Objective To characterize the cultivable bacterial diversity patterns and extracellular enzyme-producing capacity in mangrove sediments from the Zhangjiang Estuary, with a particular focus on the distribution of dominant Bacillus sensu lato and the environmental factors shaping their assemblages. Methods Bacterial isolates were obtained by dilution plating. Taxonomic identification was performed by 16S rRNA gene sequencing. Plate-based assays were used to evaluate the activities of eight extracellular enzymes. Results In total, 1 392 isolates were obtained, representing 97 genera of 4 phyla. Bacillus sensu lato constituted the dominant assemblage (57.8%). Preliminary screening suggested 263 isolates (18.9%) as putative novel taxa, largely concentrated in Bacillus and allied genera such as Halobacillus. The Shannon diversity of cultivable bacteria was higher in the core mangrove zone and at the estuarine outlet than at the inlet (P<0.05), and the community composition differed among sites (P<0.05), being mainly associated with salinity and metal ions. By contrast, the community structure of Bacillus sensu lato was comparatively stable across space and was primarily associated with pH and carbon-nitrogen nutrient variables. Enzyme screening showed the highest positive rates for proteases (64.2%) and lipases (52.6%). Isolates affiliated with Bacillus sensu lato displayed higher positive rates than the overall community across multiple enzymes, indicating broad metabolic potential. Conclusion Mangrove sediments from the Zhangjiang Estuary harbor abundant cultivable bacterial resources. In addition to the dominant Bacillus-related taxa, Pseudomonadota and Bacteroidota appear to be key components underpinning overall community diversity. The high ecological stability and multi-substrate degradation capacity of Bacillus sensu lato, together with other bacterial groups, contribute to element cycling in mangrove sediments.

Objective The saline-alkaline habitats in Xinjiang harbor rich and unique microbial resources. This study employed the culture-dependent way to explore the culturable microbial resources and reveal their diversity and potential functions from seven different saline-alkaline habitats, including Barkol Lake and Aiding Lake in Xinjiang. Methods Soil and sediment samples were collected from the seven saline-alkaline habitats. Thirteen modified media were designed and used for strain isolation via the gradient dilution plating method. The 16S rRNA gene sequencing, phylogenetic analysis, and multi-condition culture were employed to analyze the taxonomic positions, suitable media, and salinity adaptability of the strains. Furthermore, potential novel taxa, anaerobic strains, and exopolysaccharide (EPS)-producing strains were screened. Results A total of 935 bacterial strains were isolated and identified as 310 species belonging to 125 genera, 54 families, 25 orders, 8 classes of 4 phyla, including 20 strains representing 15 potential novel taxa. The dominant culturable taxa were Bacillota, Pseudomonadota, and Actinomycetota. In addition, 52 strains (20 species) of anaerobic bacteria were obtained, with the genus Halomonas being dominant. The microbial resources varied significantly among different media, and R2A was the most effective medium, screening out 108 species. Bacillus was dominant under no salt stress (0 NaCl), and Marinobacter was one of the important genera under moderate salt stress (5% NaCl). However, the genus Halomonas kept being dominant under low-salt (0 NaCl), moderate-salt (5% NaCl), or high-salt (10% NaCl) stress. To obtain the functional strains with extremely strong stress resistance, we screened 15 EPS-producing strains under high-salt and high-alkali conditions. Among them, Marivirga harenae EGI S10258 and Halomonas alkaliantarctica EGI S10283 showed the highest EPS titer, which reached 4.5 g/L. Conclusion The saline-alkaline habitats in Xinjiang were rich with culturable microbial resources. The application of a multi-condition culture approach significantly enhances the depth and breadth of microbial resource exploration. This study provides important microbial resources and data support for subsequent research on systematic taxonomy, ecological adaptation mechanisms, and resource utilization by getting potential novel species and functional strains.

Objective To address problems such as the poor structure and fertility degradation in strongly acidic soils, we isolated acid-tolerant exopolysaccharide (EPS)-producing microorganisms, constructed a composite microbial inoculant, and evaluated its improvement effects on the structure and comprehensive fertility of acidic soils. Methods Target strains were obtained through primary and secondary screening from strongly acidic soils (pH<4.5) in Nanchuan, Chongqing and Qujing, Yunnan. After their antagonistic activity and plant growth-promoting traits were assessed, a composite microbial inoculant was constructed. A laboratory soil culture experiment was conducted to investigate changes in nutrient contents and aggregate composition in strongly acidic soils treated with different inoculants, comprehensively evaluate the fertility-improving effects of the inoculants, and clarify the correlation between aggregate formation and EPS content. Results Three strains—Paraburkholderia fungorum C3, Burkholderia cepacia A13, and Cystobasidium minutum B14—with acid tolerance and high EPS-producing capabilities were successfully isolated and screened out. All the strains exhibited the capabilities of secreting indole-3-acetic acid (IAA), synthesizing siderophores, and solubilizing phosphorus. When these strains were applied individually or as a composite inoculant to soils, the composite inoculant showed the best effect of improving soil nutrients, increasing the content of soil organic matter, alkaline-hydrolyzable nitrogen, available phosphorus, and available potassium by 4.51%, 13.92%, 4.92%, and 3.71%, respectively. Application of all the inoculants effectively promoted the formation of soil macro-aggregates, among which the single-strain inoculant C3 had the most significant effect in promoting aggregate formation, increasing the soil mean weight diameter (MWD) by 19.39%. The integrated fertility index of the soil treated with the composite inoculant reached 0.61, indicating the optimal comprehensive improvement effect. The single-strain inoculant C3 and the composite inoculant significantly increased the soil EPS content by 53.17% and 35.79%, respectively. Correlation analysis results showed that soil EPS had significantly positive correlations with macro-aggregate content and MWD, significantly promoting the formation and enhancing the stability of soil macro-aggregates. Conclusion The composite inoculant composed of the three acid-tolerant EPS-producing strains screened in this study effectively improved the soil structure and enhanced the integrated soil fertility. These findings lay a theoretical foundation for the development of biological agents for acidic soil remediation.

Fusarium proliferatum is a critical pathogenic fungus causing soybean root rot. A halotolerant biocontrol strain Bacillus sp. YH7-4 was isolated from the Yuncheng Salt Lake. Objective To investigate strain YH7-4 in terms of the effect on soybean growth and the control efficacy against soybean root rot. Additionally, we sought to elucidate the antifungal mechanisms of this strain and identify antimicrobial genes through whole genome sequencing. Methods The plate dual-culture method was adopted to assess the antifungal activity of strain YH7-4. Pot experiments were conducted to evaluate the safety of the strain to soybean seedlings and the control efficacy against root rot. Illumina and PacBio platforms were used for whole genome sequencing of YH7-4. Subsequent analyses included metabolic system assessment, virulence factor prediction, transporter analysis, identification of genes related to biocontrol functions, comparative genomics, and biochemical assays. Results Strain YH7-4 demonstrated the inhibition rates exceeding 75.00% against several plant pathogens, including F. proliferatum, Phytophthora sojae, Colletotrichum truncatum, and Phomopsis longicolla. Pot experiments showed that at the OD₆₀₀ value of 0.8, YH7-4 suspension significantly increased the root length and dry weight of soybean seedlings, while excessively high concentrations abolished this effect. The control efficacy of YH7-4 against F. proliferatum-induced soybean root rot reached 56.02%. Whole genome sequencing revealed a genome of 3 945 352 bp with the G+C content of 46.51% and 3 756 predicted coding genes. These genes were annotated against databases including NR, Swiss-Prot, Pfam, COG, GO, and KEGG, with 3 753, 3 537, 3 358, 3 082, 1 756, and 2 845 sequences successfully annotated, respectively. Among the proteins encoded by these genes, 130 proteins belonged to the CAZy family. Twelve secondary metabolite biosynthetic gene clusters were identified, including eight known biosynthetic gene clusters for antibiotics (surfactin, macrolactin H, bacillaene, fengycin, difficidin, bacillibactin, bacilysin, and butirosin A/butirosin B) and four gene clusters with unknown functions. Additionally, two siderophore-related genes, one gene encoding 2,3-butanediol (associated with induced systemic resistance), and 15 genes involved in biofilm formation were identified. Comparative genomics analysis indicated that YH7-4 was a strain of Bacillus velezensis and shared 2 898 orthologous core gene clusters. Biochemical characterization showed that YH7-4 had the ability to produce amylase, protease, pectinase, and cellulase. Conclusion The halotolerant strain B. velezensis YH7-4 isolated from the Yuncheng Salt Lake shows excellent control efficacy against soybean root rot. Its genome harbors genes linked to biocontrol traits and antimicrobial substance production, which makes this strain a promising candidate for managing soybean root rot and other plant fungal diseases. This study applies salt lake-derived bacteria to plant roots, demonstrating their influence on soybean growth while providing a theoretical basis for further elucidating the antifungal mechanisms of B. velezensis YH7-4.

Para-ethoxyaniline (ETH), a widely used industrial raw material and intermediate, persists in the environment, posing potential risks to ecosystems and human health. Objective To isolate an efficient ETH-degrading strain from activated sludge, optimize its degradation conditions, and elucidate the gene regulatory mechanisms and metabolic pathways under ETH stress by transcriptomic and mass spectrometric analyses. Methods A strain capable of utilizing ETH as the sole carbon source was isolated from activated sludge and identified through morphological observation, physiological and biochemical tests, and phylogenetic tree construction based on 16S rRNA gene sequences. The effects of temperature, pH, and initial ETH concentration on bacterial growth and degradation efficiency were examined. Transcriptome sequencing was employed to identify differentially expressed genes (DEGs), with selected up-regulated DEGs validated by real-time reverse transcription quantitative (RT-qPCR). Furthermore, mass spectrometry was employed to investigate the metabolic pathways. Results A highly efficient ETH-degrading strain, designated DQ78 and identified as Pseudomonas sp., was isolated. Under optimal conditions (28 ℃, pH 8.0, 4 mmol/L ETH, and 1% inoculum), it completely degraded ETH within 40 h. Three metabolic intermediates were identified, allowing the proposal of a preliminary degradation pathway. Transcriptomic analysis revealed 3 380 DEGs under ETH stress, including 1 609 up-regulated and 1 771 down-regulated genes. GO enrichment indicated up-regulated genes were primarily involved in 57 GO terms such as amino acid metabolism, cell motility, iron binding, and transport, which might activate the synthesis of ETF-degrading enzymes and enhance substrate uptake and transmembrane metabolism of intermediates. The down-regulated genes were enriched in 58 GO terms such as peptide metabolism and synthesis, ribosomal structure, and cellular components, suggesting a metabolic reallocation toward stress adaptation. KEGG analysis predicted 183 up-regulated pathways and 184 down-regulated pathways such as flagellar assembly, sulfur metabolism, and extracellular biosynthesis under ETH stress, indicating enhanced chemotaxis, enzyme secretion, and stress-resistant substance synthesis. Conclusion Strain DQ78 achieved complete degradation of ETH within 40 h, being a promising candidate for the bioremediation of ETH-contaminated environments. Transcriptomic analysis reveals the molecular regulatory mechanism of this strain in response to ETH, which lays a theoretical foundation for further exploring the genetic foundation of microbial degradation of organic pollutants.

Litchi (Litchi chinensis Sonn.) is one of the important tropical and subtropical fruits in China. However, litchi downy blight caused by the infection of Peronophythora litchii (Peronophythora litchii Chen ex Ko et al.) a severe disease damaging litchi during production, storage, and transportation, seriously threatening the healthy development of China’s litchi industry. Objective We screened effective antagonistic bacteria against P. litchii and evaluated their plant growth-promoting potential, aiming to enrich the resources of antagonistic bacteria against P. litchii. Methods Soil samples from the litchi rhizosphere were collected, and the bacteria in the samples were isolated through a high-throughput isolation and culture method. The strains were identified by means of 16S rRNA gene sequence analysis. The antagonistic strains against P. litchii were screened via the plate confrontation method, and the plant growth-promoting functions [phosphorus solubilization, potassium solubilization, nitrogen fixation, siderophore secretion, and indole-3-acetic acid (IAA) production] of the antagonistic strains were further evaluated through functional plates. Results A total of 327 bacterial strains were isolated in this study, among which 92 (28.13%) strains were identified as antagonists (with mycelial growth inhibition rates>40%) against P. litchii. These antagonistic strains belonged to 4 phyla, 6 classes, 12 orders, 20 families, and 42 genera, with Bacillota and Pseudomonadota being the dominant phyla, and Bacillus and Paenibacillus as the dominant genera. Functional evaluation of the 92 antagonistic strains revealed that 55 (59.8%) strains exhibited more than one plant growth-promoting function, while 30 (32.6%) strains possessed three or more such functions. Through comprehensive evaluation of antagonistic activity and plant growth-promoting functions, one Brevibacillus strain T101, four Paenibacillus strains (T431, T270, T327, and T234a), and one Paraburkholderia strain R116b were identified as the most promising strains for biocontrol applications. Conclusion Multiple antagonistic strains against P. litchi,with functions of phosphorus solubilization, potassium solubilization, nitrogen fixation, siderophore secretion, and IAA production, are screened out, which provides efficient strain resources for the green control of litchi downy blight.

Objective To identify high-quality yeast strains in the Xinjiang traditional milk wine fermentation system and screen specialized strains suitable for the milk wine fermentation, thereby providing a theoretical basis and strain reserves for the development of dedicated fermentation agents. Methods With alcohol production, ester production, lactose utilization ability, as well as acid (pH), glucose, and ethanol tolerance as screening criteria, the gradient dilution separation method combined with selective media was employed to isolate yeast strains. Morphological observation and molecular biological identification were conducted to determine the taxonomic status of the strains. The growth characteristics, carbon source utilization ability, and biosafety of the strains were investigated. The fermentation flavor contributions of the strains were evaluated through sensory assessment and electronic nose technology. Results Forty yeast strains were isolated and purified from Xinjiang traditional milk wine starter and traditional fermented dairy products. After multiple rounds of screening, two strains (J17 and J23) with excellent functions were obtained, tolerating pH 2.5, 350 g/L glucose, and 47.34 g/L ethanol. They were identified as Kluyveromyces marxianus and Pichia kudriavzevii,respectively. The growth curves of the two strains showed that the logarithmic phase began at the time point of 4 h and the stationary phase started at 12 h and 18 h, respectively. The co-culture test confirmed no antagonistic effects and demonstrated symbiotic relationships between the two strains. Carbon source utilization tests indicated that both strains efficiently utilized seven carbon sources, including glucose, lactose, and sucrose, demonstrating strong metabolic adaptability. Biosafety testing revealed that neither strain exhibited hemolytic activity and was sensitive to antifungal drugs such as ketoconazole, meeting the safety standards for food fermentation strains. Electronic nose analysis revealed that the 1:1 mixed strain (HJ) fermentation of milk wine substrate exhibited significantly higher response values for flavor compounds such as alkanes, sulfides, alcohols, and aldehydes/ketones than the single-strain fermentation groups and controls. Both the cumulative contribution rate of PCA and the cumulative discriminant rate of LDA reached 99.97%. Sensory assessment demonstrated that the HJ fermented milk wine scored higher than that of other strain combinations in four dimensions: appearance, aroma, taste, and style. Conclusion K. marxianus J17 and P. kudriavzevii J23 demonstrate high tolerance, broad-spectrum carbon source utilization ability, excellent biosafety, and synergistic aroma enhancement, showing the potential as specialized fermentation agents for milk wine production and providing high-quality microbial resources for the fermentation of traditional milk wine.

Kitchen waste contains recalcitrant lipids that are prone to rancidification and can cause environmental pollution. Objective To isolate efficient lipase-producing strains from kitchen waste, optimize their enzyme production conditions, and evaluate the lipid-degrading potential of their extracellular products in kitchen waste. Methods Lipase-producing strains were isolated from canteen swill via the neutral red medium and identified based on morphological characteristics and 16S rRNA gene sequences. Lipase production conditions were optimized through single-factor experiments and response surface methodology. The properties of the lipase and the emulsification performance of extracellular polymeric substances (EPS) were analyzed. Results A strain designated C24202, exhibiting strong lipase- and biosurfactant-producing activity, was isolated and identified as Stenotrophomonas maltophilia. The fermentation conditions were optimized as follows: lactose 10.0 g/L, yeast extract 7.5 g/L, emulsified soybean oil 40.0 g/L, FeSO₄ 8.0 g/L, and incubation at 34 ℃ and initial pH 6.5 for 72 h. Under these conditions, the lipase activity reached (229.64±2.17) U/mL, representing a 2.55-fold increase compared with the pre-optimization level. The lipase exhibited an optimal temperature of 60 ℃ and retained 50.70% of its activity after incubation at 50 ℃ for 6 h, demonstrating good thermal stability. The EPS produced by strain C24202 showed strong emulsifying capacity, with an EI₂₄ value of 46.92%. FTIR analysis suggested that the EPS may be polymeric glycolipopeptide-type biosurfactants. Conclusion Strain C24202 possesses dual capabilities of producing thermostable lipase and biosurfactants, demonstrating promising potential for lipid degradation and the treatment of oil-containing wastewater.

Objective To explore microbial resources suitable for the ecological restoration of saline-alkaline soils and elucidate their stress tolerance and plant growth-promoting traits, thereby providing a theoretical basis for biotechnology-driven sustainable agricultural development. Methods Plant growth-promoting rhizobacteria (PGPR) were isolated and screened from the rhizosphere soils of three representative halophytes—Tamarix ramosissima, Lycium ruthenicum, and Kalidium foliatum—growing in the Minqin Oasis, Gansu Province, northwestern China. Selected strains were taxonomically identified by 16S rRNA gene sequence analysis. Their functional traits were systematically evaluated, including nitrogen fixation, phosphate solubilization, and production of indole-3-acetic acid (IAA), exopolysaccharides (EPS), and siderophores. In addition, stress tolerance under salinity, drought, pH, and temperature gradients, as well as antagonistic activity against six common phytopathogenic fungi, was assessed. Results A total of 62 bacterial isolates were obtained, among which seven multifunctional PGPR strains (HL3, HL6, HL12, HG3, HG8, HG12, and HG24) were selected and identified as Priestia filamentosa, Bacillus atrophaeus, Pantoea endophytica, Peribacillus frigoritolerans, Bacillus aryabhattai, Bacillus subtilis subsp. stercoris,and Paenibacillus peoriae, respectively. All the selected strains exhibited at least two plant growth-promoting traits. Notably, strains HL6 and HG24 simultaneously possessed nitrogen-fixing ability, phosphate-solubilizing capacity, and the ability to produce IAA, EPS and siderophores, showcasing pronounced multifunctionality. Stress tolerance assays showed that strains HL3 and HL6 tolerated up to 12% NaCl, while HL3 and HG8 withstood osmotic stress equivalent to -20 bar. Most strains remained active under alkaline conditions (pH 9.0) and within a temperature range of 28-45 ℃. Antagonistic assays revealed that HL6 inhibited all six tested phytopathogenic fungi, and HG24 exhibited broad-spectrum antagonistic activity against five pathogens, with the strongest inhibition observed against Alternaria solani. Conclusion This study demonstrates that PGPR isolated from the rhizosphere of halophytes in arid regions possess diverse plant growth-promoting functions and strong stress tolerance. These multifunctional and resilient strains represent valuable microbial resources for saline-alkaline soil remediation and the development of locally adapted biofertilizers, contributing to sustainable agriculture and ecological restoration in arid environments.

Objective To isolate and characterize plant growth-promoting rhizobacteria (PGPR) from the roots of the rice variety YTZ and the backcross progeny H8 with tolerance to low nitrogen and low phosphorus, and evaluate the potential of PGPR in promoting the growth of rice seedlings. Methods Bacterial strains were isolated by plate streaking and taxonomically identified through 16S rRNA gene sequencing. Functional traits, including phosphate solubilization, nitrogen fixation, and indole-3-acetic acid (IAA) production, were assessed for strain selection. Whole-genome sequencing was performed to mine functional genes and elucidate potential molecular mechanisms of target strains. Pot experiments were conducted to evaluate strain effects on the physicochemical properties of soil and nutrient (nitrogen and phosphorus) uptake of seedlings, while 16S rRNA gene amplicon sequencing was employed to analyze rhizosphere microbial community dynamics. In addition, synthetic microbial consortia and carrier combinations were developed and assessed for application feasibility. Results Seven strains with phosphate-solubilizing and nitrogen-fixing capabilities were obtained, and their IAA production was quantitatively determined. Five representative strains were selected for pot experiments. Among them, B. altitudinis Hxx04 exhibited the strongest plant growth-promoting effect, increasing the fresh weight by 47.2% and plant height by 48.6%, while significantly enhancing nitrogen and phosphorus uptake efficiency of rice seedlings. Inoculation with Hxx04 led to marked reductions in soil total nitrogen, alkali-hydrolyzable nitrogen, total phosphorus, and available phosphorus, indicating improved nutrient uptake by rice plants. Rhizosphere community analysis revealed increased microbial abundance following inoculation, which supported the nitrogen supply for seedling growth. Furthermore, a synthetic microbial consortium centered on B. altitudinis Hxx04 performed optimally when being inoculated with the carrier combination of bentonite and straw. Conclusion B. altitudinis Hxx04 demonstrated high efficiency in nitrogen and phosphorus utilization and significantly promoted rice growth (evidenced by increased fresh weight and plant height), thereby reducing chemical fertilizer dependence. Its dual contribution to yield enhancement and environmental sustainability highlights its potential as a valuable microbial resource for green agriculture, supporting the goal of coordinating nutrient use efficiency with ecological conservation in rice production.