control expression of the gene compared to the native 5’UTRof said gene. In a preferred embodiment of present invention, said 5’UTR of interest is selected from thelist consisting of SEQ ID NO 18 and 19. Additionally, and / or alternatively, the expression levels of a gene can be amended by modifying the copy number of a gene. The term “modifying” as used herein is to be understood as “increasing” or “decreasing”. Additionally, and / or alternatively, the expression levels of a gene can be amended by expressing the gene from a different locus on the chromosome compared to its native location on the chromosome. Additionally, and / or alternatively, the expression levels of a gene can be amended by introduction of a transcriptional unit of said gene on the chromosome of the cell and / or on a vector that is used to transform said cell. Additionally, and / or alternatively, the expression levels of a gene can be amended by the choice of vector that is used to express the gene from. Types of vectors that can be used herein comprise but are not limited to high-copy plasmids, low-copy plasmids, episomal vectors, cosmids. In a preferred embodiment of the method and / or cell of present invention, the cell expresses a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and N- acylneuraminate cytidylyltransferase as described herein. In a preferred embodiment of the method and / or cell of the invention, the cell is modified in the expression or activity of a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, an N- acetylneuraminate synthase and / or N-acylneuraminate cytidylyltransferase as described herein. Preferably, said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase is an endogenous protein of the cell with a modified expression or activity, preferably said endogenous hydrolyzing UDP-N-acetyl-D- glucosamine-2-epimerase is overexpressed; alternatively said hydrolyzing UDP-N-acetyl-D-glucosamine- 2-epimerase is a heterologous protein that is heterogeneously introduced and expressed in said cell, preferably overexpressed. Said endogenous hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase can have a modified expression in the cell which also expresses a heterologous hydrolyzing UDP-N-acetyl-D- glucosamine-2-epimerase. Preferably, said N-acetylneuraminate synthase is an endogenous protein of the cell with a modified expression or activity, preferably said endogenous N-acetylneuraminate synthase is overexpressed; alternatively said N-acetylneuraminate synthase is a heterologous protein that is heterogeneously introduced and expressed in said cell, preferably overexpressed. Said endogenous N-acetylneuraminate synthase can have a modified expression in the cell which also expresses a heterologous N- acetylneuraminate synthase. Preferably, said N-acylneuraminate cytidylyltransferase is an endogenous protein of the cell with a modified expression or activity, preferably said endogenous N-acylneuraminate cytidylyltransferase is overexpressed; alternatively said N-acylneuraminate cytidylyltransferase is a heterologous protein that is heterogeneously introduced and expressed in said cell, preferably overexpressed. Said endogenous N- acylneuraminate cytidylyltransferase can have a modified expression in the cell which also expresses a heterologous N-acylneuraminate cytidylyltransferase. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2- epimerase activity and comprises an amino acid sequence comprising a conserved motif [ACILM][GST]N[ST][ST]XXXX[DE][ACGILMST][ACDEGIMPQSTV] with SEQ ID NO 08, wherein X can be anyamino acid residue. The X present in said conserved motif indicates that any single amino acid is possible.Herein, the amino acid can be one of the 20 common amino acids encoded in the genetic code of life (i.e. A, R, N, D, C, Q, E, G, H, I, L, K, M, F, P, S, T, W, Y or V) or can be a modified amino acid (e.g. due to decomposition of a common amino acid like e.g. L-ornithine, or modified by e.g. hydroxylation, carboxylation, phosphorylation, methylation, acetylation, glycosylation, ADP-ribosylation or ubiquitination of a common amino acid). If multiple Xs are present, like in SEQ ID NO 08, each X is an amino acid that results from a new, independent selection made out of the list of possible amino acid residues. In this way, each X present in the conserved motif with SEQ ID NO 08 refers to the same amino acid or to a different amino acid. In a preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl- D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase activity and comprises, consists of or consists essentially of an amino acid sequence that is at least 80 % identical over a stretch of at least 150 amino acid residues to any one of the amino acid sequences as represented by SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09. In a more preferred embodiment, the hydrolyzing UDP-N- acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase activity and comprises, consists of or consists essentially of an amino acid sequence that is at least 80 % identical over a stretch of at least 200 amino acid residues to any one of the amino acid sequences as represented by SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2- epimerase activity and comprises an amino acid sequence comprising an IPR domain selected from thelist comprising IPR003331, IPR020004 and IPR029767 as defined by InterPro 90.0 as released on 4th August2022. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2- epimerase activity and comprises an amino acid sequence comprising a PF02350 motif as defined by PFAM 32.0 as released in September 2018. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2- epimerase activity and comprises an amino acid sequence comprising a cd03786 motif as defined by CDD v3.17 as released in September 2016. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2- epimerase activity and comprises an amino acid sequence comprising a panther domain selected from the list comprising PTHR43174 and PTHR43174:SF3 as defined by PANTHER 17.0 as released on 23rdFebruary 2022. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2- epimerase activity and comprises an amino acid sequence that is at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 96 %, at least 97 %, at least 98 %, at least 98.5 %, or at least 99 % identical to any one of the amino acid sequences as represented by SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09 over astretch of at least 150, at least 160, at least 170, at least 180, at least 190, at least 200, at least 210, atleast 220, at least 230, at least 240, at least 250, at least 260, at least 270, at least 280, at least 290 or at least 300 amino acid residues. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2- epimerase activity and comprises an amino acid sequence that is at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 96 %, at least 97 %, at least 98 %, at least 98.5 %, or at least 99 % identical to any one of the full-length amino acid sequences as represented by SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase comprises an amino acid sequence as represented by any one of SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09 and comprising UDP-N-acetyl-D-glucosamine-2- epimerase activity. In another and / or additional preferred embodiment of the method and / or cell of present invention, the hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase is a nnaA polypeptide or a neuC polypeptide. In a preferred embodiment of the method and / or cell of present invention, the cell is modified with one or more expression modules. Said expression modules are also known as transcriptional units and comprise polynucleotides for expression of recombinant genes including coding gene sequences and appropriate transcriptional and / or translational control signals that are operably linked to the coding genes. Said control signals comprise promoter sequences, untranslated regions (UTR) including 5’UTR and 3’UTR sequences, ribosome binding sites, terminator sequences. Said expression modules can contain elements for expression of one single recombinant gene but can also contain elements for expression of more recombinant genes or can be organized in an operon structure for integrated expression of two or more recombinant genes. Said polynucleotides may be produced by recombinant DNA technology using techniques well-known in the art. Methods which are well known to those skilled in the art to construct expression modules include, for example, in vitro recombinant DNA techniques, synthetic techniques, andin vivo genetic recombination. See, for example, the techniques described in Sambrook et al. (2001)Molecular Cloning: a laboratory manual, 3rd Edition, Cold Spring Harbor Laboratory Press, CSH, New York or to Current Protocols in Molecular Biology, John Wiley and Sons, N.Y. (1989 and yearly updates). The expression of each of said expression modules can be constitutive or is created by a natural or chemical inducer. As used herein, constitutive expression should be understood as expression of a gene that is transcribed continuously in an organism. Expression that is created by a natural inducer should be understood as a facultative or regulatory expression of a gene that is only expressed upon a certain natural condition of the host (e.g. organism being in labour, or during lactation), as a response to an environmental change (e.g. including but not limited to hormone, heat, cold, pH shifts, light, oxidative or osmotic stress / signalling), or dependent on the position of the developmental stage or the cell cycle of said host cell including but not limited to apoptosis and autophagy. Expression that is created by a chemical inducer should be understood as a facultative or regulatory expression of a gene that is only expressed upon sensing of external chemicals (e.g. IPTG, arabinose, lactose, allo-lactose, rhamnose or fucose) via an inducible promoter or via a genetic circuit that either induces or represses the transcription or translation of said polynucleotide to a polypeptide. The expression modules can be integrated in the genome of said cell or can be presented to said cell on a vector. Said vector can be present in the form of a plasmid, cosmid, phage, liposome, or virus, which is to be stably transformed / transfected into said metabolically engineered cell. Such vectors include, among others, chromosomal, episomal and virus-derived vectors, e.g., vectors derived from bacterial plasmids, from bacteriophage, from transposons, from yeast episomes, from insertion elements, from yeast chromosomal elements, from viruses, and vectors derived from combinations thereof, such as thosederived from plasmid and bacteriophage genetic elements, such as cosmids and phagemids. These vectorsmay contain selection markers such as but not limited to antibiotic markers, auxotrophic markers, toxin- antitoxin markers, RNA sense / antisense markers. The expression system constructs may contain control regions that regulate as well as engender expression. Generally, any system or vector suitable to maintain, propagate or express polynucleotides and / or to express a polypeptide in a host may be used for expression in this regard. The appropriate DNA sequence may be inserted into the expression system by any of a variety of well-known and routine techniques, such as, for example, those set forth in Sambrook et al., see above. For recombinant production, cells can be genetically engineered to incorporate expression systems or portions thereof or polynucleotides of the invention. Introduction of a polynucleotide into the cell can be effected by methods described in many standard laboratory manuals, such as Davis et al., Basic Methods in Molecular Biology, (1986), and Sambrook et al., 1989, supra. As used herein an expression module comprises polynucleotides for expression of at least one recombinant gene. Said recombinant gene is involved in the expression of a polypeptide acting in the synthesis of at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides as described herein; or said recombinant gene is linked to other pathways in said cell that are not involved in the synthesis of at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides as described herein. Said recombinant genes encode endogenous proteins with a modified expression or activity, preferably said endogenous proteins are overexpressed; or said recombinant genes encode heterologous proteins that are heterogeneously introduced and expressed in said modified cell, preferably overexpressed. The endogenous proteins can have a modified expression in the cell which also expresses a heterologous protein. In a preferred embodiment, the expression of each of said expression modules present in said metabolically engineered cell is constitutive or tuneable as described herein. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell comprises one or more pathway(s) for monosaccharide synthesis. More preferably, the cell isgenetically engineered to comprise one or more pathway(s) for monosaccharide synthesis. Said pathwaysfor monosaccharide synthesis comprise enzymes like e.g. carboxylases, decarboxylases, isomerases, epimerases, reductases, enolases, phosphorylases, carboxykinases, kinases, phosphatases, aldolases, hydrolases, dehydrogenases, enzymes involved in the synthesis of one or more nucleoside triphosphate(s)like UTP, GTP, ATP and CTP, enzymes involved in the synthesis of any one or more nucleoside mono- ordiphosphates like e.g. UMP and UDP, respectively, and enzymes involved in the synthesis of phosphoenolpyruvate (PEP). In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell comprises one or more pathway(s) for phosphorylated monosaccharide synthesis. More preferably, the cell is genetically engineered to comprise one or more pathway(s) for phosphorylated monosaccharide synthesis. Said pathways for phosphorylated monosaccharide synthesis comprise enzymes involved in the synthesis of one or more monosaccharide(s), one or more nucleoside mono-, di- and / or triphosphate(s) and enzymes involved in the synthesis of phosphoenolpyruvate (PEP) like e.g., but not limited to PEP synthase, carboxylases, decarboxylases, isomerases, epimerases, reductases, enolases, phosphorylases, carboxykinases, kinases, phosphatases, aldolases, hydrolases and dehydrogenases. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell comprises one or more pathways for the synthesis of one or more nucleotide-activated sugars. More preferably, the cell is genetically engineered to comprise one or more pathway(s) for the synthesis of one or more nucleotide-activated sugars. Said pathways for nucleotide-activated sugar synthesis comprise enzymes like e.g. PEP synthase, carboxylases, decarboxylases, isomerases, epimerases, reductases, enolases, phosphorylases, carboxykinases, kinases, phosphatases, aldolases, hydrolases, dehydrogenases, mannose-6-phosphate isomerase, phosphomannomutase, mannose-1-phosphate guanylyltransferase, GDP-mannose 4,6-dehydratase, GDP-L-fucose synthase, L-fucokinase / GDP-fucose pyrophosphorylase, L-glutamine—D-fructose-6-phosphate aminotransferase, glucosamine-6-phosphate deaminase, phosphoglucosamine mutase, N-acetylglucosamine-6-phosphate deacetylase, N- acylglucosamine 2-epimerase, UDP-N-acetylglucosamine 2-epimerase, N-acetylglucosamine-6P 2- epimerase, glucosamine 6-phosphate N-acetyltransferase, N-acetylglucosamine-6-phosphate phosphatase, N-acetylmannosamine-6-phosphate 2-epimerase, N-acetylmannosamine-6-phosphate phosphatase, N-acetylmannosamine kinase, phosphoacetylglucosamine mutase, N-acetylglucosamine-1- phosphate uridylyltransferase, glucosamine-1-phosphate acetyltransferase, sialic acid synthase, N- acetylneuraminate lyase, N-acylneuraminate-9-phosphate synthase, N-acylneuraminate-9-phosphatase,CMP-sialic acid synthase, d-arabinose 5-phosphate isomerase, KDO-8P synthase, KDO 8-phosphatephosphatase, CMP-KDO synthetase, galactose-1-epimerase, galactokinase, glucokinase, galactose-1-phosphate uridylyltransferase, UDP-glucose 4-epimerase, glucose-1-phosphate uridylyltransferase and / or phosphoglucomutase.In another and / or additional preferred embodiment of the method and / or cell of present invention, thecell expresses at least one enzyme selected from the list comprising, consisting of or consisting essentially of an N-acylglucosamine 2-epimerase like is known e.g. from several species including Bacteroides ovatus, E. coli, Homo sapiens, Rattus norvegicus, a Neu5Ac synthase, a CMP sialic acid synthase like is known e.g. from Neisseria meningitidis, and a sialyltransferase. N-acetylglucosamine (GlcNAc) can be added to the cell and / or can be provided by an enzyme expressed in the cell or by the mechanism of the cell. Such cell producing GlcNAc can express a phosphatase converting GlcNAc-6-phosphate into GlcNAc, like any oneor more of e.g. the E. coli HAD-like phosphatase genes comprising, consisting of or consisting essentiallyof aphA, Cof, HisB, OtsB, SurE, Yaed, YcjU, YedP, YfbT, YidA, YigB, YihX, YniC, YqaB, YrbL, AppA, Gph, SerB, YbhA, YbiV, YbjL, Yfb, YieH, YjgL, YjjG, YrfG and YbiU, PsMupP from Pseudomonas putida, ScDOG1 from S.cerevisiae and BsAraL from Bacillus subtilis as described in WO18122225. Preferably, the cell is modifiedto produce GlcNAc. More preferably, the cell is modified for enhanced GlcNAc production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knockout of a glucosamine-6-phosphate deaminase, an N-acetylglucosamine-6-phosphate deacetylase and / or an N-acetyl-D-glucosamine kinase and over-expression of an L-glutamine—D- fructose-6-phosphate aminotransferase and / or a glucosamine 6-phosphate N-acetyltransferase.In an alternative and / or additional preferred embodiment of the method and / or cell of present invention,the cell expresses at least one enzyme selected from the list comprising, consisting of or consisting essentially of an N-acetylmannosamine-6-phosphate 2-epimerase like is known e.g. from several speciesincluding E. coli, Haemophilus influenzae, Enterobacter sp., Streptomyces sp., an N-acylneuraminate-9-phosphate synthetase, an N-acylneuraminate-9-phosphatase like is known e.g. from CandidatusMagnetomorum sp. HK-1 or Bacteroides thetaiotaomicron, a Neu5Ac synthase, a CMP sialic acid synthaselike is known e.g. from Neisseria meningitidis, and a sialyltransferase. N-acetyl-D-glucosamine 6- phosphate (GlcNAc-6P) can be added to the cell and / or can be provided by an enzyme expressed in the cell or by the metabolism of the cell. Such cell producing GlcNAc-6P can express an enzyme converting, e.g., GlcN6P, which is to be added to the cell, to GlcNAc-6P. This enzyme may be a glucosamine 6- phosphate N-acetyltransferase from several species including Saccharomyces cerevisiae, Kluyveromyces lactis, Homo sapiens. Preferably, the cell is modified to produce GlcNAc-6P. More preferably, the cell is modified for enhanced GlcNAc-6P production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knockout of a glucosamine-6-phosphate deaminase, an N-acetylglucosamine-6-phosphate deacetylase and over-expression of an L-glutamine—D- fructose-6-phosphate aminotransferase and / or a glucosamine 6-phosphate N-acetyltransferase.In an alternative and / or additional preferred embodiment of the method and / or cell of present invention,the cell expresses at least one enzyme selected from the list comprising, consisting of or consisting essentially of a bifunctional UDP-GlcNAc 2-epimerase / kinase like is known e.g. from several speciesincluding Homo sapiens, Rattus norvegicus and Mus musculus, an N-acylneuraminate-9-phosphatesynthetase, an N-acylneuraminate-9-phosphatase like is known e.g. from Candidatus Magnetomorum sp.HK-1 or Bacteroides thetaiotaomicron, a Neu5Ac synthase, a CMP sialic acid synthase like is known e.g.from Neisseria meningitidis, and a sialyltransferase. UDP-GlcNAc is provided by an enzyme expressed in the cell or by the metabolism of the cell. Additionally, UDP-GlcNAc can be added to the cell. Such cell producing an UDP-GlcNAc can express enzymes converting, e.g. GlcNAc, which is to be added to the cell, to UDP-GlcNAc. These enzymes may be an N-acetyl-D-glucosamine kinase, an N-acetylglucosamine-6- phosphate deacetylase, a phosphoglucosamine mutase, and an N-acetylglucosamine-1-phosphate uridylyltransferase / glucosamine-1-phosphate acetyltransferase from several species including Homo sapiens, Escherichia coli. Preferably, the cell is modified to produce UDP-GlcNAc. More preferably, the cell is modified for enhanced UDP-GlcNAc production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knock-out of an N-acetylglucosamine-6- phosphate deacetylase, over-expression of an L-glutamine—D-fructose-6-phosphate aminotransferase, over-expression of a phosphoglucosamine mutase, and over-expression of an N-acetylglucosamine-1- phosphate uridylyltransferase / glucosamine-1-phosphate acetyltransferase.In an alternative and / or additional preferred embodiment of the method and / or cell of present invention,the cell expresses at least one enzyme selected from the list comprising, consisting of or consistingessentially of a d-arabinose 5-phosphate isomerase, a KDO-8P synthase, a KDO 8-phosphate phosphatase,a CMP-KDO synthetase from different species like e.g. Escherichia coli, Pseudomonas aeruginosa,Agrobacterium sp. and a sialyltransferase. Preferably, the cell is capable to make CMP-KDO. Morepreferably, the cell is modified to produce CMP-KDO. More preferably, the cell is modified for enhanced CMP-KDO production. Said modification can be any one or more selected from the list comprising,consisting of or consisting essentially of over-expression of a d-arabinose 5-phosphate isomerase, a KDO-8P synthase, a KDO 8-phosphate phosphatase and / or a CMP-KDO synthetase encoding gene.According to another and / or additional preferred embodiment of the method and / or cell of present invention, the cell further comprises a pathway selected from the list comprising, consisting of or consisting essentially of fucosylation pathway, galactosylation pathway, N-acetylglucosaminylation pathway, N-acetylgalactosaminylation pathway, mannosylation pathway and N- acetylmannosaminylation pathway. According to another and / or additional preferred embodiment of the method and / or cell of present invention, the cell is genetically engineered to comprise at least one pathway selected from the list comprising, consisting of or consisting essentially of fucosylation pathway, galactosylation pathway, N- acetylglucosaminylation pathway, N-acetylgalactosaminylation pathway, mannosylation pathway and N- acetylmannosaminylation pathway. According to another and / or additional preferred embodiment of the method and / or cell of present invention, the cell comprises at least one pathway selected from the list comprising, consisting of or consisting essentially of fucosylation pathway, galactosylation pathway, N-acetylglucosaminylation pathway, N-acetylgalactosaminylation pathway, mannosylation pathway and N- acetylmannosaminylation pathway wherein at least one of said pathway(s) has / have been genetically engineered. According to another and / or additional preferred embodiment, the cell as described herein comprises a fucosylation pathway comprising at least one enzyme selected from the list comprising, consisting of or consisting essentially of mannose-6-phosphate isomerase, phosphomannomutase, mannose-1- phosphate guanylyltransferase, GDP-mannose 4,6-dehydratase, GDP-L-fucose synthase, fucose permease, fucose kinase, fucose-1-phosphate guanylyltransferase, fucosyltransferase. According to another and / or additional preferred embodiment, the cell as described herein comprises a galactosylation pathway comprising at least one enzyme selected from the list comprising, consisting of or consisting essentially of galactose-1-epimerase, galactokinase, glucokinase, galactose-1-phosphate uridylyltransferase, UDP-glucose 4-epimerase, glucose-1-phosphate uridylyltransferase, phosphoglucomutase, galactosyltransferase. According to another and / or additonal preferred embodiment, the cell as described herein comprises anN-acetylglucosaminylation pathway comprising at least one enzyme selected from the list comprising,consisting of or consisting essentially of L-glutamine—D-fructose-6-phosphate aminotransferase, N- acetylglucosamine-6-phosphate deacetylase, phosphoglucosamine mutase, N-acetylglucosamine-1- phosphate uridylyltransferase / glucosamine-1-phosphate acetyltransferase, N- acetylglucosaminyltransferase. According to another and / or additonal preferred embodiment, the cell as described herein comprises anN-acetylgalactosaminylation pathway comprising at least one enzyme selected from the list comprising,consisting of or consisting essentially of L-glutamine—D-fructose-6-phosphate aminotransferase,phosphoglucosamine mutase, N-acetylglucosamine 1-phosphate uridylyltransferase, glucosamine-1-phosphate acetyltransferase, bifunctional N-acetylglucosamine-1-phosphateuridyltransferase / glucosamine-1-phosphate acetyltransferase, UDP-N-acetylglucosamine 4-epimerase,UDP-glucose 4-epimerase, N-acetylgalactosamine kinase, UDP-N-acetylgalactosamine pyrophosphorylaseand a glycosyltransferase transferring GalNAc. According to another and / or additonal preferred embodiment, the cell as described herein comprises anmannosylation pathway comprising at least one enzyme selected from the list comprising, consisting ofor consisting essentially of mannose-6-phosphate isomerase, phosphomannomutase, mannose-1- phosphate guanylyltransferase and mannosyltransferase. According to another and / or additonal preferred embodiment, the cell as described herein comprises anN-acetylmannosaminylation pathway comprising at least one enzyme selected from the list comprising,consisting of or consisting essentially of L-glutamine—D-fructose-6-phosphate aminotransferase, glucosamine-6-phosphate deaminase, phosphoglucosamine mutase, N-acetylglucosamine-6-phosphate deacetylase, glucosamine 6-phosphate N-acetyltransferase, N-acetylglucosamine-1-phosphate uridyltransferase, glucosamine-1-phosphate acetyltransferase, glucosamine-1-phosphate acetyltransferase, bifunctional N-acetylglucosamine-1-phosphate uridyltransferase / glucosamine-1-phosphate acetyltransferase, UDP-GlcNAc 2-epimerase, ManNAc kinase and a glycosyltransferasetransferring ManNAc. According to another and / or additional preferred embodiment of the method and / or cell of present invention, the cell is capable to produce and / or produces N-acetylmannosamine (ManNAc). ManNAc can be provided by an enzyme expressed in the cell or by the mechanism of the cell. In a specific embodiment, the cell expresses a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase that converts UDP-GlcNAc into ManNAc. Additionally, the cell producing ManNAc can further express an N- acylglucosamine 2-epimerase like is known e.g. from several species including Bacteroides ovatus, E. coli,Homo sapiens, Rattus norvegicus that converts GlcNAc into ManNAc. In another and / or additionalpreferred embodiment of the method and / or cell of present invention, the cell comprises a pathway for production of ManNAc. In a more preferred embodiment, the cell is modified for enhanced ManNAc production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knock-out of N-acetylmannosamine kinase, over-expression of N- acetylneuraminate lyase, overexpression of a hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase. According to another and / or additional preferred embodiment of the method and / or cell of present invention, the cell is capable to produce and / or produces N-acetylmannosamine-6-phosphate (ManNAc- 6-phosphate). In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell comprises a pathway for production of ManNAc-6-phosphate. ManNAc-6-phosphate can be provided by an enzyme expressed in the cell or by the mechanism of the cell. Such cell producing ManNAc-6-phosphate can express a bifunctional UDP-GlcNAc 2-epimerase / kinase like is known e.g. fromseveral species including Homo sapiens, Rattus norvegicus and Mus musculus that converts UDP-GlcNAcinto ManNAc-6-phosphate. Alternatively, and / or additionally, the cell producing ManNAc-6-phosphate can express an N-acetylmannosamine-6-phosphate 2-epimerase that converts GlcNAc-6-phosphate into ManNAc-6-phosphate. UDP-GlcNAc and / or GlcNAc-6-phosphate can be added to the cell and / or providedby an enzyme expressed in the cell or by the mechanism of the cell as described herein. In a morepreferred embodiment, the cell is modified for enhanced ManNAc-6-phosphate production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of over-expression of N-acetylglucosamine-6-phosphate deacetylase, over-expression of N- acetyl-D-glucosamine kinase, over-expression of phosphoglucosamine mutase, over-expression of N- acetylglucosamine-1-phosphate uridylyltransferase / glucosamine-1-phosphate acetyltransferase. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein is capable to produce and / or produces any one or more nucleotide-activated sugars. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein comprises a pathway for the synthesis of one or more nucleotide- activated sugars. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein is genetically engineered for production of any one or more nucleotide-activated sugars. Preferably, the nucleotide-activated sugar is selected from the listcomprising, consisting of or consisting essentially of UDP-N-acetylglucosamine (UDP-GlcNAc), UDP-N-acetylgalactosamine (UDP-GalNAc), UDP-N-acetylmannosamine (UDP-ManNAc), UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal), GDP-mannose (GDP-Man), UDP-glucuronate, UDP-galacturonate, UDP-2- acetamido-2,6-dideoxy--L-arabino-4-hexulose, UDP-2-acetamido-2,6-dideoxy--L-lyxo-4-hexulose, UDP-N- acetyl-L-rhamnosamine (UDP-L-RhaNAc or UDP-2-acetamido-2,6-dideoxy-L-mannose), dTDP-N- acetylfucosamine, UDP-N-acetylfucosamine (UDP-L-FucNAc or UDP-2-acetamido-2,6-dideoxy-L- galactose), UDP-N-acetyl-L-pneumosamine (UDP-L-PneNAC or UDP-2-acetamido-2,6-dideoxy-L-talose), UDP-N-acetylmuramic acid, UDP-N-acetyl-L-quinovosamine (UDP-L-QuiNAc or UDP-2-acetamido-2,6-dideoxy-L-glucose), CMP-sialic acid (e.g. CMP-Neu5Ac, CMP-Neu4Ac, CMP-Neu5Ac9N3, CMP-Neu4,5Ac2,CMP-Neu5,7Ac2, CMP-Neu5,9Ac2, CMP-Neu5,7(8,9)Ac2, CMP-Neu5Gc or CMP-KDO), GDP-fucose (GDP-Fuc), GDP-rhamnose and UDP-xylose. In a more preferred embodiment, the cell is capable to synthesizeat least the nucleotide-activated sugar CMP-Neu5Ac. In another more preferred embodiment, the cell is capable to synthesize at least the nucleotide-activated sugar CMP-KDO. In an even more preferred embodiment, the cell uses at least one of the synthesized nucleotide-activated sugars in the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein. Additionally, or alternatively, the cell used herein is optionally genetically engineered to express the de novo synthesis of CMP-Neu5Ac. CMP-Neu5Ac can be provided by an enzyme expressed in the cell or by the metabolism of the cell. Such cell producing CMP-Neu5Ac can express an enzyme converting, e.g., sialic acid to CMP-Neu5Ac. This enzyme may be a CMP-sialic acid synthetase, like the N-acylneuraminate cytidylyltransferase from several species including Homo sapiens, Neisseria meningitidis, and Pasteurella multocida. Preferably, the cell is modified to produce CMP-Neu5Ac. More preferably, the cell is modified for enhanced CMP-Neu5Ac production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knock-out of an N-acetylglucosamine-6-phosphate deacetylase, knock-out of a glucosamine-6-phosphate deaminase, over-expression of a CMP-sialic acid synthetase, and over-expression of an N-acetyl-D-glucosamine-2-epimerase encoding gene. Additionally, or alternatively, the cell used herein is optionally genetically engineered to express the de novo synthesis of CMP-KDO. CMP-KDO can be provided by an enzyme expressed in the cell or by the metabolism of the cell. Such cell producing CMP-KDO can express an enzyme converting, e.g., KDO to CMP-KDO. This enzyme may be a CMP-KDO synthetase, like the 3-deoxy-manno-octulosonatecytidylyltransferase kdsB from several species including Escherichia coli, Arabidopsis thaliana, Pseudomonas aeruginosa, Xanthomonas campestris. Preferably, the cell is modified to produce CMP-KDO. More preferably, the cell is modified for enhanced CMP-KDO production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of over-expression ofa d-arabinose 5-phosphate isomerase, a KDO-8P synthase, a KDO 8-phosphate phosphatase and / or aCMP-KDO synthetase encoding gene. Additionally, or alternatively, the cell used herein is optionally genetically engineered to express the de novo synthesis of GDP-fucose. GDP-fucose can be provided by an enzyme expressed in the cell or by the metabolism of the cell. Such cell producing GDP-fucose can express an enzyme converting, e.g., fucose, which is to be added to the cell, to GDP-fucose. This enzyme may be, e.g., a bifunctional fucose kinase / fucose-1-phosphate guanylyltransferase, like Fkp from Bacteroides fragilis, or the combination of one separate fucose kinase together with one separate fucose-1-phosphate guanylyltransferase like theyare known from several species including Homo sapiens, Sus scrofa and Rattus norvegicus. Preferably, thecell is modified to produce GDP-fucose. More preferably, the cell is modified for enhanced GDP-fucose production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knock-out of an UDP-glucose:undecaprenyl-phosphate glucose-1-phosphate transferase encoding gene, over-expression of a GDP-L-fucose synthase encoding gene, over-expression of a GDP-mannose 4,6-dehydratase encoding gene, over-expression of a mannose-1-phosphate guanylyltransferase encoding gene, over-expression of a phosphomannomutase encoding gene and over- expression of a mannose-6-phosphate isomerase encoding gene. Additionally, or alternatively, the cell used herein is optionally genetically engineered to express the de novo synthesis of UDP-Gal. UDP-Gal can be provided by an enzyme expressed in the cell or by the metabolism of the cell. Such cell producing UDP-Gal can express an enzyme converting, e.g. UDP-glucose, to UDP-Gal. This enzyme may be, e.g., the UDP-glucose-4-epimerase GalE like as known from several species including Homo sapiens, Escherichia coli, and Rattus norvegicus. Preferably, the cell is modified to produce UDP-Gal. More preferably, the cell is modified for enhanced UDP-Gal production. Said modification can be any one or more selected from the list comprising, consisting of or consisting essentially of knock-out of a bifunctional 5’-nucleotidase / UDP-sugar hydrolase encoding gene, knock-out of a galactose-1-phosphate uridylyltransferase encoding gene and over-expression of a UDP-glucose-4- epimerase encoding gene. Additionally, or alternatively, the cell used herein is optionally genetically engineered to express the de novo synthesis of UDP-GalNAc. UDP-GalNAc can be synthesized from UDP-GlcNAc by the action of a single-step reaction using a UDP-N-acetylglucosamine 4-epimerase like e.g. wbgU from Plesiomonasshigelloides, gne from Yersinia enterocolitica or wbpP from Pseudomonas aeruginosa serotype O6.Preferably, the cell is modified to produce UDP-GalNAc. More preferably, the cell is modified for enhanced UDP-GalNAc production. Additionally, or alternatively, the cell used herein is optionally genetically engineered to express the de novo synthesis of UDP-ManNAc. UDP-ManNAc can be synthesized directly from UDP-GlcNAc via an epimerization reaction performed by a UDP-GlcNAc 2-epimerase (like e.g. cap5P from Staphylococcusaureus, RffE from E. coli, Cps19fK from S. pneumoniae, and RfbC from S. enterica). Preferably, the cell ismodified to produce UDP-ManNAc. More preferably, the cell is modified for enhanced UDP-ManNAc production. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein possesses, preferably expresses, more preferably overexpresses one or moregenes selected from the list comprising, consisting of or consisting essentially of mannose-6-phosphateisomerase, phosphomannomutase, mannose-1-phosphate guanylyltransferase, GDP-mannose 4,6- dehydratase, GDP-L-fucose synthase, fucose permease, fucose kinase, fucose-1-phosphate guanylyltransferase, L-glutamine—D-fructose-6-phosphate aminotransferase, phosphoglucosamine mutase, N-acetylglucosamine-6-P deacetylase, N-acylglucosamine 2-epimerase, UDP-N- acetylglucosamine 2-epimerase, N-acetylmannosamine-6-phosphate 2-epimerase, UDP-GlcNAc 2- epimerase / kinase, glucosamine 6-phosphate N-acetyltransferase, N-acetylglucosamine-6-phosphate phosphatase, phosphoacetylglucosamine mutase, N-acetylglucosamine 1-phosphate uridylyltransferase, glucosamine-1-phosphate acetyltransferase, bifunctional N-acetylglucosamine-1-phosphate uridyltransferase / glucosamine-1-phosphate acetyltransferase, sialic acid synthase, N-acetylneuraminate lyase, N-acylneuraminate-9-phosphate synthase, N-acylneuraminate-9-phosphatase, sialic acidtransporter, CMP kinase, CMP-sialic acid synthase, d-arabinose 5-phosphate isomerase, KDO-8P synthase,KDO 8-phosphate phosphatase, CMP-KDO synthetase, galactose-1-epimerase, galactokinase, glucokinase, galactose-1-phosphate uridylyltransferase, UDP-glucose 4-epimerase, glucose-1-phosphate uridylyltransferase, phosphoglucomutase, UDP-N-acetylglucosamine 4-epimerase, N-acetylgalactosamine kinase and UDP-N-acetylgalactosamine pyrophosphorylase.In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein possesses, preferably expresses, more preferably overexpresses, one or more glycosyltransferase(s) selected from the list comprising, consisting of or consisting essentially of fucosyltransferases, sialyltransferases, galactosyltransferases, glucosyltransferases, mannosyltransferases, N-acetylglucosaminyltransferases, N-acetylgalactosaminyltransferases, N- acetylmannosaminyltransferases, xylosyltransferases, glucuronyltransferases, galacturonyltransferases, glucosaminyltransferases, N-glycolylneuraminyltransferases, rhamnosyltransferases, N- acetylrhamnosyltransferases, UDP-4-amino-4,6-dideoxy-N-acetyl-beta-L-altrosamine transaminases, UDP-N-acetylglucosamine enolpyruvyl transferases and fucosaminyltransferases. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein is genetically engineered to express and / or to over-express one or more glycosyltransferase(s) selected from the list comprising, consisting of or consisting essentially of fucosyltransferases, sialyltransferases, galactosyltransferases, glucosyltransferases, mannosyltransferases, N-acetylglucosaminyltransferases, N-acetylgalactosaminyltransferases, N-acetylmannosaminyltransferases,xylosyltransferases, glucuronyltransferases, galacturonyltransferases, glucosaminyltransferases, N- glycolylneuraminyltransferases, rhamnosyltransferases, N-acetylrhamnosyltransferases, UDP-4-amino- 4,6-dideoxy-N-acetyl-beta-L-altrosamine transaminases, UDP-N-acetylglucosamine enolpyruvyl transferases and fucosaminyltransferases.In a preferred embodiment, the fucosyltransferase is selected from the list comprising, consisting of orconsisting essentially of alpha-1,2-fucosyltransferase, alpha-1,3-fucosyltransferase, alpha-1,3 / 4- fucosyltransferase, alpha-1,4-fucosyltransferase and alpha-1,6-fucosyltransferase. In an alternative and / or additional embodiment, the sialyltransferase is selected from the list comprising, consisting of or consisting essentially of alpha-2,3-sialyltransferase, alpha-2,6-sialyltransferase, and alpha-2,8- sialyltransferase. In an alternative and / or additional embodiment, the galactosyltransferase is selected from the list comprising, consisting of or consisting essentially of beta-1,3-galactosyltransferase, N- acetylglucosamine beta-1,3-galactosyltransferase, beta-1,4-galactosyltransferase, N-acetylglucosamine beta-1,4-galactosyltransferase, alpha-1,3-galactosyltransferase and alpha-1,4-galactosyltransferase. In an alternative and / or additional embodiment, the glucosyltransferase is selected from the list comprising, consisting of or consisting essentially of alpha-glucosyltransferase, beta-1,2-glucosyltransferase, beta-1,3- glucosyltransferase and beta-1,4-glucosyltransferase. In an alternative and / or additional embodiment, the mannosyltransferase is selected from the list comprising, consisting of or consisting essentially of alpha-1,2-mannosyltransferase, alpha-1,3-mannosyltransferase and alpha-1,6-mannosyltransferase. Inan alternative and / or additional embodiment, the N-acetylglucosaminyltransferase is selected from thelist comprising, consisting of or consisting essentially of galactoside beta-1,3-N-acetylglucosaminyltransferase and beta-1,6-N-acetylglucosaminyltransferase. In an alternative and / oradditional embodiment, the N-acetylgalactosaminyltransferase is selected from the list comprising, consisting of or consisting essentially of alpha-1,3-N-acetylgalactosaminyltransferase. In a further preferred embodiment, the cell is modified in the expression or activity of at least one of said glycosyltransferases. In a preferred embodiment, said glycosyltransferase is an endogenous protein of the cell with a modified expression or activity, preferably said endogenous glycosyltransferase is overexpressed; alternatively said glycosyltransferase is a heterologous protein that is heterogeneously introduced and expressed in said cell, preferably overexpressed. Said endogenous glycosyltransferase can have a modified expression in the cell which also expresses a heterologous glycosyltransferase. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein is capable to produce and / or produces phosphoenolpyruvate (PEP). Preferably, the cell comprises a pathway for production of PEP. In another and / or additional preferred embodiment, the cell as described herein is modified for enhanced production and / or supply of PEP compared to a non-modified progenitor. In a preferred embodiment and as a means for enhanced production and / or supply of PEP, one or more PEP-dependent, sugar-transporting phosphotransferase system(s) is / are disrupted such as but not limited to: 1) the N-acetyl-D-glucosamine Npi-phosphotransferase (EC 2.7.1.193), which is for instance encodedby the nagE gene (or the cluster nagABCD) in E. coli or Bacillus species, 2) ManXYZ which encodes theEnzyme ll Man complex (mannose PTS permease, protein-Npi- phosphohistidine-D-mannosephosphotransferase) that imports exogenous hexoses (mannose, glucose, glucosamine, fructose, 2- deoxyglucose, mannosamine, N-acetylglucosamine, etc.) and releases the phosphate esters into the cell cytoplasm, 3) the glucose-specific PTS transporter (for instance encoded by PtsG / Crr) which takes up glucose and forms glucose-6-phosphate in the cytoplasm, 4) the sucrose-specific PTS transporter which takes up sucrose and forms sucrose-6-phosphate in the cytoplasm, 5) the fructose-specific PTS transporter(for instance encoded by the genes fruA and fruB and the kinase fruK which takes up fructose and formsin a first step fructose-1-phosphate and in a second step fructose1,6 bisphosphate, 6) the lactose PTStransporter (for instance encoded by lacE in Lactococcus casei) which takes up lactose and forms lactose-6-phosphate, 7) the galactitol-specific PTS enzyme which takes up galactitol and / or sorbitol and forms galactitol-1-phosphate or sorbitol-6-phosphate respectively, 8) the mannitol-specific PTS enzyme which takes up mannitol and / or sorbitol and forms mannitol-1-phosphate or sorbitol-6-phosphate respectively, and 9) the trehalose-specific PTS enzyme which takes up trehalose and forms trehalose-6-phosphate. In another and / or additional preferred embodiment and as a means for enhanced production and / or supply of PEP, the full PTS system is disrupted by disrupting the PtsIH / Crr gene cluster. In another and / or additional preferred embodiment, the cell is further modified to compensate for the deletion of a PTS system of a carbon source by the introduction and / or overexpression of the corresponding permease. These are e.g. permeases or ABC transporters that comprise but are not limitedto transporters that specifically import lactose such as e.g. the transporter encoded by the LacY gene fromE. coli, sucrose such as e.g. the transporter encoded by the cscB gene from E. coli, glucose such as e.g. thetransporter encoded by the galP gene from E. coli, fructose such as e.g. the transporter encoded by thefruI gene from Streptococcus mutans, or the Sorbitol / mannitol ABC transporter such as the transporterencoded by the cluster SmoEFGK of Rhodobacter sphaeroides, the trehalose / sucrose / maltose transportersuch as the transporter encoded by the gene cluster ThuEFGK of Sinorhizobium meliloti and the N-acetylglucosamine / galactose / glucose transporter such as the transporter encoded by NagP of Shewanellaoneidensis. Examples of combinations of PTS deletions with overexpression of alternative transportersare: 1) the deletion of the glucose PTS system, e.g. ptsG gene, combined with the introduction and / oroverexpression of a glucose permease (e.g. galP of glcP), 2) the deletion of the fructose PTS system, e.g.one or more of the fruB, fruA, fruK genes, combined with the introduction and / or overexpression offructose permease, e.g. fruI, 3) the deletion of the lactose PTS system, combined with the introduction and / or overexpression of lactose permease, e.g. LacY, and / or 4) the deletion of the sucrose PTS system, combined with the introduction and / or overexpression of a sucrose permease, e.g. cscB. In a further preferred embodiment, the cell is modified to compensate for the deletion of a PTS system of a carbon source by the introduction of carbohydrate kinases, such as glucokinase (EC 2.7.1.1, EC 2.7.1.2, EC 2.7.1.63), galactokinase (EC 2.7.1.6), and / or fructokinase (EC 2.7.1.3, EC 2.7.1.4). In another and / or additional preferred embodiment and as a means for enhanced production and / or supply of PEP, the cell is modified by the introduction of or modification in any one or more of the listcomprising, consisting of or consisting essentially of phosphoenolpyruvate synthase activity (EC: 2.7.9.2encoded for instance in E. coli by ppsA), phosphoenolpyruvate carboxykinase activity (EC 4.1.1.32 or EC4.1.1.49 encoded for instance in Corynebacterium glutamicum by PCK or in E. coli by pckA, resp.),phosphoenolpyruvate carboxylase activity (EC 4.1.1.31 encoded for instance in E. coli by ppc),oxaloacetate decarboxylase activity (EC 4.1.1.112 encoded for instance in E. coli by eda), pyruvate kinaseactivity (EC 2.7.1.40 encoded for instance in E. coli by pykA and pykF), pyruvate carboxylase activity (EC6.4.1.1 encoded for instance in B. subtilis by pyc) and malate dehydrogenase activity (EC 1.1.1.38 or EC1.1.1.40 encoded for instance in E. coli by maeA or maeB, resp.).In another and / or additional preferred embodiment and as a means for enhanced production and / or supply of PEP, the cell is modified by a reduced activity of phosphoenolpyruvate carboxylase activity,and / or pyruvate kinase activity, preferably a deletion of the genes encoding for phosphoenolpyruvatecarboxylase, the pyruvate carboxylase activity and / or pyruvate kinase. According to another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein comprises a modification for reduced production of acetatecompared to a non-modified progenitor. Said modification can be any one or more selected from the listcomprising, consisting of or consisting essentially of overexpression of an acetyl-coenzyme A synthetase, a full or partial knock-out or rendered less functional pyruvate dehydrogenase and a full or partial knock- out or rendered less functional lactate dehydrogenase. In a further aspect, the cell is modified in the expression or activity of at least one acetyl-coenzyme A synthetase like e.g. acs from E. coli, S. cerevisiae, H. sapiens, M. musculus. In a preferred embodiment, said acetyl-coenzyme A synthetase is an endogenous protein of the cell with a modified expression or activity, preferably said endogenous acetyl-coenzyme A synthetase is overexpressed; alternatively, said acetyl-coenzyme A synthetase is a heterologous protein that is heterogeneously introduced and expressed in said cell, preferably overexpressed. Said endogenous acetyl-coenzyme A synthetase can have a modified expression in the cell which also expresses a heterologous acetyl-coenzyme A synthetase. In an alternative and / or additional further aspect, the cell is modified in the expression or activity of atleast one pyruvate dehydrogenase like e.g. from E. coli, S. cerevisiae, H. sapiens and R. norvegicus. In apreferred embodiment, the cell has been modified to have at least one partially or fully knocked out or mutated pyruvate dehydrogenase encoding gene by means generally known by the person skilled in the art resulting in at least one protein with less functional or being disabled for pyruvate dehydrogenase activity. In a more preferred embodiment, the cell has a full knock-out in the poxB encoding gene resulting in a cell lacking pyruvate dehydrogenase activity. In an alternative and / or additional further aspect, the cell is modified in the expression or activity of atleast one lactate dehydrogenase like e.g. from E. coli, S. cerevisiae, H. sapiens and R. norvegicus. In apreferred embodiment, the cell has been modified to have at least one partially or fully knocked out or mutated lactate dehydrogenase encoding gene by means generally known by the person skilled in the artresulting in at least one protein with less functional or being disabled for lactate dehydrogenase activity.In a more preferred embodiment, the cell has a full knock-out in the ldhA encoding gene resulting in a cell lacking lactate dehydrogenase activity. According to another preferred aspect, the cell comprises a lower or reduced expression and / or abolished, impaired, reduced or delayed activity of any one or more of the proteins comprising, consisting of or consisting essentially of beta-galactosidase, galactoside O-acetyltransferase, N-acetylglucosamine- 6-phosphate deacetylase, glucosamine-6-phosphate deaminase, N-acetylglucosamine repressor, ribonucleotide monophosphatase, EIICBA-Nag, UDP-glucose:undecaprenyl-phosphate glucose-1- phosphate transferase, L-fuculokinase, L-fucose isomerase, N-acetylneuraminate lyase, N- acetylmannosamine kinase, N-acetylmannosamine-6-phosphate 2-epimerase, EIIAB-Man, EIIC-Man, EIID- Man, ushA, galactose-1-phosphate uridylyltransferase, glucose-1-phosphate adenylyltransferase, glucose-1-phosphatase, ATP-dependent 6-phosphofructokinase isozyme 1, ATP-dependent 6- phosphofructokinase isozyme 2, glucose-6-phosphate isomerase, aerobic respiration control protein, transcriptional repressor IclR, lon protease, glucose-specific translocating phosphotransferase enzyme IIBC component ptsG, glucose-specific translocating phosphotransferase (PTS) enzyme IIBC component malX, enzyme IIAGlc, beta-glucoside specific PTS enzyme II, fructose-specific PTS multiphosphoryl transfer protein FruA and FruB, ethanol dehydrogenase aldehyde dehydrogenase, pyruvate-formate lyase, acetate kinase, phosphoacyltransferase, phosphate acetyltransferase, pyruvate decarboxylase. In another and / or additional preferred embodiment of the method and / or cell of present invention, one or more gene(s) involved in one or more reductive pathway(s) in the cell of present invention is / are rendered less functional compared to a non-modified progenitor or is / are knocked-out. Examples of a reductive pathway comprise but are not limited to the reductive acetyl-CoA-pathway, the reductive pyrimidine catabolic pathway, the reductive citric acid cycle, the thiol-redox pathway and the reductive glycine pathway. In another and / or additional preferred embodiment, one or more gene(s) involved in one or more reductive pathway(s) is / are rendered less functional by insertion, deletion and / or modification of one or more nucleotide(s) in one or more polynucleotide sequence(s) selected from the list comprising, consisting of or consisting essentially of promoter sequence, ribosome binding site, untranslated region, coding sequence and transcription terminator sequence of said one or more gene(s). Herein, said one or more gene(s) may be selected from the list comprising, consisting of or consisting essentially of gene(s) encoding formate dehydrogenase, formate–tetrahydrofolate ligase, methenyltetrahydrofolate cyclohydrolase, glycine dehydrogenase / decarboxylating, glycine cleavagesystem protein, glutamate dehydrogenase, glycine reductase complex, CO2 reductase, folate synthetase,folate cyclohydrolase, folate dehydrogenase, folate reductase, methyltransferase, pyruvate synthase, phosphotransacetylase, acetate kinase, ATPase, acetyl-CoA carbonylase / synthase, methylenetetrahydrofolate reductase, methylenetetrahydrofolate dehydrogenase, methyltetrahydrofolate∶corrinoid / iron-sulfur protein methyltransferase, methenyltetrahydrofolate cyclohydrolase, pyruvate: ferredoxin oxidoreductase, serine hydroxymethyltransferase, dihydropyrimidine dehydrogenase, dihydropyrimidinase, β-ureidopropionase, ribulose-1,5-bisphosphate carboxylase, ATP citrate lyase, citrate synthase, aconitase, isocitrate dehydrogenase, 2-ketoglutarate dehydrogenase, 2-ketoglutarate ferredoxin oxidoreductase, succinyl-CoA synthetase, succinyl-CoA– acetoacetate-CoA-transferase, fumarate reductase, succinate dehydrogenase, fumarase, malate dehydrogenase, isocitrate lyase, malate synthase, phosphoenol pyruvate carboxykinase, hhosphoenol pyruvate carboxylase, malic enzyme, pyruvate carboxylase / oxaloacetate decarboxylase, pyruvate dehydrogenase, pyruvate ferredoxin oxidoreductase, KatG catalase, alkylhydroperoxide reductase, DNA- binding ferritin-like protein, glutaredoxin, ferric homeostasis regulator, manganese transporter, OxyS, OxyR, glutathione reductase, thioredoxin reductase, thioredoxin-disulphide reductase and glutamine synthetase. Preferably, said one or more genes involved in one or more reductive pathway(s) is / are selected from the list comprising, consisting of or consisting essentially of a glutathione reductase and a thioredoxin reductase. In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell as described herein possesses, preferably expresses, more preferably overexpresses, at least one gene selected from the list comprising, consisting of or consisting essentially of genes encoding a disulfide bond isomerase, a thiol oxidase and a chaperone. According to another preferred embodiment of the method and / or cell of present invention, the cellcomprises a catabolic pathway for selected mono-, di- or oligosaccharides which is at least partiallyinactivated, the mono-, di-, or oligosaccharides being involved in and / or required for the production of said at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said milk oligosaccharide mixture as described herein. According to another and / or additional preferred embodiment of the method and / or cell of present invention, the cell is capable to produce, preferably produces, said at least one sialylated milk oligosaccharide and / or said at least one non-sialylated milk oligosaccharide from one or more precursor(s). Preferably said precursor is lactose. Herein, the precursor is fed to the cell from the cultivation or incubation medium. In another preferred embodiment, the cell is capable to produce, preferably produces, one or more precursor(s) for the synthesis of said at least one sialylated milk oligosaccharide and / or said at least one non-sialylated milk oligosaccharide of the milk oligosaccharide mixture as described herein. More preferably, the cell is capable to produce, preferably produces, all of said one or more precursor(s) for the synthesis of said at least one sialylated milk oligosaccharide and / or said at least one non-sialylated milk oligosaccharide of the milk oligosaccharide mixture as described herein. In another and / or additional preferred embodiment, the cell is genetically engineered for the production of at least one of said one or more precursor(s) for the synthesis of said at least one sialylated milk oligosaccharide and / or said at least one non-sialylated milk oligosaccharide of the milk oligosaccharide mixture as described herein. More preferably, the cell is genetically engineered for the production of all of said one or more precursor(s) for the synthesis of said at least one sialylated milk oligosaccharide and / or said at least one non-sialylated milk oligosaccharide of the milk oligosaccharide mixture as described herein. In another and / or additional preferred embodiment, at least one of said one or more precursor(s) is internalized in said cell via one or more membrane protein(s). In a more preferred embodiment, said one or more precursor(s) is selected from the list comprising, consisting of or consisting essentially of sialic acid, a sialic acid residue, Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4;Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc; KDO, CMP-sialic acid, CMP-Neu5Ac, glucose, galactose,GlcNAc, GalNAc, UDP-Gal, UDP-GlcNAc, and UDP-GalNAc.Additionally, or alternatively, the cell as described herein is optionally genetically engineered to import aprecursor and / or an acceptor in said cell, by the introduction and / or overexpression of a transporter able to import the respective precursor and / or acceptor in the cell. Such transporter is for example amembrane protein belonging to the major facilitator superfamily (MFS), the ATP-binding cassette (ABC)transporter family or the PTS system involved in the uptake of e.g., mono-, di- and / or oligosaccharides.Additionally, or alternatively, the cell as described herein is optionally genetically engineered to producepolyisoprenoid alcohols like e.g., phosphorylated dolichol that can act as lipid carrier.Additionally, or alternatively, the cell as described herein is an E. coli or yeast with a lactose permeasepositive phenotype. Preferably, said lactose permease is coded by the gene LacY or LAC12, respectively.Additionally, or alternatively, the cell as described herein is optionally genetically engineered to importlactose in the cell, by the introduction and / or overexpression of a lactose permease, like e.g., encoded bythe LacY gene or the LAC12 gene.Additionally, or alternatively, the cell as described herein expresses a membrane protein that is atransporter protein involved in transport of compounds, like e.g., at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milkoligosaccharides as defined in present invention out of the cell. In the context of present invention, itshould be understood that said at least one sialylated milk oligosaccharide and / or at least one non- sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides is preferably produced intracellularly. The skilled person will further understand that a fraction or substantially all of said produced at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides remains intracellularly and / or is excreted outside the cell either passively or through active transport.In a preferred embodiment of the method and / or cell of present invention, the cell as described hereinexpresses a membrane transporter protein or a polypeptide having transport activity hereby transportingcompounds across the outer membrane of the cell wall. In another preferred embodiment of the methodand / or cell of present invention, the cell as described herein expresses more than one membranetransporter protein or polypeptide having transport activity hereby transporting compounds across theouter membrane of the cell wall. In a more preferred embodiment, the cell is modified in the expressionor activity of said membrane transporter protein or polypeptide having transport activity. Said membrane transporter protein or polypeptide having transport activity is an endogenous protein of the cell with a modified expression or activity, preferably said endogenous membrane transporter protein or polypeptide having transport activity is overexpressed; alternatively said membrane transporter protein or polypeptide having transport activity is a heterologous protein that is heterogeneously introduced and expressed in said cell, preferably overexpressed. Said endogenous membrane transporter protein or polypeptide having transport activity can have a modified expression in the cell which also expresses a heterologous membrane transporter protein or polypeptide having transport activity. In a more preferred embodiment, the membrane transporter protein or polypeptide having transport activity is selected from the list comprising, consisting of or consisting essentially of porters, P-P-bond- hydrolysis-driven transporters, ^-barrel porins, auxiliary transport proteins and phosphotransfer-driven group translocators. In an even more preferred embodiment, the porters comprise MFS transporters, sugar efflux transporters and siderophore exporters. In another more preferred embodiment of the method and / or cell of the invention, the P-P-bond-hydrolysis-driven transporters comprise ABC transporters and siderophore exporters. In another preferred embodiment, the membrane transporter protein or polypeptide having transport activity controls the flow over the outer membrane of the cell wall of at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides. In an alternative and / or additional preferred embodiment, the membrane transporter protein or polypeptide having transport activity controls the flow over the outer membrane of the cell wall of one or more precursor(s) to be used in said production of at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides. In another preferred embodiment, the membrane transporter protein or polypeptide having transport activity provides improved production of at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides. In an alternative and / or additional preferred embodiment, the membrane transporter protein or polypeptide having transport activity provides enabled efflux of at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides. In an alternative and / or additional preferred embodiment, the membrane transporter protein or polypeptide having transport activity provides enhanced efflux of at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides.Preferably, the cell as described herein is transformed to comprise at least one nucleic acid sequenceencoding a protein selected from the list comprising, consisting of or consisting essentially of a lactose transporter like e.g. the LacY or lac12 permease, a glucose transporter, a galactose transporter, a transporter for a nucleotide-activated sugar like for example a transporter for UDP-GlcNAc, a transporter protein involved in transport of at least one sialylated milk oligosaccharide and / or at least one non- sialylated milk oligosaccharide of said mixture of at least two milk oligosaccharides out of the cell. In another preferred embodiment, the cell as described herein expresses a membrane transporter protein belonging to the family of MFS transporters like e.g., an MdfA polypeptide of the multidrug transporter MdfA family from species comprising, consisting of or consisting essentially of E. coli (UniProt ID P0AEY8),Cronobacter muytjensii (UniProt ID A0A2T7ANQ9), Citrobacter youngae (UniProt ID D4BC23) andYokenella regensburgei (UniProt ID G9Z5F4). In another preferred embodiment, the cell as describedherein expresses a membrane transporter protein belonging to the family of sugar efflux transporters like e.g., a SetA polypeptide of the SetA family from species comprising, consisting of or consisting essentiallyof E. coli (UniProt ID P31675, sequence version 03 (11 Oct 2004)) and Citrobacter koseri (UniProt IDA0A078LM16). In another preferred embodiment, the cell as described herein expresses a membranetransporter protein belonging to the family of siderophore exporters like e.g., the E. coli entS (UniProt IDP24077, sequence version 02 (01 Nov 1997)), the K. ascorbata entS (UniProt ID A0A378GQ13) and the E.coli iceT (UniProt ID A0A024L207). In another preferred embodiment, the cell as described hereinexpresses a membrane transporter protein belonging to the family of ABC transporters like e.g., oppFfrom E. coli (UniProt ID P77737), lmrA from Lactococcus lactis subsp. lactis bv. diacetylactis (UniProt IDA0A1V0NEL4) and Blon_2475 from Bifidobacterium longum subsp. infantis (UniProt ID B7GPD4). In a more preferred embodiment, the cell expresses more than one membrane transporter protein selected from the list comprising, consisting of or consisting essentially of a lactose transporter like e.g. the LacY or lac12 permease, a fucose transporter, a glucose transporter, a galactose transporter, a transporter for a nucleotide-activated sugar like for example a transporter for UDP-GlcNAc, UDP-Gal and / or GDP-Fuc, theMdfA protein from E. coli (UniProt ID P0AEY8), the MdfA protein from Cronobacter muytjensii (UniProt IDA0A2T7ANQ9), the MdfA protein from Citrobacter youngae (UniProt ID D4BC23), the MdfA protein fromYokenella regensburgei (UniProt ID G9Z5F4), the SetA protein from E. coli (UniProt ID P31675, sequenceversion 03 (11 Oct 2004)), the SetA protein from Citrobacter koseri (UniProt ID A0A078LM16), the entSprotein from E. coli (UniProt ID P24077, sequence version 02 (01 Nov 1997)), the entS protein from K.ascorbata (UniProt ID A0A378GQ13), the iceT protein from E. coli (UniProt ID A0A024L207), the oppFprotein from E. coli (UniProt ID P77737), the lmrA protein from Lactococcus lactis subsp. lactis bv.diacetylactis (UniProt ID A0A1V0NEL4) and Blon_2475 from Bifidobacterium longum subsp. infantis(UniProt ID B7GPD4). Preferably, the cell is transformed to comprise at least one nucleic acid sequence encoding a membrane transporter protein selected from the list comprising, consisting of or consisting essentially of asiderophore exporter, a major facilitator superfamily (MFS) transporter, an ATP-binding cassette (ABC)transporter or a sugar efflux transporter. In another and / or additional preferred embodiment of the method and / or cell of present invention, the at least one sialylated milk oligosaccharide present in said mixture of at least two milk oligosaccharides of present invention is a sialylated milk oligosaccharide having at least one sialic acid residue selected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3- deoxymanno-octulonic acid (KDO). In an additional preferred embodiment of the method and / or cell of present invention, the at least one sialylated milk oligosaccharide present in said mixture of at least two milk oligosaccharides of present invention is selected from the list comprising, consisting of or consisting essentially of a sialylated mammalian milk oligosaccharide (MMO), a sialylated human milk oligosaccharide (HMO), N- acetyllactosamine containing sialylated milk oligosaccharide, lacto-N-biose containing sialylated milk oligosaccharide, 3’sialyllactose (3’SL), 6’sialyllactose (6’SL), 3'-sialyllactosamine, 6’-sialyllactosamine, oligosaccharide comprising 6’-sialyllactosamine, oligosaccharide comprising 6’-sialyllacto-N-biose; 3,6- disialyllactose, 6,6’-disialyllactose (Neu5Ac-^2,6-Gal-^1,4-(Neu5Ac-^2,6)-Glc), 8,3-disialyllactose, sialylated lacto-N-triose, sialylated tetrasaccharide (Neu5Ac-α2,3-Gal-β1,4-GlcNAc-β1,4-GlcNAc), sialyllacto-N-tetraose a (LSTa, Neu5Ac-^2,3-Gal-^1,3-GlcNAc-^1,3-Gal-^1,4-Glc), KDOα-2,3Galβ- 1,3GlcNAcβ-1,3Galβ-1,4Glc, sialyllacto-N-tetraose b (LSTb, Gal-^1,3-[Neu5Ac-^2,6]-GlcNAc-^1,3-Gal- ^1,4-Glc), sialyllacto-N-tetraose c (LSTc, Neu5Ac-^2,6-Gal-^1,4-GlcNAc-^1,3-Gal-^1,4-Glc), sialyllacto-N- tetraose d (LSTd, Neu5Ac-α2,3-Gal-β1,4-GlcNAc-β1,3-Gal-β1,4-Glc), Neu5Ac-^2,6-(Neu5Ac-^2,3-Gal- ^1,3)-GlcNAc-^1,3-Gal-^1,4-Glc (DSLNT, disialyllacto-N-tetraose), Neu5Ac-^2,6-Gal-^1,4-GlcNAc-^1,3- [Neu5Ac-^2,6]-Gal-^1,4-Glc (DSLNnT, disialyllacto-N-neotetraose), monosialyllacto-N-hexaose, disialyllacto-N-hexaose I, disialyllacto-N-hexaose II, monosialyllacto-N-neohexaose I, monosialyllacto-N- neohexaose II, disialyllacto-N-neohexaose, 3'-sialyl-3-fucosyllactose, fucodisialyllacto-N-hexaose, disialomonofucosyllacto-N-neohexaose, monofucosylmonosialyllacto-N-octaose (sialyl Lea), sialyllacto-N- fucohexaose II, disialyllacto-N-fucopentaose II, monofucosyldisialyllacto-N-tetraose, Neu5Ac-a2,3-Gal- b1,4-GlcNAc-b1,3-Gal, Neu5Ac-a2,3-Gal-b1,3-GlcNAc-b1,3-Gal, 3’-KDO-lactose, 3’-KDO-lactosamine, 3’- KDO-lacto-N-biose, 3’-KDO-6’sialyllactose, 3’KDO-8-sialyllactose, KDO-2,3Galβ-1,3GalNacβ-1,3Galα- 1,4Galβ-1,4Gal, KDOα-2,3Galβ-1,4GlcNacβ-1,3Galβ-1,4Glc, 3’-KDO-3-fucosyllactose, Neu5Ac-a2,8- Neu5Ac-a2,3-Gal-b1,3-GlcNAc-b1,3-Gal, 3'-Sialyl-2'-fucosyllactose, 6'-Sialyl-2'-fucosyllactose, 6'-Sialyl-3- fucosyllactose, Neu5Ac-a2,6-(Neu5Ac-a2,3-)Gal-b1,4-Glc, 3'-Sialyl-3-fucosyllactosamine, Fuc-a1,4- (Neu5Ac-a2,3-Gal-b1,3-)GlcNAc, 6’-Sialyllacto-N-biose, 3’-Sialyllacto-N-biose, Neu5Ac-a2,6-(GlcNAc-b1,3- )Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,3-Gal-b1,4-(Fuc- a1,3-)GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-)Gal-b1,4- Glc, Neu5Ac-a2,6-(Gal-b1,4-GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4- (Fuc-a1,3-)Glc, Neu5Ac-a2,6-Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Neu5Ac-a2,3-Gal-b1,3- GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Neu5Ac-a2,3-(Fuc-a1,2-)Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Fuc-a1,2-Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Fuc-a1,2-)Gal-b1,3-GlcNAc- b1,3-Gal-b1,4-Glc, Fuc-a1,4-(Neu5Ac-a2,3-Gal-b1,3-)GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac- a2,6-Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-(Fuc-a1,3-)Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-(Fuc-a1,2-)Gal-b1,3- GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-Gal-b1,3- GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,3)-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6- (Neu5Ac-a2,3-Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,3-GlcNAc-b1,3)- Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-(Neu5Ac-a2,3)-Gal-b1,3-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac- a2,6-(Neu5Ac-a2,3-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,4-GlcNAc- b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-(Neu5Ac-a2,3)-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,4- GlcNAc-b1,3)-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-GlcNAc- b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-GlcNAc- b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,3-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-Glc, 6’-KDO- lactose, 6’-KDO-lactosamine, 6’-KDO-lacto-N-biose, KDO-lacto-N-triose, KDO-lacto-N-tetraose, KDO-lacto- N-tetraose, and combinations thereof. In another and / or additional preferred embodiment of the method and / or cell of present invention, the at least one non-sialylated milk oligosaccharide present in said mixture of at least two milk oligosaccharides of present invention is selected from the list comprising, consisting of or consisting essentially of non-sialylated neutral milk oligosaccharide, non-sialylated neutral MMO, non-sialylated neutral HMO, non-sialylated negatively charged oligosaccharide, non-sialylated negatively charged MMO, non-sialylated negatively charged HMO, sulphated milk oligosaccharides, 2'-fucosyllactose (2’FL), 3- fucosyllactose (3FL), 4-fucosyllactose (4FL), 6-fucosyllactose (6FL), 2',3-difucosyllactose (diFL), lacto-N- triose II (LN3, GlcNAcβ1-3Galβ1-4Glc), lacto-N-tetraose (LNT, Galβ1-3GlcNAcβ1-3Galβ1-4Glc), lacto-N- neotetraose (LNnT, Galβ1-4GlcNAcβ1-3Galβ1-4Glc), lacto-N-fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N-fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N-difucohexaose II, Fuc-a1,2-Gal-b1,3-GlcNAc- b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal-b1,4- (Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-Glc, Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2- Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,4-(Fuc-a1,2-Gal-b1,3-)GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose,3'-galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, a1,3- galactosyl-3-fucosyllactose, Gal-a1,3-(Fuc-a1,2-)Gal-b1,4-(Fuc-a1,3-)Glc, GalNAc-a1,3-(Fuc-a1,2-)Gal- b1,4-(Fuc-a1,3-)Glc, 2-fucosyllactulose, 3-fucosyl-N-acetyllactosamine, 2'-fucosyl-N-acetyllactosamine, difucosyl-N-acetyllactosamine, 4-fucosyllacto-N-biose, 2'-fucosyllacto-N-biose, difucosyllacto-N-biose, GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, GlcNAc-b1,6-(GlcNAc-b1,3-)Gal-b1,4-Glc, lacto-N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N-novopentaose I, lacto- N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N-heptaose, lacto-N- octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N-decaose, lacto-N-neodecaose, para lacto-N-neodecaose (pLNnD), a1,3-galactosyllacto-N-neotetraose, GlcNAc-b1,3-Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc, GlcNAc-b1,6-(Gal-b1,4-GlcNAc-b1,3-)Gal-b1,4-Glc and GlcNAc-b1,6-(Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc, 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,4-Glc; 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,4- Glc; 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,4-Glc; Gal-^1,4-GlcNAc-^1,6-[3-SO3-Gal-^1,3-Gal- ^1,3]-Gal-^1,4-Glc; 3-SO3-Gal-^1,4-GlcNAc-^1,6-[Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; Gal-^1,4-GlcNAc-^1,6- [3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; 3-SO3-Gal-^1,4-GlcNAc-^1,6-[Gal-^1,3-Gal-^1,3-Gal- ^1,3]-Gal-^1,4-Glc. According to another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide selected from the list comprising and 3’SL, 6’SL, LSTa, LSTb, LSTc, LSTd, DSLNT and DSLNnT and at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N-fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N- fucopentaose III, lacto-N-fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N- difucohexaose I, lacto-N-difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'-galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N-neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N- hexaose, lacto-N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N- neopentaose, lacto-N-novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N- neoheptaose, para lacto-N-heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto- N-decaose, novo lacto-N-decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises (1) 3’SL and / or 6’SL and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTd. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises (1) 3’SL and / or LSTa and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N-fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTd. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises (1) 3’SL and / or LSTd and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment,said mixture further comprises DSLNT. In another more preferred embodiment, said mixture furthercomprises DSLNnT. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises (1) LSTa and / or LSTd and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment,said mixture further comprises DSLNT. In another more preferred embodiment, said mixture furthercomprises DSLNnT. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTc. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises (1) 6’SL and / or LSTb and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N-fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises 3’SL. In another more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTd. In another more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises (1) 6’SL and / or LSTc and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises 3’SL. In another more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTd. In another more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 3’SL, 6’SL, LSTa, LSTc, LSTd, 2’FL, 3-FL, DiFL, LNT,LNnT, LNFP-I, LNFP-II, LNFP-III, LNFP-V, LNFP-VI, LNnFP-I, LNDFH-I, LNDFH-II and LNnDFH. In anotherpreferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 2’FL, 3-FL, LNT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises twelve or more oligosaccharides selected from the list consisting of 3’SL, 6’SL, LSTa, LSTc, LSTd, 2’FL, 3-FL, DiFL, LNT, LNnT, LNFP-I, LNFP-II, LNFP-III, LNFP-V, LNFP- VI, LNnFP-I, LNDFH-I, LNDFH-II and LNnDFH. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 2’FL, 3-FL, LNT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 2’FL, 3-FL, LNnT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 2’FL, 3-FL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNT, 3’SL, 6’SL and sialic acid. In anotherpreferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNnT, 3’SL, 6’SL and sialic acid. In anotherpreferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL and sialic acid. In anotherpreferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNT, 3’SL, 6’SL and l-fucose. In anotherpreferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNnT, 3’SL, 6’SL and l-fucose. In anotherpreferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL and l-fucose. In anotherpreferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNT, 3’SL, 6’SL, sialic acid and l-fucose. In another preferred embodiment of the method and / or cell of present invention, the mixture of at leasttwo milk oligosaccharides of present invention comprises 2’FL, 3-FL, LNnT, 3’SL, 6’SL, sialic acid and l-fucose. In another preferred embodiment of the method and / or cell of present invention, the mixture ofat least two milk oligosaccharides of present invention comprises 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL, sialicacid and l-fucose. In another preferred embodiment of the method and / or cell of present invention, themixture of at least two milk oligosaccharides of present invention comprises 2’FL, DiFL, LNT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 2’FL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 2’FL, DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises 2’FL, 3FL, DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferredembodiment of the method and / or cell of present invention, the mixture of at least two milkoligosaccharides of present invention comprises 2’FL, 3-FL, LNT, LNnT, 3’SL and 6’SL.According to another and / or additional preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein comprises two or more sialylated milk oligosaccharides. According to another and / or additional preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein comprises less sialylated milk oligosaccharide than non-sialylated milk oligosaccharides. In another preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein comprises less non-sialylated milk oligosaccharide than sialylated milk oligosaccharides. In another and / or additional preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide andat least one non-sialylated milk oligosaccharide as described herein does not comprise free sialic acid,wherein said free sialic acid is selected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO). In another and / or additional preferred embodiment of the method and / or cell of present invention, themixture of at least two milk oligosaccharides of present invention further comprises free sialic acidselected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO). In another and / or additional preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention further comprises a monosaccharide. In another and / or additional preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention further comprises a disaccharide. In another and / or additional preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention further comprises lactose. In a more preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide and sialic acid. In another more preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide, lactose and sialic acid. In another more preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide and lactose. In another more preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide, lactose and free sialic acid wherein said mixture comprises less than 10 % lactose and / or less than 5 % free sialic acid. In an even more preferred embodiment, said mixture comprises less than 9 % lactose. In an even more preferred embodiment, said mixture comprises less than 8 % lactose. In another even more preferred embodiment, said mixture comprises less than 7 %, less than 6 %, less than 5 %, less than 4 %, less than 3 %, less than 2 %, less than 1 % lactose. In an additional and / or alternative more preferred embodiment, said mixture comprises less than 5 % free sialic acid. In an even more preferred additional and / or alternative embodiment, said mixture comprises less than 4 %, less than 3 %, less than 2 %, less than 1 %, less than 0.5 %, less than 0.1 % free sialic acid. In another more preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide,at least one non-sialylated milk oligosaccharide and l-fucose. In another more preferred embodiment ofthe method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide, at least one non-sialylated milkoligosaccharide, lactose and l-fucose. In another more preferred embodiment of the method and / or cell of present invention, the mixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide, free sialic acidand l-fucose. In another more preferred embodiment of the method and / or cell of present invention, themixture of at least two milk oligosaccharides of present invention comprises at least one sialylated milkoligosaccharide, at least one non-sialylated milk oligosaccharide, lactose, free sialic acid and l-fucose.In another and / or additional preferred embodiment of the method and / or cell of present invention, the cell is selected from the list consisting of prokaryotic cells and eukaryotic cells, optionally, said cell is selected from the list consisting of yeast cells, bacterial cells, archaebacterial cells, algae cells, fungal cells, plant cells, animal cells, insect cells, protozoan cells. Preferably, the cell is a bacterium, fungus, yeast, a plant cell, an animal cell, or a protozoan cell. The latter bacterium preferably belongs to the phylum of the Proteobacteria or the phylum of the Firmicutes or the phylum of the Cyanobacteria or the phylum Deinococcus-Thermus or the phylum of Actinobacteria. The latter bacterium belonging to the phylum Proteobacteria belongs preferably to the family Enterobacteriaceae, preferably to the species Escherichia coli. The latter bacterium preferably relates to any strain belonging to the species Escherichia coli such asbut not limited to Escherichia coli B, Escherichia coli C, Escherichia coli W, Escherichia coli K12, Escherichiacoli Nissle. More specifically, the latter term relates to cultivated Escherichia coli strains - designated as E.coli K12 strains - which are well-adapted to the laboratory environment, and, unlike wild type strains, havelost their ability to thrive in the intestine. Well-known examples of the E. coli K12 strains are K12 Wildtype, W3110, MG1655, M182, MC1000, MC1060, MC1061, MC4100, JM101, NZN111 and AA200. Hence,the present invention specifically relates to a mutated and / or transformed Escherichia coli cell or strainas indicated above wherein said E. coli strain is a K12 strain. More preferably, the Escherichia coli K12strain is E. coli MG1655. The latter bacterium belonging to the phylum Firmicutes belongs preferably tothe Bacilli, preferably Lactobacilliales, with members such as Lactobacillus lactis, Leuconostocmesenteroides, or Bacillales with members such as from the genus Bacillus, such as Bacillus subtilis or, B.amyloliquefaciens. The latter Bacterium belonging to the phylum Actinobacteria, preferably belonging tothe family of the Corynebacteriaceae, with members Corynebacterium glutamicum or C. afermentans, orbelonging to the family of the Streptomycetaceae with members Streptomyces griseus or S. fradiae. Thelatter bacterium belonging to the phylum Proteobacteria, preferably belonging to the family of the Vibrionaceae, with member Vibrio natriegens. The latter yeast preferably belongs to the phylum of the Ascomycota or the phylum of the Basidiomycota or the phylum of the Deuteromycota or the phylum of the Zygomycetes. The latter yeast belongs preferably to the genus Saccharomyces (with members like e.g. Saccharomyces cerevisiae, S. bayanus, S. boulardii), Zygosaccharomyces, Pichia (with members like e.g. Pichia pastoris, P. anomala, P. kluyveri), Komagataella, Hansenula, Kluyveromyces (with members like e.g. Kluyveromyces lactis, K. marxianus, K. thermotolerans), Debaromyces, Candida, Schizosaccharomyces, Schwanniomyces, Torulaspora, Yarrowia (like e.g. Yarrowia lipolytica) or Starmerella (like e.g. Starmerella bombicola). The latter yeast is preferably selected from Pichia pastoris, Yarrowia lipolitica, Saccharomyces cerevisiae, Kluyveromyces lactis, Hansenula polymorpha, Kluyveromyces marxianus, Pichia methanolica, Pichia stipites, Candida boidinii, Schizosaccharomyces pombe, Schwanniomyces occidentalis, Torulaspora delbrueckii, Zygosaccharomyces rouxii, and Zygosaccharomyces bailii. The latter fungus belongs preferably to the genus Rhizopus, Dictyostelium, Penicillium, Mucor or Aspergillus. Plant cells include cells of flowering and non-flowering plants, as well as algal cells, for example Chlamydomonas, Chlorella, etc. Preferably, said plant is a tobacco, alfalfa, rice, tomato, cotton, rapeseed, soy, maize, or corn plant. The latter animal cell is preferably derived from non-human mammals (e.g. cattle, buffalo, pig, sheep, mouse, rat, primate (e.g., chimpanzee, orangutan, gorilla, monkey (e.g., Old World, New World), lemur), dog, cat, rabbit, horse, cow, goat, ox, deer, musk deer, bovid, whale, dolphin, hippopotamus, elephant, rhinoceros, giraffe, zebra, lion, cheetah, tiger, panda, red panda, otter), birds (e.g. chicken, duck, ostrich, turkey, pheasant), fish (e.g. swordfish, salmon, tuna, sea bass, trout, catfish), invertebrates (e.g. lobster, crab, shrimp, clams, oyster, mussel, sea urchin), reptiles (e.g. snake, alligator, turtle), amphibians (e.g. frogs) or insects (e.g. fly, nematode) or is a genetically engineered cell line derived from human cells excludingembryonic stem cells. Both human and non-human mammalian cells are preferably selected from the listcomprising, consisting of or consisting essentially of an epithelial cell like e.g., a mammary epithelial cell, an embryonic kidney cell (e.g., HEK293 or HEK 293T cell), a fibroblast cell, a COS cell, a Chinese hamster ovary (CHO) cell, a murine myeloma cell like e.g. an N20, SP2 / 0 or YB2 / 0 cell, an NIH-3T3 cell, a non- mammary adult stem cell or derivatives thereof such as described in WO21067641, a lactocyte derived from mammalian induced pluripotent stem cells, preferably human induced pluripotent stem cells, a lactocyte as part of mammary-like gland organoids, a post-parturition mammary epithelium cell, a polarized mammary cell, preferably a polarized mammary cell selected from the list comprising, consisting of or consisting essentially of live primary mammary epithelial cells, live mammary myoepithelial cells, live mammary progenitor cells, live immortalized mammary epithelial cells, live immortalized mammary myoepithelial cells, live immortalized mammary progenitor cells, a non-mammary adult stem cell or derivatives thereof as well-known to the person skilled in the art from e.g., WO2021 / 219634, WO 2022 / 054053, WO 2021 / 141762, WO 2021 / 142241, WO 2021 / 067641 and WO2021 / 242866. The latterinsect cell is preferably derived from Spodoptera frugiperda like e.g., Sf9 or Sf21 cells, Bombyx mori,Mamestra brassicae, Trichoplusia ni like e.g., BTI-TN-5B1-4 cells or Drosophila melanogaster like e.g.,Drosophila S2 cells. The latter protozoan cell preferably is a Leishmania tarentolae cell.Another aspect provides for a cell to be stably cultured in a cultivation or incubation medium, wherein said cultivation or incubation medium can be any type of growth medium comprising, consisting of or consisting essentially of minimal medium, complex medium or growth medium enriched in certain compounds like, for example, but not limited to, vitamins, trace elements, amino acids. The cell as used herein is capable to grow on a monosaccharide, disaccharide, oligosaccharide, polysaccharide, polyol, glycerol, a complex medium or a mixture thereof as the main carbon source. With the term main is meant the most important carbon source for the cell for the production of theoligosaccharide mixture of interest, biomass formation, carbon dioxide and / or by-products formation(such as acids and / or alcohols, such as acetate, lactate, and / or ethanol), i.e.20, 30, 40, 50, 60, 70, 75, 80,85, 90, 95, 98, 99 % of all the required carbon is derived from the above-indicated carbon source. In oneembodiment of the invention, said carbon source is the sole carbon source for said organism, i.e.100 % of all the required carbon is derived from the above-indicated carbon source. Common main carbon sources comprise but are not limited to glucose, glycerol, fructose, sucrose, maltose, lactose, arabinose, malto-oligosaccharides, maltotriose, sorbitol, xylose, rhamnose, galactose, mannose, methanol, ethanol, trehalose, starch, cellulose, hemi-cellulose, molasses, corn-steep liquor, high-fructose syrup, acetate, citrate, lactate and pyruvate. As used herein, a precursor as defined herein cannot be used as a carbon source for the production of the oligosaccharide mixture of present invention. In a preferred embodiment of the method of present invention, the cultivation or incubation medium contains at least one carbon source selected from the list comprising, consisting of or consisting essentially of a monosaccharide, disaccharide, oligosaccharide, polysaccharide, polyol, glycerol, a complex medium including molasses, corn steep liquor, peptone, tryptone or yeast extract. Preferably, said carbon source is selected from the list comprising, consisting of or consisting essentially of glucose, glycerol, fructose, sucrose, maltose, lactose, arabinose, maltooligosaccharides, maltotriose, sorbitol, xylose, rhamnose, galactose, mannose, methanol, ethanol, trehalose, starch, cellulose, hemi-cellulose, molasses, corn-steep liquor, high-fructose syrup, acetate, citrate, lactate and pyruvate. In another and / or additional preferred embodiment of the method of present invention, the cultivation or incubation medium contains at least one compound selected from the list comprising, consisting of or consisting essentially of lactose, GlcNAc-β1,3-Gal-β1,4-Glc (lacto-N-triose, LN3), Gal-β1,3-GlcNAc-β1,3- Gal-β1,4-Glc (lacto-N-tetraose, LNT), Gal-β1,4-GlcNAc-β1,3-Gal-β1,4-Glc (lacto-N-neotetraose, LNnT), galactose, glucose, sialic acid, Neu5Ac, CMP-sialic acid, CMP-Neu5Ac, CMP-KDO, GlcNAc, GalNAc, UDP- GlcNAc, UDP-GalNAc, and UDP-galactose (UDP-Gal). In the scope of the present invention, permissive conditions are understood to be conditions relating to physical or chemical parameters including but not limited to temperature, pH, pressure, osmotic pressure and product / donor / precursor / acceptor concentration. In a particular embodiment, the permissive conditions may include a temperature-range of about 30 + / -20 degrees centigrade, a pH-range of 2.0 – 10.0, preferably a pH range of 3.0 – 7.0.According to another and / or additional preferred embodiment of the method of the invention, the conditions permissive to produce a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein comprise the use of a cultivation or incubation medium comprising at least one precursor and / or acceptorfor the production of said at least one sialylated milk oligosaccharide and / or at least one non-sialylatedmilk oligosaccharide in said milk oligosaccharide mixture as described herein. Preferably, the cultivationor incubation medium contains at least one precursor and / or acceptor, wherein said precursor is selected from the list comprising, consisting of or consisting essentially of a monosaccharide like e.g. galactose, glucose, fucose, sialic acid, GlcNAc, GalNAc; a nucleotide-activated sugar like e.g. CMP-sialic acid, CMP- Neu5Ac, CMP-KDO, UDP-Gal, UDP-GlcNAc, GDP-fucose; a disaccharide like e.g. lactose; and an oligosaccharide like e.g. lacto-N-triose (LN3), lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT), and / or wherein said acceptor is selected from the list comprising, consisting of or consisting essentially ofa disaccharide like e.g. lactose; an oligosaccharide like e.g. LN3, LNT, LNnT.In a more preferred embodiment of the method of the invention, said precursor is selected from the list comprising, consisting of or consisting essentially of sialic acid, a sialic acid residue, Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3;Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc; KDO, CMP-sialic acid, CMP-Neu5Ac, glucose,galactose, GlcNAc, GalNAc, UDP-Gal, UDP-GlcNAc, and UDP-GalNAc. In another more preferred embodiment of the method of the invention, said acceptor is selected from the list comprising, consistingof or consisting essentially of lactose, LN3, LNT and LNnT.According to an alternative and / or additional embodiment of the method of the invention, the conditions permissive to produce said mixture of at least two milk oligosaccharides comprising at least one sialylatedmilk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein, comprisethe use of a cultivation or incubation medium and adding to said cultivation or incubation medium at least one precursor and / or acceptor feed for the production of said at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said milk oligosaccharide mixture. According to an alternative embodiment of the method of the invention, the conditions permissive to produce said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein, comprise the use of a cultivation or incubation medium wherein said cultivation or incubation medium lacks any precursor and / or acceptor for the production of said at least one sialylated milk oligosaccharide and / or at least onenon-sialylated milk oligosaccharide of said milk oligosaccharide mixture, and is combined with a furtheraddition to said cultivation or incubation medium of at least one precursor and / or acceptor feed for the production of said at least one sialylated milk oligosaccharide and / or at least one non-sialylated milk oligosaccharide of said milk oligosaccharide mixture. In a more preferred embodiment of the method of the invention, said precursor is selected from the list comprising, consisting of or consisting essentially of sialic acid, a sialic acid residue, Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3;Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc; KDO, CMP-sialic acid, CMP-Neu5Ac, glucose,galactose, GlcNAc, GalNAc, UDP-Gal, UDP-GlcNAc, and UDP-GalNAc. In another more preferred embodiment of the method of the invention, said acceptor is selected from the list comprising, consisting of or consisting essentially of lactose, LN3, LNT and LNnT. According to an embodiment of the method of the invention, the cultivation or incubation is contained in a reactor or incubator, as defined herein. The volume of said reactor or incubator ranges from microlitre (µL) scale to 10.000 m3 (cubic meter). In a preferred embodiment, the volume of said reactor or incubator ranges from 250 mL (millilitre) to 10.000 m3 (cubic meter). In a preferred embodiment, the method for the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylatedmilk oligosaccharide as described herein comprises at least one of the following steps:i) Use of a cultivation or incubation medium comprising at least one precursor and / or acceptor;ii) Adding to the cultivation or incubation medium in a reactor or incubator at least one precursorand / or acceptor feed wherein the total reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said precursor and / or acceptor feed; iii) Adding to the cultivation or incubation medium in a reactor or incubator at least one precursorand / or acceptor feed wherein the total reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than two-fold of the volume of the cultivation or incubation medium before the addition of said precursor and / or acceptor feed and wherein preferably, the pH of said precursor and / or acceptor feed is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor and / or acceptor feed is kept between 20°C and 80°C; iv) Adding at least one precursor and / or acceptor feed in a continuous manner to the cultivation orincubation medium over the course of 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursor and / or acceptor feeding solution; v) Adding at least one precursor and / or acceptor feed in a continuous manner to the cultivation orincubation medium over the course of 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursor and / or acceptor feeding solution and wherein the concentration of said precursorand / or acceptor feeding solution is 50 g / L, preferably 75 g / L, more preferably 100 g / L, more preferably 125 g / L, more preferably 150 g / L, more preferably 175 g / L, more preferably 200 g / L, more preferably 225 g / L, more preferably 250 g / L, more preferably 275 g / L, more preferably 300 g / L, more preferably 325 g / L, more preferably 350 g / L, more preferably 375 g / L, more preferably, 400 g / L, more preferably 450 g / L, more preferably 500 g / L, even more preferably, 550 g / L, most preferably 600 g / L; and wherein preferably, the pH of said precursor and / or acceptor feeding solution is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor and / or acceptor feeding solution is kept between 20°C and 80°C; said method resulting in the production of at least 25 g / L, preferably at least 30 g / L, more preferably at least 40 g / L, more preferably at least 50 g / L, more preferably at least 75 g / L, more preferably at least 90 g / L, more preferably at least 100 g / L, more preferably at least 125 g / L, more preferably at least 150 g / L, more preferably at least 175 g / L, more preferably at least 200 g / L of total milk oligosaccharides in the final volume of the cultivation or incubation. In a more preferred embodiment of the method of the invention, said precursor is selected from the list comprising, consisting of or consisting essentially of sialic acid, CMP-sialic acid, CMP-Neu5Ac, glucose, galactose, GlcNAc, GalNAc, UDP-GlcNAc, UDP-GalNAc and UDP-Gal. In another more preferred embodiment of the method of the invention, said acceptor is selected from the list comprising, consisting of or consisting essentially of lactose, LN3, LNT and LNnT. In another and / or additional preferred embodiment, the method for the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein comprises at least one of the following steps:i) Use of a cultivation or incubation medium comprising at least one precursor and / or acceptor;ii) Adding to the cultivation or incubation medium in a reactor or incubator at least one precursor and / oracceptor in one pulse or in a discontinuous (pulsed) manner wherein the total reactor or incubator volume ranges from 250 mL (millilitre) to 10.000 m3(cubic meter), preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two- fold, more preferably less than two-fold of the volume of the cultivation or incubation medium before the addition of said precursor and / or acceptor feed pulse(s);iii) Adding to the cultivation or incubation medium in a reactor or incubator at least one precursor and / oracceptor feed in one pulse or in a discontinuous (pulsed) manner wherein the total reactor or incubator volume ranges from 250 mL (millilitre) to 10.000 m3(cubic meter), preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than two-fold of the volume of the cultivation or incubation medium before the addition of said precursor and / or acceptor feed and wherein preferably, the pH of said precursor and / or acceptor feed pulse(s) is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor and / or acceptor feed pulse(s) is kept between 20°C and 80°C;iv) Adding at least one precursor and / or acceptor feed in a discontinuous (pulsed) manner to the cultivation or incubation medium over the course of 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 10 hours, 12 hours, 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursor and / or acceptor feeding solution;v) Adding at least one precursor and / or acceptor feed in a discontinuous (pulsed) manner to thecultivation or incubation medium over the course of 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 10 hours, 12 hours, 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursor and / or acceptor feeding solution and wherein preferably, the pH of said precursor and / or acceptorfeeding solution is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor and / or acceptor feeding solution is kept between 20°C and 80°C; said method resulting in the production of at least 25 g / L, preferably at least 30 g / L, more preferably at least 40 g / L, more preferably at least 50 g / L, more preferably at least 75 g / L, more preferably at least 90 g / L, more preferably at least 100 g / L, more preferably at least 125 g / L, more preferably at least 150 g / L, more preferably at least 175 g / L, more preferably at least 200 g / L of total milk oligosaccharides in the final volume of the cultivation or incubation. In a more preferred embodiment of the method of the invention, said precursor is selected from the list comprising, consisting of or consisting essentially of sialic acid, CMP-sialic acid, CMP-Neu5Ac, glucose, galactose, GlcNAc, GalNAc, UDP-GlcNAc, UDP-GalNAc and UDP- Gal. In another more preferred embodiment of the method of the invention, said acceptor is selected from the list comprising, consisting of or consisting essentially of lactose, LN3, LNT and LNnT. In another and / or additional preferred embodiment, the method for the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein comprises at least one of the following steps: i) Use of a cultivation or incubation medium comprising at least 50, more preferably at least 75,more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of precursor per litre of initial reactor or incubator volume wherein the reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter); ii) Use of a cultivation or incubation medium comprising at least 50, more preferably at least 75,more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of acceptor per litre of initial reactor or incubator volume wherein the reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter); iii) Adding to the cultivation or incubation medium in a reactor or incubator a precursor feedcomprising at least 50, more preferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of precursor per litre of initial reactor or incubator volume wherein the reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two- fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said precursor feed;iv) Adding to the cultivation or incubation medium in a reactor or incubator a precursor feedcomprising at least 50, more preferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of precursor per litre of initial reactor or incubator volume wherein the reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter) in one pulse or in a discontinuous (pulsed) manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said precursor feed;v) Adding to the cultivation or incubation medium in a reactor or incubator an acceptor feedcomprising at least 50, more preferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of acceptor per litre of initial reactor or incubator volume wherein the reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said acceptor feed;vi) Adding to the cultivation or incubation medium in a reactor or incubator an acceptor feedcomprising at least 50, more preferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of acceptor per litre of initial reactor or incubator volume wherein the reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), in one pulse or in a discontinuous (pulsed) manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two- fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said acceptor feed;vii) Adding to the cultivation or incubation medium a precursor feed comprising at least 50, morepreferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of precursor per litre of initial reactor or incubator volume whereinthe total reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said precursor feed and wherein preferably, the pH of said precursor feed is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor feed is kept between 20°C and 80°C;viii) Adding to the cultivation or incubation medium a precursor feed comprising at least 50, more preferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of precursor per litre of initial reactor or incubator volume wherein the total reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), in one pulse or in a discontinuous (pulsed) manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two- fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said precursor feed and wherein preferably, the pH of said precursor feed is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor feed is kept between 20°C and 80°C;ix) Adding to the cultivation or incubation medium an acceptor feed comprising at least 50, morepreferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of acceptor per litre of initial reactor or incubator volume wherein the total reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said acceptor feed and wherein preferably, the pH of said acceptor feed is set between 2.0 and 10.0 and wherein preferably, the temperature of said acceptor feed is kept between 20°C and 80°C;x) Adding to the cultivation or incubation medium an acceptor feed comprising at least 50, morepreferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of acceptor per litre of initial reactor or incubator volume wherein the total reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter), in one pulse or in a discontinuous (pulsed) manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two- fold, more preferably less than 2-fold of the volume of the cultivation or incubation medium before the addition of said acceptor feed and wherein preferably, the pH of said acceptor feed is set between 2.0 and 10.0 and wherein preferably, the temperature of said acceptor feed is kept between 20°C and 80°C;xi) Adding a precursor and / or acceptor feed in a continuous manner to the cultivation or incubationmedium over the course of 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursor and / or acceptor feeding solution;xii) Adding at least one precursor and / or acceptor feed in a discontinuous (pulsed) manner to thecultivation or incubation medium over the course of 5 minutes, 10 minutes, 30 minutes, 1 hour, 2hours, 4 hours, 10 hours, 12 hours, 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursorand / or acceptor feeding solution;xiii) Adding a precursor feed in a continuous manner to the cultivation or incubation medium overthe course of 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursor feeding solution andwherein the concentration of said precursor feeding solution is 50 g / L, preferably 75 g / L, more preferably 100 g / L, more preferably 125 g / L, more preferably 150 g / L, more preferably 175 g / L, more preferably 200 g / L, more preferably 225 g / L, more preferably 250 g / L, more preferably 275 g / L, more preferably 300 g / L, more preferably 325 g / L, more preferably 350 g / L, more preferably 375 g / L, more preferably, 400 g / L, more preferably 450 g / L, more preferably 500 g / L, even more preferably, 550 g / L, most preferably 600 g / L; and wherein preferably the pH of said precursor feeding solution is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor feeding solution is kept between 20°C and 80°C; xiv) Adding an acceptor feed in a continuous manner to the cultivation or incubation medium overthe course of 1 day, 2 days, 3 days, 4 days, 5 days by means of an acceptor feeding solution andwherein the concentration of said acceptor feeding solution is 50 g / L, preferably 75 g / L, more preferably 100 g / L, more preferably 125 g / L, more preferably 150 g / L, more preferably 175 g / L,more preferably 200 g / L, more preferably 225 g / L, more preferably 250 g / L, more preferably 275 g / L, more preferably 300 g / L, more preferably 325 g / L, more preferably 350 g / L, more preferably 375 g / L, more preferably, 400 g / L, more preferably 450 g / L, more preferably 500 g / L, even more preferably, 550 g / L, most preferably 600 g / L; and wherein preferably the pH of said acceptor feeding solution is set between 2.0 and 10.0 and wherein preferably, the temperature of saidacceptor feeding solution is kept between 20°C and 80°C; xv) Adding a precursor and / or acceptor feed in a discontinuous (pulsed) manner to the cultivationor incubation medium over the course of 5 minutes, 10 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 10 hours, 12 hours, 1 day, 2 days, 3 days, 4 days, 5 days by means of a precursor feeding solution and wherein the concentration of said precursor and / or acceptor feeding solution is 50g / L, preferably 75 g / L, more preferably 100 g / L, more preferably 125 g / L, more preferably 150 g / L, more preferably 175 g / L, more preferably 200 g / L, more preferably 225 g / L, more preferably 250 g / L, more preferably 275 g / L, more preferably 300 g / L, more preferably 325 g / L, more preferably 350 g / L, more preferably 375 g / L, more preferably, 400 g / L, more preferably 450 g / L, more preferably 500 g / L, even more preferably, 550 g / L, most preferably 600 g / L; and whereinpreferably the pH of said precursor and / or acceptor feeding solution is set between 2.0 and 10.0 and wherein preferably, the temperature of said precursor and / or acceptor feeding solution is kept between 20°C and 80°C; said method resulting in the production of at least 25 g / L, preferably at least 30 g / L, more preferably at least 40 g / L, more preferably at least 50 g / L, more preferably at least 75 g / L, more preferably at least 90 g / L, more preferably at least 100 g / L, more preferably at least 125 g / L, more preferably at least 150 g / L, more preferably at least 175 g / L, more preferably at least 200 g / L of total milk oligosaccharides in the final volume of the cultivation or incubation. In a more preferred embodiment of the method of the invention,said precursor is selected from the list comprising, consisting of or consisting essentially of sialic acid,CMP-sialic acid, CMP-Neu5Ac, glucose, galactose, GlcNAc, GalNAc, UDP-GlcNAc, UDP-GalNAc and UDP- Gal. In another more preferred embodiment of the method of the invention, said acceptor is selected from the list comprising, consisting of or consisting essentially of lactose, LN3, LNT and LNnT. In a more preferred embodiment, the method for the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide as described herein comprises at least one of the following steps:i) Use of a cultivation or incubation medium comprising at least 50, more preferably at least 75, morepreferably at least 100, more preferably at least 120, more preferably at least 150 grams of lactose per litre of initial reactor or incubator volume wherein the reactor or incubator volume ranges from 250 mL to 10.000 m3(cubic meter);ii) Adding to the cultivation or incubation medium in a reactor or incubator a lactose feed comprising atleast 50, more preferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 gram of lactose per litre of initial reactor or incubator volume wherein the total reactor or incubator volume ranges from 250 mL (millilitre) to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than two-fold of the volume of the cultivation or incubation medium before the addition of said lactose feed;iii) Adding to the cultivation or incubation medium in a reactor or incubator a lactose feed comprising atleast 50, more preferably at least 75, more preferably at least 100, more preferably at least 120, more preferably at least 150 grams of lactose per litre of initial reactor or incubator volume wherein thetotal reactor or incubator volume ranges from 250 mL (millilitre) to 10.000 m3(cubic meter), preferably in a continuous manner, and preferably so that the final volume of the cultivation or incubation medium is not more than three-fold, preferably not more than two-fold, more preferably less than two-fold of the volume of the cultivation or incubation medium before the addition of said lactose feed and wherein preferably, the pH of said lactose feed is set between 2.0 and 10.0, preferably between 3.0 and 7.0, and wherein preferably, the temperature of said lactose feed is kept between 20°C and 80°C;iv) Adding a lactose feed in a continuous manner to the cultivation or incubation medium over the courseof 1 day, 2 days, 3 days, 4 days, 5 days by means of a feeding solution;v) Adding a lactose feed in a continuous manner to the cultivation or incubation medium over the courseof 1 day, 2 days, 3 days, 4 days, 5 days by means of a feeding solution and wherein the concentrationof said lactose feeding solution is 50 g / L, preferably 75 g / L, more preferably 100 g / L, more preferably 125 g / L, more preferably 150 g / L, more preferably 175 g / L, more preferably 200 g / L, more preferably 225 g / L, more preferably 250 g / L, more preferably 275 g / L, more preferably 300 g / L, more preferably 325 g / L, more preferably 350 g / L, more preferably 375 g / L, more preferably, 400 g / L, more preferably 450 g / L, more preferably 500 g / L, even more preferably, 550 g / L, most preferably 600 g / L; andwherein preferably, the pH of said lactose feed is set between 2.0 and 10.0, preferably between 3.0 and 7.0 and wherein preferably, the temperature of said lactose feed is kept between 20°C and 80°C; said method resulting in the production of at least 25 g / L, preferably at least 30 g / L, more preferably at least 40 g / L, more preferably at least 50 g / L, more preferably at least 75 g / L, more preferably at least 90 g / L, more preferably at least 100 g / L, more preferably at least 125 g / L, more preferably at least 150 g / L, more preferably at least 175 g / L, more preferably at least 200 g / L of total milk oligosaccharides in the final volume of the cultivation or incubation. Preferably the lactose feed is accomplished by adding lactose from the beginning of the cultivation or incubation in a concentration of at least 5 mM, preferably in a concentration of 30, 40, 50, 60, 70, 80, 90, 100, 150 mM, more preferably in a concentration > 300 mM. In another embodiment of the methods, the lactose feed is accomplished by adding lactose to the cultivation or incubation medium in a concentration, such that throughout the production phase of the cultivation or incubation a lactose concentration of at least 5 mM, preferably 10 mM or 30 mM is obtained. In a further embodiment of the methods described herein the cells are cultivated or incubated for at least about 60, 80, 100, or about 120 hours or in a continuous manner. In a preferred embodiment, a carbon source is provided, preferably sucrose, in the cultivation medium for 3 or more days, preferably up to 7 days; and / or provided, in the cultivation medium, at least 100,advantageously at least 105, more advantageously at least 110, even more advantageously at least 120grams of sucrose per litre of initial cultivation volume in a continuous manner, so that the final volume of the cultivation medium is not more than three-fold, advantageously not more than two-fold, more advantageously less than two-fold of the volume of the cultivation medium before the cultivation. Preferably, when performing the method as described herein, a first phase of exponential cell growth is provided by adding a carbon source, preferably glucose or sucrose, to the cultivation medium before the lactose is added to the cultivation medium in a second phase. In an alternative preferable embodiment, in the method as described herein, the lactose is added already in the first phase of exponential growth together with the carbon-based substrate. In another preferred embodiment, the methods of present invention result in the production of 0.1 g / L or more, preferably 0.5 g / L or more, more preferably 1 g / L or more, more preferably 5 g / L or more, even more preferably 10 g / L or more, even more preferably 20 g / L or more, even more preferably 30 g / L or more, even preferably 40 g / L or more, most preferably 50 g / L or more of total milk oligosaccharides. In another and / or additional preferred embodiment, the cell of present invention produces 0.1 g / L or more, preferably 0.5 g / L or more, more preferably 1 g / L or more, more preferably 5 g / L or more, even more preferably 10 g / L or more, even more preferably 20 g / L or more, even more preferably 30 g / L or more, even preferably 40 g / L or more, most preferably 50 g / L or more of total milk oligosaccharides. According to another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide,at least one non-sialylated milk oligosaccharide and free sialic acid. In another preferred embodiment, themethods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide,lactose and free sialic acid. In another preferred embodiment, the methods of present invention result inthe production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milkoligosaccharide, at least one non-sialylated milk oligosaccharide and lactose. In another preferredembodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide, lactose and free sialic acid wherein said mixture comprises less than 10 % lactose and / or less than 5 % free sialic acid. In a more preferred embodiment, said mixture comprises less than 9 % lactose. In an even more preferred embodiment, said mixture comprises less than 8 % lactose. In another even more preferred embodiment, said mixture comprises less than 7 %, less than 6 %, less than 5 %, less than 4 %, less than 3 %, less than 2 %, less than 1 % lactose. In an additional and / or alternative morepreferred embodiment, said mixture comprises less than 5 % of free sialic acid. In an even more preferredadditional and / or alternative embodiment, said mixture comprises less than 4 %, less than 3 %, less than2 %, less than 1 %, less than 0.5 %, less than less than 0.2 %, and / or less than 0.1 % of free sialic acid,wherein free said sialic acid is selected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4;Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO). In a mostpreferred embodiment, said mixture does not comprise free sialic acid as defined herein. In another morepreferred embodiment, the methods of present invention result in the production of a mixture of at leasttwo milk oligosaccharides of present invention comprising at least one sialylated milk oligosaccharide, atleast one non-sialylated milk oligosaccharide and l-fucose. In another more preferred embodiment, themethods of present invention result in the production of a mixture of at least two milk oligosaccharidesof present invention comprising at least one sialylated milk oligosaccharide, at least one non-sialylatedmilk oligosaccharide, lactose and l-fucose. In another more preferred embodiment, the methods ofpresent invention result in the production of a mixture of at least two milk oligosaccharides of presentinvention comprising at least one sialylated milk oligosaccharide, at least one non-sialylated milkoligosaccharide, free sialic acid and l-fucose. In another more preferred embodiment, the methods ofpresent invention result in the production of a mixture of at least two milk oligosaccharides of presentinvention comprising at least one sialylated milk oligosaccharide, at least one non-sialylated milkoligosaccharide, lactose, free sialic acid and l-fucose. In another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide selected from the list comprising and 3’SL, 6’SL, LSTa, LSTb, LSTc, LSTd, DSLNT and DSLNnT and at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising (1) 3’SL and / or 6’SL and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTd. In another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising (1) 3’SL and / or LSTa and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTd. In another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising (1) 3’SL and / or LSTd and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising (1) LSTa and / or LSTd and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTc. In another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising (1) 6’SL and / or LSTb and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises 3’SL. In another more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTd. In another more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment, the methods of present invention result in the production of a mixture of at least two milk oligosaccharides comprising (1) 6’SL and / or LSTc and (2) at least one non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises 3’SL. In another more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTd. In another more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 3’SL, 6’SL, LSTa, LSTc, LSTd, 2’FL, 3-FL, DiFL, LNT, LNnT, LNFP-I, LNFP-II, LNFP-III, LNFP-V, LNFP-VI, LNnFP-I, LNDFH-I, LNDFH-II and LNnDFH. In another preferred embodiment,the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising twelve or more oligosaccharides selected from the list consisting of 3’SL, 6’SL, LSTa, LSTc, LSTd, 2’FL, 3-FL, DiFL, LNT, LNnT, LNFP-I, LNFP-II, LNFP-III, LNFP-V, LNFP-VI, LNnFP-I, LNDFH-I, LNDFH-II and LNnDFH. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, 3- FL, LNnT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharidemixture comprising 2’FL, 3-FL, LNT, 3’SL, 6’SL and sialic acid. In another preferred embodiment, themethods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, 3-FL, LNnT, 3’SL, 6’SL and sialic acid. In another preferred embodiment, the methods of present inventionresult in the production of an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL andsialic acid. In another preferred embodiment, the methods of present invention result in the productionof an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL, 6’SL and l-fucose. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixturecomprising 2’FL, 3-FL, LNnT, 3’SL, 6’SL and l-fucose. In another preferred embodiment, the methods ofpresent invention result in the production of an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, LNnT,3’SL, 6’SL and l-fucose. In another preferred embodiment, the methods of present invention result in theproduction of an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL, 6’SL, sialic acid and l-fucose. Inanother preferred embodiment, the methods of present invention result in the production of anoligosaccharide mixture comprising 2’FL, 3-FL, LNnT, 3’SL, 6’SL, sialic acid and l-fucose. In anotherpreferred embodiment, the methods of present invention result in the production of an oligosaccharidemixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL, sialic acid and l-fucose. In another preferredembodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, DiFL, LNT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, 3FL, DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in the production of an oligosaccharide mixture comprising 2’FL, DiFL, LNT, LNnT,3’SL and 6’SL. In another preferred embodiment, the methods of present invention result in theproduction of an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SL and 6’SL.According to another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide and sialic acid. In another preferredembodiment, the cell of present invention is capable of producing and / or produces a mixture of at leasttwo milk oligosaccharides comprising at least one sialylated milk oligosaccharide, at least one non- sialylated milk oligosaccharide, lactose and sialic acid. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide and lactose. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide, at least one non-sialylated milk oligosaccharide, lactose and sialic acid wherein said mixture comprises less than 10 % lactose and / or less than 5 % free sialic acid. In a more preferred embodiment, said mixture comprises less than 9 % lactose. In an even more preferred embodiment, said mixture comprises less than 8 % lactose. In another even more preferred embodiment, said mixture comprises less than 7 %, less than 6 %, less than 5 %, less than 4 %, less than 3 %, less than 2 %, less than 1 % lactose. In an additional and / or alternative more preferred embodiment, said mixture comprises lessthan 5 % free sialic acid. In an even more preferred additional and / or alternative embodiment, said mixture comprises less than 4 %, less than 3 %, less than 2 %, less than 1 %, less than 0.5 %, less than 0.1 % free sialic acid.In another preferred embodiment, the cell of present invention is capable of producing and / or producesa mixture of at least two milk oligosaccharides of present invention comprising at least one sialylated milkoligosaccharide, at least one non-sialylated milk oligosaccharide and l-fucose. In another preferredembodiment, the cell of present invention is capable of producing and / or produces a mixture of at leasttwo milk oligosaccharides of present invention comprising at least one sialylated milk oligosaccharide, atleast one non-sialylated milk oligosaccharide, lactose and l-fucose. In another preferred embodiment, thecell of present invention is capable of producing and / or produces a mixture of at least two milkoligosaccharides of present invention comprising at least one sialylated milk oligosaccharide, at least onenon-sialylated milk oligosaccharide, free sialic acid and l-fucose. In another preferred embodiment, thecell of present invention is capable of producing and / or produces a mixture of at least two milkoligosaccharides of present invention comprising at least one sialylated milk oligosaccharide, at least onenon-sialylated milk oligosaccharide, lactose, free sialic acid and l-fucose. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide selected from the list comprising and 3’SL, 6’SL, LSTa, LSTb, LSTc, LSTd, DSLNT and DSLNnT and at leastone non-sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT,lacto-N-fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N-fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N-difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'- galactosyllactose, 3'-galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N-neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N- hexaose, lacto-N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N- neopentaose, lacto-N-novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N- neoheptaose, para lacto-N-heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto- N-decaose, novo lacto-N-decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising (1) 3’SL and / or 6’SL and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTd. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising (1) 3’SL and / or LSTa and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTd. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising (1) 3’SL and / or LSTd and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising (1) LSTa and / or LSTd and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment,said mixture further comprises DSLNT. In another more preferred embodiment, said mixture furthercomprises DSLNnT. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTc. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising (1) 6’SL and / or LSTb and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises 3’SL. In another more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTc. In another more preferred embodiment, said mixture further comprises LSTd. In another more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment, the cell of present invention is capable of producing and / or produces a mixture of at least two milk oligosaccharides comprising (1) 6’SL and / or LSTc and (2) at least one non- sialylated milk oligosaccharide selected from the list comprising 2’FL, 3-FL, DiFL, LN3, LNT, LNnT, lacto-N- fucopentaose I, lacto-N-neofucopentaose I, lacto-N-fucopentaose II, lacto-N-fucopentaose III, lacto-N- fucopentaose V, lacto-N-fucopentaose VI, lacto-N-neofucopentaose V, lacto-N-difucohexaose I, lacto-N- difucohexaose II, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a), 6'-galactosyllactose, 3'- galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N-hexaose, para-lacto-N- neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, lacto- N-pentaose (LN5), lacto-N-neopentaose, para lacto-N-pentaose, para lacto-N-neopentaose, lacto-N- novopentaose I, lacto-N-heptaose (LN7), lacto-N-neoheptaose, para lacto-N-neoheptaose, para lacto-N- heptaose, lacto-N-octaose (LNO), lacto-N-neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N-neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N-nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N- decaose, lacto-N-neodecaose and para lacto-N-neodecaose (pLNnD). In a more preferred embodiment, said mixture further comprises 3’SL. In another more preferred embodiment, said mixture further comprises LSTa. In another more preferred embodiment, said mixture further comprises LSTb. In another more preferred embodiment, said mixture further comprises LSTd. In another more preferred embodiment, said mixture further comprises DSLNT. In another more preferred embodiment, said mixture further comprises DSLNnT. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 3’SL, 6’SL, LSTa, LSTc, LSTd, 2’FL, 3-FL, DiFL, LNT, LNnT, LNFP-I,LNFP-II, LNFP-III, LNFP-V, LNFP-VI, LNnFP-I, LNDFH-I, LNDFH-II and LNnDFH. In another preferredembodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising twelve or more oligosaccharides selected from the list consisting of 3’SL, 6’SL, LSTa, LSTc, LSTd, 2’FL, 3-FL, DiFL, LNT, LNnT, LNFP-I, LNFP-II, LNFP-III, LNFP-V, LNFP-VI, LNnFP-I, LNDFH-I, LNDFH-II and LNnDFH. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, 3-FL, LNnT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SLand 6’SL In another preferred embodiment, the cell of present invention is capable of producing and / orproduces an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL, 6’SL and sialic acid. In anotherpreferred embodiment, the cell of present invention is capable of producing and / or produces anoligosaccharide mixture comprising 2’FL, 3-FL, LNnT, 3’SL, 6’SL and sialic acid. In another preferredembodiment, the cell of present invention is capable of producing and / or produces an oligosaccharidemixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL and sialic acid. In another preferred embodiment, thecell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising2’FL, 3-FL, LNT, 3’SL, 6’SL and l-fucose. In another preferred embodiment, the cell of present invention iscapable of producing and / or produces an oligosaccharide mixture comprising 2’FL, 3-FL, LNnT, 3’SL, 6’SLand l-fucose. In another preferred embodiment, the cell of present invention is capable of producingand / or produces an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL and l-fucose. Inanother preferred embodiment, the cell of present invention is capable of producing and / or produces anoligosaccharide mixture comprising 2’FL, 3-FL, LNT, 3’SL, 6’SL, sialic acid and l-fucose. In another preferredembodiment, the cell of present invention is capable of producing and / or produces an oligosaccharidemixture comprising 2’FL, 3-FL, LNnT, 3’SL, 6’SL, sialic acid and l-fucose. In another preferred embodiment,the cell of present invention is capable of producing and / or produces an oligosaccharide mixturecomprising 2’FL, 3-FL, LNT, LNnT, 3’SL, 6’SL, sialic acid and l-fucose. In another preferred embodiment, thecell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, DiFL, LNT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL, 3FL, DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capable of producing and / or produces an oligosaccharide mixture comprising 2’FL,DiFL, LNT, LNnT, 3’SL and 6’SL. In another preferred embodiment, the cell of present invention is capableof producing and / or produces an oligosaccharide mixture comprising 2’FL, 3-FL, LNT, LNnT, 3’SL and 6’SL.According to the present invention, the methods as described herein preferably comprises a step of separating the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide of present invention from thecultivation or incubation, thereby recovering said milk oligosaccharide mixture from the cultivation or incubation medium and / or the cell. The terms “separating from said cultivation or incubation” means harvesting, collecting, or retrieving saidmilk oligosaccharide mixture from the cell and / or the medium of its cultivation or incubation.The mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide can be separated in a conventional manner from the aqueous culture medium, in which the cell was cultivated or incubated. In case said milk oligosaccharide mixture is still present in the cells producing the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharideconventional manners to free or to extract said milk oligosaccharide mixture out of the cells can be used,such as cell destruction using high pH, heat shock, sonication, French press, homogenization, enzymatichydrolysis, chemical hydrolysis, solvent hydrolysis, detergent, hydrolysis, etc. The cultivation or incubation medium and / or cell extract together and separately can then be further used for separating said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide.This preferably involves clarifying said milk oligosaccharide mixture to remove suspended particulates andcontaminants, particularly cells, cell components, insoluble metabolites and debris produced by culturingor incubating the genetically engineered cell. In this step, said milk oligosaccharide mixture can be clarifiedin a conventional manner. Preferably, said milk oligosaccharide mixture is clarified by centrifugation,flocculation, decantation and / or filtration. Another step of separating said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide preferably involves removing substantially all the eventually remaining proteins, peptides, amino acids, RNA and DNA, and any endotoxins and glycolipids that could interfere with the subsequent separation step, from said milk oligosaccharide mixture, preferably after it has been clarified. In this step, remaining proteins and related impurities can be removed from said milk oligosaccharide mixture in a conventional manner. Preferably, remaining proteins, salts, by-products, colour, endotoxinsand other related impurities are removed from said milk oligosaccharide mixture by ultrafiltration,nanofiltration, two-phase partitioning, reverse osmosis, microfiltration, activated charcoal or carbon treatment, treatment with non-ionic surfactants, enzymatic digestion, tangential flow high-performance filtration, tangential flow ultrafiltration, electrophoresis (e.g. using slab-polyacrylamide or sodium dodecyl sulphate-polyacrylamide gel electrophoresis (PAGE)), affinity chromatography (using affinity ligands including e.g. DEAE-Sepharose, poly-L-lysine and polymyxin-B, endotoxin-selective adsorber matrices), ion exchange chromatography (such as but not limited to cation exchange, anion exchange, mixed bed ion exchange, inside-out ligand attachment), hydrophobic interaction chromatography and / or gel filtration (i.e., size exclusion chromatography), particularly by chromatography, more particularly by ion exchange chromatography or hydrophobic interaction chromatography or ligand exchange chromatography or electrodialysis. With the exception of size exclusion chromatography, remaining proteins and related impurities are retained by a chromatography medium or a selected membrane. In a further preferred embodiment, the methods as described herein also provide for a further purification of the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide of present invention. A further purification of saidmilk oligosaccharide mixture may be accomplished, for example, by use of (activated) charcoal or carbon,nanofiltration, ultrafiltration, ion exchange, electrophoresis, enzymatic treatment or ion exchange, temperature adjustment, pH adjustment or pH adjustment with an alkaline or acidic solution to remove any remaining DNA, protein, LPS, endotoxins, or other impurity. Alcohols, such as ethanol, and aqueous alcohol mixtures can also be used. Another purification step is accomplished by crystallization, evaporation or precipitation of said milk oligosaccharide mixture. Another purification step is to dry, e.g. spray dry, lyophilize, spray freeze dry, freeze spray dry, band dry, belt dry, vacuum band dry, vacuum belt dry, drum dry, roller dry, vacuum drum dry or vacuum roller dry the produced milk oligosaccharide mixture. In an exemplary embodiment, the separation and purification of the mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide is made in a process, comprising the following steps in any order: a) contacting the cultivation or incubation or a clarified version thereof with a nanofiltration membrane with a molecular weight cut-off (MWCO) of 600-3500 Da ensuring the retention of the produced milk oligosaccharide mixture and allowing at least a part of the proteins, salts, by-products, colour and other related impurities to pass, b) conducting a diafiltration process on the retentate from step a), using said membrane, with an aqueous solution of an inorganic electrolyte, followed by optional diafiltration with pure water to remove excess of the electrolyte, c) and collecting the retentate enriched in said milk oligosaccharide mixture in the form of a saltfrom the cation of said electrolyte. In an alternative exemplary embodiment, the separation and purification of said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide is made in a process, comprising the following steps in any order:subjecting the cultivation or incubation or a clarified version thereof to two membrane filtration steps using different membranes, wherein: -one membrane has a molecular weight cut-off of between ab...

Claims

Claims1. A cell metabolically engineered for the production of a mixture of at least two milk oligosaccharidescomprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide, said cell comprising: -a pathway for production of said at least one sialylated milk oligosaccharide, wherein saidpathway comprises production of UDP-N-acetylglucosamine (UDP-GlcNAc), conversion of said UDP-GlcNAc into N-acetylmannosamine (ManNAc) by action of a hydrolyzing UDP-N-acetyl-D- glucosamine-2-epimerase, and conversion of said ManNAc into CMP-sialic acid by consecutive action of an N-acetylneuraminate synthase and an N-acylneuraminate cytidylyltransferase, and -a pathway for production of said at least one non-sialylated milk oligosaccharide,characterized in that the amount of said at least one sialylated milk oligosaccharide produced in said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide is determined by: -choice of said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminatesynthase and / or N-acylneuraminate cytidylyltransferase, -swapping the native promoter of any one of the genes encoding said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase with a promoter of interest, -swapping the native 5’untranslated region (5’UTR) of any one of the genes encoding saidhydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N- acylneuraminate cytidylyltransferase with a 5’UTR of interest, -modifying the copy number of any one of the genes encoding said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase, and / or -expressing any one of the genes encoding said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase or N-acylneuraminate cytidylyltransferase from a different locus on the chromosome and / or from a vector that is used to transform said cell.

2. Cell according to claim 1, wherein said cell expresses said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase, N-acetylneuraminate synthase and N-acylneuraminate cytidylyltransferase.

3. Cell according to any one of claim 1 or 2, wherein said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase has hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase activity and: -comprises an amino acid sequence comprising a conserved motif with SEQ ID NO 08,- comprises, consists of or consists essentially of an amino acid sequence that is at least 80 %identical over a stretch of at least 150 amino acid residues and / or at least 200 amino acid residues, to any one of the amino acid sequences as represented by SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09,- comprises an IPR domain selected from the list comprising IPR003331, IPR020004 and IPR029767as defined by InterPro 90.0 as released on 4thAugust 2022, -comprises a PF02350 motif as defined by PFAM 32.0 as released in September 2018,- comprises a cd03786 motif as defined by CDD v3.17 as released in September 2016,- comprises a panther domain selected from the list comprising PTHR43174 and PTHR43174:SF3 asdefined by PANTHER 17.0 as released on 23rdFebruary 2022, -is at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 96 %, at least 97 %, at least 98%, at least 98.5 %, or at least 99 % identical to any one of the amino acid sequences as represented by SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09 over a stretch of at least 150, at least 160, at least 170, at least 180, at least 190, at least 200, at least 210, at least 220, at least 230, at least 240, at least 250, at least 260, at least 270, at least 280, at least 290 or at least 300 amino acid residues, -is at least 80 %, at least 85 %, at least 90 %, at least 95 %, at least 96 %, at least 97 %, at least 98%, at least 98.5 %, or at least 99 % identical to any one of the full-length amino acid sequences as represented by SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09, and / or -as represented by any one of SEQ ID NOs 01, 02, 03, 04, 05, 06, 07 or 09.

4. Cell according to any one of previous claims, wherein said hydrolyzing UDP-N-acetyl-D-glucosamine-2-epimerase is a nnaA polypeptide or a neuC polypeptide.

5. Cell according to any one of previous claims, wherein said:- promoter of interest is selected from the list consisting of SEQ ID NO 15, 16 and 17, and / or- 5’UTR of interest is selected from the list consisting of SEQ ID NO 18 and 19.

6. Cell according to any one of previous claims, wherein said mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide further comprises: -free sialic acid selected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2;Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO), -a monosaccharide, and / or- a disaccharide.

7. Cell according to any one of previous claims, wherein said mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide comprises: -less sialylated milk oligosaccharide than non-sialylated milk oligosaccharides, or- less non-sialylated milk oligosaccharide than sialylated milk oligosaccharides.

8. Cell according to any one of previous claims, wherein the relative abundance of the sialylated milkoligosaccharides in said mixture of at least two milk oligosaccharides comprising at least onesialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide is:- less than 49.9 % on the total amount of milk oligosaccharides present in said mixture, and / or- 5 to 20 % on the total amount of milk oligosaccharides present in said mixture.

9. Cell according to any one of previous claims, wherein the relative abundance of the sialylated milkoligosaccharides in said mixture of at least two milk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide is: -30 to 75 %, 30 to 60 %, or 50 % on the total amount of milk oligosaccharides present in saidmixture, -50 to 75 %, 60 to 75 %, 60 to 65 %, or 62 % on the total amount of milk oligosaccharides presentin said mixture, or -30 to 55 %, 35 to 50 %, 40 to 45 %, or 45 % on the total amount of milk oligosaccharides presentin said mixture.

10. Cell according to any one of previous claims, wherein said mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide comprises two or more sialylated milk oligosaccharides.

11. Cell according to any one of previous claims, wherein said mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide: -does not comprise free sialic acid, or- comprises less than 1 %, less than 0.5 %, less than 0.2 %, and / or less than 0.1 % of free sialic acid,wherein said free sialic acid is selected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO).

12. Cell according to any one of previous claims, wherein said pathway for production of said at least onesialylated milk oligosaccharide is a sialylation pathway.

13. Cell according to any one of previous claims, wherein said cell:- is genetically engineered to comprise a sialylation pathway,- comprises a sialylation pathway wherein said sialylation pathway has been geneticallyengineered, and / or -is genetically engineered for production of a sialic acid residue.

14. Cell according to any one of previous claims, wherein said pathway for production of said at least onenon-sialylated milk oligosaccharide is selected from the list comprising, consisting of or consisting essentially of fucosylation pathway, galactosylation pathway, N-acetylglucosaminylation pathway, N- acetylgalactosaminylation pathway, mannosylation pathway and N-acetylmannosaminylation pathway.

15. Cell according to any one of previous claims, wherein said cell:- further comprises a pathway selected from the list comprising, consisting of or consistingessentially of fucosylation pathway, galactosylation pathway, N-acetylglucosaminylation pathway, N-acetylgalactosaminylation pathway, mannosylation pathway and N- acetylmannosaminylation pathway, -is genetically engineered to comprise at least one pathway selected from the list comprising,consisting of or consisting essentially of fucosylation pathway, galactosylation pathway, N- acetylglucosaminylation pathway, N-acetylgalactosaminylation pathway, mannosylation pathway and N-acetylmannosaminylation pathway, and / or -comprises at least one pathway selected from the list comprising, consisting of or consistingessentially of fucosylation pathway, galactosylation pathway, N-acetylglucosaminylation pathway, N-acetylgalactosaminylation pathway, mannosylation pathway and N- acetylmannosaminylation pathway wherein at least one of said pathway(s) has / have been genetically engineered.

16. Cell according to any one of previous claims, wherein:- one or more gene(s) involved in one or more reductive pathway(s) in said cell is / are rendered lessfunctional or is / are knocked-out, -said cell possesses, expresses and / or overexpresses at least one gene selected from the listcomprising, consisting of or consisting essentially of genes encoding disulfide bond isomerase, thiol oxidase, chaperone, glycosyltransferase, -said cell is capable to produce and / or produces a nucleotide-activated sugar,- said cell is capable to produce and / or produces UDP-GlcNAc and ManNAc,- said cell is capable to produce and / or produces phosphoenolpyruvate (PEP),- said cell is modified for enhanced production and / or supply of phosphoenolpyruvate (PEP)compared to a non-modified progenitor, and / or -said cell comprises a modification for reduced production of acetate compared to a non-modifiedprogenitor.

17. Cell according to any one of previous claims, wherein said at least one sialylated milk oligosaccharideis: -a sialylated milk oligosaccharide having at least one sialic acid residue selected from the listconsisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO), and -selected from the list comprising, consisting of or consisting essentially of a sialylated mammalianmilk oligosaccharide (MMO), a sialylated human milk oligosaccharide (HMO), N-acetyllactosamine containing sialylated milk oligosaccharide, lacto-N-biose containing sialylated milk oligosaccharide, 3’sialyllactose (3’SL), 6’sialyllactose (6’SL), 3'-sialyllactosamine, 6’- sialyllactosamine, oligosaccharide comprising 6’-sialyllactosamine, oligosaccharide comprising 6’-sialyllacto-N-biose; 3,6-disialyllactose, 6,6’-disialyllactose (Neu5Ac-^2,6-Gal-^1,4-(Neu5Ac-^2,6)- Glc), 8,3-disialyllactose, sialylated lacto-N-triose, sialylated tetrasaccharide (Neu5Ac-α2,3-Gal- β1,4-GlcNAc-β1,4-GlcNAc), sialyllacto-N-tetraose a (LSTa, Neu5Ac-^2,3-Gal-^1,3-GlcNAc-^1,3- Gal-^1,4-Glc), KDOα-2,3Galβ-1,3GlcNAcβ-1,3Galβ-1,4Glc, sialyllacto-N-tetraose b (LSTb, Gal- ^1,3-[Neu5Ac-^2,6]-GlcNAc-^1,3-Gal-^1,4-Glc), sialyllacto-N-tetraose c (LSTc, Neu5Ac-^2,6-Gal- ^1,4-GlcNAc-^1,3-Gal-^1,4-Glc), sialyllacto-N-tetraose d (LSTd, Neu5Ac-α2,3-Gal-β1,4-GlcNAc- β1,3-Gal-β1,4-Glc), Neu5Ac-^2,6-(Neu5Ac-^2,3-Gal-^1,3)-GlcNAc-^1,3-Gal-^1,4-Glc (DSLNT, disialyllacto-N-tetraose), Neu5Ac-^2,6-Gal-^1,4-GlcNAc-^1,3-[Neu5Ac-^2,6]-Gal-^1,4-Glc (DSLNnT, disialyllacto-N-neotetraose), monosialyllacto-N-hexaose, disialyllacto-N-hexaose I, disialyllacto-N-hexaose II, monosialyllacto-N-neohexaose I, monosialyllacto-N-neohexaose II, disialyllacto-N-neohexaose, 3'-sialyl-3-fucosyllactose, fucodisialyllacto-N-hexaose, disialomonofucosyllacto-N-neohexaose, monofucosylmonosialyllacto-N-octaose (sialyl Lea), sialyllacto-N-fucohexaose II, disialyllacto-N-fucopentaose II, monofucosyldisialyllacto-N-tetraose, Neu5Ac-a2,3-Gal-b1,4-GlcNAc-b1,3-Gal, Neu5Ac-a2,3-Gal-b1,3-GlcNAc-b1,3-Gal, 3’-KDO-lactose, 3’-KDO-lactosamine, 3’-KDO-lacto-N-biose, 3’-KDO-6’sialyllactose, 3’KDO-8-sialyllactose, KDO- 2,3Galβ-1,3GalNacβ-1,3Galα-1,4Galβ-1,4Gal, KDOα-2,3Galβ-1,4GlcNacβ-1,3Galβ-1,4Glc, 3’-KDO- 3-fucosyllactose, Neu5Ac-a2,8-Neu5Ac-a2,3-Gal-b1,3-GlcNAc-b1,3-Gal, 3'-Sialyl-2'- fucosyllactose, 6'-Sialyl-2'-fucosyllactose, 6'-Sialyl-3-fucosyllactose, Neu5Ac-a2,6-(Neu5Ac-a2,3- )Gal-b1,4-Glc, 3'-Sialyl-3-fucosyllactosamine, Fuc-a1,4-(Neu5Ac-a2,3-Gal-b1,3-)GlcNAc, 6’- Sialyllacto-N-biose, 3’-Sialyllacto-N-biose, Neu5Ac-a2,6-(GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac- a2,6-(Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,3-Gal-b1,4-(Fuc-a1,3-)GlcNAc- b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,4-GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,3-GlcNAc-b1,3-)Gal- b1,4-(Fuc-a1,3-)Glc, Neu5Ac-a2,6-Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Neu5Ac-a2,3- Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Neu5Ac-a2,3-(Fuc-a1,2-)Gal-b1,3-GlcNAc-b1,3- Gal-b1,4-Glc, Neu5Ac-a2,6-(Fuc-a1,2-Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Fuc- a1,2-)Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc, Fuc-a1,4-(Neu5Ac-a2,3-Gal-b1,3-)GlcNAc-b1,3-Gal- b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-(Fuc-a1,3-)Glc, Neu5Ac- a2,6-(Neu5Ac-a2,6-(Fuc-a1,2-)Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,3- GlcNAc-b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-Gal-b1,3-GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6- (Neu5Ac-a2,3)-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,3-Gal-b1,3-GlcNAc- b1,3-)Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,3-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac- a2,6-(Neu5Ac-a2,6-(Neu5Ac-a2,3)-Gal-b1,3-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac- a2,3-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,4-GlcNAc-b1,3)-Gal- b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-(Neu5Ac-a2,3)-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,6-(Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-Gal-b1,4-GlcNAc-b1,3-Gal- b1,4-GlcNAc-b1,3-Gal-b1,4-Glc, Neu5Ac-a2,6-(Neu5Ac-a2,6-(Neu5Ac-a2,6-Gal-b1,4-GlcNAc- b1,3)-Gal-b1,4-GlcNAc-b1,3)-Gal-b1,4-Glc, Neu5Ac-a2,3-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-GlcNAc- b1,3-Gal-b1,4-Glc, 6’-KDO-lactose, 6’-KDO-lactosamine, 6’-KDO-lacto-N-biose, KDO-lacto-N- triose, KDO-lacto-N-tetraose, KDO-lacto-N-tetraose, and combinations thereof.

18. Cell according to any one of previous claims, wherein said at least one non-sialylated oligosaccharideis selected from the list comprising, consisting of or consisting essentially of non-sialylated neutral milk oligosaccharide, non-sialylated neutral MMO, non-sialylated neutral HMO, non-sialylatednegatively charged oligosaccharide, non-sialylated negatively charged MMO, non-sialylated negatively charged HMO, sulphated milk oligosaccharides, 2'-fucosyllactose (2’FL), 3-fucosyllactose (3FL), 4-fucosyllactose (4FL), 6-fucosyllactose (6FL), 2',3-difucosyllactose (diFL), lacto-N-triose II (LN3, GlcNAcβ1-3Galβ1-4Glc), lacto-N-tetraose (LNT, Galβ1-3GlcNAcβ1-3Galβ1-4Glc), lacto-N-neotetraose (LNnT, Galβ1-4GlcNAcβ1-3Galβ1-4Glc), lacto-N-fucopentaose I, lacto-N-neofucopentaose I, lacto-N- fucopentaose II, lacto-N-fucopentaose III, lacto-N-fucopentaose V, lacto-N-fucopentaose VI, lacto-N- neofucopentaose V, lacto-N-difucohexaose I, lacto-N-difucohexaose II, Fuc-a1,2-Gal-b1,3-GlcNAc- b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal-b1,4-GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal- b1,4-(Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-Glc, Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,2-Gal-b1,4-(Fuc-a1,3-)GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, Fuc-a1,4-(Fuc-a1,2-Gal-b1,3- )GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, monofucosyllacto-N-hexaose-III, difucosyllacto-N-hexaose (a),6'-galactosyllactose, 3'-galactosyllactose, lacto-N-hexaose, lacto-N-neohexaose, para-lacto-N- hexaose, para-lacto-N-neohexaose, difucosyl-lacto-N-hexaose, difucosyl-lacto-N-neohexaose, trifucosyllacto-N-hexaose, a1,3-galactosyl-3-fucosyllactose, Gal-a1,3-(Fuc-a1,2-)Gal-b1,4-(Fuc-a1,3- )Glc, GalNAc-a1,3-(Fuc-a1,2-)Gal-b1,4-(Fuc-a1,3-)Glc, 2-fucosyllactulose, 3-fucosyl-N- acetyllactosamine, 2'-fucosyl-N-acetyllactosamine, difucosyl-N-acetyllactosamine, 4-fucosyllacto-N- biose, 2'-fucosyllacto-N-biose, difucosyllacto-N-biose, GlcNAc-b1,3-Gal-b1,4-(Fuc-a1,3-)Glc, GlcNAc- b1,6-(GlcNAc-b1,3-)Gal-b1,4-Glc, lacto-N-pentaose (LN5), lacto-N-neopentaose, para lacto-N- pentaose, para lacto-N-neopentaose, lacto-N-novopentaose I, lacto-N-heptaose (LN7), lacto-N- neoheptaose, para lacto-N-neoheptaose, para lacto-N-heptaose, lacto-N-octaose (LNO), lacto-N- neooctaose, iso lacto-N-octaose, para lacto-N-octaose, iso lacto-N-neooctaose, novo lacto-N- neooctaose, para lacto-N-neooctaose (pLNnO), iso lacto-N-nonaose, novo lacto-N-nonaose, lacto-N- nonaose (LN9), lacto-N-decaose, iso lacto-N-decaose, novo lacto-N-decaose, lacto-N-neodecaose, para lacto-N-neodecaose (pLNnD), a1,3-galactosyllacto-N-neotetraose, GlcNAc-b1,3-Gal-b1,3- GlcNAc-b1,3-Gal-b1,4-Glc, GlcNAc-b1,6-(Gal-b1,4-GlcNAc-b1,3-)Gal-b1,4-Glc and GlcNAc-b1,6-(Gal-b1,3-GlcNAc-b1,3-)Gal-b1,4-Glc, 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,4-Glc; 3-SO3-Gal-^1,3-Gal-^1,3-Gal- ^1,3-Gal-^1,4-Glc; 3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,3-Gal-^1,4-Glc; Gal-^1,4-GlcNAc-^1,6- [3-SO3-Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; 3-SO3-Gal-^1,4-GlcNAc-^1,6-[Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; Gal-^1,4-GlcNAc-^1,6-[3-SO3-Gal-^1,3-Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc; 3-SO3-Gal-^1,4-GlcNAc- ^1,6-[Gal-^1,3-Gal-^1,3-Gal-^1,3]-Gal-^1,4-Glc.

19. Cell according to any one of previous claims, wherein said cell is:- selected from the list consisting of prokaryotic cells, eukaryotic cells, yeast cells, bacterial cells,archaebacterial cells, algae cells, fungal cells, plant cells, animal cells, insect cells, protozoan cells, and / or -an E. coli or yeast with a lactose permease positive phenotype, preferably wherein said lactosepermease is coded by the gene LacY or LAC12, respectively.

20. Method for the production of a mixture of at least two milk oligosaccharides comprising at least onesialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide by a cell, the method comprising: i. cultivating and / or incubating a cell of any one of previous claims, in cultivation and / or incubationmedium under conditions permissive to produce said mixture of at least two milk oligosaccharidescomprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide, ii. optionally, followed by separation and / or purification of said mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide from said cultivation and / or incubation.

21. Method according to claim 20, wherein the method comprises:- Using a cultivation or incubation medium comprising one or more precursor(s) that is / areused for production of said at least one sialylated milk oligosaccharide and / or said at least one non-sialylated milk oligosaccharide in said mixture of at least two milk oligosaccharidescomprising at least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide, and / or -Adding to the cultivation or incubation medium one or more precursor(s) that is / are used forproduction of said at least one sialylated milk oligosaccharide and / or said at least one non- sialylated milk oligosaccharide in said mixture of at least two milk oligosaccharides comprisingat least one sialylated milk oligosaccharide and at least one non-sialylated milk oligosaccharide.

22. Method according to any one of claim 20 or 21, wherein:- said method results in the production of 0.1 g / L or more, 0.5 g / L or more, 1 g / L or more, 5 g / L ormore, 10 g / L or more, 20 g / L or more, 30 g / L or more, 40 g / L or more, and / or 50 g / L or more of total milk oligosaccharides, -said cell produces 0.1 g / L or more, 0.5 g / L or more, 1 g / L or more, 5 g / L or more, 10 g / L or more,20 g / L or more, 30 g / L or more, 40 g / L or more, and / or 50 g / L or more of total milk oligosaccharides,- said mixture of at least two milk oligosaccharides comprising at least one sialylated milkoligosaccharide and at least one non-sialylated milk oligosaccharide further comprises a monosaccharide, a disaccharide and / or free sialic acid selected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3- deoxymanno-octulonic acid (KDO), -said mixture of at least two milk oligosaccharides comprising at least one sialylated milkoligosaccharide and at least one non-sialylated milk oligosaccharide comprises less sialylated milk oligosaccharide than non-sialylated milk oligosaccharides, or comprises less non-sialylated milkoligosaccharide than sialylated milk oligosaccharides, -the relative abundance of the sialylated milk oligosaccharides in said mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide is less than 49.9 %, 5 to 20 %, 30 to 75 %, 30 to 60 %, 50 %, 50 to 75 %, 60 to 75 %, 60 to 65 %, 62 %, 30 to 55 %, 35 to 50 %, 40 to 45 % or 45 % on the total amountof milk oligosaccharides present in said mixture, -said mixture of at least two milk oligosaccharides comprising at least one sialylated milkoligosaccharide and at least one non-sialylated milk oligosaccharide comprises two or moresialylated milk oligosaccharides, and / or -said mixture of at least two milk oligosaccharides comprising at least one sialylated milkoligosaccharide and at least one non-sialylated milk oligosaccharide does not comprise free sialicacid, or comprises less than 1 %, less than 0.5 %, less than 0.2 %, and / or less than 0.1 % of freesialic acid, wherein said free sialic acid is selected from the list consisting of Neu4Ac; Neu5Ac; Neu4,5Ac2; Neu5,7Ac2; Neu5,8Ac2; Neu5,9Ac2; Neu4,5,9Ac3; Neu5,7,9Ac3; Neu5,8,9Ac3; Neu4,5,7,9Ac4; Neu5,7,8,9Ac4; Neu4,5,7,8,9Ac5; Neu5Gc and 2-keto-3-deoxymanno-octulonic acid (KDO).

23. Method according to any one of claims 20 to 22, wherein said mixture of at least two milkoligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide is further separated and / or purified from the cell, cultivation and / or incubation.

24. Use of a cell according to any one of claims 1 to 19 for the production of a mixture of at least twomilk oligosaccharides comprising at least one sialylated milk oligosaccharide and at least one non- sialylated milk oligosaccharide.

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