[Objective] Long-term and excessive application of chemical fertilizers leads to soil degradation and an imbalanced microbial community structure in soil. The combination of organic active substances with chemical fertilizers is considered an important approach for controlling soil degradation and maintaining microbial community stability. [Methods] Metagenomics was employed to study the effects of combining the bioactive substance γ-polyglutamic acid (γ-PGA) with chemical fertilizer on soil microbial community and function in cotton fields. Four fertilization groups were designed: chemical fertilizer (NK), chemical fertilizer combined with γ-PGA aqueous solution (YT), chemical fertilizer combined with γ-PGA granules (GT), and no fertilizer (CK). [Results] GT and YT groups outperformed NK and CK groups in terms of cotton growth and soil nutrient content. The combination of γ-PGA with chemical fertilizer significantly increased the microbial abundance and diversity in soil, while chemical fertilizer alone did not improve soil microbial diversity. In addition, the application of γ-PGA changed soil microbial community composition. Compared with the NK group, YT and GT groups showed a 9.70%–12.72% decrease in the relative abundance of Proteobacteria and 13.33%–20.90% and 8.09%–13.01% increases in the relative abundance of Bacteroidetes and Actinobacteria, respectively. In addition, the relative abundance of Rhizophagus (a genus of mycorrhiza fungi) increased by 19.71% in the YT group. The functional gene analysis showed that GT and YT significantly increased the abundance of functional genes related to amino acid biosynthesis, secondary metabolite biosynthesis, and ABC transporters. [Conclusion] The application of γ-PGA has the potential of improving soil microbial diversity and ecosystem stability in Xinjiang cotton fields.

[Objective] We isolated the aerobic bacteria capable of effectively degrading polylactic acid (PLA) and characterized the bacterial growth and degradation, aiming to lay a theoretical foundation for the bioremediation of PLA contaminated environment. [Methods] The degrading bacterium was identified by 16S rRNA gene sequencing. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were employed to analyze the morphological and chemical changes of PLA films before and after degradation. [Results] A strain of Bacillus sp. JA-4 was screened from activated sludge, and it caused the PLA weight loss of 10.6% after 30 days. The weight loss of PLA reached 5.6% after incubation with the strain at an inoculation amount of 20%, pH 8.0, and 30 ℃ for 7 days. Gelatin significantly enhanced the biodegradation of PLA. In the presence of 3% gelatin, the weight loss of PLA reached 23.1% after 10 days of degradation, and the degradation rate was greatly increased. FTIR results indicated that Bacillus sp. JA-4 degraded PLA by hydrolyzing the ester bonds. [Conclusion] This study enriched the microbial resources for the biodegradation of PLA and provided technical support for the effective degradation of PLA waste in the environment.

[Objective] To systematically analyze the enzymatic properties of transglutaminase (TGase) from Streptomyces mobaraensis CGMCC 4.1851 (strain XM4) and subsequently develop a high-yielding strain by engineering for achieving efficient expression of TGase in Streptomyces with reduced fermentation duration and enhanced production efficiency. [Methods] The pH of the fermentation broth and TGase activity were measured to assess the fermentation characteristics of strain XM4. TGase from XM4 was purified by alcohol precipitation combined with ion-exchange chromatography. The reaction conditions (pH, temperature, metal ions) were optimized for the enzyme, and the enzymatic kinetics were tested. The catalytic efficiency was evaluated by casein cross-linking experiments. Subsequently, genetic engineering was employed to enhance the modified strain through heterologous expression and replacement of the ribosome-binding site (RBS), followed by measurement of TGase production. [Results] TGase from strain XM4 exhibited good activity and stability within the range of pH 4.0–11.0, with the highest activity at 50 ℃ and pH 10.0. The modification realized efficient expression of TGase in S. mobaraensis, inceasing the production by 103.3% compared with the original strain and reducing the fermentation time to 24 h. [Conclusion] TGase from strain XM4 demonstrates excellent acid-base tolerance and thermal stability, demonstrating broad application prospects in the food industry, especially dairy processing. Additionally, the engineered strain enables efficient production of TGase, providing new options for the industrial production and application of TGase.

The pneumococcal vaccines play an indispensable role in defending against various invasive and non-invasive diseases caused by Streptococcus pneumoniae. The capsular polysaccharide is a key antigen, while the impurity residues in the capsular polysaccharide cause side effects of pneumococcal polysaccharide vaccines and conjugate vaccines. As the global demand for high-valent pneumococcal vaccines covering a wide range of serotypes keeps increasing, it is urgent and crucial to develop efficient and scalable production technologies for high-purity capsular polysaccharide antigens. The safety and quality attributes of capsular polysaccharide are influenced by multiple factors encompassing the selection of pathogen strains, formulation of culture media, control of fermentation processes, and purification technologies. Following the concept of Quality by Design (QbD) and the process development path, this article systematically summarizes the knowledge and experience throughout the entire process ranging from upstream strain screening and optimization, refined fermentation process design, to downstream purification, aiming to provide comprehensive and in-depth theoretical guidance and practical strategies for building and improving the production system of capsular polysaccharide.

[Objective] Certain strains of Ligilactobacillus salivarius possess excellent probiotic properties and strong potential for application. This study characterized strain ATCC 11741 in terms of the growth characteristics, stress tolerance, and adhesion capacity, aiming to provide a theoretical basis for the utilization of L. salivarius. [Methods] L. salivarius ATCC 11741's accuracy was verified through morphological observations and 16S rRNA gene sequencing; its growth characteristics were investigated by tracking growth and acid production curves; additionally, a range of tolerance tests, including those with acid, alkali, bile salts, hyperosmolarity and temperature, were conducted to evaluate its tolerance; lastly, self-aggregation and hydrophobicity experiments were used to indirectly determine its adhesion. [Results] The growth curve of L. salivarius ATCC 11741 was formed like a "S". The strain reached its highest acid production between 2–7 h, stabilizing at pH 4.3 after 14 h. After being cultured in the MRS medium at pH 2.0 for 4 h, the strain had a survival rate of 50.48% and grew well in the pH 4.0–11.0 range. Following 2 h of incubation in the MRS medium with 0.10% bile salt, the strain's survival rate was 94.440 0%. In the MRS medium with 6% NaCl, the strain continued to proliferate. The growth of strain ATCC 11741 was significantly affected by temperature, being promoted at 30–42 ℃ and inhibited at 20 ℃ and 50 ℃. At the 5 h mark, the strain's hydrophobicity (measured by the hydrocarbon compound adhesion method) was 44.5% and its self-aggregation rate was 41.4%. [Conclusion] L. salivarius ATCC 11741 is a strain with fast growth, strong tolerance to acids, alkali, and salts, moderate tolerance to bile salt, a wide range of suitable temperatures, and strong adhesion capacity.

[Objective] To screen microbial strains with high production of exopolysaccharides (EPS) and provide strain resources for the development of soil improvement agents. [Methods] The string test with a LB-aniline blue plate was employed to qualitatively screen the strains of plant growth-promoting rhizobacteria (PGPR) with EPS production. After fermentation with each strain in four media, the EPS content in the fermentation liquid was determined by low temperature alcohol precipitation and the sulfate-anthranone colorimetric method, on the basis of which the PGPR strain with high EPS production was screened out. The fermentation conditions of the strain screened out were optimized by orthogonal test with EPS content in fermentation liquid as the indicator. The influence of the fermentation liquid of strain F1 on the content of macro-aggregates in sandy loam soil was analyzed by the petri dish culture experiment. [Results] Eight EPS-producing PGPR strains were primarily screened out, among which strain F1 had the highest EPS production. PDA was the best medium for F1 to produce EPS, with the EPS content of 867.54 μg/mL. Based on morphological, physiological and biochemical characteristics, phylogenetic analysis based on 16S rRNA gene sequence, and also average nucleotide identity analysis, F1 was identified as a strain of Bacillus megaterium. The optimal culture conditions for F1 to produce EPS were 28 ℃ and 180 r/min for 24 h, under which the EPS yield reached 1 123.39 μg/mL. After F1 was incubated in sandy loam soil for 40 days, the content of water-stable macro-aggregates with the grain diameter > 0.25 mm in the soil increased by 4.44 times compared with that of the control. [Conclusion] Strain F1 with high EPS production can promote the formation of water-stable macro-aggregates in sandy loam soil. The optimal conditions for F1 to produce of EPS was incubation in PDA at 28 ℃ and 180 r/min for 24 h.

[Objective] Multipurpose bioorganic fertilizers contribute to the sustainable development of the Carya cathayensis Sarg. industry. This work aims to explore the resources of phosphorus (P)-mobilizing bacteria (PMBs) with plant growth-promoting effects from the rhizosphere soil of C. cathayensis Sarg. [Methods] PMBs were isolated with the dilution-plate coating method and identified based on 16S rRNA gene homology. Moreover, plate and liquid culture tests were conducted to determine their biological functions. [Results] A total of 34 strains of PMBs were isolated from the rhizosphere soil of C. cathayensis Sarg. These PMBs belonged to 10 genera of four phyla: Bacillota, Proteobacteria, Actinobacteriota, and Gracilicutes. Among them, Bacillus (12 strains), Burkholderia (9 strains), and Pseudomonas (5 strains) were the dominant genera, with the strains accounting for 76.47% of the total isolated PMBs. After inoculation of PMBs, the content of soluble P produced by PMBs was 7.01–49.97, 3.61–27.11, 4.56–342.82, 27.71–544.53, and 3.28–27.17 mg/L in the culture media with AlPO₄, FePO₄, Ca₃(PO₄)₂, sodium phytate, and lecithin as the sole P source, respectively. Twenty-three strains were capable of simultaneously mobilize insoluble inorganic and organic P components. Additionally, 20, 7, 23, 12, 10, 14, and 13 strains of PMBs could produce indole-3-acetic acid (IAA), siderophores, extracellular protease, β-1, 3-glucanase, cellulase, phosphatase, and lipase, respectively, among which strains S3-6L and S3-22L exhibited five biological functions. [Conclusion] The PMBs identified in this study possess high P mobilization capability and multiple biological functions, enriching the resources of PMB strains and laying a foundation for the development of efficient, green, and composite microbial fertilizers for C. cathayensis Sarg.

[Objective] To clarify the domestication characteristics and resistant mechanism of wild watermelon plants and provide a theoretical basis and technical support for building a new evaluation system for watermelon breeding and developing beneficial microorganisms, we compared the endophytic microbial community structure in roots between wild and cultivated watermelon varieties. [Methods] High-throughput sequencing was employed to reveal the community structures of endophytic microorganisms (bacteria and fungi) in the roots of wild and cultivated watermelon varieties. [Results] The phyla and genera of endophytic bacteria and fungi in the roots were significantly different between wild and cultivated watermelon varieties. The roots of wild watermelon varieties had significantly higher relative abundance of Nocardioides and Microbacterium than those of cultivated watermelon varieties. Actinoplanes, Mycobacterium, Lechevalieria, Amycolatopsis, Bradyrhizobium, and Rhodococcus were the special dominant endophytic bacterial genera in the roots of wild watermelon varieties. The relative abundance of unclassified_o__Chaetothyriale in the roots of wild watermelon varieties was significantly higher than that in cultivated watermelon varieties. unclassified__o_Chaetothyriales, Preussia, and unclassified_f__Microascaceae were the dominant endophytic fungi specific to wild watermelon varieties. [Conclusion] The beneficial bacteria, such as Nocardioides, Microbacterium, and Rhodococcus, which were capable of fixing nitrogen, solubilizing phosphorus, secreting siderophores, and producing bioactive substances and antibiotics, and the growth hormone-producing fungi, such as Preussia, were lost in the roots of cultivated watermelon varieties after the domestication of wild watermelon. Therefore, it can be concluded that parts of endophytic microorganisms in the roots disappear during the domestication process of watermelon varieties, which is a major reason for the weak resistance of cultivated watermelon varieties to stresses. In addition, the bacterial genera such as Nocardioides, Microbacterium, and Rhodococcus and the fungal genus Preussia can be taken as the candidate microbial resources for enhancing watermelon resistance.

[Objective] Pseudomonas as one of the dominant spoilage bacteria highly form biofilms in chilled meat products and processing environment when contaminating single or mixed with other species. This study aims to investigate the antibiofilm properties of the cell-free supernatants (CFSs) of three Bacillus species isolated from fermented food and rice seeds on Pseudomonas lundensis (PL) or and Acinetobacter johnsonii (AJ) as mono- or dual-species. [Methods] Biofilm biomass, extracellular polymeric substances (EPSs), and biofilm structure were measured by crystal violet staining, spectrophotometry, confocal laser scanning microscopy (CLSM), respectively, as well as transcription of biofilm-related genes determined by qPCR. [Results] The CFSs of Bacillus amyloliquefaciens ZG08, B. velezensis B5, and B. subtilis YB11 inhibited the biofilm formation of PL and AJ without affecting their growth. The treatment with 50% CFSs of ZG08 and B5 decreased the cell viability of two biofilms by 12.73%–21.04%, which was higher than that of YB11 (0.15%–4.38%). The inhibition rates of 50% CFSs of the three strains were 59.75%–79.59% against the PL biofilm and 63.62%–78.57% against the biofilm of PL+AJ, in which the CFS of YB11 had weaker activity. The content of exopolysaccharides and exoprotein in the two biofilms treated with these CFSs were reduced by 53.77%–73.30% and 54.84%–62.38%, respectively. The treatment with the three CFSs also reduced the adhesive cells, loosened biofilm structures, and thinned their thickness by 57.63%–74.49% and 60.43%–64.64%, respectively. Moreover, the CFSs of ZG08 and B5 effectively eradicated by 41.77%–69.79% against the mature biofilms of PL and PL+AJ, compared to weak activity of YB11. In addition, the antibiofilm activities of the three CFSs were stable under four enzyme digestion and heating conditions. Compared with the control, the CFSs of ZG08 and B5 significantly down-regulated the expression of six biofilm-related genes, lapA, alg44, pelG, luxR, wspR, and rpoS. [Conclusion] The CFSs of ZG08 and B5 have strong antibiofilm activities against PL and AJ as mono- or dual-species.

[Objective] Within the framework of global climate governance and considering the pivotal role of the Yellow River basin in China's ecological progress, this study focused on the Inner Mongolia segment of the Yellow River in July 2023. [Methods] We collected the surface sediment, water, and gas samples, with the aim of investigating the dissolved nitrous oxide (N₂O) concentration in the water, the N₂O emission flux (FN₂O) at the water-air interface, and the microbial community composition and diversity in surface sediments. [Results] The results revealed that the dissolved nitrous oxide (N₂O) concentration in the water of this segment varied between 0.547 8 mg/m³ and 0.598 2 mg/m³, with an average of 0.574 1 mg/m³. The FN₂O at the water-air interface ranged from −3.645 3 mg/(m²·d) to 4.392 5 mg/(m²·d), averaging 1.086 1 mg/(m²·d), which suggested this area was a net source of atmospheric N₂O. FN₂O showed a significantly positive correlation with pH and a significantly negative correlation with potential. The surface sediments harbored 7 784 operational taxonomic units (OTUs), with Proteobacteria (average abundance of 35.13%) being dominant. Ammonia-oxidizing archaea (AOA), a category of nitrifying bacteria, presented low abundance, with 116 OTUs among which unclassified_d__Unclassified (average abundance of 31.69%) was the dominant genus. For denitrifying bacteria, 3 660 OTUs were identified, with unclassified_k__norank_d__Bacteria (average abundance of 63.12%) being the dominant genus. In view of the scarcity of N₂O data for the Inner Mongolia section of the Yellow River, the findings of this study enrich the N₂O data repository of the Yellow River. [Conclusion] This study not only augments our understanding of the microbial community structure and functionality in sediments but also supports the conservation and purification of the Yellow River.