Leclercia adecarboxylata strain sw-03 and application thereof in degrading pla / pbat plastics

Abstract

The present application relates to the technical field of environmental microbial degradation of plastics, and particularly relates to a non-decarboxylation klebsiella SW-03 and application thereof in degrading PLA / PBAT plastics, the non-decarboxylation klebsiella SW-03 strain is preserved in Guangdong Microbial Culture Collection Center on December 5, 2025, the preservation number is GDMCC NO:67412, and the preservation address is the 5th floor of the 59th building of the Institute of Microbiology, Guangdong Academy of Sciences, 100, Middle Martyrs Road, Guangzhou City; the non-decarboxylation klebsiella SW-03 is isolated from eutrophic lake environment, can take PLA / PBAT plastics as the only carbon source, realizes the biodegradation of PLA / PBAT plastic film under normal temperature environment, and solves the problems of the current plastic degradation functional strain resource shortage and limited application scene.

Description

Technical Field

[0001] This invention relates to the field of environmental microbial degradation of plastics, specifically to a non-decarboxylating Cladosporium strain SW-03 and its application in the degradation of PLA / PBAT plastics. Background Technology

[0002] Polylactic acid / polybutylene adipate terephthalate (PLA / PBAT) is one of the most widely used biodegradable plastic systems. This plastic combines the advantages of both PLA and PBAT, possessing both good mechanical strength and toughness, and has been applied in packaging bags, agricultural mulch films, and other fields. However, the degradation of this blended plastic is heavily dependent on specific conditions such as industrial composting (e.g., high temperature, high humidity, and specific microbial environments). In the natural environment, the degradation rate is significantly slowed and uncontrollable. If it fails to enter an effective degradation system, it will remain in the environment for a long time and break down, posing a potential risk of microplastic pollution.

[0003] Utilizing microorganisms and their secreted enzymes to degrade PLA / PBAT is a key biotechnological approach for achieving its environmentally friendly treatment. Existing research indicates that some microorganisms can specifically hydrolyze the ester bonds in the PLA / PBAT molecular chain by secreting extracellular enzymes such as lipases and keratinases, thereby gradually depolymerizing it into low-molecular-weight oligomers and monomers, ultimately mineralizing it into carbon dioxide and water. Currently, most reported PLA / PBAT-degrading microorganisms have been isolated from habitats such as compost, soil, or the ocean, while a systematic understanding of the corresponding microbial resources in inland freshwater ecosystems (such as lakes and rivers) remains limited. Since freshwater environments are important sinks for plastics and are rich in microbial resources, effectively promoting material degradation and element cycling, and possessing unique physicochemical conditions distinct from other ecosystems (such as temperature fluctuation range, pH, nutrient levels, and native microbiota), they may also harbor highly efficient PLA / PBAT-degrading bacteria that are yet to be discovered. Therefore, the targeted screening and identification of indigenous microbial strains with high degradation activity against PLA / PBAT at room temperature from freshwater environments, and the elucidation of their degradation mechanisms and metabolic pathways, are of significant scientific value and application potential for developing bioremediation technologies suitable for natural water bodies or low-energy conditions, and promoting the closed-loop recycling of biodegradable plastics.

[0004] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0005] The purpose of this invention is to address the current problems of scarce resources, limited application scenarios, and insufficient treatment methods for plastic degradation functional bacteria. It provides a non-decarboxylating Leukobacter SW-03 strain and its application in the degradation of PLA / PBAT plastics.

[0006] To achieve the above objectives, this invention discloses a non-decarboxylated Reichelckii strain SW-03, which was deposited on December 5, 2025, at the Guangdong Provincial Center for Microbial Culture Collection (GDMCC) with accession number GDMCC NO:67412 and address 5th Floor, Building 59, Institute of Microbiology, Guangdong Academy of Sciences, No. 100 Xianlie Middle Road, Guangzhou.

[0007] The present invention also discloses the application of the above-mentioned non-decarboxylating Leucobacterium SW-03 in the degradation of PLA / PBAT plastics, wherein the non-decarboxylating Leucobacterium SW-03 uses PLA / PBAT plastics as the sole carbon source for degradation.

[0008] The non-decarboxylating Leucobacterium SW-03 degrades PLA / PBAT plastic using it as the sole carbon source. Specifically, this involves co-culturing the non-decarboxylating Leucobacterium SW-03 with PLA / PBAT plastic, including the following steps:

[0009] S1, prepare active bacterial solution from strain SW-03;

[0010] S2, the bacterial culture obtained in step S1 is inoculated into a mineral salt culture medium containing PLA / PBAT plastic for co-culture to degrade the PLA / PBAT plastic.

[0011] In step S1, the specific steps for preparing the bacterial solution are as follows:

[0012] S11. Non-decarboxylated Leucobacterium SW-03 was cultured in LB medium with constant temperature and shaking for 8-12 h. When the OD600 was 1.2-1.4, 30 mL of the turbid liquid was taken and the bacterial cells were collected.

[0013] S12, wash 2-3 times with PBS buffer to remove residual LB medium, and resuspend in mineral salt medium to obtain active bacterial solution. The volume of mineral salt medium is the same as the volume of medium centrifuged in step S11.

[0014] In step S12, the mineral salt culture medium is prepared as follows: 1g K2HPO4, 1g KH2PO4, 1g MgSO4·7H2O, 1g NH4NO3, 0.005g NaCl, 0.05g FeCl3, 0.02g CaCl2, 0.002g FeSO4·7H2O, 0.002g ZnSO4·7H2O, and 0.001g MnSO4·H2O are dissolved in 999mL of distilled water, and the pH is adjusted to 7.2.

[0015] In step S2, the liquid culture medium is a liquid mineral salt culture medium, and the preparation method of the liquid mineral salt culture medium is as follows: dissolve 1g K2HPO4, 1g KH2PO4, 1g MgSO4·7H2O, 1g NH4NO3, 0.005g NaCl, 0.05g FeCl3, 0.02g CaCl2, 0.002g FeSO4·7H2O, 0.002g ZnSO4·7H2O, and 0.001g MnSO4·H2O in 999mL of distilled water, and adjust the pH value to 7.2.

[0016] In step S2, the volume ratio of bacterial culture to liquid culture medium containing PLA / PBAT plastic is 1:9, and the inoculation amount is 10% v / v.

[0017] In step S2, the co-cultivation conditions are: 28 ℃~30 ℃, 180 rpm.

[0018] The present invention also discloses a formulation for degrading PLA / PBAT plastics, wherein the active ingredient of the formulation includes non-decarboxylating Leukobacter SW-03.

[0019] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention successfully obtained a bacterial strain with a clear degradation function for PLA / PBAT plastic from summer water samples of Chaohu Lake, an inland freshwater lake in China, through targeted enrichment and purification. The strain was identified as *Leclercia adecarboxylata* SW-03. This strain exhibits good biodegradability of untreated PLA / PBAT blend films at room temperature and can effectively colonize the plastic surface to form a biofilm, thereby initiating bio-erosion of the material. A 21-day degradation culture experiment with four consecutive passages confirmed that the degradation effect tended to be stable, achieving a film mass loss rate of 4.44%. Comprehensive characterization analysis using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and water contact angle analysis showed that after degradation, the film surface exhibited significant cracks, grooves, and pits, and the chemical structure changed, with weakened ester bond characteristic peaks. Simultaneously, surface hydrophilicity increased and thermal stability decreased, all providing direct evidence of microbial degradation. The SW-03 strain and its degradation method provided by this invention mainly rely on the natural metabolism of microorganisms, which is environmentally friendly and easy to operate. It provides a new microbial resource and biotechnology strategy for the removal of PLA / PBAT biodegradable plastics in the environment and the control of microplastic pollution in freshwater bodies, and has broad application prospects. Attached Figure Description

[0020] Figure 1Phylogenetic tree of non-decarboxylating Leclercia adecarboxylata SW-03;

[0021] Figure 2 The image shows the weight loss of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days. CK is the control group, and SW-03 is the experimental group.

[0022] Figure 3 SEM images of non-decarboxylating Leclercia adecarboxylata SW-03 co-cultured with PLA / PBAT plastic film for 21 days, where A, B, and C are control groups, and D, E, and F are experimental groups;

[0023] Figure 4 The image shows the ATR-FTIR of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days. CK is the control group, and SW-03 is the experimental group.

[0024] Figure 5 The carbonyl index of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days is shown in the figure. CK is the control group and SW-03 is the experimental group.

[0025] Figure 6 The figure shows the ester bond index of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days. CK is the control group and SW-03 is the experimental group.

[0026] Figure 7 The terminal hydroxyl index of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days is shown in the figure. CK is the control group and SW-03 is the experimental group.

[0027] Figure 8 The image shows the WCA curve of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days, where CK is the control group and SW-03 is the experimental group.

[0028] Figure 9The image shows the XRD pattern of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days. CK is the control group and SW-03 is the experimental group.

[0029] Figure 10 The image shows a TGA image of non-decarboxylating Leclercia adecarboxylata SW-03 after co-culturing with PLA / PBAT plastic film for 21 days. CK is the control group, and SW-03 is the experimental group. Detailed Implementation

[0030] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0031] Important strains used in this invention:

[0032] The non-decarboxylating Leclercia used in this invention was isolated and identified by Anhui University of Technology and has been deposited at the Guangdong Provincial Microbial Culture Collection Center (GDMCC; address: 5th Floor, Building 59, Institute of Microbiology, Guangdong Academy of Sciences, No. 100 Xianlie Middle Road, Guangzhou) on December 5, 2025; accession number: GDMCC NO:67412; classification name: non-decarboxylating Leclercia (Leclercia adecarboxylata) SW-03.

[0033] Example 1

[0034] Isolation, purification, and identification of non-decarboxylating Leclercia adecarboxylata strain SW-03:

[0035] 1. Isolation and purification of strain SW-03:

[0036] This embodiment takes Chaohu Lake (central area approximately 31°52′N, 117°38′E) in central Anhui Province, China as the research object. Water samples were systematically collected from multiple representative stations covering the lake center, lake shore and the estuary areas of major rivers flowing into the lake, including the Nanfei River, Shiwuli River, Pai River, Hangbu River and Baishitian River. Microbial enrichment and separation experiments were carried out simultaneously at all stations.

[0037] The specific method was as follows: 150 mL of water sample was added to a 500 mL Erlenmeyer flask, along with 150 mL of carbon-free mineral salt culture medium and a piece of untreated PLA / PBAT plastic film (2.5 cm × 3 cm × 50 μm) as the main carbon source. The flasks were incubated at 30 °C and 180 rpm under constant temperature and light conditions with shaking, and water was added periodically. On day 21, varying degrees of microbial colonization and degradation were observed on the surface of the plastic film in the cultures at each site. Subsequently, bacterial cells were collected from the film samples at all sites, and the samples were dispersed by vortexing with sterile physiological saline and serially diluted. to Afterwards, the cultures were separated on LB agar plates using the dilution plating method, and pure cultures were obtained through multiple streak purifications. Among them, a pure strain with smooth surface and pale yellow coloration, named SW-03, was obtained from the isolate at site 8 (Hangbu River estuary, coordinates 117.38210°, 31.55880°). A single colony was picked and inoculated into LB liquid medium and cultured at 30℃ and 180 rpm until OD... 600 Approximately 1.2, and then stored at -80°C for a long period using the glycerol preservation method.

[0038] The carbon-free mineral salt culture medium used for separation and purification is prepared as follows: 1g K2HPO4, 1g KH2PO4, 1g MgSO4·7H2O, 1g NH4NO3, 0.005g NaCl, 0.05g FeCl3, 0.02g CaCl2, 0.002g FeSO4·7H2O, 0.002g ZnSO4·7H2O, and 0.001g MnSO4·H2O are dissolved in 999ml of distilled water. The pH is adjusted to approximately 7.2, and the solution is then autoclaved.

[0039] The LB liquid medium used consisted of 10 g / L tryptone, 5 g / L yeast extract, and 10 g / L sodium chloride (NaCl); the LB solid medium consisted of 10 g / L tryptone, 5 g / L yeast extract, 5 g / L sodium chloride (NaCl), and 15 g / L agar.

[0040] 2. Molecular biological identification of strain SW-03:

[0041] The single bacterial strain obtained from the above isolation and purification was amplified by PCR using broad-spectrum bacterial primers. The bacterial samples were then transferred to Nanjing Qingke Biotechnology Co., Ltd. for bidirectional sequencing to obtain its full-length 16S rRNA gene sequence. BLAST alignment of this sequence was performed using the NCBI database to screen for strain sequences with high similarity, and a phylogenetic tree was constructed using MEGA 12.0 software.

[0042] 16S rRNA sequence alignment analysis in the NCBI database showed that this strain was highly similar to non-decarboxylated Cladosporium and their phylogenetic positions were close. Combined with its physiological and biochemical characteristics, and such as... Figure 1 The phylogenetic tree shown indicates that this strain was preliminarily identified as a non-decarboxylating Leclercia and named *Leclercia adecarboxylata* SW-03. Therefore, this strain, which can be used for the degradation of PLA / PBAT plastics, is not limited to the strains isolated from the field mentioned above.

[0043] Finally, strain SW-03 was deposited, and the deposit information is as follows: deposit date: December 5, 2025; depositary institution: Guangdong Provincial Microbial Culture Collection Center (GDMCC); deposit number: GDMCC NO:67412; depositary address: 5th Floor, Building 59, Institute of Microbiology, Guangdong Academy of Sciences, No. 100 Xianlie Middle Road, Guangzhou; classification and name: non-decarboxylated Leclercia SW-03.

[0044] The 16S rRNA gene sequence of this strain is shown below:

[0045]

[0046] Example 2

[0047] Co-culture experiment of strain SW-03 with PLA / PBAT blended plastic:

[0048] 1. Preparation of microplastic samples:

[0049] To ensure the consistency of experimental materials and the accuracy of subsequent characterization and recovery weighing, this embodiment uses PLA / PBAT blended plastic film as the standard degradation substrate. The specific preparation method is as follows: Commercially available PLA / PBAT plastic bags (composed of 15% PLA, 80% PBAT, and 5% plasticizer) are cut into uniform 2.5 cm × 3 cm film sheets. The films are then immersed in a 75% (v / v) ethanol solution for 30 minutes, followed by repeated rinsing three times with sterile deionized water to remove residual ethanol. The cleaned films are then sterilely air-dried in a laminar flow hood. After complete drying, each film is weighed and its initial mass is recorded as the benchmark for calculating the mass loss rate in subsequent co-culture experiments.

[0050] 2. Activation and culture of microbial strains:

[0051] Non-decarboxylated Leucobacter SW-03 was streaked onto LB agar plates and incubated at 30°C for 18-36 hours. Single colonies were picked and transferred to Erlenmeyer flasks containing 100 mL of LB liquid medium and incubated at 30°C and 180 rpm for 8-12 hours until the bacterial growth rate reached OD. 600 The value reached approximately 1.2. The culture was centrifuged at 4°C and 6000 × g for 5 minutes, and the bacterial pellet was collected. The pellet was washed 2 to 3 times with sterile phosphate-buffered saline (PBS, pH 7.2) to thoroughly remove residual culture medium components. The washed bacterial suspension was resuspended in sterile carbon-free mineral salt medium, and the OD value of the suspension was adjusted. 600 Step 1.2 yields a uniform inoculum solution.

[0052] 3. Co-culture experiment:

[0053] Add 90 mL of sterile, carbon-free mineral salt medium and a surface-sterilized PLA / PBAT blend plastic film to a 150 mL Erlenmeyer flask. Inoculate the previously prepared non-decarboxylating Leucella SW-03 bacterial suspension at a 10% (v / v) inoculation rate. Uninoculated medium and film were used as blank controls. Each treatment was performed in quadruplicate. All Erlenmeyer flasks were continuously cultured in a 30°C, 180 rpm constant-temperature shaking incubator. A degradation cycle was defined as 21 days. After each cycle, the film was removed for subsequent analysis of morphology, chemical structure, and surface property changes. Simultaneously, 10 mL of the culture from that cycle was used as inoculum and transferred to a new Erlenmeyer flask containing 90 mL of fresh, carbon-free mineral salt medium and a sterilized film to begin the next cycle. This subculturing process was repeated 3 to 4 times until the film mass loss rate stabilized, indicating that the strain's degradation activity had reached a steady state. All operations were performed in a laminar flow hood to ensure a sterile environment.

[0054] 4. Results of co-culture experiment:

[0055] (1) Mass loss of PLA / PBAT blended plastic film:

[0056] To quantify the degradation efficacy of strain SW-03 on PLA / PBAT films, after each 21-day degradation cycle, the following procedure was followed to process and calculate the mass loss of the films: The films were removed from the conical flasks using sterile forceps and placed in a 50 mL centrifuge tube containing sterile 1×PBS buffer (pH 7.2). The tubes were vortexed at 2500 rpm for 30 minutes, then transferred to 75% (v / v) ethanol solution and ultrasonically cleaned for 20 minutes. The films were then washed 2-3 times with sterile deionized water. Finally, the cleaned films were placed in a clean bench and air-dried in the dark for 24 hours until constant weight. The mass of the dried films was weighed using an analytical balance, and the mass loss rate (weight loss percentage) was calculated using the following formula: Weight loss percentage (%) = [(Initial film mass – Degraded film mass) / Initial film mass] × 100%. Figure 2 The analysis of the mass loss data shows that after 21 days of treatment with strain SW-03, the weight loss rate of the PLA / PBAT film reached 4.44%, while the film mass of the control group without bacterial inoculation did not change significantly during the same period. This result indicates that the non-decarboxylating Cladosporium SW-03 can effectively utilize PLA / PBAT blended plastic film as a carbon source for growth and exert substantial biodegradation effects on it.

[0057] (2) Surface morphology changes of PLA / PBAT blended plastic film before and after degradation:

[0058] The surface erosion effect of strain SW-03 on PLA / PBAT films was observed by field emission scanning electron microscopy on the degraded, cleaned, and dried film samples. The results are as follows: Figure 3 As shown, compared with the smooth and flat surface of the uninoculated control group film, the surface morphology of the film after 21 days of degradation by strain SW-03 changed significantly. The surface became rough, with obvious wrinkles, pits, and pores of varying depths, indicating signs of biodegradation. This morphological comparison clearly demonstrates that strain SW-03 can successfully colonize and grow on the film surface, using PLA / PBAT as the main carbon source. It erodes the plastic matrix through direct physical adhesion and biochemical action, leading to the destruction of its surface structure. This microscopically confirms that this strain has a clear biodegradation ability for PLA / PBAT plastics.

[0059] (3) Changes in surface functional groups of PLA / PBAT blended plastic films before and after degradation:

[0060] To elucidate the effect of strain SW-03 on the chemical structure of PLA / PBAT films, total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) was used to characterize the surface functional groups of the films before and after degradation, with a spectral scanning range of 400 to 4000 cm⁻¹. The results are as follows: Figure 4 As shown, compared with the undegraded control film, the infrared spectrum of the film degraded by strain SW-03 showed systematic changes, indicating significant alterations in chemical structure. Specifically, the methylene group (attributed to the PBAT aliphatic chain)... ) in 2851 (Symmetric stretching vibration) and 2918 The intensity of the characteristic absorption peak at (asymmetric stretching vibration) is significantly weakened; at the same time, the intensity of the methyl group attributable to PLA is significantly reduced. ) in 2873 and 2957 The absorption peak intensity at 1710 also decreased. These changes collectively indicate that the CH bonds in the main chain and side chains of the plastic polymer underwent breaking and oxidation. The most critical change occurred in the carbonyl (C=O) region: located at 1710... The intensity of the characteristic absorption peak of the ester bond at this point decreases, and the peak shape broadens, which is a direct indication of hydrolysis or breakage of the ester bond. Furthermore, at 1016... Nearby (CO stretching vibration) and 3410 The relatively enhanced band intensity near the OH stretching vibration further confirms the formation of hydroxyl and carboxyl functional groups in the hydrolysis products. In summary, ATR-FTIR spectroscopy clearly reveals at the molecular level that the non-decarboxylating Leucella SW-03 achieves substantial biodegradation of the blended plastic by disrupting key chemical bonds such as ester bonds in the PLA / PBAT film.

[0061] (4) Changes in various indices of PLA / PBAT blended plastic film before and after degradation:

[0062] To quantitatively analyze the chemical structural changes of PLA / PBAT films during biodegradation, this embodiment uses ATR-FTIR spectroscopy, selecting characteristic functional group absorption peaks for area integration calculation, and normalizing using the absorption peaks of stable structural units as internal standards. Specifically, the carbonyl index is represented by the characteristic absorption peak of the C=O stretching vibration in the ester bond (~1710). Peak area calculation; ester bond index is based on the characteristic absorption peak of the COC stretching vibration in the ester group (~1101). Peak area calculation; terminal hydroxyl index with broad absorption band of OH stretching vibration (~3410) The peak area was calculated. All the above indices are based on the characteristic absorption peak (~727) of the out-of-plane bending vibration of the benzene ring in the terephthalic acid unit of the PBAT chain. Peak area was used as an internal standard for calibration to eliminate the influence of fluctuations in test conditions. After treatment with strain SW-03, the characteristic indices of the film changed significantly. Figures 5-7 Data analysis showed that, compared with the uninoculated control group, the ester bond index of the treated film increased from 0.40 to 0.42, confirming the breakage of ester bonds in the polymer backbone. Simultaneously, the terminal hydroxyl index significantly increased from 0.020 to 0.025, further confirming the generation of numerous terminal hydroxyl groups after chain breakage, providing direct chemical evidence for the degradation reaction. Furthermore, the carbonyl index decreased from 3.44 to 3.36, reflecting the reduction of carbonyl-containing polymer segments during degradation due to chain breakage, fragmentation, and the loss of some small molecule products. These mutually corroborating index changes quantitatively demonstrate that the non-decarboxylating Cladosporium SW-03 can effectively disrupt the molecular chain chemical structure of PLA / PBAT films, achieving their biodegradation.

[0063] (5) Changes in surface hydrophobicity of PLA / PBAT blended plastic film before and after degradation

[0064] To characterize the effect of SW-03 degradation on the surface properties of PLA / PBAT films, the changes in hydrophilicity / hydrophobicity of the film surface were analyzed using an optical contact angle meter system. The cleaned and dried film samples were fixed flat on a glass slide, and 10 µL of ultrapure water was dropped onto the surface using a microsyringe. Measurements were taken at three different locations for each sample, and the results were averaged. Contact angle measurement results (…) Figure 8The results clearly show that the control group (CK) film, without SW-03 treatment, exhibited a water contact angle of 107.65°±0.86°, displaying typical hydrophobic properties. However, the film treated with SW-03 showed a significantly reduced water contact angle to 88.2°±2.99°. This change indicates a fundamental shift in the material's surface properties from hydrophobic to hydrophilic. This phenomenon is highly consistent with the previously detected significant increase in the content of hydrophilic functional groups (such as hydroxyl groups) in FTIR spectroscopy. Both findings confirm that the SW-03 strain not only colonizes the film surface during metabolism but also effectively hydrolyzes and breaks ester bonds in polymer molecular chains, thereby introducing hydrophilic groups onto the material surface and altering its interfacial properties.

[0065] (6) Changes in crystallinity of PLA / PBAT blended plastic film before and after degradation

[0066] X-ray diffraction (XRD) analysis was performed on PLA / PBAT plastic films before and after degradation. Figure 9 The study found that treatment with non-decarboxylating Leucobacterium SW-03 significantly reduced the intensity of characteristic diffraction peaks in the film, and decreased its crystallinity from 44.77% in the control group to 38.04%. This finding differs from the traditional model of "preferential erosion of amorphous regions and relative increase in crystallinity" commonly observed in biodegradation, suggesting that SW-03 may possess a unique degradation mechanism. Specifically, its secreted enzyme system can directly act on and destroy crystalline regions in the polymer that are typically more difficult to degrade. Further analysis indicated that this significant reduction in crystallinity may be related to the efficient attack of specific segments of PLA / PBAT by the SW-03 enzyme system. For PBAT, its biodegradability mainly depends on aliphatic segments (such as butylene adipate, PBA), and SW-03 likely preferentially depolymerizes these PBA segments in PBAT and the entire aliphatic backbone of PLA. Simultaneously, crystal structure defects within the blend (e.g., introduced by comonomers or generated at the two-phase interface) may also increase the sensitivity of crystalline regions to enzymatic hydrolysis. Therefore, the overall decrease in crystallinity not only directly confirms that SW-03 can overcome the energy barrier of crystal structure to achieve deep degradation, but also reveals its excellent degradation ability on PLA / PBAT plastic film.

[0067] (7) Thermogravimetric analysis of PLA / PBAT blended plastic film before and after degradation

[0068] The effect of degradation treatment by strain SW-03 on the thermal stability of PLA / PBAT films was investigated. Thermogravimetric analysis was performed, and the DTG curve, which reflects the instantaneous thermal decomposition rate, was analyzed in detail. Figure 10Analysis showed that during the main thermal decomposition stage (350℃ to 600℃), the DTG curves of the experimental group films treated with SW-03 consistently remained above those of the control group, indicating that the instantaneous weight loss rate at the same temperature point was consistently higher. Particularly at the characteristic peak temperature corresponding to the maximum polymer decomposition rate, the peak value of the experimental group was significantly higher. This phenomenon directly proves that the thermal stability of PLA / PBAT films systematically decreased after SW-03 biological treatment. The fundamental reason is that the strain disrupted the molecular chain structure of the plastic during degradation (e.g., reduced molecular weight, broken chemical bonds), making it more susceptible to segmental thermal decomposition in subsequent thermal analysis, thus accelerating the thermal decomposition process with lower energy input. Therefore, the changes in the DTG curves, from the perspective of thermal behavior, provide supplementary evidence that SW-03 effectively biodegrades PLA / PBAT films.

[0069] In summary, this invention successfully isolated, screened, and identified a novel strain with a clear degradation function for PLA and PBAT plastics from the water of Chaohu Lake, a typical inland freshwater lake, named *Leclercia adecarboxylata* SW-03. This strain can grow using untreated PLA / PBAT blended plastic films as the main carbon source, achieving effective biodegradation through colonization and erosion, leading to the destruction of film surface morphology, breakage of key chemical bonds, decrease in crystallinity, and reduction in thermal stability. The SW-03 strain of this invention provides a microbial resource with independent intellectual property rights for the conversion and removal of biodegradable PLA and PBAT plastics in the environment, and also provides a new strain reserve and feasible solution for developing microplastic pollution bioremediation technologies for freshwater bodies, demonstrating significant environmental application potential.

[0070] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A non-decarboxylating Leucobacterium strain SW-03, characterized in that, The non-decarboxylated Leucobacterium SW-03 strain was deposited on December 5, 2025, at the Guangdong Provincial Center for Microbial Culture Collection (GDMCC NO:67412); the deposit address is 5th Floor, Building 59, Institute of Microbiology, Guangdong Academy of Sciences, No. 100 Xianlie Middle Road, Guangzhou.

2. The application of the non-decarboxylating Leucobacterium SW-03 as described in claim 1 in the degradation of PLA / PBAT plastics.

3. The application of the non-decarboxylating Cladosporium SW-03 as described in claim 2 in the degradation of PLA / PBAT plastics, characterized in that, The non-decarboxylating Leukobacter SW-03 degrades PLA / PBAT plastic using PLA / PBAT plastic as the sole carbon source.

4. The application of the non-decarboxylating Cladosporium SW-03 as described in claim 3 in the degradation of PLA / PBAT plastics, characterized in that, The non-decarboxylating Leukobacter SW-03 degrades PLA / PBAT plastic using the sole carbon source, specifically including the following steps: S1, prepare active bacterial solution from strain SW-03; S2, the bacterial culture obtained in step S1 is inoculated into a mineral salt culture medium containing PLA / PBAT plastic for co-culture to degrade the PLA / PBAT plastic.

5. The application of the non-decarboxylating Cladosporium SW-03 as described in claim 4 in the degradation of PLA / PBAT plastics, characterized in that, In step S1, the specific steps for preparing the bacterial solution are as follows: S11. Non-decarboxylated Leucobacterium SW-03 was cultured in LB medium with constant temperature and shaking for 8-12 h. When the OD600 was 1.2-1.4, 30 mL of the turbid liquid was taken and the bacterial cells were collected. S12, wash 2-3 times with PBS buffer to remove residual LB medium, and resuspend in mineral salt medium to obtain active bacterial solution. The volume of mineral salt medium is the same as the volume of medium centrifuged in step S11.

6. The application of the non-decarboxylating Cladosporium SW-03 as described in claim 4 in the degradation of PLA / PBAT plastics, characterized in that, In step S2, the volume ratio of bacterial culture to liquid culture medium containing PLA / PBAT plastic is 1:9, and the inoculation amount is 10% v / v.

7. The application of the non-decarboxylating Cladosporium SW-03 as described in claim 4 in the degradation of PLA / PBAT plastics, characterized in that, In step S2, the co-cultivation conditions are: 28 ℃~30 ℃, 180 rpm.

8. A formulation for degrading PLA / PBAT plastics, characterized in that, The active ingredient in the formulation includes non-decarboxylated Leukocytobacter SW-03.

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