Serratia marcescans strain for producing prodigiosin from bean dregs and application of the strain in preparation of composite film

Abstract

This invention discloses a strain of *Serratia marcescens* that produces squalene from soybean residue and its application in composite membrane preparation, belonging to the field of microbial fermentation and biomaterials technology. The technical problem this invention aims to solve is how to produce squalene from soybean residue and modify composite membranes with the product. This invention first protects a strain of *Serratia marcescens*. Serratia marcescens The strain, designated BD 2025, is registered with the China General Microbiological Culture Collection Center (CGMCC) under number CGMCC No. 35196. Using this strain, a yield of 15.9862 mg / g of styraxanthin can be achieved from soybean residue. Furthermore, the styraxanthin-containing modified composite membrane prepared from this product promotes uniform distribution of the membrane matrix and improves the mechanical properties of the composite membrane.

Description

Technical Field

[0001] This application belongs to the field of microbial fermentation and biomaterials technology, specifically relating to a strain of Serratia marcescens that produces serotonin from soybean residue and its application in the preparation of composite membranes. Background Technology

[0002] Prodigiosin (CAS No. 82-89-3) is a linear tripyrrole compound composed of three pyrrole rings, possessing immunosuppressive, antibacterial, antimalarial, anticytotoxic, anticancer, and anti-aging functions. Currently, microbial fermentation using *Serratia marcescens* is the main biosynthetic method for producing prodigiosin. However, prodigiosin is extremely expensive, and the cost of traditional carbon and nitrogen sources in its fermentation medium accounts for a large proportion, severely limiting its commercial development. Therefore, developing a new fermentation process that can significantly reduce production costs is crucial for promoting the practical application of this high-value natural product.

[0003] Soybean residue, as the largest byproduct of soybean processing, is produced in high quantities but suffers from significant resource waste. It is rich in nutrients such as protein, carbohydrates (mainly dietary fiber), and minerals (calcium, iron, phosphorus, etc.), and can serve as a cheap nitrogen source to support microbial growth. However, methods for using soybean residue as a fermentation medium for styraxanthin have not yet been reported.

[0004] In recent years, environmentally friendly composite films made from biodegradable polymer materials have shown great potential to replace traditional plastic films in food packaging, agricultural mulching, and other fields due to their environmental friendliness. Among them, films made from high-amylose corn starch blended with polyvinyl alcohol (PVA) have attracted much attention due to their good film-forming properties, biocompatibility, and degradability. However, these composite films still face several key technical bottlenecks in practical applications: First, insufficient mechanical properties; the mechanical strength and flexibility of pure starch / PVA films often fail to meet the durability requirements of actual packaging materials. Second, strong hydrophilicity, resulting in poor moisture barrier properties and high water solubility, making them prone to swelling, deformation, or even dissolution in high-humidity environments, thus limiting their application range. Third, non-uniform microstructure; during film formation, pores or phase separation easily form, resulting in a loose and insufficiently dense film structure, which not only affects mechanical properties but also reduces their barrier properties against water vapor, oils, and other substances. In existing technologies, modification is typically achieved by adding inorganic nanoparticles, crosslinking agents, or other synthetic polymers. However, these methods may affect the biodegradability of the material, or involve complex processes, high costs, or limited improvement effects. Therefore, there is an urgent need to find a green modifier that is naturally derived, biodegradable, and can comprehensively improve the mechanical properties, water resistance, and microstructure of starch / PVA-based composite films. Summary of the Invention

[0005] The technical problems to be solved by this invention include: (1) how to identify and screen Serratia marcescens strains with the ability to utilize soybean residue and apply them to the production process of serotonin; and (2) how to optimize composite membranes using the fermentation products of the above strains.

[0006] To solve the above-mentioned technical problems, the present invention first provides a strain of Serratia marcescens (Serratia marcescens). Serratia marcescens )BD 2025.

[0007] The Serratia marcescens provided by this invention ( Serratia marcescens Serratia marcescens BD 2025, with the registration number CGMCC No. 35196 at the China General Microbiological Culture Collection Center (CGMCC), was deposited on August 8, 2025, at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, 100101, China. This strain will be referred to as *Serratia marcescens* BD 2025 below.

[0008] Serratia marcescens BD 2025, after incubation on nutrient agar (NA) plates at 30°C for 2 days, exhibits the following characteristics: single colonies are red, round and raised, with neat edges and a smooth, moist surface; they have a fishy odor and produce red pigment. Gram staining is negative. The optimal growth temperature is 28-37°C, and the pH is 5-12. Serratia marcescens strain BD2025 possesses the nucleotide sequence shown in SEQ ID No. 1.

[0009] Cultures of Serratia marcescens BD 2025 and / or metabolites of Serratia marcescens BD 2025 are also within the scope of protection of this invention.

[0010] In this document, the culture of Serratia marcescens BD 2025 is a substance obtained by culturing Serratia marcescens BD 2025 in a culture medium; the culture contains Serratia marcescens BD 2025 and substances secreted into the culture medium, such as fermentation products.

[0011] In this article, the metabolite of *Serratia marcescens* BD 2025 is a substance obtained by culturing *Serratia marcescens* BD 2025 in a culture medium and then removing *Serratia marcescens* BD 2025. The metabolite contains substances secreted by *Serratia marcescens* BD 2025 into the culture medium but does not contain *Serratia marcescens* BD 2025 itself; specifically, it can be a squalene extract. The squalene extract can be prepared as follows: *Serratia marcescens* BD 2025 is cultured in a culture medium, and the fermentation product (containing *Serratia marcescens* BD 2025 and substances secreted into the culture medium, said substances containing squalene) is collected. Squalene is then extracted from the fermentation product to obtain the squalene extract.

[0012] In the above text, the culture medium is a fermentation culture medium, which can be a solid culture medium with soybean residue as the nitrogen source and glycerol as the carbon source.

[0013] In this article, the fermentation medium can specifically be a solid culture medium obtained by mixing soybean residue and glycerol.

[0014] The soybean residue is a byproduct of soybean processing and is extremely inexpensive. Before use, the moisture content of the soybean residue can be adjusted to 70% by mass.

[0015] In this article, the mass percentage of glycerol in the fermentation medium can be 0-20%. This 0-20% can independently be 0%, 6%, 8%, 10%, 15%, or 20%.

[0016] The culture of Serratia marcescens BD 2025 described above has at least one of the following functions (W1-W3): W1. Preparation of styrax erythrin; W2, Preparation of composite membrane modifier; W3, degrades soybean residue.

[0017] The metabolites of the aforementioned *Serratia marcescens* BD 2025 have at least one of the following functions (W1-W2): W1. Preparation of styrax erythrin; W2. Preparation of composite membrane modifier.

[0018] In this article, the composite membrane modifier specifically describes its modification effect on any one or more of R1-R12 composite membranes: R1. Reduce the thickness of the composite membrane; R2. Increase the compactness of the composite membrane; R3. Increase the uniformity of the composite membrane; R4. Enhances the tensile strength of the composite membrane; R5. Increase the elongation at break of the composite membrane; R6. Reduce the water solubility of the composite membrane; R7. Improve the water resistance of the composite membrane; R8. Inhibit the swelling rate of the composite membrane; R9. Reduce the oil permeability coefficient of the composite membrane; R10 improves the oil-blocking performance of the composite membrane; R11 promotes a uniform and dense surface morphology of the composite membrane; R12, inhibits the formation of bubbles on the surface of the composite membrane.

[0019] The composite membrane described above is obtained by casting and drying a film-forming matrix solution and then peeling it off. The film-forming matrix solution is obtained by mixing a film-forming matrix in water. The film-forming matrix includes polyvinyl alcohol (PVA), high-amylose corn starch, and glycerol.

[0020] When the composite membrane modifier is used, it is added to the film-forming matrix solution to obtain a membrane solution containing styraxone. The membrane solution containing styraxone is cast, dried, and then peeled off to obtain a composite membrane containing styraxone.

[0021] To address the above technical problems, the present invention also provides a product containing Serratia marcescens BD 2025 or / and a culture of Serratia marcescens BD 2025 or / and metabolites of Serratia marcescens BD 2025.

[0022] The product may be a microbial agent or a microecological preparation containing the microbial agent.

[0023] The above-mentioned microbial agents can be liquid or solid.

[0024] The product can be in various dosage forms, such as liquid, emulsion, suspension, powder, granules, wettable powder or water-dispersible granules.

[0025] The active ingredient of the above products may be Serratia marcescens BD 2025 or / and a culture of Serratia marcescens BD 2025 or / and a metabolite of Serratia marcescens BD 2025. The active ingredient of the above products may also contain other biological or non-biological components. Other active ingredients of the above products can be determined by those skilled in the art based on the effects of the products.

[0026] The use of *Serratia marcescens* BD 2025 or / and cultures of *Serratia marcescens* BD 2025 or / and metabolites of *Serratia marcescens* BD 2025 or / and the products thereof in the preparation of serotonin is within the scope of protection of this invention.

[0027] The application of *Serratia marcescens* BD 2025 or / and cultures of *Serratia marcescens* BD 2025 or / and metabolites of *Serratia marcescens* BD 2025 or / and the products thereof in modified composite membranes falls within the scope of protection of this invention.

[0028] The application of Serratia marcescens BD 2025 or / and cultures of Serratia marcescens BD 2025 or / and the product thereof in the degradation of soybean residue is within the scope of protection of this invention.

[0029] The method for culturing the aforementioned Serratia marcescens BD 2025 is also within the scope of protection of this invention.

[0030] The method for culturing *Serratia marcescens* BD 2025 provided by the present invention includes the step of culturing *Serratia marcescens* BD 2025 in a fermentation medium.

[0031] The present invention also provides a method for degrading soybean residue, comprising the step of fermenting the Serratia marcescens BD 2025 with soybean residue as a substrate.

[0032] The present invention also provides a method for producing squalene, comprising the steps of fermenting the Serratia marcescens BD 2025 with soybean residue as a substrate and extracting squalene from the fermentation product.

[0033] In the above method, the *Serratia marcescens* BD 2025 is fermented using soybean residue as a substrate. The culture medium used is a solid culture medium composed of soybean residue and glycerol. The mass percentage of glycerol in the solid culture medium is 0-20%, and the mass percentage of water in the soybean residue is 70%.

[0034] In the above method, the fermentation conditions are as follows: static culture, fermentation time of 48 hours, and fermentation temperature of 30°C.

[0035] The present invention also provides a method for preparing a composite membrane containing squalene, wherein the composite membrane containing squalene is prepared by adding squalene active ingredient to a film-forming matrix solution; the squalene active ingredient is extracted from a culture of Serratia marcescens BD2025 and / or metabolites of Serratia marcescens BD 2025; the film-forming matrix solution is obtained by mixing a film-forming matrix in water, and the film-forming matrix includes polyvinyl alcohol (PVA), high-amylose corn starch, and glycerol.

[0036] In the above method, the active ingredient of squalene is powdered squalene or squalene extract from the culture of Serratia marcescens BD 2025 and / or the metabolites of Serratia marcescens BD 2025.

[0037] The above method for preparing a composite membrane containing styraxin specifically includes the following steps: 1) The film-forming matrix is ​​mixed in water and stirred at 90-95 °C to form a film-forming matrix solution; 2) Add the active ingredient of styraxin to the film-forming matrix solution and continue stirring and mixing to obtain a film-forming matrix solution containing styraxin; 3) After casting and drying the film-forming matrix solution containing styraxin, peel off the film to obtain the composite film containing styraxin.

[0038] In the above method, when the active ingredient of sphagnum molybdate is added to the film-forming matrix solution, the amount of sphagnum molybdate added to the film-forming matrix solution is 10-40 mg / 100 mL of film-forming matrix solution when the active ingredient of sphagnum molybdate is in powder form.

[0039] In the above method, when the active ingredient of sphagnum molybdate is added to the film-forming matrix solution, the amount of sphagnum molybdate added is 1-5 mL / 100 mL of film-forming matrix solution when the active ingredient of sphagnum molybdate is sphagnum molybdate extract.

[0040] In one embodiment of the present invention, the film-forming matrix solution is specifically prepared by mixing 2 g of polyvinyl alcohol (PVA), 5 g of high amylose corn starch and 1.5 g of glycerol in 100 mL of water to obtain 100 mL of film-forming matrix solution.

[0041] This invention screened out a strain of *Serratia marcescens* BD 2025 capable of utilizing soybean residue. This strain is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 35196, dated August 8, 2025. Based on *Serratia marcescens* BD 2025, this invention discloses a method for producing squalene from soybean residue. Using soybean residue as a solid-state fermentation medium, the yield of squalene was 15.9862 mg / g after 48 h. This invention also provides a composite membrane containing squalene, comprising the following raw materials: squalene or squalene extract and a film-forming matrix; the film-forming matrix comprises polyvinyl alcohol (PVA), high-amylose corn starch, and glycerol. Compared to composite membranes without the addition of squalene or its extract, the use of squalene promotes uniform distribution of the membrane matrix and improves the mechanical properties of the composite membrane.

[0042] The beneficial effects of this invention are as follows: 1. The Serratia marcescens strain BD 2025 provided by the present invention uses waste soybean residue as raw material to produce serotonin, which reduces the production cost of serotonin and also reuses the soybean residue as waste.

[0043] 2. The optimized soybean residue fermentation medium has excellent styraxanthin synthesis capacity, with a styraxanthin yield of 15.9862 mg / g, which can well meet the requirements of industrial production of styraxanthin and has good application prospects.

[0044] 3. The composite membrane based on styrax rubigin and extract modification provided by the present invention can promote uniform distribution of membrane matrix and improve the mechanical properties of composite membrane.

[0045] Preservation Instructions Strain name: BD 2025 Latin name: Serratia marcescens Classification and nomenclature: Serratia marcescens ( Serratia marcescens ) Preservation Institution: China General Microbiological Culture Collection Center, China Microbiological Culture Collection Committee Abbreviation of depositary institution: CGMCC Address: No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing Deposit date: August 8, 2025 CGMCC Registration Number: CGMCC No. 35196 Attached Figure Description Figure 1 The *Serratia marcescens* strain screened in Example 1 of this invention (… Serratia marcescens Photo of strain BD2025.

[0046] Figure 2 This is a phylogenetic tree for the identification of Serratia marcescens strain BD 2025 in Example 1 of this invention.

[0047] Figure 3 The figures show the experimental results for different carbon sources in Example 2 of this invention. Different lowercase letters in the figure indicate significant differences at the 0.05 significance level.

[0048] Figure 4 The figures show the experimental results for different glycerol concentrations in Example 2 of this invention. Different lowercase letters in the figure indicate significant differences at the 0.05 significance level.

[0049] Figure 5 The results are for the detection of styraxin isolated in Example 3 of this invention.

[0050] Figure 6 The figure shows the effect of the addition of styracil in Example 4 of this invention on the thickness of the high amylose corn starch / PVA composite film. Different lowercase letters in the figure indicate significant differences at the 0.05 significance level.

[0051] Figure 7 The figure illustrates the effect of the addition of cymoxanil on the mechanical properties of the high amylose corn starch / PVA composite film in Example 4 of this invention. Different letters in the figure indicate significant differences at the 0.05 significance level, and uppercase and lowercase letters are used to distinguish different measurement index groups.

[0052] Figure 8 This figure illustrates the effect of the addition of styracil in Example 4 of the present invention on the moisture content and water solubility of the high amylose corn starch / PVA composite film. Different lowercase letters in the figure indicate significant differences at the 0.05 significance level.

[0053] Figure 9 The effect of adding styraxin to the swelling rate of the high amylose corn starch / PVA composite film in Example 4 of this invention.

[0054] Figure 10 The figure shows the effect of the addition of styracil in Example 4 of this invention on the oil permeability coefficient of the high amylose corn starch / PVA composite membrane. Different lowercase letters in the figure indicate significant differences at the 0.05 significance level.

[0055] Figure 11 This invention relates to the effect of adding styraxin on the microstructure of the high amylose corn starch / PVA composite membrane in Example 4.

[0056] Figure 12 The effect of adding lecithin extract in Example 5 of this invention on the appearance and morphology of high amylose corn starch / PVA composite membrane.

[0057] Figure 13 This figure illustrates the effect of adding styraxin extract on the thickness of the high-amylose corn starch / PVA composite membrane in Example 1 of this invention. Different lowercase letters in the figure indicate significant differences at the 0.05 significance level.

[0058] Figure 14 The figure illustrates the effect of adding styraxin extract in Example 1 of this invention on the mechanical properties of the high amylose corn starch / PVA composite membrane. Different letters in the figure indicate significant differences at the 0.05 significance level; uppercase and lowercase letters are used to distinguish different measurement index groups. Detailed Implementation

[0059] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0060] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0061] In the following examples, unless otherwise specified, the first position of each nucleotide sequence in the sequence listing is the 5' terminal nucleotide of the corresponding DNA / RNA, and the last position is the 3' terminal nucleotide of the corresponding DNA / RNA.

[0062] Serratia marcescens in the following examples ( Serratia marcescens BD 2025 was deposited with the China General Microbiological Culture Collection Center (CGMCC) on the application date of this application, at No. 3, No. 1, Beichen West Road, Chaoyang District, Beijing. The deposit date was August 8, 2025, and the CGMCC registration number was CGMCC No. 35196.

[0063] The soybean residue in the following examples was provided by Shandong Yuwang Group.

[0064] Unless otherwise specified, the quantitative experiments in the following examples were all repeated three times, and the results were averaged.

[0065] Example 1: Serratia marcescens (Serratia marcescens) Serratia marcescens BD 2025 Screening and Evaluation 1. Screening of Serratia marcescens Take 5g of soybean residue and shake well in 95mL of sterile water. Use a 10-fold dilution method to obtain samples of different concentrations. Take 100 μL from each dilution and spread it onto NA medium (purchased from Qingdao High-Tech Industrial Park Haibo Biotechnology Co., Ltd.). Incubate at 30℃ with the medium inverted. After colonies grow on the medium, pick single colonies and streak them onto fresh medium until single colonies appear on the medium with consistent morphology. Purification is considered complete when this is achieved.

[0066] 2. Morphological observation One of the isolated and purified strains was designated BD 2025 and inoculated into NA medium. After incubation at 30°C for 2 days, distinct red colonies were observed. Figure 1 The colonies of strain BD 2025 are round and raised, with neat edges and a smooth, moist surface. They have a fishy odor and produce red pigment.

[0067] The strain BD 2025 was tested and found to be a Gram-negative bacterium with an optimal growth temperature of 28-37℃ and a pH of 5-12.

[0068] 3. Strain identification Strain BD 2025 was sent to Beijing Qingke Biotechnology Co., Ltd. for identification. The gene fragment of strain BD 2025 was obtained by PCR amplification, and the sequencing results showed that the gene of strain BD 2025 contained the nucleotide sequence shown in SEQ ID No.1.

[0069] SEQ ID No. 1: The obtained sequence (SEQ ID No. 1) was compared for homology using NCBI online BLAST, and the strain was preliminarily identified as *Serratia marcescens*. A phylogenetic tree was constructed using the neighbor-joining method in MEGA. Figure 2 This strain belongs to the same clade as *Serratia marcescens* 1, indicating that it is most closely related to *Serratia marcescens* 1. Combined with morphological observations, the isolated strain BD 2025 was confirmed to be *Serratia marcescens*. Serratia marcescens ).

[0070] Example 2 Screening of carbon sources for fermentation production 1. Screening of carbon source types To determine the optimal carbon source for the production of styrax, glycerol, starch, glucose, fructose, and granulated sugar, each with a mass percentage of 2%, were selected as alternative carbon sources for solid-state fermentation experiments.

[0071] Various single-carbon-source fermentation media were prepared by mixing 2% carbon source (glycerol, starch, glucose, fructose or granulated sugar) with soybean residue (commercially purchased, a by-product of soybean processing, with the moisture content of the soybean residue adjusted to 70% before use).

[0072] Serratia marcescens BD 2025 was statically cultured in nutrient broth (NB) at 30°C for 12 hours. Then, it was inoculated at 5% (w / w) into various sterilized single-carbon-source fermentation media, stirred thoroughly, and incubated at 30°C. Three replicates were set up for each carbon source fermentation medium. The yield of serratin was measured after 48 hours of incubation.

[0073] By comparing the effects of single carbon sources—2% glycerol, starch, glucose, fructose, and granulated sugar—on the yield of pyruvic erythrin, the results are as follows: Figure 3 As shown, glycerol was ultimately determined to be the optimal carbon source for production.

[0074] 2. Screening of carbon source content Solid-state fermentation experiments were conducted with fermentation medium containing 0%, 6%, 8%, 10%, 15%, and 20% glycerol by mass.

[0075] Glycerol and soybean residue (the moisture content of the soybean residue was adjusted to 70% by mass before use) were mixed to obtain fermentation media with different glycerol concentrations of 0%, 6%, 8%, 10%, 15% and 20% by mass.

[0076] The cultured Serratia marcescens BD 2025 bacterial suspension (same as the bacterial suspension in Example 1) was inoculated at 5% by weight into sterilized fermentation media of different glycerol concentrations. After thorough mixing, the culture was incubated statically at 30°C. Three replicates were set up for each glycerol concentration fermentation medium. The yield of styraxin was measured after 48 h of incubation.

[0077] The results are as follows Figure 4 As shown in the figure. This determined that the highest yield of styraxin was 15.9862 mg / g when the glycerol content was 10% by mass.

[0078] Example 3: Isolation and Detection Method of Pyruvicin Based on the weight of the raw materials, fermentation was carried out using a culture medium composed of soybean residue (the moisture content of soybean residue was 70%) and 10% glycerol, with the same fermentation parameters as in Example 2.

[0079] Methanol was added to the product after 48 h of fermentation, and ultrasonic extraction was performed under the following conditions: ultrasonic power 720 W; ultrasonic time 30 min; extraction temperature 30 °C. The product was centrifuged, the supernatant was collected, and filtered through a 0.22 μm filter to obtain the styraxin extract. Subsequently, the organic solvent was removed by rotary evaporation and the product was freeze-dried to obtain a red solid powder. The freeze-drying process included pre-cooling, primary drying (sublimation), and secondary drying (elution). The pre-freezing temperature was -80 °C, the primary drying (sublimation) temperature was -20 °C, and the secondary drying (elution) temperature was 30 °C.

[0080] The resulting red solid powder was dissolved in acidic methanol and filtered through a 0.22 μm organic filter membrane before being analyzed by HPLC. Column: Aligent Zorbax SB-C18. Mobile phase: Acetonitrile: Ammonium acetate (5% aqueous solution) = 85:15. Flow rate: 1 mL / min, isocratic elution. Detection wavelength: 535 nm. Detection temperature: 40 ℃. Detection time: 10 min. Injection volume: 10 μL.

[0081] The retention time of the peak of prodigiosin standard (Shanghai Yuanye Biotechnology Co., Ltd., catalog number: B24589-250ug) at 535 nm was 6.597 min; the retention time of the maximum peak of the sample was 6.680 min. Figure 5 The retention time of the peak value was basically consistent with that of the standard. Therefore, the pigment was identified as styraxin. The purity was determined to be 91.28% using peak area normalization.

[0082] Example 4: The effect of styraxin on the performance of organic membranes This embodiment is used to illustrate the effect of the styraxin provided in Example 3 on improving the performance of organic composite membranes.

[0083] The film-forming matrix of the composite membrane includes high amylose, corn starch, and glycerol (as a plasticizer), and the specific preparation steps are as follows: Weigh 5 g of high-amylose corn starch and add it to 100 mL of distilled water. Add 2 g of polyvinyl alcohol (PVA, CAS No. 9002-89-5) and 1.5 g of glycerol. After magnetic stirring in a 95 ℃ water bath for 45 min, add different amounts (10 mg, 20 mg, 30 mg, and 40 mg) of powdered styraxone (preparation method see Example 3). Continue magnetic stirring for 20 min to obtain a styraxone / high-amylose corn starch / PVA composite film-forming matrix solution, which is the film-forming matrix solution containing styraxone. A blank control group with 0 mg of styraxone was set up, i.e., the film-forming matrix solution without styraxone was used, and all other conditions were the same.

[0084] 100 mL of film-forming matrix solutions with different contents of squalene were introduced into an acrylic mold, allowed to stand at room temperature for 1 h, and then dried in a constant temperature drying oven at 37 ℃ for 16 h. After drying, the film was peeled off to obtain squalene / high amylose corn starch / PVA composite films containing different contents of squalene, named S / PVA-0, S / PVA-20, S / PVA-20 and S / PVA-40 (S / PVA-20, S / PVA-20 and S / PVA-40 are all composite films containing squalene). The amount of squalene added was 0 mg / 100 mL of film-forming matrix solution, 20 mg / 100 mL of film-forming matrix solution, 30 mg / 100 mL of film-forming matrix solution and 40 mg / 100 mL of film-forming matrix solution, respectively.

[0085] The properties of the prepared styraxone / high amylose corn starch / PVA composite films S / PVA-0, S / PVA-20, S / PVA-20 and S / PVA-40 containing different contents of styraxone were measured, mainly including thickness, mechanical properties, moisture content, water solubility, swelling ratio, oil permeability coefficient and scanning electron microscopy images. The specific steps are as follows: (1) Thickness: 15 measurement points were randomly selected using a micrometer (error 0.01 mm), and the average value of the results was taken.

[0086] like Figure 6As shown, the amount of thiamethoxam added significantly regulates the thickness of the high-amylose corn starch / PVA composite membrane. Experimental data indicate that when the addition amount is 20-30 mg / 100 mL of film-forming matrix solution, the composite membrane thickness is significantly reduced (p<0.05), indicating that thiamethoxam can promote the densification of the membrane matrix. However, when the addition amount is increased to 40 mg, the membrane thickness increases instead, suggesting that excessive addition may lead to an imbalance of intermolecular forces. The optimal addition amount of 20-30 mg / 100 mL of film-forming matrix solution achieves the best membrane compactness and uniformity.

[0087] (2) Mechanical properties: The mechanical properties of the membrane were tested using a texture analyzer, including tensile strength and elongation at break. The test was repeated at least three times and the average value of the results was taken.

[0088] like Figure 7 As shown, the addition of styracil significantly affected the mechanical properties of the composite membrane. Within the addition range of 20-30 mg / 100 mL, the tensile strength and elongation at break of the composite membrane were significantly improved (p<0.05), indicating that styracil can enhance the mechanical properties of the membrane matrix through intermolecular interactions.

[0089] (3) Moisture content and water solubility: After weighing the membrane (3×3 cm) (m1), dry it in a constant temperature drying oven at 103 ± 2 ℃ until constant weight (m2), and calculate the moisture content according to Formula 1: Formula 1 The dried membrane was placed in 50 mL of deionized water and shaken on a shaker at 25 °C for 24 h. It was then dried in a constant temperature drying oven at 103 ± 2 °C until constant weight (m³). The water solubility was calculated according to Formula 2. Formula 2 like Figure 8 As shown, the introduction of styracil has a regulatory effect on the moisture content and water solubility of the composite membrane. Although different addition amounts did not significantly reduce the moisture content (p<0.05), appropriate addition (20-30 mg / 100 mL) significantly reduced water solubility (p<0.05). Mechanistic studies indicate that styracil can bind to free hydroxyl groups in the membrane matrix, reducing the exposure of hydrophilic groups, thereby inhibiting water molecule permeation and improving the membrane's water resistance.

[0090] (4) Swelling rate: Weigh the membrane (3×3 cm) (m4) and let it stand in 50 mL of deionized water for 24 h. Then wipe the surface dry with filter paper and weigh it (m5). Calculate the swelling rate according to formula 3: Formula 3 like Figure 9As shown, the addition of styracil has a certain inhibitory effect on the swelling rate of the composite membrane. At an addition amount of 20-30 mg / 100 mL, the swelling rate shows a decreasing trend. This is attributed to the hydrogen bonding between styracil and starch / PVA molecular chains, which reduces the pores that water molecules can penetrate. At the same time, the dense membrane structure further restricts water permeation.

[0091] (5) Oil permeability coefficient: Add 5 mL of peanut oil to a 15 mL centrifuge tube, tightly cover the opening of the centrifuge tube with the membrane, tie it with a rubber band, and invert it onto the weighed filter paper. Let it stand in a desiccator for 48 h, then weigh the filter paper and calculate the oil permeability coefficient according to formula 4: Formula 4 Where: P is the oil permeability coefficient (g•mm•(m)) 2 •d) -1 ); △m is the difference in filter paper mass before and after (g); FT is the membrane thickness (mm); A is the effective area of ​​the membrane (m²). 2 ); T is the placement time (d).

[0092] like Figure 10 As shown, the addition of styracil significantly reduced the oil permeability coefficient of the composite membrane (p<0.05). Experiments confirmed that styracil can enhance the density of the membrane matrix through hydrophobic interactions, thereby effectively blocking oil penetration and giving the composite membrane excellent oil resistance and enhanced oil-blocking performance.

[0093] (6) Scanning electron microscopy images: The surface morphology of the film was observed using a scanning electron microscope.

[0094] like Figure 11 As shown, scanning electron microscopy analysis indicates that the addition of appropriate amounts of styraxin (10-30 mg / 100 mL) can significantly improve the surface morphology of the composite membrane, giving it a more uniform and dense microstructure.

[0095] In conclusion, the composite membrane exhibits the best overall performance when the amount of lecithin added is 20-30 mg / 100 mL of the film-forming matrix solution.

[0096] Example 5: The effect of erythromycin extract on improving the organic membrane properties This example illustrates the effect of the strychnine extract provided in Example 3 on improving the performance of organic membranes.

[0097] The film-forming matrix comprises high amylose, corn starch, and glycerol, and the specific preparation steps are as follows: 5 g of high-amylose corn starch was weighed into 100 mL of distilled aqueous solution, and 2 g of polyvinyl alcohol (PVA) and 1.5 g of glycerol were added. After magnetic stirring in a 95 ℃ water bath for 45 min, different amounts (1 mL and 5 mL) of styraxin extract were added, and magnetic stirring was continued at 95 ℃ for 20 min to obtain a styraxin extract / high-amylose corn starch / PVA composite film-forming matrix solution (i.e., a film-forming matrix solution containing styraxin). The solutions were designated as S / PVA-1 mL and S / PVA-5 mL according to the amount of styraxin extract added. A blank control group (S / PVA-0, i.e., directly prepared using the film-forming matrix solution) with 0 mL of styraxin extract added was set up, with all other conditions being the same.

[0098] 100 mL of film-forming matrix solution was poured into an acrylic mold and dried in a constant temperature drying oven at 30 ℃ for 16 h. After drying, the film was peeled off to obtain a styraxin extract / high amylose corn starch / PVA composite film. Among them, S / PVA-1 mL and S / PVA-5 mL are composite films containing styraxin, and S / PVA-0 mL is a composite film without styraxin.

[0099] The performance of the composite membranes prepared above containing different amounts of styrax rubigin extract was determined, mainly including the appearance characteristics, thickness and mechanical properties of the membranes.

[0100] (1) Membrane appearance characteristics: such as Figure 12 As shown, the addition of styracin extract significantly improved the surface morphology of the high-amylose corn starch / PVA composite membrane. Experimental results indicated that the number of bubbles on the membrane surface decreased significantly with increasing styracin extract dosage; when the dosage reached 5 mL, bubble formation on the membrane surface was completely inhibited. Furthermore, the introduction of styracin extract significantly improved the structural integrity of the composite membrane, resulting in a smoother and more uniform membrane surface.

[0101] (2) Thickness: 15 measurement points were randomly selected using a micrometer (error 0.01 mm), and the average value of the results was taken.

[0102] like Figure 13 As shown, the addition of styracil extract significantly affected the thickness of the high-amylose corn starch / PVA composite membrane (p<0.05). Experimental data showed that the addition of styracil extract significantly reduced the thickness of the composite membrane (p<0.05). This phenomenon is attributed to the fact that styracil extract can promote the densification and homogenization of the membrane matrix structure, thereby forming a more compact film structure.

[0103] (3) Mechanical properties: The mechanical properties of the membrane are tested using a texture analyzer, including tensile strength and elongation at break. The test is repeated at least three times and the average value is taken.

[0104] like Figure 14 As shown, the addition of 5 mL of styraxone extract significantly improved the tensile strength of the composite membrane (p<0.05), while its elongation at break only changed slightly. Specifically, compared with the control group, the tensile strength of the experimental group increased by approximately 12.2%, while the change in elongation at break was not significant (p<0.05). This result indicates that the addition of styraxone extract can effectively enhance the mechanical strength of the membrane material while maintaining its ductility.

[0105] The present invention has been described in detail above. Those skilled in the art will recognize that the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. While specific embodiments have been provided, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein.

Claims

1. Serratia marcescens, characterized by: The *Serratia marcescens* is *Serratia marcescens*. Serratia marcescens Its strain number is BD 2025, and its registration number at the China General Microbiological Culture Collection Center is CGMCC No. 35196.

2. A culture of Serratia marcescens BD 2025 and / or metabolites of Serratia marcescens BD 2025, characterized in that: The culture is a substance obtained by culturing Serratia marcescens BD 2025 as described in claim 1 in a culture medium, containing Serratia marcescens BD 2025 and substances secreted into the culture medium; the metabolite is a substance obtained by culturing Serratia marcescens BD 2025 as described in claim 1 in a culture medium and then removing Serratia marcescens BD 2025, containing substances secreted into the culture medium by Serratia marcescens BD 2025, but not containing Serratia marcescens BD 2025.

3. The culture of *Serratia marcescens* BD 2025 and / or the metabolites of *Serratia marcescens* BD 2025 as described in claim 2, characterized in that: The culture medium is a fermentation culture medium, which is a solid culture medium using soybean residue as a nitrogen source and glycerol as a carbon source.

4. A product, characterized in that: Cultures of Serratia marcescens BD 2025 as described in claim 1 or / and Serratia marcescens BD 2025 as described in any of claims 2-3 and / or metabolites of Serratia marcescens BD 2025.

5. The use of the Serratia marcescens BD 2025 of claim 1 or / and the metabolites or cultures of Serratia marcescens BD 2025 of any one of claims 2-3 or / and the product of claim 4 in the preparation of serotonin.

6. The use of Serratia marcescens BD 2025 of claim 1 or / and the metabolites or cultures of Serratia marcescens BD 2025 of any one of claims 2-3 or / and the product of claim 4 in modified composite membranes.

7. The use of the Serratia marcescens BD 2025 of claim 1 or / and the culture of Serratia marcescens BD 2025 of any one of claims 2-3 or / and the product of claim 4 in the degradation of soybean residue.

8. A method for degrading soybean residue, characterized in that: The method includes the step of fermenting the Serratia marcescens BD 2025 of claim 1 with soybean residue as a substrate.

9. A method for producing styraxin, characterized in that: The method includes the step of fermenting Serratia marcescens BD2025 as described in claim 1 with soybean residue as a substrate, and extracting serotonin from the fermentation product.

10. A method for preparing a composite membrane containing styraxin, characterized in that: The composite membrane containing squalene is prepared by adding squalene active ingredient to the film-forming matrix solution; the squalene active ingredient is extracted from the culture of Serratia marcescens BD 2025 as described in any one of claims 2-3 and / or the metabolites of Serratia marcescens BD 2025; the film-forming matrix solution is obtained by mixing the film-forming matrix in water, and the film-forming matrix includes polyvinyl alcohol, high-amylose corn starch and glycerol.

Images