[Objective] To explore the diversity of culturable bacteria in the mudflat sediments of the Pearl River Estuary in Guangdong Province and to mine strain resources capable of degrading microplastics from these sediments. [Methods] Five media were used for microbial isolation, and phylogenetic analysis was performed by MEGA-X software. The polyethylene terephthalate (PET) medium was selected to screen PET microplastic-degrading strains, and then gene function annotation was performed. [Results] A total of 265 bacterial strains belonging to 71 genera, 32 families of 4 phyla were isolated, including 168 (63.40%) strains of Pseudomonadota, 38 (14.34%) strains of Actinomycetota, 31 (11.70%) strains of Bacillota, and 28 (10.56%) strains of Bacteroidota. Based on the homology of 16S ribosomal RNA (16S rRNA) gene sequences, it was hypothesized that 59 of these strains might be potential new species. From the isolated strains, one PET microplastic-degrading strain was screened. [Conclusion] This study successfully obtained unique microbial resources from the tidal flats of Xiangzhou District, Zhuhai City and one strain capable of degrading PET and using PET as the sole carbon source.

The karst seasonal rainforest of northern tropics in Guangxi is a unique forest ecosystem in China. However, the soil microbial diversity and its maintenance mechanism remain unclear. [Objective] This study explored the distribution characteristics and influencing factors of soil bacterial diversity in a karst seasonal rainforest of northern tropics, aiming to provide a reference for analyzing soil microbial diversity and its maintenance mechanisms in this region. [Methods] Soil samples were collected from a long-term dynamic monitoring plot in the karst rainforest of northern tropics (referred to as the Nonggang plot). The composition and distribution pattern of soil bacterial community were analyzed by 16S rRNA gene amplicon sequencing, and the potential influencing factors were identified by the correlation analysis. [Results] The soil in Nonggang plot harbored a total of 5 841 bacterial operational taxonomic units (OTUs), which were annotated to 1 501 species belonging to 677 genera, 373 families, 242 orders, 104 classes of 35 phyla. The dominant bacterial phyla were Proteobacteria, Actinobacteriota, and Acidobacteriota. The dominant bacterial phylum was Proteobacteria in both the depression and the slope habitats, and Actinobacteriota in the hilltop habitat. The number of total and specific bacterial OTUs displayed a pattern of depression>slope>hilltop habitats. The hilltop habitat association had the fewest total OTUs but the most specific OTUs. The soil bacterial alpha diversity indexes (Chao1, Sobs, Shannon, and Simpson) were not significantly different between the depression and slope habitats, while they were significantly lower in the hilltop habitat. Similarly, the hilltop habitat association had the lowest bacterial alpha diversity indexes than the other associations. The principal coordinate analysis (PCoA) of beta diversity showed differences in the bacterial communities among different habitats and associations. The linear discriminant analysis effect size (LEfSe) identified more differential groups in the depression and hilltop habitats than in the slope habitat. The Spearman correlation analysis, Mantel test and redundancy analysis (RDA) indicated that elevation was the primary factor influencing the distribution of soil bacteria in Nonggang plot, followed by soil organic carbon, available nitrogen, and available phosphorus. Tax4Fun predicted that there were significant differences in the function of soil bacterial communities among different habitats and associations, especially in the hilltop habitat. [Conclusion] This study revealed the community composition and diversity distribution pattern of soil bacteria in Nonggang plot and identified elevation as the primary factor affecting the distribution. These results contribute to the understanding of soil bacterial diversity and its maintaining mechanism in the karst seasonal rainforest of the northern tropics in Guangxi.

[Objective] To explore the diversity of halophilic bacteria in the magnesium sulfate-subtype Da Qaidam Salt Lake, compare the effects of different culture conditions on the diversity of halophilic bacteria, and screen the extracellular functional enzymes of halophilic bacteria. [Methods] Illumina MiSeq was used to analyze the diversity of bacteria in the Da Qaidam Salt Lake. Thirteen media, 2 salinities, 8 enrichment culture periods, and 6 dilution gradients were selected to isolate halophilic bacteria, and the taxonomic status of the strains was determined by 16S rRNA gene sequencing and BLAST sequence alignment. According to the sequencing results, 45 representative strains of different species belonging to 18 genera were selected and 7 media were used to screen the strains with activities of functional enzymes including protease, cellulase, amylase, and esterase. [Results] A total of 244 bacterial OTUs were obtained by culture-free high-throughput sequencing in the Da Qaidam Salt Lake. The strains with clear taxonomic status were annotated to 153 genera, 133 families, 92 orders, 53 classes of 19 phyla, with Pseudomonadota and Actinomycetota being the dominant phyla. A total of 593 strains of halophilic bacteria were isolated from the mixed water and mud samples of the Da Qaidam Salt Lake, belonging to 22 genera, 12 families, 8 orders, 5 classes of 4 phyla, of which 11 strains may belong to potential new species. Pseudomonadota and Bacillota were the dominant phyla, and Halomonas, Virgibacillus, and Bacillus were the dominant genera. The number of halophilic bacteria isolated under the culture with 10% NaCl was significantly higher than that with 18% NaCl, indicating that moderately halophilic bacteria were dominant among culturable halophilic bacteria. The media with better isolation performance were 2216E, 1/2 R2A, 1/10 2216E, and 1/10 TSA, all of which are oligotrophic media. The optimal enrichment culture periods ranged from 7 to 30 days. The undiluted samples obtained the best isolation results, followed by dilution gradients of 10^-1 and 10^-2. Among the 45 representative strains, 40.0%, 31.1%, 40.0%, and 82.22% of the strains had activities of protease, cellulase, amylase, and esterase, respectively. [Conclusion] Optimization of the isolation and culture conditions can significantly improve the diversity of halophilic bacteria that can be cultured in salt lakes. The high diversity and high halophilic enzyme activities of the culturable halophilic bacteria from the Da Qaidam Salt Lake provide a basis for further application of these halophilic bacteria.

The high salt concentration of Emerald Lake in Mangya, Qinghai Province, makes it an ideal environment for mining halophilic (halotolerant) microorganisms. [Objective] To mine the halophilic (halotolerant) microbial resources in the Emerald Lake, compare the morphological characteristics of halophilic (halotolerant) bacteria exposed to different concentrations of NaCl, and explore the response of halophilic (halotolerant) microorganisms to NaCl stress. [Method] Lake water, lake salt, and lakeshore saline soil samples were collected from the nearshore area of the Emerald Lake. The halophilic (halotolerant) bacteria were isolated by eight different media with three salt concentrations (10%, 15%, and 20%). The colony morphology, cell morphology, and internal structures of three strains of halophilic (halotolerant) bacteria exposed to different concentrations of NaCl were observed by optical microscopy, scanning electron microscopy, and transmission electron microscopy, respectively. [Results] A total of 58 strains of halophilic (halotolerant) bacteria were isolated, including 31 strains of halotolerant bacteria and 27 strains of halophilic bacteria, belonging to 16 genera. Halobacillus (40.7%) and Bacillus (19.3%) were the dominant genera of halophilic bacteria and halotolerant bacteria, respectively. The strains tolerant to Na⁺, Mg²⁺, K⁺, and Ca²⁺ accounted for 84.5%. The cell lengths of Virgibacilluslitoralis TRM 83602 and Piscibacillussalipiscarius TRM 83622 exposed to different concentrations of NaCl were significantly different, while that of Brevibacteriumepidermidis TRM 83610 did not change significantly. [Conclusion] The Emerald Lake harbors abundant halophilic (halotolerant) bacteria. NaCl concentrations can affect the growth, reproduction, colony morphology, cell morphology, and internal structures of halophilic (halotolerant) bacteria. This study enriches the understanding about the microbial resources in the Emerald Lake, providing abundant strain resources for further development and utilization of halophilic (halotolerant) microorganisms.

[Objective] To investigate the structural characteristics of microbial communities in the soil samples with varying salt types and their associations with salt ions, thus laying a theoretical foundation for the amelioration of saline-alkali soil. [Methods] Soil samples were collected from three regions: Shijiazhuang (LC), Hengshui (SZ), and Cangzhou (HX) at 38°N. The total soluble salt content (TSS), salt ions, enzyme activities, and microbial community structures were measured. Mantel analysis was performed to examine the correlations between soil salt characteristics and microbial community structures. [Results] In the LC, SZ, and HX regions, the levels of soil electric conductivity, TSS, Na⁺, Cl^-, SO₄^2-, and NO₃^- showed a significant increasing trend, while the activities of four soil enzymes (invertase, alkaline phosphate, urease, and catalase) exhibited significant decreases, indicating that nutrient cycling was inhibited in saline-alkali soil. The β diversity of bacteria and fungi exhibited significant differences among the soil samples of three salt types. The α diversity of both bacteria and fungi in SZ showed significant differences from that in LC. In HX, the abundance of halophilic phyla such as Gemmatimonadota and Myxococcota, as well as the taxa with the function of ureolysis, significantly increased, while that of nitrogen-fixing taxa decreased. Mantel analysis indicated that salt ions such as Na⁺ and Cl^- had significantly negative correlations with microbial community composition but positive correlations with halophilic bacteria, such as Gemmatimonadota. [Conclusion] Microbial communities in the soil samples with different salt types exhibited significant differences. Salt ions drove structural changes of microbial communities in soil by inhibiting non-halophilic microorganisms and selectively enriching halophilic species. The alterations in microbial communities and the reduction in soil enzyme activities are key factors contributing to the impairment of nutrient cycling and supply in saline-alkali soil. This study lays a theoretical foundation for the regulation of key microbial populations in the amelioration of saline-alkali soil.

Fruiting bodies represent pivotal resources with medicinal and edible values, hosting a diverse array of microbes. Although studies have elucidated the composition and structures of bacterial communities inhabiting fruiting bodies, the diversity and biological functions of fruiting body-associated microbes remains elusive. The symbiotic associations between fruiting bodies and their microbial inhabitants play integral roles in promoting the growth, enhancing the adaptation to environmental stresses, and facilitating the accumulation of secondary metabolites of host fungi. Additionally, these fruiting body-associated microbes exhibit promising biomedical properties, including antibacterial, antioxidant, and anti-tumor activities. This paper reviews the recent advancements in the isolation and cultivation techniques of these associated microbes, delineates the diversity of associated bacteria, actinomycetes, and fungi, elucidates their biological activities, and provide insights into the intricate interactions between associated microbes and their host fungi. This review offers avenues for the future research and utilization of fruiting body-associated microbes.

Plant endophytes are non-pathogenic microbial groups residing inside or in the interstices of plant tissue. They constitute a pivotal component of the plant microecological environment. These organisms are distinguished by their remarkable biodiversity and wide distribution across diverse regions of the host plant. Plant endophytes exhibit high species diversity, host plant diversity, habitat diversity, and functional diversity. They can secrete hormones that regulate plant growth and enhance the nutrient absorption capacity of their hosts to promote plant growth. Additionally, endophytes can promote plant growth indirectly by enhancing the host plant resistance to abiotic and biotic stresses. Notably, these endophytes are capable of producing substantial secondary metabolites, which exhibit antimicrobial, antiviral, antioxidant, and other biological activities. This capacity offers considerable potential for the development of novel pharmaceuticals, the extraction of natural products, and the creation of biopesticides. Endophytes have a wide range of applications in agriculture, industry, and medicine. They can be used as biocontrol agents to enhance crop yields or used for the production of natural pigments and perfumes and the development of novel pharmaceuticals. However, the research on plant endophytes still faces many challenges in species identification and function verification, molecular mechanism analysis of endophyte-host interactions, practical application technology, and safety evaluation.

Tomato bacterial wilt caused by Ralstonia solanacearum seriously affects the yield and quality of tomato and brings serious economic losses and challenges to the tomato planting industry. [Objective] To achieve efficient biocontrol of tomato bacterial wilt by Streptomyces, providing a solid theoretical foundation for the development of biocontrol agents. [Methods] Six biocontrol strains of actinomyces (AB_1 to AB_6) exhibiting potent inhibitory activities against R. solanacearum were isolated from soil samples. The morphological, physiological, biochemical, and taxonomical characteristics of these strains were determined. Additionally, the extracellular enzyme activities and rhizosphere colonization abilities of the strains were analyzed. Furthermore, a greenhouse pot experiment was conducted to evaluate the biocontrol efficacy of these strains against tomato bacterial wilt. [Results] The inhibitory zone diameters of the strains against R. solanacearum ranged from 1.76 cm to 6.76 cm. Comparative analysis of the 16S rRNA gene sequences revealed that all the six strains belonged to the Streptomyces. The sequence similarities between strain AB_1 and Streptomyces gardneri, AB_2 and S. pratensis, AB_3 and S. diastatochromogenes, AB_4 and S. canus, AB_5 and S. albiflavescens, and AB_6 and S. gramineus were 98.67%, 97.59%, 97.33%, 96.54%, 96.94%, and 97.34%, respectively. Pot experiments demonstrated that these six Streptomyces strains prevented tomato bacterial wilt with the efficacy ranging from 69.23% to 100.00%. All the six strains successfully colonized the tomato rhizosphere and exhibited activities of diverse extracellular enzymes including esterase, amylase, and urease. Additionally, they displayed extensive utilization of carbon and nitrogen sources along with robust tolerance towards variations in pH and salt concentrations. [Conclusion] The six strains of Streptomyces exhibited remarkable environmental adaptability and demonstrated efficient colonization in the tomato rhizosphere. Moreover, they displayed potent antagonistic activity against tomato bacterial wilt in pot experiments. These findings align with the principles of sustainable agriculture and provide both theoretical and experimental evidence for utilizing Streptomyces as a preventive and management strategy against tomato bacterial wilt.

[Objective] To better control the pollution of nitrate and sulfide in mariculture tailwater and reduce the ecological risks caused by the discharge of the tailwater, this study screened a halotolerant desulfurizing and denitrifying bacterial strain and studied its growth characteristics. [Methods] A dilution coating-repeat dish sandwish culture method was used to isolate and screen halotolerant desulfurizing and denitrifying bacterial strains, which were identified by morphological observation and 16S rRNA gene sequence comparison. Based on single factor experiments, the key factors affecting desulfurizing and denitrifying effects, including carbon source, temperature, salinity, pH, and inoculation amount, were optimized, and the strain tolerance threshold to sulfide (S^2-) was explored. [Results] A strain Stutzerimonas stutzeri D1-2 was isolated from sulfur-based mixotrophic denitrifying sludge. This strain was able to simultaneously remove sulfide and nitrate from the environment with organic carbon sources. With sodium lactate as the optimal carbon source, strain D1-2 showed the best performance at an inoculation amount of 1.5%. The strain showed the removal rates of S₂O₃^2- and NO₃^--N both greater than 80% at 15-35 ℃, salinities of 10‰-50‰, and initial pH 6.0-8.0. It demonstrated significant tolerance at an initial S^2- concentration of 50 mg/L, with the removal rates of S^2- and NO₃^--N reaching 97.91% and 94.67%, respectively. [Conclusion] This study reports the heterotrophic sulfur-oxidizing capacity of S. stutzeri. The halotolerant strain S. stutzeri D1-2 capable of simultaneously desulfurizing and denitrifying has a potential application value in the control of sulfide and nitrate pollution in mariculture tailwater.