Composition for growth media and / or crop solutions and / or plants

Abstract

The present invention relates to a composition for growth media and / or crop solutions and / or plants comprising the combination of: - a carboxylic acid, - a polysaccharide, - calcium, and - a microalgae. The invention additionally relates to the use of the composition according to the invention to promote the formation of bacterial biofilms and / or the maturation thereof on the growth medium, the rhizosphere and / or the roots of a plant.

Description

Composition for growing media and / or growing solutions and / or plants Technical Field

[0001] The present invention relates to the field of compositions intended for plants and / or soil having a beneficial effect on them. It relates in particular to a composition based on microalgae, an organic fraction and a mineral fraction to promote the formation of bacterial biofilms. Prior art

[0002] Soil is an active, living, dynamic, and biodiverse ecosystem on Earth. It is home to thousands of prokaryotic and eukaryotic life forms. The responses of the microbial community are influenced by the surrounding soil environment. As a natural resource, soil plays a vital role in biodiversity and contributes to many other ecosystem services. Soil is said to be prolific due to the activity of microorganisms at an adequate rate for optimal plant development and growth. Even though they are abundantly present, soil nutrients and other essential elements are poorly available to plants. Through various processes (physical, chemical, and biological), root-associated microorganisms play a major role in soil formation and fertility.

[0003] Thus, a wide variety of microorganisms and macroorganisms exist in symbiosis in the rhizosphere. Bacteria are the most predominant.

[0004] Traditionally, bacterial cells have been identified and characterized as individual cells evolving independently among other cells. However, in nature, >90% of bacterial biomass grows as biofilm.

[0005] A biofilm is defined as an aggregate of microorganisms whose cells are enclosed in a matrix of extracellular polymeric substance (EPS) adhering to each other and / or to a surface (IUPAC).

[0006] Biofilm formation is a complex process involving several stages: i. Attachment of planktonic bacteria to the biotic or abiotic surface by chemotaxis processes, ii. Cell adhesion and loss of motility, iii. Production of exopolymers (EPS), iv. Biofilm maturation phases where biofilm architecture and primary microcolonies develop by the process of Quorum Sensing (QS), v. Dispersal phase: planktonic cells disperse from the microcolonies by the process of Quorum Quenching (QQ).

[0007] Biofilms represent a form of bacterial resistance compared to planktonic (i.e., free-living and isolated) forms. In the medical field, strategies for combating pathogens target biofilms. Conversely, and surprisingly, biofilms are of major interest in agriculture and plant growth and nutrition. It is therefore necessary to seek to stimulate their formation, particularly in the soil and on root surfaces.

[0008] Biofilms provide benefits for both plants and soil. For plants, they promote the benefits of PGPR1 (Plant Growth Promoting Rhizobacteria) organisms. Biofilms near root systems increase stress tolerance (biotic and abiotic). Extracellular polymeric substances play a central role in nutrient availability (nitrogen, phosphorus, etc.). For example, the establishment of a symbiosis between nitrogen-fixing rhizobia and plants.

[0009] For soil, biofilm stabilizes the environment in which microorganisms thrive, acting as a carbon and nutrient reserve. It provides protection against desiccation and promotes aggregation and adhesion. Microbial activity is increased tenfold within biofilms.

[0010] The inventors surprisingly discovered that the association of microalgae with a carboxylic acid, a polysaccharide and calcium made it possible to promote the formation of bacterial biofilms and / or their maturation in the soil, the rhizosphere and / or the roots of a plant. Statement of the invention

[0011] The present invention relates to a composition for culture media and / or culture solutions and / or plants comprising the combination: - a carboxylic acid, advantageously in a content of between 1% and 5% by weight relative to the total weight of the combination, - a polysaccharide, advantageously in a content of between 15% and 27% by weight relative to the total weight of the association, - calcium, advantageously in a content of between 43% and 69% by weight relative to the total weight of the combination, and - a microalgae, advantageously in the form of an extract, more advantageously in a content of between 15% and 25% by weight relative to the total weight of the association.

[0012] For the purposes of the present invention, the term "composition for culture media and / or culture solutions and / or plants" means a composition intended to be administered to culture media and / or culture solutions and / or to plants, in particular cultivated plants, in order to provide them with a benefit. Advantageously, this composition is phytosanitarily acceptable.

[0013] For the purposes of the present invention, the term "phytosanitarily acceptable" means that it is acceptable for use on plants or growing media and / or growing solutions, i.e. non-polluting for the environment and non-toxic for humans (users).

[0014] For the purposes of the present invention, the term “growing medium” means any soil or medium on which a crop can grow, such as, for example, artificial soil, cultivated agricultural soil, uncultivated agricultural soil, peat, compost, rock wool or coconut fiber.

[0015] For the purposes of the present invention, the term "culture solution" means any solution which allows the cultivation of a plant such as, for example, irrigation water, liquid solution intended for fertigation by sprinkling or drip irrigation, hydroponic bath or aeroponic solution.

[0016] The expression "plant" is intended to designate in this application the plant considered as a whole, including its root system, its vegetative system, the seeds, grains and fruits.

[0017] The plants according to the invention may be chosen from field crops such as cereals (wheat, corn, barley), protein crops (peas), oilseeds (soybean, sunflower), Solanaceae crops (potato), Amaranthaceae crops (beetroot), specialized crops such as in particular market gardening (lettuce, spinach, onion, shallot, tomato, melon), vines, arboriculture (pear, apple, nectarine), or horticulture. In particular, the plant may belong to the order of monocotyledons, preferably to the Poaceae family. Poaceae, commonly called grasses, include in particular most of the species commonly called "grasses" and "cereals". Among the Poaceae, mention may be made of wheat, rice, barley, oats, rye, sugar cane, meadow and corn.

[0018] Legumes belong to the Fabaceae family. Legumes play an important role in the food sector due to their high protein and essential amino acid content. Examples of leguminous plants, but not limited to, are soybeans, peanuts, beans, peas, especially of the species P. sativum, lentils, chickpeas, broad beans, field beans, vetches, grass vetch, alfalfa, clover, lupin, mung beans (germinated soybean sprouts), licorice, rosewood, birdsfoot trefoil, sainfoin, rooibos, and fenugreek.

[0019] The composition according to the invention therefore comprises the combination of a carboxylic acid, a polysaccharide, calcium, and a microalgae.

[0020] The term "carboxylic acid" should be understood in its common sense, that is to say an acid of formula R-COOH, where R is hydrogen or an organic group, advantageously R is an organic group comprising between 1 and 10 carbon atoms. The carboxylic acid that can be used in the combination according to the invention may be a monocarboxylic acid or a polycarboxylic acid, advantageously a tricarboxylic acid. Advantageously, it is a weak acid, in particular an organic acid. In the context of the present invention, the carboxylic acid may be chosen from methanoic acid, ethanoic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, benzoic acid, 2-hydroxybenzoic acid, 2-mercaptopropanoic acid.In a preferred embodiment, the carboxylic acid is selected from formic acid, acetic acid, lactic acid, citric acid, oxalic acid, propionic acid, malic acid, tartaric acid, fumaric acid, gluconic acid, sorbic acid and butyric acid, preferably the carboxylic acid is selected from formic acid, citric acid, acetic acid and lactic acid. In a particularly preferred embodiment, the carboxylic acid is citric acid.

[0021] Advantageously, the carboxylic acid is present in the combination in a content of between 1% and 5% by weight, advantageously between 2% and 4% by weight, more advantageously between 3% and 4% by weight, in particular between 3% and 3.5% by weight, more particularly in a content of 3.3% by weight, relative to the total weight of the combination.

[0022] In the context of the present invention, the carboxylic acid makes it possible to promote the formation of EPS in synergy with the calcium of the association according to the invention.

[0023] In the context of the present invention the terms "between ... and ..." and "from ... to ..." mean that the limits of the range are included.

[0024] For the purposes of the present invention, the term "polysaccharide" means any polymer of the carbohydrate family consisting of several oses linked together by osidic bonds. It may be a homopolysaccharide (consisting of the same monosaccharide) or a heteropolysaccharide (formed of different monosaccharides). Advantageously, it is a heteropolysaccharide, more advantageously of plant origin, even more advantageously with a chain linear. The polysaccharide usable in the context of the present invention may be chosen from starch, inulin, cellulose and a pectin. It is advantageously a pectin, more advantageously having a degree of methylation of between 5% and 80%, even more advantageously of between 50% and 80%, more particularly of between 60% and 80%, even more particularly of between 70% and 80%, for example 71%.

[0025] Advantageously, the polysaccharide is present in the combination in a content of between 15% and 27% by weight, advantageously between 20% and 25% by weight, more particularly in a content of 22% by weight, relative to the total weight of the combination.

[0026] In the context of the present invention, the polysaccharide helps and promotes the formation of EPS in the biofilm.

[0027] The calcium that can be used in the context of the present invention may be a calcium salt (carbonate, citrate, malate, lactate, gluconate, etc.) or a marine calcium. Advantageously, it is a marine calcium.

[0028] For the purposes of the present invention, the term "marine calcium" means calcium derived from marine shellfish of the Maërl type. Maërl is an accumulation of coralline algae rich in limestone.

[0029] Advantageously, the calcium is present in the combination in a content of between 43% and 69% by weight, advantageously between 45% and 65% by weight, more advantageously between 50% and 60% by weight, in particular between 52% and 56% by weight, more particularly in a content of 54.8% by weight, relative to the total weight of the combination.

[0030] In the context of the present invention, calcium plays a role in the structuring of EPS. It acts as a binder to promote the cohesion of the biofilm.

[0031] The microalgae that can be used in the context of the present invention are advantageously eukaryotic microalgae, more advantageously chosen from the group consisting of Chioreiia vulgaris, Chioreiia sorokiniana, Nannochioropsis sp, Skeietonema sp, Phaeodactyium sp, Dunaliella sp, Haematococcus pluvialis, Isochrysis sp and their mixtures, even more advantageously chosen from the group consisting of Chlorella vu / garis, Chlorella sorokiniana, Isochrysis sp and their mixtures.

[0032] In particular, the microalgae that can be used in the context of the present invention is in the form of biomass or extract, more advantageously in the form of extract.

[0033] In the context of the present invention, the microalgae is an inducer of biofilm formation (quorum sensing).

[0034] The term "extract" refers to the product resulting from an extraction from a source. For example, the source may be a biological source, such as cells. When referring to cells, the term "extract" therefore refers to the product resulting from the extraction of the contents of cells. Thus, for example, the term "microalgae extract" refers to the product resulting from the extraction of the contents of the cells of a microalgae. The extraction may be carried out with an aqueous solvent or an organic solvent, advantageously an aqueous solvent, more advantageously with water as the sole solvent. In particular, the extract may be water-soluble.The extraction can be carried out by any extraction method well known to those skilled in the art such as hot decoction, maceration, extrusion, extraction under subcritical conditions, extraction assisted by ultrasound, with or without grinding such as ultrasonic grinding or using a mixer, advantageously by maceration. The extraction can be carried out at a temperature ranging from 4°C to 300°C, including room temperature, i.e. a temperature of approximately 20°C.

[0035] Thus advantageously the microalgae extract is an extract of a eukaryotic microalgae, advantageously chosen from the group consisting of Chlorella vu / garis, Chlorella sorokiniana, Nannochloropsis sp, Skeletonema sp, Phaeodacty / um sp, Dunaliella sp, Haematococcus pluvialis, Isochrysis sp and their mixtures, more advantageously chosen from the group consisting of Chlorella vu / garis, Chlorella sorokiniana, Isochrysis sp and their mixtures.

[0036] Advantageously, the microalgae, in particular the microalgae extract, is present in the association in a content of between 15% and 25% in weight, advantageously between 17% and 23% by weight, more advantageously between 18% and 22% by weight, more particularly in a content of 20% by weight, relative to the total weight of the association.

[0037] Advantageously, the combination according to the invention is present in the composition for soils and / or plants according to the invention in a content of between 0.1% and 20%, in particular between 0.15% and 10%, more particularly between 0.2% and 1%, even more particularly in a content of 0.25%, by weight relative to the total weight of the composition.

[0038] The composition according to the invention may further comprise a phytosanitarily acceptable excipient. It may also further comprise other ingredients outside the combination according to the invention. Thus the composition may comprise natural or synthetic biostimulant compounds such as amino acids, growth regulators, humic substances, plant extracts, microbial extracts, minerals such as nitrogen, phosphorus, potassium, molybdenum, sulfur, magnesium, iron, chlorine, manganese, zinc, boron, boric acid, disodium octaborate tetrahydrate, calcium borate, magnesium borate, sodium borosilicate, sodium tetraborate decahydrate, sodium borate, sodium tetraborate, disodium tetraborate, lime, gypsum, superphosphate, iron sulfate, iron chelate, ferritin, zinc oxide, zinc sulfate, zinc chelate, potassium nitrate,calcium nitrate, magnesium nitrate, ammonium phosphate, ammonium sulfate, magnesium sulfate, monopotassium phosphate, calcium carbonate, ammonium nitrate sulfate, ammonium thiosulfate, ammoniacal liquor, calcium cyanamide, crotonylidene diurea, diacyandiamide, isobutylidene diurea, sodium nitrate, potassium carbonate, potassium chloride, potassium magnesium sulfate, potassium metaphosphate, potassium sulfate, calcium chloride, calcium oxide, calcitic limestone, dolomitic limestone, magnesium ammonium phosphate, magnesium oxide, copper chelates, cupric ammonium phosphate, copper sulfate, copper frits, copper polyflavonoid, malachite, azurite, cuprous oxide, cupric oxide, cupric acetate, boron frits, ferric sulfate, ferrous sulfate, ferrous ammonium sulfate, ferrous ammonium phosphate, ferrous oxalate, ferrous carbonate, iron lignosulfonate, iron polyflavonoid, iron frits, iron methoxyphenylpropane, ferrous oxide, ferric oxide, iron ammonium polyphosphate, manganese oxide, manganese methoxyphenyl propane, manganese frits, manganese chloride, manganese carbonate, manganese sulfate, manganese chelate, manganese ammonium phosphate, manganese polyflavonoid, ammonium molybdate, sodium molybdate, molybdenum frits, molybdenum trioxide, molybdenum disulfide, zinc frits, zinc carbonate, zinc phosphate, zinc ammonium phosphate,zinc sulfide, zinc lignosulfonate, zinc polyflavonoid or a combination thereof and / or any excipient suitable for administration to a culture medium and / or culture solution and / or plant.,

[0039] The composition according to the invention may be in solid form, in particular in the form of powder, granules or microgranules, in the form of a liquid suspension or in the form of a gel or in water-soluble form. In particular, the composition is not lyophilized or dehydrated.

[0040] Advantageously, the composition according to the present invention may be a fertilizer, in particular a fertilizer or amendment, the fertilizer advantageously being a simple, binary or ternary solid fertilizer of the organo-mineral fertilizer or organic fertilizer type, or a water-soluble fertilizer and the amendment advantageously being an organo-mineral or organic amendment.

[0041] The term "fertilizer" means a substance, or mixture of substances, whether natural or synthetic, used in agriculture, horticulture and forestry to improve growing media, particularly their structure, and to fertilize cultivated plants. Fertilizers include fertilizers and amendments.

[0042] The term "fertilizer" refers to fertilizing materials whose main function is to provide plants with elements directly useful for their nutrition (major fertilizing elements, secondary fertilizing elements and trace elements).

[0043] The term "amendment" refers to a substance intended to improve the quality of growing media, and in particular intended to improve the pH of growing media. Advantageously, the amendment is chosen from basic mineral amendments of the limestone and / or limestone and magnesium type; humus amendments of the compost or manure type.

[0044] The present invention further relates to a culture medium comprising the composition according to the invention.

[0045] The present invention further relates to a culture solution comprising the composition according to the invention.

[0046] The present invention further relates to the use of the composition according to the invention for plants and / or culture media and / or culture solutions.

[0047] The present invention relates in particular to the use of the composition according to the invention or of the culture support according to the invention or of the culture solution according to the invention to promote the formation of bacterial biofilms and / or its maturation at the level of the culture support, the rhizosphere and / or the roots of a plant.

[0048] Advantageously, the use according to the invention is to improve plant growth and / or improve nutrient availability such as N-fixation or solubilization, and / or improve plant stress tolerance, such as biotic and / or abiotic stress, and / or protect growing media against desiccation and / or improve the formation and / or stability of growing media aggregates, and / or stabilize the development environment of the microorganisms of the growing media and / or increase the abundance and microbial activity of the growing media.

[0049] In an advantageous embodiment, the use according to the invention is by root application, open field or above ground. The composition according to the invention can be applied on the surface or mixed with the supports and / or culture solutions. In particular in the case of culture solutions it is rather a mixture. In the case of culture supports, the composition according to the invention can be applied on the surface or mixed with the support, for example with the first layers of the support. The application can be carried out directly on the culture support, on the entire surface of the culture support or in a localized manner in the region of the roots of the plants to be treated, by any suitable distribution means, such as for example by spraying in the case of a liquid suspension.

[0050] Advantageously, the composition according to the invention is used by application at a concentration of 1 kilogram to 100 kilograms of the composition per hectare, in one or more times. Those skilled in the art will know how to adapt the quantities to be used depending on the chosen application method. In particular, relatively smaller quantities are used when the composition according to the invention is applied in the root region while relatively larger quantities are used when the composition is applied over the entire surface of the growing medium. The composition according to the invention can be used in a single application or in sequential application.

[0051] The application can take place before and / or during the growth of the cultivated plants, before and / or after germination of the plants, for example during transplanting in the case of plants requiring transplanting. Advantageously, it takes place after germination.

[0052] The present invention will be better understood upon reading the description of the drawings and examples which follow, which are given for non-limiting information purposes. Brief description of the drawings

[0053] Figure 1 represents the quantity of biofilm obtained in mg in the presence of the compositions tested under the conditions of the example.

[0054] Figure 2 represents the quantity of wrinkles (textural nuance) in the presence (combination of the 4) and absence (control) of the association according to the invention under the conditions of the example.

[0055] Figure 3 shows the enlarged photograph of the presence or absence of wrinkles under the conditions of the example. EXAMPLE

[0056] When cultured in liquid media, Bacillus subtilis is known to produce surface films that are architecturally rich and complex. These structures are called wrinkles. They confer several advantages to biofilm development. They increase the surface-to-volume ratio, improving oxygenation. This increased surface area allows for greater aerial dispersion. The wrinkles promote the formation of a complex network of liquid channels within the biofilm, which facilitates the movement of nutrients. This very distinct morphotype is observed when the biofilm is mature. Materials and methods Biological material

[0057] For the experiments, the Bacillus subtilis strain was chosen. This model was chosen because it is widely referenced as a phytobeneficial strain of type PGPR 7 (Plant Growth Promoting Rhizobacteria). This strain is referenced as a model for the study of biofilm and its ability to produce a stable and quantifiable biofilm. Culture environments and conditions

[0058] Strain conservation is carried out from fresh culture diluted with 80% glycerol (40% final) and stored at -80°C. These cryotubes serve as a starting point for all experiments, in order to prevent genetic degeneration by repeated subculturing.

[0059] In summary: The culture is conducted according to the following chronology: i. Isolation from the cryotube; ii. Liquid preculture; iii. Culture and production of biofilm in dishes; iv. Reading.

[0060] In detail: Cells from cryotubes are plated by quadrant method on TSA agar (Tripton: 15g / L; soy peptone: 5g / L; NaCl: 5g / L; Agar: 15g / L). The isolation is incubated at 30°C for 24h (precisely). At least 10 colonies are suspended in TSB medium (Tripton: 15g / L; soy peptone: 5g / L; NaCl: 5g / L). The preculture is incubated at 30°C, 150 rpm (agitation promotes the growth of the cells in planktonic form), for 15h (precisely). The preculture is calibrated (with TSB) at a D0600nm= 1 with the UV spectrophotometer (ClarioStar Plus, BMG Labtech). This inoculum is used to inoculate at 1 / 10 (final DO600nm = 0.1) the Petri dishes, previously filled with TSB medium (with or without supplementation of the products to be tested). The dishes are incubated at 30°C, without shaking, for 48 hours. Quantitative analysis of biofilm

[0061] In summary: Biofilm mass measurement is performed according to the following chronology: i. biofilm production; ii. Harvest; iii. Freeze-drying; iv. Weighing.

[0062] In detail: After growing the strain in a petri dish, a biofilm layer forms on the surface and on the walls of the dishes. The subnatant is gently removed so as not to break / remove the biofilm. The entire biofilm is harvested using a rake and transferred into a 50 mL bottle. The samples are then freeze-dried. The total dry biomass can then be measured. Qualitative analysis of the biofilm

[0063] In summary: The analysis of the quality (production of wrinkles) of the biofilm is carried out according to the following chronology: i. plaque biofilm production; ii. Imaging; iii. Texture analysis.

[0064] In detail: The strain preculture steps are the same as for biofilm quantification. The culture step is carried out in a 24-well plate (in TSB supplemented with the products to be tested). The plate is incubated at 30°C, without shaking, for 48 hours. After biofilm production, imaging is carried out. The camera used is the Exo GigE exol38CGE camera. The camera is coupled to a VI 624-MPZ objective with a focal length of 16mm and the image is taken in the focal plane at a height of 34cm. Subsequently, on each modality, an image extraction (representative of the sample) is carried out. A texture analysis is then carried out. The processing of the results is carried out on the “autocorrelation” and “cluster shade” data according to the method described in Haralick RM, Shanmugam K and Dinstein I (1973 Textural features for image classification IEEE Transactions on Systems, Man, and Cybernetics 3 610-21). Results

[0065] 5 compositions were tested: - Citric acid (Sigma) at 0.08g / L in TSB medium; - Pectin with a methylation degree of 71% (Cargill) at 0.55g / L in TSB medium; - Marine calcium at 1.37g / L in TSB medium; - Extract of the microalgae Isochrysis, obtained by aqueous extraction (Necton) at 0.5g / L in TSB medium; - Combination of the 4 compounds according to the invention at 2.5g / L in TSB medium, the combination comprising 3.3% citric acid, 22% pectin, 54.8% marine calcium and 20% microalgae extract, by weight relative to the total weight of the combination

[0066] The ability of the compounds to promote biofilm production was thus tested alone and in combination. Culture in the absence of compounds was chosen as the basal level of biofilm production (under our culture conditions). Biofilm production

[0067] The results are shown in Figure 1.

[0068] In the absence of the compound (Control), there is a production of 22.3 ± 3.8 mg of biofilm. In the presence of the compounds alone there is no significant difference compared to the control. In the presence of the object of the invention there is an increase of + 80% in the quantity of biofilm. These data demonstrate that each compound isolated has no measurable effect on the biofilm but that the combination of the four results in a strong increase in biofilm production. Biofilm maturity

[0069] The purpose of this invention is to promote both biofilm production and biofilm maturity. With the aim of producing more mature biofilm.

[0070] Culture in the absence of compounds was chosen as the basal level of biofilm production (in our culture conditions). Treatment with the combination of products was tested.

[0071] The results are presented in Figures 2 and 3.

[0072] Under normal growth conditions, the film formed on the surface of the culture opacifies the medium, but does not form wrinkles. This results in a surface that appears homogeneous. In the presence of the combination of compounds according to the invention, a 60% increase in texture nuance is observed. These results reflect an increase in the capacity of a biofilm to mature by forming wrinkles.

[0073] The results showed that the contribution of the composition according to the invention stimulates the formation of bacterial biofilm. The morphology of the biofilm is also modified by the contribution of said composition and results in the presence of wrinkles on the surface of the biofilm. These increase the surface / volume ratio and allow better regulation of oxygen by the bacteria.

Claims

Claims

1. Composition for culture media and / or culture solutions and / or plants comprising the combination: - a carboxylic acid in a content of between 1% and 5% by weight relative to the total weight of the association, - a polysaccharide in a content of between 15% and 27% by weight relative to the total weight of the association, - calcium in a content of between 43% and 69% by weight relative to the total weight of the association, and - a microalgae, advantageously in the form of an extract, in a content of between 15% and 25% by weight relative to the total weight of the association.

2. Composition according to claim 1, characterized in that the carboxylic acid is citric acid.

3. Composition according to any one of claims 1 or 2, characterized in that the polysaccharide is a pectin, advantageously having a degree of methylation of between 5% and 80%.

4. Composition according to any one of claims 1 to 3, characterized in that the calcium is a marine calcium.

5. Composition according to any one of claims 1 to 4, characterized in that the microalga is a eukaryotic microalga, advantageously chosen from the group consisting of Chlorella vu / garis, Chlorella sorokiniana, Nannoch / oropsis sp, Skeletonema sp, Phaeodactylum sp, Dunaliella sp, Haematococcus pluvialis, Isochrysis sp and their mixtures, more advantageously chosen from the group consisting of Chlorella vu / garis, Chlorella sorokiniana, Isochrysis sp and their mixtures.

6. Composition according to any one of claims 1 to 5, characterized in that it further comprises a phytosanitarily acceptable excipient

7. Composition according to any one of claims 1 to 6, characterized in that it is in solid form, in particular in powder, granule or microgranule form, in liquid form or in gel form.

8. Composition according to any one of claims 1 to 7, characterized in that it is a fertilizer, in particular a fertilizer or amendment, the fertilizer advantageously being a simple, binary or ternary solid fertilizer of the organo-mineral fertilizer or organic fertilizer type, or a water-soluble fertilizer and the amendment advantageously being an organo-mineral or organic amendment.

9. A culture medium comprising the composition according to any one of claims 1 to 8.

10. A culture solution comprising the composition according to any one of claims 1 to 8.

11. Use of the composition according to any one of claims 1 to 8 or of the culture medium according to claim 9 or of the culture solution according to claim 10, to promote the formation of bacterial biofilms and / or its maturation at the level of the culture medium, the rhizosphere and / or the roots of a plant.

12. Use according to claim 11 for improving plant growth and / or improving nutrient availability and / or improving plant stress tolerance and / or protecting growing media against desiccation and / or improving the formation and / or stability of growing media aggregates, and / or stabilizing the development environment of the microorganisms of the growing media and / or increasing the microbial abundance and activity of the growing media.

13. Use according to any one of claims 11 or 12 by root application, open field or above ground.

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