Objective To prepare the chlamydospore wettable powder with significant control efficacy against tomato bacterial wilt from Cladophialophora guangxiense HX2, a dark septate endophyte (DSE). Methods Single-factor experiments were carried out to screen the types and dosages of carriers, wetting agents, dispersants, and ultraviolet protectants for the wettable powder. Pot experiments were conducted to evaluate the effects of soaking tomato seeds with four concentrations (T1: 1×10⁸ CFU/mL; T2: 1×10⁷ CFU/mL; T3: 1×10⁶ CFU/mL; T4: 1×10⁵ CFU/mL) for 30 min on tomato plant growth, tomato bacterial wilt, and activities of five defense enzymes—peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonialyase (PAL), catalase (CAT), and superoxide dismutase (SOD). Results The formulation was optimized as follows: 25% chlamydospore suspension, 8% dispersant polyethylene glycol (PEG8000) and wetting agent Tween-60 at a mass ratio of 1:3, 0.5%-1.5% UV protectant ascorbic acid (VC), and white carbon black as the carrier to make up the remaining proportion to 100%. The wettable powder prepared according to this formulation had the chlamydospore content of 2.35×10⁸ CFU/g, the wetting time of 24.25 s, a suspension rate of 73.8%, pH 5.71, the moisture content of 16.67%, and the fineness of 98.81%. All indicators met the requirements of the national standard GB 20287—2006 Microbial Inoculants in Agriculture. The results of pot experiments indicated that the T2 treatment exhibited a significant plant growth-promoting effect, increasing the root length, plant height, stem diameter, fresh weight, and dry weight by 47.39%, 31.82%, 24.64%, 89.45%, and 90.97%, respectively, compared with the control group. On day 30 after pathogen inoculation, the control efficacy of this treatment against tomato bacterial wilt reached 50.9%, which was significantly higher than that of the Trichoderma harzianum treatment. Moreover, the T2 treatment significantly enhanced the activities of the five defense enzymes. Conclusion The HX2 chlamydospore wettable powder prepared in this study has good control efficacy against tomato bacterial wilt. This study provides a technical basis for the large-scale popularization and application of this agent.

Excessive nitrogen input caused by eutrophication in nearshore waters is a major environmental stressor driving the global degradation of seagrass beds. Objective To screen and identify efficient aerobic denitrifying bacteria from seagrass bed ecosystems and elucidate their nitrogen removal performance and mechanisms, thus providing microbial resources for alleviating nitrogen loading and restoring eutrophic seagrass beds. Methods Aerobic denitrifying bacteria were isolated and screened from seagrass rhizosphere sediments in Zhifu Bay, Yantai by enrichment-domestication culture and bromothymol blue assay. The taxonomic status of the strains was determined by 16S rRNA gene sequencing. On the basis of nitrogen removal performance, an efficient aerobic denitrifying strain was selected. Single-factor and orthogonal experiments were conducted to optimize its denitrification conditions, and nitrogen balance experiments and whole-genome sequencing were employed to elucidate its nitrogen removal pathways and key functional genes. Results A total of 34 denitrifying strains were isolated from seagrass rhizosphere sediments in Zhifu Bay, Yantai. The dominant genera were Pseudomonas and Acinetobacter. A strain designated as Pseudomonas sp. S22 with high denitrification performance was selected. The denitrification conditions of this strain were optimized as follows: sodium succinate as the carbon source, C/N=15, pH 9.0, salinity (S)=30‰, and T=28 ℃. Under these conditions, the strain achieved a removal rate of 99.99% for 140 mg/L nitrate nitrogen within 36 h, demonstrating excellent nitrogen removal efficiency. Nitrogen balance analysis revealed that approximately 59.64% of the initial nitrate nitrogen was converted to gaseous nitrogen, confirming that denitrification was the dominant nitrogen removal pathway. Genomic sequencing revealed that strain S22 carried key functional genes for aerobic denitrification, including napA and nirS, providing a genetic basis for its denitrification phenotype at the molecular level. Conclusion This study systematically isolated and identified aerobic denitrifying bacteria from seagrass beds in northern China. Strain S22 exhibits outstanding nitrogen removal performance and environmental adaptability. Nitrogen balance and genomic analyses confirm that denitrification is its primary nitrogen removal pathway and the strain carries key functional genes for aerobic denitrification. Strain S22 can serve as a potential microbial resource for reducing nitrogen loading in seagrass beds. This study provides both a valuable strain and a theoretical basis for the future development of microbe-seagrass synergistic remediation technologies.

Objective To address the problems of rhizospheric microenvironment deterioration and medicinal quality decline caused by continuous cropping obstacles of Fritillaria unibracteata Hsiao et K. C. Hsia, this study explored the regulatory effects of different concentrations of salicylic acid (SA) under continuous and non-continuous cropping patterns and clarified the optimal SA concentration and underlying mechanism for alleviating continuous cropping obstacles, aiming to provide a theoretical basis for optimizing cultivation techniques. Methods A pot experiment was conducted with two cultivation patterns (continuous cropping and non-continuous cropping) and six SA concentration gradients (0, 20, 50, 100, 200, and 500 μmol/L). The changes in root exudates, soil physicochemical properties, soil enzyme activities, alkaloid content, and microbial community structure were determined. Correlation analysis and redundancy analysis (RDA) were performed to elucidate the regulation mechanism. Results SA exerted significant concentration-specific regulatory effects on the rhizospheric microenvironment and alkaloid biosynthesis of F. unibracteata, showcasing a significant interaction effect with cultivation patterns. Total phenolic acids in root exudates increased under 20 μmol/L and 500 μmol/L SA treatments (P<0.05), and organic acids reached the peak under 200 μmol/L SA treatment. The soil organic carbon and soil organic matter in the non-continuous cropping group were significantly higher than those in the continuous cropping group. SA at 50 μmol/L optimized soil pH, increased the supply of available phosphorus and ammonium nitrogen, and enhanced the activities of urease and acid phosphatase. Pseudomonadota and Ascomycota were the dominant phyla in bacterial and fungal communities, respectively. SA at 500 μmol/L enriched beneficial microorganisms such as Streptomyces, inhibited pathogens, and specifically increased the content of peimisine and sipeimine. RDA results showed that SA remodeled the microbial community by regulating the composition of root exudates, thereby mediating alkaloid biosynthesis. Conclusion SA at 50 μmol/L SA is suitable for optimizing rhizosphere nutrient supply and enzyme activities, and that at 500 μmol/L is suitable for effectively alleviating continuous cropping obstacles and promoting the accumulation of medicinal alkaloids. SA achieves rhizospheric ecological restoration and medicinal quality improvement through a synergistic pathway of regulating root exudate composition, remodeling microbial community structure, and repairing rhizospheric interaction network. This study provides a new approach for the management of continuous cropping obstacles for F. unibracteata.

Objective The microbial communities preserved within vertebrate bone remains serve as crucial biological archives recording their burial processes and environmental histories. However, how bone microbial communities respond to environmental changes across different geographical and chronological scales, as well as their specific indicative potential in paleoenvironmental reconstruction, remains unclear. This study aims to reveal the spatio-temporal variation patterns of vertebrate bone microbial communities in northern China and evaluate their feasibility as paleoenvironmental biomarkers. Methods Ancient DNA extraction and shotgun metagenomic sequencing techniques were employed to analyze the microbial community composition of 43 animal bone fossil or subfossil samples collected from different geographical regions (Northeast and Northwest China) and geological periods (Late-Pleistocene and Holocene) in northern China. Diversity statistics and differential species identification were combined to systematically compare the spatio-temporal variation characteristics of community structures. Results Microbial communities exhibited significant differences across both geographical regions and geological periods. Samples from Northeast China showed higher microbial diversity, being dominated by soil-derived taxa such as Acidobacteria sp. GGB63485, while samples from Northwest China were dominated by freshwater and chemoautotrophic taxa including Curvibacter and Sulfuricaulis. Cold-tolerant and oligotrophic taxa were enriched in Late-Pleistocene samples, while taxa associated with aquatic environments and plant degradation were more prominent in Holocene samples. Conclusion The compositional differences of microbial communities in bone remains are jointly driven by local environmental factors and temporal climate change. The structural characteristics can effectively reflect paleoenvironmental conditions including soil type, hydrological status, redox potential, and temperature changes. This study provides empirical evidence and methodological approaches for paleoenvironmental reconstruction with skeletal microbiomes, expands the boundaries of traditional paleoenvironmental indicator systems, and offers new perspectives for understanding the assembly mechanisms and ecological responses of microbial communities during long-term burial.

Objective To screen the microbial strains capable of efficiently activating soil cadmium, addressing the technical bottleneck of low efficiency in cadmium-contaminated soil remediation by hyperaccumulators. Methods Farmland soils with potential Cd contamination were collected from various locations in Hunan Province. Acid-producing bacteria were initially screened via the bromocresol purple discoloration method. The pH of the fermentation broth, cadmium chloride tolerance, and cadmium carbonate activation capacity were compared among strains to identify dominant strains, which were then subjected to species identification. On this basis, bacterial strains with application potential were further screened. The desorption effect of the selected strain on soil cadmium under different carbon and nitrogen sources was investigated through shake flask experiments. Pot experiments were carried out to analyze the activation effect on soil cadmium under different nutrient conditions. Results A total of 372 acid-producing bacterial strains were isolated via the bromocresol purple discoloration method. Through comprehensive screening based on the ratio of the discoloration zone diameter (D) to the colony diameter (d) on solid plates, fermentation broth pH, cadmium chloride tolerance, and cadmium carbonate activation assays, four elite strains, designated HT-B1, HTQ-B1, QBS-B2, and MY-B1, were selected. They were identified as Staphylococcus epidermidis, Staphylococcus hominis, Priestia megaterium, and Acinetobacter sp., respectively, based on molecular evidence. In accordance with microbial fertilizer safety standards, strain QBS-B2 was prioritized for further study. This strain exhibited a minimum fermentation broth pH of 3.65 and achieved a cadmium carbonate activation rate of 92.27%. Culture with glucose as the carbon source and ammonium chloride as the nitrogen source were found to be optimal for enhancing cadmium desorption from soil by strain QBS-B2. Under these conditions, the soluble cadmium concentration reached 170.77 μg/L, which was 66.5 times higher than that of the control group, corresponding to a soil cadmium desorption rate of 46.21%. Furthermore, strain QBS-B2 significantly increased the content of available cadmium and available phosphorus in the soil. The application of compound fertilizer enhanced the cadmium activation of QBS-B2, resulting in a soil cadmium activation rate of 17.37%. The application of organic fertilizer significantly promoted the colonization and growth of the strain in the soil and increased the available phosphorus content by 5.9 times compared with the control. Conclusion This study provides elite microbial resources for the development of cadmium-activating microbial inoculants and bio-organic fertilizers based on P. megaterium QBS-B2. Furthermore, it establishes a theoretical foundation and demonstrates application potential for bio-augmented phytoextraction in the remediation of cadmium-contaminated soils.

Objective To determine the composition, diversity, functional metabolic characteristics, and their association with environmental factors of the microbial community in Xiaochaidan Salt Lake, and to evaluate its ecological functions and potential risk as a reservoir for antibiotic resistance genes (ARGs). Methods Metagenomic sequencing was applied to water-sediment mixed samples from the lake. Databases including non-redundant protein database (NR), clusters of orthologous groups of proteins (COG), Kyoto encyclopedia of genes and genomes (KEGG), carbohydrate-active enzymes database (CAZy), and comprehensive antibiotic resistance database (CARD) were used to annotate microbial taxonomy, functional genes, metabolic pathways, and ARGs. Additionally, Hellinger transformation-based principal component analysis (tb-PCA) was conducted to link microbial community structures with environmental factors. Results The salt lake exhibited high microbial diversity (Shannon index: 5.620-6.112), with a total of 16 850 identified species. Bacteria dominated the microbial community (relative abundance of 91.89%), mainly represented by Pseudomonadota (57.22%) and Bacteroidota (14.64%). Archaea (3.77%) were absolutely dominated by Euryarchaeota (92.64%). Siphoviridae and saprotrophic Oomycetes were the most dominant taxa in the viral and eukaryotic communities, respectively. Association analysis with environmental factors demonstrated that bacterial distribution was primarily driven by Cl^-, whereas archaeal community distribution was co-driven by Na⁺, Cl^-, and SO₄^2-. Metabolic functions related to amino acid and carbohydrate metabolism were highly active, as reflected by the enrichment of glycosyltransferase and glycoside hydrolase genes. Notably, diverse ARGs were detected, which were primarily conferred by efflux pump systems (e.g., novA). Conclusion Xiaochaidan Salt Lake harbors a complex and functionally synergistic microbial ecosystem. Local differences in ionic concentrations represent the primary driver of niche differentiation between bacteria and archaea. To adapt to this extreme habitat, indigenous microbes have evolved a strategy that integrates conservative osmoregulation and flexible carbon metabolism. The high abundance of efflux pump-associated ARGs implies that this hypersaline lake serves as a natural reservoir for ARGs, underscoring the potential risk of their ecological dissemination.

Objective To investigate the sedimentary characteristics of dolomite, the bacterial community structure, and their relationships with environmental factors in the sediments of Jibuhulangtu Salt Lake, Inner Mongolia. Methods Sediments were collected from four sites along an offshore-to-nearshore transect in Jibuhulangtu Salt Lake. Bacterial community composition, mineralogical characteristics, and physicochemical parameters of sediments were analyzed by 16S rRNA gene sequencing, X-ray diffraction with Rietveld refinement, and scanning electron microscopy with energy-dispersive spectroscopy, and ion chromatography. Results After removal of soluble salts, the dolomite content in the sediments ranged from 48.75% to 75.28%. The dolomite particles primarily exhibited a nano-spherical shape and transformed from regular spheres to spherical aggregates with the increase in depth. The Mg/Ca molar ratios of the dolomite ranged from 0.87 to 1.46, approaching the stoichiometric value (1.00) of ideal dolomite. At the phylum level, the five most abundant bacterial groups were Actinomycetota, Pseudomonadota, Gemmatimonadota, Chloroflexota, and Acidobacteriota. The sulfate-reducing phylum Desulfobacterota was also abundant (4.23%). Alpha diversity analysis revealed significant differences in bacterial community diversity among sampling sites (P<0.05), with site J4 exhibiting the highest species richness but the lowest evenness. Redundancy analysis indicated that the concentrations of SO₄^2-, Mg²⁺, K⁺, Ca²⁺, Cl^-, and F^- were the key environmental factors significantly shaping the bacterial community structure. Conclusion Dolomite is abundant in the sediments of Jibuhulangtu Salt Lake. Its formation is likely attributable to the extremely high sulfate concentrations and high Mg/Ca ratio of the lake water, as well as the metabolic activities of key functional groups such as sulfate-reducing bacteria.

Objective To isolate and identify secondary metabolites from the deep-sea-derived fungus Talaromyces muroii SCSIO 40439 and evaluate their biological activities. Methods The strain SCSIO 40439 was fermented on a rice medium. The resulting extract was subjected to silica gel column, Sephadex LH-20 column, and semipreparative high performance liquid chromatography (HPLC) to obtain compounds. Structure elucidation was performed via high-resolution electrospray ionization mass spectrum (HRESIMS), nuclear magnetic resonance (NMR), and X-ray crystal diffraction and comparison with literature data. Antimicrobial activity was assessed through the filter paper disk diffusion method, while tyrosinase inhibitory activity was measured based on the rate of dopamine oxidation. Results Four compounds were isolated from the fermentation extract of T. muroii SCSIO 40439, including a new orsellinic acid-cysteine dimer dioscysmycine A (1) and three known polyketides: alternariol (2), altenusin (3), and 3′-hydroxyalternariol 5-O-methyl ether (4). Compound 1 exhibited tyrosinase inhibitory activity with an inhibition rate of 58% (the positive control, kojic acid, showed an inhibition rate of 90%). Compound 2 inhibited the growth of Staphylococcus aureus ATCC 29213 and methicillin-resistant S. aureus ATCC 43300. Conclusion This study expands the known structural diversity of secondary metabolites of Talaromyces and identified a candidate inhibitor for tyrosinase. Furthermore, the findings provide a new biosynthetic gene cluster of alternariol.

Objective To investigate the differences in the structure and function of rhizosphere soil microbial communities between two dominant halophytes—Suaeda salsa and Phragmites australis—in Yuncheng Salt Lake Wetland and to reveal their associations with soil environmental factors, thereby providing a theoretical basis for the ecological restoration of saline-alkali wetlands. Methods Rhizosphere soil samples of S. salsa and P. australis, as well as bare beach soil sample without plant cover, were collected as research objects. Metagenomic sequencing was employed to analyze the microbial community structure and functional genes, and key soil physicochemical properties were determined. Results The total dissolved solids (TDS), pH, and Cl^- concentration in the rhizosphere soils of S. salsa and the bare beach were higher than those in the rhizosphere of P. australis (P<0.05). The microbial diversity and abundance in the rhizosphere soils of both plant species were significantly higher than those in the bare beach soil. The bare beach soil was significantly enriched with the viral phylum Cressdnaviricota, while the rhizosphere soil of S. salsa was significantly enriched with the psychrophilic genus Algoriphagus. Both the rhizosphere soil of S. salsa and the bare beach soil showed co-enrichment of the genera Halomonas and Salegentibacter. TDS was the key factor driving the structures and functional distribution of soil microbial communities, with a contribution rate of 64.40%. Compared with the bare beach, the plant rhizospheres significantly increased the abundance of functional genes related to carbon (e.g., acdB and acs), nitrogen (e.g., gdh_K15371 and nasA), and sulfur (e.g., sudA and dmdB) cycling. Conclusion S. salsa and P. australis shape distinct rhizosphere microenvironments through different survival strategies, which enhance microbial diversity and the abundance of functional genes associated with element cycling, thereby improving the stability and functioning of the saline-alkali wetland ecosystem. This study provides a theoretical foundation for utilizing plant-microbe interactions in the bioremediation and sustainable agricultural use of saline-alkali land.

Objective To explore the regulatory effect of the synergistic and efficient remediation of petroleum-contaminated soil by Rhodococcus sp. OS62 and Pseudomonas sp. P35. Methods High-throughput sequencing was employed to determine the bacterial community structure and diversity during the remediation of petroleum-contaminated soil. Redundancy analysis, non-metric multidimensional scale analysis, Mantel test, and molecular ecological network analysis were performed to evaluate the changes of the soil microbial community structure and the correlations of petroleum degradation efficiency with soil physicochemical factors, soil enzyme activities, and bacterial community structure during the remediation process. Results The addition of the bacterial consortium significantly increased the activities of soil dehydrogenase, lipase, polyphenol oxidase, and catalase and the remediation efficiency, and its remediation effect was better than that of strain OS62 with excellent petroleum degradation ability or strain P35 with weak petroleum degradation ability. Correlation analysis showed that soil petroleum residue was positively correlated with soil total nitrogen and nitrate nitrogen content and negatively correlated with soil enzyme activities and nitrite nitrogen content. The addition of Rhodococcus sp. OS62 or Pseudomonas sp. P35 had mild influences on soil microbial alpha diversity and molecular ecological network. Both strains had great contributions to the differences of bacterial community structure. Under different treatments, Nocardioides occupied a dominant position and were hub nodes in the molecular ecological network, while Mantel test showed that Nocardioides had a weak correlation with soil petroleum residue. Conclusion This study clarified that Pseudomonas sp. P35 with weak petroleum degradation ability could cooperate with Rhodococcus sp. OS62 with high petroleum degradation ability to enhance soil enzyme activities and improve the remediation efficiency of petroleum-contaminated soil. It provides a theoretical basis and practical reference for optimizing the application of bacteria consortium in bioremediation of petroleum-contaminated soil.