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Abstract: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.

Abstract: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.

Abstract: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.

Abstract: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 Virgibacillus litoralis TRM 83602 and Piscibacillus salipiscarius TRM 83622 exposed to different concentrations of NaCl were significantly different, while that of Brevibacterium epidermidis 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.

Abstract: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.

Abstract: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.

Abstract: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.

Abstract: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.

Abstract: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.

Abstract:Objective To screen and identify the plant growth-promoting bacterial strain with saline-alkali tolerance and evaluate its functions.Methods The rhizosphere soil of wheat was collected from different saline-alkali regions, and the highly efficient saline-alkali-tolerant bacterial strain was isolated by enrichment under saline-alkali condition and dilution coating. The antifungal spectrum and plant growth-promoting effects of the isolate were evaluated in vitro, and the nitrogenase activity was measured by an ELISA kit. The strain was identified based on the morphological, physiological, biochemical characteristics and phylogenetic analysis. The effect of the strain on wheat growth under salt stress was investigated by a pot experiment.Results A highly abundant bacterium with saline-alkali tolerance was enriched from rhizosphere soil and designated as TaRb44, which could grow normally under 3% NaCl and pH 10.0. Strain TaRb44 showed strong antagonism against soil-borne pathogenic fungi such as Fusarium pseudograminearum causing wheat crown rot, Fusarium oxysporum f. sp. niveum causing watermelon Fusarium wilt, and Fusarium oxysporum f. sp. cubense causing banana wilt, as well as Botrytis cinerea causing gray mold of postharvest tomatoes. Further tests showed that strain TaRb44 produced a variety of plant growth-promoting substances such as siderophores, amylase, and cellulase, and it had nitrogen fixation activity with the nitrogenase level of 65.50 U/L. Finally, the strain TaRb44 was identified as Paenibacillus polymyxa, which significantly promoted the growth of wheat seedlings and increased the root biomass under both salt stress and non-salt stress conditions.Conclusion In this study, P. polymyxa TaRb44 was obtained with much excellent properties such as disease prevention, plant growth promotion, and saline-alkali tolerance. It serves as an elite strain for developing new microbial fertilizer and soil amendments in the future.

Abstract:Objective To screen out a strain that can degrade lignocellulose for the application of lignocellulose deposited by delayed harvest of alfalfa under inappropriate climate and mechanical matching and provide strain resources for the efficient use of alfalfa. Methods The primary screening was carried out by culture with alkali lignin and sodium carboxymethyl cellulose. Based on color changes and fading circles, the strain with the ability to secrete ligninase and cellulase was screened out. The target strain was identified by 16S rRNA gene sequencing and whole genome sequencing, and then Kyoto encyclopedia of genes and genomes (KEGG) and carbohydrate-active enzymes (CAZy) were employed to annotate gene functions based on the whole genome sequence. The microstructure of the alfalfa stems degraded by the strain was observed by scanning electron microscopy. The nutrient and microbial community changes in alfalfa hay treated with the strain were evaluated. Results A strain S1 producing ligninase and cellulase was identified as Bacillus cereus by whole genome sequencing. A total of 305 genes involved in carbohydrate metabolism were annotated, including 139 genes encoding CAZy. After treatment with this strain, the microstructure of vascular bundles in alfalfa stems changed significantly. The crude protein content in alfalfa hay increased, while the lignin, neutral detergent fiber, and acid detergent fiber content and the alpha-diversity of microorganisms decreased over time. Conclusion The screened strain identified as B. cereus demonstrates a robust ability to degrade lignocellulose.

Abstract:Objective To mine the macrofungal strains capable of efficiently degrading straw at low temperatures, thereby improving the utilization efficiency of straw resources, we measured the lignocellulose degradation abilities of 955 macrofungal strains.Methods First, we employed the plate method to screen the strains with carboxymethyl cellulase, xylanase, and laccase activities. Then, we carried out a filter paper degradation test to screen the cellulose-degrading strains. Finally, we performed liquid fermentation with the selected strains and measured their enzyme activities on days three, six, nine, and 12 to identify the dominant strains with strong lignocellulose-degrading abilities.Results We identified 11 macrofungal strains exhibiting strong lignocellulose degradation capabilities at a low temperature (15 ℃). The 11 strains were Trametes suaveolens, Irpex lacteus, Crucibulum laeve, Stereum hirsutum, Pleurotus ostreatus, Phlebia acerina, Agaricus xanthodermus, Neofomitella fumosipora, Pholiota multicingulata, Abortiporus biennis, and Armillaria cepistipes. Notably, C. laeve, A. xanthodermus, and P. multicingulata were newly reported for their high lignocellulose-degrading abilities. The maximum activities of carboxymethyl cellulase, xylanase, and laccase in the 11 strains reached 262.31, 91.03, and 196.50 U/mL, respectively. T. suaveolens exhibited carboxymethyl cellulase activity of 168.17 U/mL at 15 ℃, which was significantly higher than that (67.88 U/mL) observed at room temperature. P. ostreatus showed the carboxymethyl cellulase activity of 150.78 U/mL and the laccase activity of 154.32 U/mL. S. hirsutum achieved the laccase activity of 63.27 U/mL at 15 ℃, which was twice the level measured at room temperature.Conclusion We successfully identified 11 macrofungal strains with strong lignocellulose-degrading abilities at 15 ℃. The findings provide valuable microbial resources for the degradation of lignocellulose in cold regions and lay a theoretical basis for application of these strains in low-temperature industries.

Abstract:Objective This study isolated and identified an algicidal bacterium from the East China Sea near Wenzhou and investigated its algicidal characteristics and mechanisms, aiming to contribute a solid scientific basis to the microbial control against red tides.Methods The strain was identified by morphological observation, physiological and biochemical tests, and 16S rRNA gene sequence analysis. The algicidal characteristics such as algicidal activity, influences of environmental factors on the algicidal activity, and algicidal specificity were assessed. The algicidal mechanism was explored by electron microscopy, measurements of photosynthetic parameters, and determination of reactive oxygen species (ROS) and malondialdehyde levels and antioxidant enzyme activities.Results The algicidal strain J75 was identified as Pseudoalteromonas sp. The algicidal rate of strain J75 against Skeletonema costatum reached 95.97% within 36 h. Strain J75 induced lysis of algal cells indirectly by secreting extracellular algicidal substances, maintaining the algicidal activity across broad ranges of temperatures (-20 °C to 80 °C) and pH levels (5.0 to 9.0). In addition, strain J75 demonstrated algicidal activities against other harmful microalgae, including Karenia mikimotoi, Prorocentrum minimum, and Phaeocystis globosa. Under the stress of J75 cell-free supernatant, the algal cells showed morphological structure damage, a significant decrease in the photosynthetic activity, elevations in the levels of ROS, membrane lipid peroxidation, activities of superoxide dismutase, catalase, and peroxidase, and the level of glutathione. These results indicated that strain J75 caused oxidative damage to algal cells, ultimately leading to algal death.Conclusion The marine algicidal bacterium Pseudoalteromonas sp. J75, which holds significant potential for the control of red tides, demonstrates its efficacy by secreting algicidal compounds that inhibit the growth of diverse red tide microalgae. The exploration of the algicidal characteristics and mechanisms of this strain provides a theoretical basis for advancing red tide management strategies.

Abstract:Objective The rhizosphere of plants hosts a diverse array of microorganisms that play a crucial role in plant growth and health. This study identified functional bacteria in the rhizosphere soil of an economic bamboo species Indosasa acutiligulata and assessed the effects of synthetic microbial communities (SynComs) on bamboo growth. The results are expected to provide implications for enhancing forest quality and utilizing beneficial microorganisms in bamboo cultivation.Methods Rhizosphere soil samples of In. acutiligulata were collected from the Jiuyi Mountain National Nature Reserve. Bacteria were isolated by the dilution culture method, and a phylogenetic tree was established by the maximum-likelihood algorithm based on 16S rRNA gene sequences. Specific media and colorimetric assays were employed to study the functions of strains. The strains with plant growth-promoting effects and no antagonistic effects between each other were combined. The effects of SynComs on the growth of Phyllostachys edulis seedlings were examined by re-inoculation experiments.Results Seventy strains of rhizosphere bacteria were isolated, representing 35 genera belonging to 21 families of four phyla. The dominant phylum was Pseudomonadota and the predominant family was Burkholderiaceae. Functional analyses revealed that 30 strains produced indole-3-acetic acid (IAA), while 16 strains produced siderophores. Among those with dual functions, there were four strains capable of solubilizing inorganic phosphorus, four strains capable of mineralizing organic phosphorus, and three strains capable of solubilizing potassium. Strains TR5, TN6, and TN26 exhibited capabilities to produce IAA and siderophores, as well as solubilize inorganic phosphorus and mineralize organic phosphorus. They were identified as Burkholderia pyrrocinia, Burkholderia paludis, and Paraburkholderia kirstenboschensis, respectively, based on physiological and biochemical properties and 16S rRNA gene sequences alignments. Re-inoculation experiments demonstrated that the SynCom FH, comprising strains TR5, TN6, and TN26, significantly enhanced the root, leaf, and rhizoma growth of Ph. edulis seedlings.Conclusion The rhizosphere of In. acutiligulata harbors diverse functional microorganisms capable of producing IAA and siderophores, solubilizing phosphorus, and releasing potassium. The re-inoculation experiments confirmed that the SynCom FH promotes the growth of Ph. edulis seedlings.

Abstract:Objective To establish a theoretical foundation for the application and development of chitinases, this study isolated and screened chitin-degrading bacteria from the intestines of amphibians, optimized their fermentation conditions, characterized their enzymatic properties, and analyzed their whole genomes.Methods A strain capable of producing chitinase was isolated from the intestinal contents of Rana kukunoris and identified based on morphological characteristics and molecular biological evidence. The enzyme production conditions of the strain were optimized by single factor and response surface methodology (RSM) experiments, and the enzymatic properties were studied. Whole genome sequencing was carried out for identification of the chitinase gene family.Results The chitin-degrading strain JD-3 was identified as Carnobacterium maltaromaticum. This strain achieved the highest enzyme activity of 12 mU/mL after fermentation with the inoculum amount of 4% at 31.4 ℃ and initial pH 4.9 for 2.47 d. The optimal reaction conditions of the enzyme were 20 ℃ and pH 3.0, and the enzyme maintained good stability at room temperature and under acidic conditions. The genome of JD-3 was 4 195 636 bp long, containing 6 circular contigs, 63 tRNA genes, 19 rRNA genes, and 3 864 protein coding sequences. Two chitinase genes belonging to the glycoside hydrolase family 18 (GH18) were identified and phylogenetically classified into two distinct categories.Conclusion We isolated an acid-tolerant chitin-degrading bacterium, C. maltaromaticum JD-3, from the intestines of plateau amphibians. The findings provide new insights into the development and utilization of microbial resources in the digestive systems of animals.

Abstract:Objective Arbuscular mycorrhizal (AM) fungi are crucial components of the plant rhizosphere microbiota, capable of forming symbiotic relationships with 72% of terrestrial plants. However, AM fungi are plant-specific symbiotic fungi in soil, and they are difficult to be enriched for isolation and achieve artificial pure culture. This study aimed to develop a non-plant symbiotic culture system based on the addition of root exudates to solve the problem of difficult in vitro culture of AM fungi.Methods The “multi-layer sandwich” culture system was used for the in vitro quasi-asymbiotic culture of AM fungal spores from soil. Molecular systematics methods were employed to identify the cultured AM fungi.Results A “multi-layer sandwich” culture system was used for the in vitro quasi-asymbiotic culture of AM fungi from soil. It was found that the root exudates of Astragalus sinicus effectively promoted the hyphal growth of AM fungi. A large number (951±45) of secondary spores were produced after 60 days of culture, exceeding those after 30 days and 45 days of culture. Further spore inoculation tests indicated that the secondary spores produced from this culture colonized the roots of A. sinicus seedlings. Two AM fungal species, Funneliformis mosseae and Paraglomus occultum, were identified by molecular characterization as suitable for the “multi-layer sandwich” culture system. Finally, a nutrient solution composed of simulated root exudate components from A. sinicus was used for the “multi-layer sandwich” culture of AM fungal spores. The results showed that the addition of root exudates significantly promoted the hyphal growth of AM fungi.Conclusion In the plant-assisted “multi-layer sandwich” culture system, the root exudates of A. sinicus can continually induce AM fungi to produce hyphae and secondary spores capable of colonizing host plants under non-symbiotic conditions. This study provides a new method for solving the problem related to the in vitro culture, isolation, and identification of AM fungi.

Abstract:A mutant strain G₉-72 with a high yield of ectoine was obtained from wild type Halomonas campaniensis after nine rounds of ultraviolet mutagenesis. The differentially expressed genes/proteins (DEGs/DEPs) and the molecular mechanism underlying the excessive increase in the ectoine yield remain to be explored for the mutant strain.Objective To explore the DEGs/DEPs between the wild type strain XH26 and G₉-72 and decipher the molecular mechanism of efficient ectoine production by conjoint analysis.Methods A non-salt (NS, 0 mol/L NaCl) group and a high-salt (HS, 1.5 mol/L NaCl) group were designed for the culture of XH26 and G₉-72. Illumina HiSeq and quantitative mass spectrometry were employed to identify the DEGs/DEPs between the two strains by transcriptomics-proteomics conjoint analysis. Furthermore, RT-qPCR was carried out to verify the expression of significant DEGs.Results The transcriptomics analysis revealed 11 amino acid metabolic pathways (44 DEGs) associated with ectoine anabolism, and the proteomics analysis revealed ten amino acid metabolic pathways (50 DEPs) associated with ectoine anabolism. The transcriptomics-proteomics conjoint analysis identified 15 significant DEGs, including seven genes (ectB, betB, betA, asd, doeD, doeC, and gabD) with up-regulated mRNA and protein level, four genes (ItaE, gdhA, gabT, and acnB) with down-regulated mRNA and protein levels, three genes (gltD, atoB, and narG) with down-regulated mRNA levels and up-regulated protein levels, and one gene narK with up-regulated mRNA level and no protein level. Additionally, the RT-qPCR results were consistent with the transcriptomics analysis.Conclusion The excessive increase in the ectoine yield of the mutant strain was associated with key genes in the ectoine metabolic pathway (including the synthesis genes asd and ectB and the catabolism genes doeD and doeC) and indirectly associated with several genes (betB, betA, ItaE, gltD, gadA, and acnB) in the upstream metabolic pathway. Notably, ectoine biosynthesis was highly associated with the Ala/Asp/Glu/His metabolic pathway (gabD, gdhA, gabT, and atoB) and nitrogen source metabolism (narK and narG).

Abstract:Objective To reveal the phylogenetic diversity of 12 marine siderophore-producing bacteria isolated from intertidal sediment samples of Naozhou Island in Leizhou Bay of South China Sea, and to unravel the components, functions, genetic diversity and genetic evolution of siderophore biosynthetic gene clusters (BGCs) of the isolates as well as representatives of Microbulbifer.Methods The phenotypic characteristics as well as the siderophore-producing activity of the strains were observed by conventional methods. The phylogenetic diversity (including taxon, species, and genetic diversity) of the strains was analyzed based on 16S rRNA gene sequences. Then, the exact phylogenetic status of the representative strain JSM ZJ756 was investigated comprehensively by means of comparative genomics analysis based on whole-genome sequences, including comparisons of G+C content, average nucleotide identity (ANI), and digital DNA-DNA hybridization (dDDH) estimated values. We then used multiple bioinformatic stools including antiSMASH 7.0, BLASTn, BLASTp, and MEGA 11 for rapid identification, annotation, and sequence alignment of BGCs, thus exploring the components, functions, genetic diversity, and genetic evolution of siderophore BGCs.Results All the 12 isolates were Gram-negative, aerobic, non-sporulating and slightly halophilic rods with siderophore-producing activity. The results of phylogenetic analyses based on 16S rRNA gene sequences as well as whole-genome sequences showed that all the 12 strains belonged to Microbulbifer, representing 6 to 8 species and forming 4 clades with Microbulbifer type strains in the phylogenetic tree. Among them, strain JSM ZJ756 should be a new member of Microbulbifer zhoushanensis. JSM ZJ756 and 9 representative strains of Microbulbifer each carried one copy of NI-siderophore BGCs, and 8 out of the 10 NI-siderophore BGCs shared the similarities ≤40% with known BGCs. According to the types and the similarities of known BGCs with the NI-siderophore BGCs identified in this study, the 10 NI-siderophore BGCs could be categorized into 5 functional subtypes: Ochrobactin (JSM ZJ756 and 2 type strains, JYFX01000060.1, similarity of 28%), Vibrioferrin (M. mangrove DD-13^T, AB082123.1, 100%; M. epialgicus DSM 18651^T, CP005094.1, 85%), Putrebactin (M. agarilyticus GP101, NIBS01000001.1, 40%), Aerobactin (M. echini JCM 30400^T, AB199785.1, 22%), and unknown functional subtype (3 type strains including M. variabilis ATCC 700307^T). The results of BLASTn and BLASTp analyses showed that the core biosynthetic gene sequences of the NI-siderophore BGCs identified were unique, and encoded novel proteins. The results of genetic evolution analysis showed that the core biosynthetic genes of the NI-siderophore BGCs found exhibited high genetic diversity. In the phylogenetic tree based on core biosynthetic gene sequences, 9 out of the 10 NI-siderophore BGCs were grouped to 3 clades, but M. agarilyticus GP101 exhibited an independent evolution path. The comparative analysis revealed the genetic evolution of NI-siderophore BGCs being consistent with that predicted based on the 16S rRNA sequences.Conclusion All the 12 siderophore-producing strains isolated from intertidal sediment samples of Naozhou Island in Leizhou Bay of South China Sea belong to Microbulbifer, demonstrating high phylogenetic diversity, and JSM ZJ756 is a new member of M. zhoushanensis. The NI-siderophore BGCs of JSM ZJ756 and representative strains of Microbulbifer are novel and showcase high diversity, which indicates that those strains possess high potential of producing a variety of novel siderophores. Moreover, strong positive correlations exist between the biological functions and genetic evolution of the NI-siderophore BGCs and the phylogeny of JSM ZJ756 and 9 representative strains of Microbulbifer. Therefore, we hypothesize that the 12 marine siderophore-producing bacteria and the representatives of Microbulbifer are typical new-resource microbes, and the taxonomy of Microbulbifer, and the metabolic mechanism and genetic evolution as well as the biotechnological potential of the NI-siderophore BGCs are worth being further explored.

Abstract:Objective To screen out a yeast strain that can efficiently assimilate ammonia nitrogen, optimize the solid-state fermentation conditions based on the nutrient composition, antioxidant activity, and amino acid content of the feed, and provide a scientific basis for the production of single-cell protein feed with this yeast strain.Methods Five strains of Candida utilis, four strains of Pichia anomala, five strains of Saccharomyces cerevisiae, and three strains of Issatchenkia orientalis were cultured with (NH₄)₂SO₄ as the sole nitrogen source. The yeast strain with the highest ammonia utilization rate and the highest glutamine synthetase (GS) activity was selected as the test strain, and then the fermentation parameters and fermentation substrates were optimized for this strain. The routine nutrient composition, content of phytate phosphorusand amino acids, and scavenging rates against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline- 6-sulfonicacid) (ABTS) free radicals of the fermented feed were determined.Results C. utilis CJ121 showed an ammonia utilization rate of 55.39% and a GS activity of 0.29 μmol/(h·g), which were higher than those of other yeast strains. The optimal fermentation process for C. utilis CJ12 was fermentation with a (NH₄)₂SO₄ addition amount of 2% and an inoculation amount of 8% for 36 h. The optimal fermentation substrate was composed of 94.8% wheat bran, 5% soybean meal, 0.1% protease, and 0.1% cellulase. After fermentation with C. utilis CJ12, the content of crude protein and organic nitrogen increased by 15.95% and 28.46%, respectively (P<0.05), while that of dry matter, crude fiber, crude fat, and phytate phosphorus decreased by 4.19%, 19.41%, 12.29%, and 13.51%, respectively (P<0.05). The total amino acid content increased after fermentation (P<0.05), with glutamine and glutamic acid levels being 111.38 times and 3.02 times those of the control group, respectively. However, the control group exhibited higher levels of tryptophan, asparagine, and 4-aminobutyric acid, which were 13.41, 8.27, and 6.41 times those of the experimental group, respectively. In addition, the scavenging abilities against DPPH and ABTS free radicals increased after fermentation (P<0.05), with the IC₅₀ values decreasing by 73.51% and 6.01%, respectively (P<0.05).Conclusion C. utilis CJ12 has high capacities of utilizing ammonia nitrogen and synthesizing glutamine. This strain improves the nutritional value and antioxidant performance of feed after solid-state fermentation, thus demonstrating the potential for producing functional single-cell protein feed.

Abstract:Amidst the escalating issues of water eutrophication and water resource scarcity, the development of high-efficiency wastewater treatment technologies has become increasingly imperative. Traditional nitrogen and phosphorus removal processes face challenges in achieving efficient simultaneous elimination of nitrogen and phosphorus due to the disparities in sludge age and the competition for carbon sources among microorganisms. Denitrifying phosphorus-accumulating organisms (DPAOs) possess the capability to remove both nitrogen and phosphorus, demonstrating significant potential in wastewater treatment. However, population-level studies often overlook cellular heterogeneity, leading to an inadequate understanding of the nitrogen and phosphorus removal mechanisms of DPAOs. Moreover, the “traditional culture-first, screen-second” method yields a limited number of efficient DPAO strains, the stability and adaptability of which face challenges in actual wastewater treatment environments. Single-cell analysis technologies provide new perspectives for a deeper understanding of microbial ecological niches and metabolic mechanisms. Coupling non-destructive single-cell phenotypic identification technologies, such as single-cell Raman spectroscopy (SCRS), with the culture method paves new avenues for the exploration of DPAO strains. This review summarizes the research status and progress in the exploration of DPAO strain resources and their metabolic mechanisms, focusing on the potential of single-cell technologies in revealing the mechanisms of nitrogen and phosphorus removal by DPAOs and in the exploration of DPAO resources. The aim is to provide a new theoretical foundation and technical support for the research and application of DPAOs, thereby promoting the development of efficient wastewater treatment technologies.

Abstract:Soybean (Glycine max) is an important cereal and oil crop in the world, and the supply-side structural reform in the agricultural sector requires an increase in the planting area of high-quality edible soybean. Due to the inherent characteristics of arable land resources in China, the domestic production of soybean is far from self-sufficiency, and there is an urgent need to increase the planting area and production of soybean domestically, reducing the dependence on imports. Rhizobia are the earliest developed microbial fertilizer, while their application area is limited in China.Objective To select suitable strains from the stored rhizobia to provide germplasm resources for alleviating food issues.Methods We reviewed taxonomic status of rhizobia preserved in the Agricultural Culture Collection of China over decades based on the 16S rRNA and recA gene sequences. The hydroponic nodulation test was carried out to assess the nodulating and soybean growth-promoting effects based on comprehensive consideration of the nodulation rate, nodule number, nodule weight, plant height, and dry weight.Results A total of 213 strains of soybean rhizobia were activated and identified, including 156 strains of Bradyrhizobium, 48 strains of Sinorhizobium, and 9 strains of Rhizobium. Among them, 149 strains were able to nodulate with soybean cultivar selected in this study, and 43 strains significantly contributed to the growth of soybean plants.Conclusion This study further clarifies the taxonomic status of preserved soybean rhizobia and evaluates their nodulating and plant growth-promoting effects, providing abundant microbial resources for the development of soybean rhizobia-based agents.

Abstract:The preservation and utilization of agricultural microbial resources are essential for achieving green and sustainable agricultural development in China. However, the current state of agricultural microbial resources in China is characterized by a limited total volume, insufficient characterization data, low preservation throughput, poor development, and low sharing efficiency. Establishing and operating advanced agricultural microbial resource repositories can provide high-quality resources for the development of innovative microbial agricultural products and ensure robust sharing of agricultural microbial resources. Based on the construction and operation experience of conventional microbial resource repositories and considering the trends of scientific development in the new era, this paper proposes several insights into the construction and operation of new agricultural microbial resource repositories as a reference for resource repository developers and managers.

Abstract:Aureobasidium spp. are a group of fungi with remarkable ecological adaptability and stress tolerance. They are ubiquitous in natural environments such as plants and can survive under extreme conditions. The genomes of Aureobasidium spp. show specific differentiation characteristics, and the strains have obviously advantage characteristics in fermentation. Aureobasidium spp. can utilize a broad spectrum of carbon sources and produce a rich variety of metabolites. Aureobasidium spp. and their metabolites have significant application potential in fields such as biomedicine, biocontrol, and food processing. This article introduces the distribution, classification, main metabolites, and multidisciplinary applications of Aureobasidium spp. In the future, with the advancement in multidisciplinary fields such as genome editing and intelligent biomanufacturing, Aureobasidium spp. are expected to play an important role in biomanufacturing and sustainable development industries.

Abstract:Edible forest mushrooms are one of the main forest foods and an essential resource for forests to achieve the functions of conserving water, bringing in economic benefits, boosting grain production, and also serving as a carbon sink. This study summarizes the current situation of the edible forest mushroom industry in China, such as benign development with imbalanced regional development, scaled planting under forests but lack of regional characteristics and deep processing products, and the advantages of edible ectomycorrhizal mushrooms with weak scientific and technological support. Suggestions are put forward on optimizing planning, promoting the investment of scientific and technological resources, accelerating digital intelligence and multi-mode development, conducting climate change monitoring, and protecting germplasm resources, in order to make positive contributions to the development of the edible forest mushroom industry and provide scientific and technological support for the practice of the big food concept.

Abstract:Objective To explore the effects of endophytic bacteria in soybean nodules on the growth of soybean seedlings under salt stress and provide reference for the high-quality development of crops in the Yellow River Basin.Methods A pot experiment was conducted with the soybean cultivar ‘Xudou 20’ under artificial climate conditions. Three groups were designed: control, salt stress, and salt stress inoculated with endophytic bacteria. The growth of soybean seedlings in each group was measured.Results Regarding strain 72, in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 200 mmol/L, the activity of catalase (CAT) in the seedlings of 21 days was the highest (2.010 0 U/g FW), which was 54.02% higher than that in the salt stress group; in the case of inoculation with the suspension at OD₆₀₀=0.33 (1:2) and the salt concentration of 300 mmol/L, the proline content was the highest (0.028 6 mg/g); in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 100 mmol/L, the proline content was 64.38% higher than that in the salt stress group. Regarding strain 146, the seedlings of 21 days in the case of inoculation with the suspension at OD₆₀₀=0.50 (1:1) and the salt concentration of 50 mmol/L had the highest CAT activity (1.350 0 U/g FW); the seedlings of 28 days in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 100 mmol/L had the CAT activity 272.73% higher than that in the salt stress group; the seedlings in the case of inoculation with the suspension at OD₆₀₀=0.75 (2:1) and the salt concentration of 150 mmol/L had the highest proline content of 0.147 0 mg/g, which was 860.78% higher than that in the salt stress group. The results indicated that inoculation with the endophytic bacterial strain 72 or 146 had a repairing effect. The increases in the CAT activity and proline content in the soybean seedlings inoculated with strain 146 over those in the salt stress group were generally higher than those in the case of inoculation with strain 72, indicating that the repairing effect of strain 146 was more obvious. The phylogenetic tree built based on 16S rRNA gene sequences showed that strains 72 and 146 had the highest similarity with Bacillus subtilis (99.45%) and B. protolyticus (100%), respectively.Conclusion Inoculating endophytic bacteria was of great significance for alleviating the effect of saline-alkali stress in the Yellow River Basin on the growth of soybean seedlings and developing biological repairing agents.

Abstract:Objective To optimize the anaerobic digestion process for methane production of hulless barley straw with mixed addition of biochar and Fe₃O₄ and investigate the feasibility of mixed addition of biochar and Fe₃O₄ in the anaerobic digestion of lignocellulosic waste.Methods We employed single factor and response surface experiments to optimize the anaerobic digestion process for methane production of hulless barley straw with mixed addition of biochar and Fe₃O₄. Metagenomics was employed to analyze the microbial community structure and methane production pathway during digestion.Results The optimal digestion conditions were 6.32% total solids, biochar-to-Fe₃O₄ ratio of 6.83:3.17, and inoculation ratio (volatile solids ratio of inoculum to hulless barley straw) of 2.51. Under these conditions, the measured value of cumulative methane production based on volatile solids was 269.04 mL/g, with a relative error of less than 5% from the predicted value (265.95 mL/g), which indicated that the model was effective. The mixed addition treatment under the optimized conditions increased the methane production of hulless barley straw (P<0.05), with the effect comparable to that of the chemical pre-treatment. Meanwhile, the treatment increased the acetic acid content while reducing the accumulation of propionic and butyric acids. Metagenomic analysis showed increases in the relative abundance of bacterial taxa such as unclassified_Bacteroidota, unclassified_Bacteria, Clostridium, and Fibrobacter, as well as acetotrophic methanogens such as Methanosarcina and Methanothrix, which promoted the utilization of acetic acid and enhanced the direct interspecies electron transfer (DIET) between microorganisms. The mixed addition of biochar and Fe₃O₄ in the anaerobic digestion system enhanced the acetotrophic methanogenic pathway, thereby enhancing methane production.Conclusion The response surface methodology can optimize the anaerobic digestion process for methane production of hulless barley straw with mixed addition of biochar and Fe₃O₄. The mixed addition of biochar and Fe₃O₄ enables efficient production of biomethane and environmentally friendly treatment of lignocellulosic waste.

Abstract:The fruiting bodies of fungi of genus Shiraia inhabiting bamboo have a medicinal use in traditional Chinese medicine. Hypocrellin A (HA), the main bioactive perylenequinone pigment from S. bambusicola fruiting bodies is a novel non-porphyrin photosensitizer with antitumor and antimicrobial properties.Objective To investigate the effects of Shiraia fruiting body-associated fungi on HA biosynthesis and develop a co-culture method for enhancing HA production.Methods Shiraia fruiting body-associated fungi were isolated and the strains influencing HA biosynthesis were screened by a plate confrontation assay. The effects of intracellular and extracellular metabolites of the strains on HA production were evaluated. A co-culture system for Shiraia sp. S9 and associated fungi was established and optimized for enhancing HA production.Results There were 34 fungal strains including 6 host Shiraia strains isolated from the fruiting bodies. Among them, Fusarium sp. SF12 and its extracellular polysaccharides significantly promoted HA biosynthesis. Fusarium sp. SF12 did not noticeably affect the growth of Shiraia sp. S9 but regulated HA synthesis by upregulating the transcription levels of key enzyme genes involved in HA biosynthesis. The total HA yield was enhanced to 209.46 mg/L on day 8 after adding spores (100 cell/mL) from Fusarium sp. SF12 to the Shiraia culture at the time point of 24 h, which was 1.93 times that of the control.Conclusion There are diverse fungi in Shiraia fruiting bodies. The co-culture of the associated fungus Fusarium sp. SF12 and the host Shiraia sp. S9 is a new technique to improve HA production.

Abstract:Objective Chitin lyases are the key enzymes for bacteria to degrade chitin. Pseudoalteromonas arabiensis N1230-9 possesses five chitin lyase-encoding genes (woc28159, woc28160, woc28161, woc27404, and woc27232). Functional identification of these five genes is crucial for determining the ability of strain to degrade chitin.Methods The distribution patterns of five chitin lyases from strain N1230-9 in 44 model strains of Pseudomonas were analyzed by bioinformatics methods. The transcription levels of five chitin lyase-encoding genes of strain N1230-9 cultured in the medium with chitin as the sole carbon source were analyzed by RT-qPCR. The mutants with deletion of chitin lyase-encoding genes were constructed by homologous recombination, and their abilities to degrade chitin were evaluated.Results Thirty-three Pseudoalteromonas strains possessed chitin lyase homologous proteins of strain N1230-9. Chitin significantly upregulated the transcription levels of woc28159, woc28160, woc28161, and woc27404, and the deletion of each of the four genes weakened the chitin-degradation ability. The transcription level of woc27232 was not affected by chitin, and the deletion of this gene did not affect the chitin-degradation ability of the strain.Conclusion WOC28159 and WOC28161 are necessary for the degradation of chitin by strain N1230-9. WOC28160 and WOC27404 endow strain N1230-9 with efficient chitin-degrading ability, while WOC27232 does not participate in the chitin degradation process.

Abstract:The dinitroaniline herbicide pendimethalin, as a pre-emergent herbicide, is widely employed for weed control in cotton fields across Xinjiang. Characterized by chemical stability, prolonged residual activity, bioaccumulative potential, and biomagnification, it is extensively applied in agricultural practice, leading to increased risks to soil ecosystems. Accordingly, the removal of pendimethalin residues has garnered increasing attention.Objective To enrich the microbial consortia with pendimethalin-degrading ability, study succession characteristics of microbial consortia during the enrichment culture process under pendimethalin stress, and identify the key microorganisms involved in pendimethalin degradation.Methods The cotton field soil under long-term pendimethalin stress was inoculated into MSM media with pendimethalin at 0, 1.2, and 12 mg/L, respectively. The succession of the microbial consortium structure under pendimethalin stress was investigated by high-throughput sequencing.Results Two microbial consortia capable of degrading pendimethalin were enriched. Among them, L4 (low-concentration group) achieved a degradation rate of 100% for 1.2 mg/L pendimethalin within 11 days, while H4 (high concentration group) showed a degradation rate of 37.2% for 12 mg/L pendimethalin over the same period. The alpha diversity of microbial consortia was considerably decreased by pendimethalin stress, and the bacteria responded to the stress more strongly than fungi. The microbial consortium structure varied with different concentrations of pendimethalin. The network stability, complexity, and modularity were diminished by pendimethalin stress. Linear discriminant analysis effect size (LEfSe) results showed that the specific bacterial taxa in the high concentration group were Achromobacter, Leifsonia, Candidatus_Nucleicultrix, Enterobacter, and Chryseobacterium. The specific bacterial taxa in the low concentration group were Methyloversatilis, Pseudoxanthomonas, Ancylobacter, Methylorubrum, Thermomonas, and Pseudoflavitalea. Talaromyces, Trichoderma, Paracremonium, Scedosporium, and Sarocladium were the specific fungal taxa. The PICRUSt2 analysis showed the pendimethalin stress significantly enriched the pathways related to degradation. The correlation analysis between microbial genera and pendimethalin degradation showed that Methylorubrum, Hyphomicrobium, Microbacterium, Rhodopseudomonas, and Fusarium had positive correlations with pendimethalin degradation in the low concentration group. Hyphomicrobium, Leifsonia, Rhodopseudomonas, Talaromyces, and Trichoderma were positively correlated with pendimethalin degradation in the high concentration group.Conclusion Two microbial consortia capable of degrading pendimethalin were successfully obtained through enrichment culture under varying concentrations of pendimethalin. Leveraging high-throughput sequencing, this study systematically explored the succession patterns of microbial consortia under pendimethalin stress. Key functional microorganisms associated with pendimethalin degradation were preliminarily identified. The findings provide a theoretical basis for the targeted screening of efficient microbial strains dedicated to pendimethalin degradation.

Abstract:Objective To address the low denitrification efficiency in high-salinity, and high-nitrate nitrogen wastewater, this study aimed to isolate and identify salt-tolerant denitrifying a strain with high efficiency. And elucidate its underlying mechanisms for enhanced nitrogen removal.Methods Morphological characterization and the analysis of its 16S rRNA gene sequence were employed for strain identification. Denitrification performance of bacterial strains was evaluated by measuring different forms of nitrogen. Exploring the mechanism of efficient denitrification of bacterial strains through the RT-qPCR analysis and the measurement of electron transport chain enzyme activity under low oxygen or low oxygen and low C/N ratio conditions.Results A halotolerant, facultative aerobic denitrifying bacterium, named W-8, was isolated from saline soil. The strain was identified as Marinobacter sp. This strain can perform denitrification under both aerobic and anaerobic conditions, particularly demonstrating a significant denitrifying activity under low-oxygen conditions (dissolved oxygen concentration<1.2 mg/L). After 48 h of culture under static conditions, W-8 achieved the NO₃^--N (97.85 mg/L) removal efficiency of 95.56% and the total nitrogen removal efficiency of 87.63%. Under low dissolved oxygen, the expression of narG and narI was significantly upregulated, and the activities of electron transport chain complex I and II were enhanced, which promoted the efficient reduction of NO₃^-. The expression of norB was significantly upregulated, promoting the reduction of NO. Under low-oxygen conditions, W-8 further improved the activity of the complex II under a low C/N ratio, reducing carbon source requirements. Under anaerobic conditions, W-8 mainly metabolized NO₃^--N through denitrification, with a gaseous nitrogen production ratio of 87.63%. Under aerobic conditions, this strain achieved nitrogen removal through denitrification combined with assimilation.Conclusion Marinobacter sp. W-8 demonstrates exceptional salt tolerance and high-efficiency denitrification. It can significantly reduce sludge production without the need for aeration or strict anaerobic conditions and has a lower demand for carbon sources. It shows great application potential and provides a theoretical and practical basis for efficient, low-cost denitrification.