[Objective] To elucidate the microbiological mechanisms and major pathways of gypsum as an amendment to reduce CH₄ emissions from saline-sodic paddy fields. [Methods] The saline-sodic wasteland was reclaimed as a paddy field, and four gypsum application treatments were set up: 0 t/hm² (CK), 15 t/hm² (G₁₅), 30 t/hm² (G₃₀), and 45 t/hm² (G₄₅), with three replications. The CH₄ emission fluxes were monitored by the closed static chamber method at the rice flowering stage, after which soil samples were collected from the tillage layer (0-15 cm) within the chamber area for metagenomic sequencing and soil physicochemical property analysis. [Results] The application of 15-45 t/hm² gypsum significantly reduced the CH₄ emission flux of saline-sodic paddy fields by 85.62%-92.64%, and the reduction amplitude increases with the increase of gypsum application rate. The dominant phyla of methanogens and methanotrophs of saline-sodic paddy soils did not change with the application of gypsum, and the relative abundance of hydrogenotrophic type of methanogens was as high as 90%. The relative abundance of Type Ⅱ methanotrophs increased by 50.00%-61.54% compared with that of the CK treatment after the gypsum application reached 30 t/hm². The alpha diversity index of both methanogens and methanotrophs increased with the increase of gypsum application rate, and the increase of the former was significantly smaller than that of the latter. Gypsum significantly decreased the relative abundance of the methanogenic functional gene torC, and increased the relative abundance of the methane oxidation functional genes pps, hdrD and rnfB. CO₃^2-+HCO₃^- and pH were the most important environmental factors of soil affecting the community structure of methanogens and methanotrophs. [Conclusion] The application of gypsum positively affected the community structure of methanogens and methanotrophs by reducing soil pH, but the negative effect of the community structure of methanotrophs on CH₄ emission flux outweighed the positive effect of the community structure of methanogens on CH₄ emission flux, thus reducing CH₄ emission. The results can provide a theoretical basis for the evaluation of ecological effects of agricultural development in saline-sodic land.

[Objective] To clarify the spatial distribution characteristics of soil organic carbon (SOC) age and microbial diversity, explore the relationship of microbial diversity and network complexity with SOC age, and quantitatively assess the relative contributions of microbial diversity, network complexity, climate, vegetation, and soil properties to SOC age. [Methods] Using global soil radiocarbon (Δ¹⁴C) data and environmental variable data, we constructed nine machine learning models for predicting SOC age and selected the best-performing model. Based on global soil microbial 16S rRNA gene data and environmental variable data, microbial network analysis, multiple regression analysis, random forest models, and structural equation modeling were employed to analyze the correlation between SOC age and soil microorganisms and identify the main driving factors of SOC age. [Results] Soil microbial richness decreased with the rise in absolute latitude (P<0.001), being higher near the equator and lower at higher latitudes. Among the nine machine learning models constructed, the rule regression model showed the best prediction performance (R²=0.77, RMSE=0.84). Soil microbial richness and Shannon index were negatively correlated with absolute latitude and SOC age (P<0.001). The global soils were classified into young (44-171 a), middle-aged (172-321 a), and old (322-5 035 a) soil groups, and the network densities followed a trend of young soil group (0.400)>middle-aged soil group (0.285)>old soil group (0.125). Multiple regression analysis, random forest models, and structural equation modeling all showed that microbial network complexity explained the largest portion of SOC age variation (34%), far surpassing vegetation (10%) and climate (6%). [Conclusion] Global soil SOC age has significantly negative correlations with soil microbial diversity and network complexity. The soil with old SOC has lower microbial diversity and simpler microbial network structure. Microbial network complexity is a key factor influencing SOC age, and its impact is significantly greater than that of vegetation and climate. These results provide new insights into the driving mechanisms of SOC age and suggest that future models of SOC dynamics should fully consider the role of microbial interaction network.

[Objective] In view of the low decomposition rate of rice straw in black soil fields of cold regions, it is crucial to isolate lignin-degrading bacteria adaptive to low temperatures to enhance the straw degradation efficiency. [Methods] Soil samples were collected in winter, and the bacterial strains capable of degrading lignin were isolated by the streak-plate method with sodium lignosulfonate as a sole carbon source. The degradation conditions was carried out through optimized by single factor experiment sand response surface methodology. [Results] Pseudomonas psychrophila BYAU-6 was isolated, exhibiting strong lignin-degrading activity in low-temperature environments (5-15 ℃). The culture conditions for strain screening were as follows: sodium lignosulfonate addition amount of 0.5 g/L, a peptone-to-yeast powder mass ratio of 5:1, initial pH 7.0, and a liquid loading volume of 80%. The optimal culture conditions for lignin degradation were determined as follows: sodium lignosulfonate addition amount of 0.3 g/L, a peptone-to-yeast powder mass ratio of 3.2:2.8, initial pH 5.3, and a liquid loading volume of 80%. Under these conditions, the lignin degradation rate increased from 12.33% to 15.78%, representing an increase of 21.9%. The results of the pot experiment showed that the control group (without inoculation) achieved a straw degradation rate of 27.0%, while the inoculation with strain BYAU-6 achieved a straw degradation rate of 37.5%, an increase of 38.89% compared with the control (P<0.05). [Conclusion] This study provides novel microbial resources for straw degradation in cold regions and valuable data for future research on lignin-degrading strains under low-temperature conditions.

Phosphorus is an essential nutrient element for plant growth and development. However, the available phosphorus in soil is extremely limited due to the presence of large amounts of organic phosphorus that is difficult to be degraded, with phytate (inositol hexaphosphate) accounting for a significant proportion. Phytases can efficiently hydrolyze phytate and release available phosphorus. [Objective] By taking advantage of the efficient hydrolysis ability of phytase, the phytase gene was gene modified in the indigenous bacteria of black soil to increase the available phosphorus content in the soil. [Methods] We employed the anchored protein pGSA for surface display of the bacterial phytaseAppA, thereby enhancing the stability and enzymatic activity of the protein as well as improving the substrate contact efficiency. Furthermore, leveraging the CRISPR-targeted gene editing technology, we precisely integrated the surface-displayed phytase fusion protein into the 16S rRNA gene of Ralstonia pickettii G3 genome, isolated from black soil to overcome the dependence of protein expression on vectors. [Results] The 16S rRNA gene site could be used as a target for gene modification without significant effect on the proliferation of the bacteria. The phytase-modified engineered bacteria showed a more than 8-fold increase in the hydrolytic ability of phytate and functioned in a wide pH range. After this indigenous engineered bacterial strain was applied to black soil, the soil phytase activity significantly increased, and the available phosphorus content rose by nearly 30%. [Conclusion] Modifying phytase by gene editing can promote the hydrolysis of phytate, increase the content of available phosphorus, and improve the phosphorus availability in the soil.

[Objective] To screening stress-tolerant and high-yielding rhizobia with growth-promoting effects on Sesbaniacannabina and provide rhizobia resources for efficient cultivation of S. cannabina in saline-alkali soil. [Methods] The culture method was used to isolate endophytic rhizobia from S. cannabina ‘Zhongkejing 1’. Based on 16S rRNA gene and whole genome sequencing, the strains were identified, and their stress tolerance and plant growth-promoting characteristics were evaluated. Their growth-promoting effects on the original host variety and other materials of S. cannabina were verified. [Results] The rhizobia isolated from the root nodule samples of S. cannabina ‘Zhongkejing 1’ were identified as a species belonging to Rhizobium. Based on the ANI and dDDH values of the whole genome sequence, the strain was identified as a new species of Rhizobium and named Rhizobium sesbaniae ZK1^T. R. sesbaniae ZK1^T can tolerate a NaCl concentration of 2.0% and survive within the range of pH 4.0-10.0, and it had the ability to dissolve organophosphorus compounds. Pot experiments were conducted to evaluate the effects of R. sesbaniae ZK1^T on the growth and nodulation of different materials of S. cannabina. The results revealed that R. sesbaniae ZK1^T promoted the growth and nodulation of these materials, while it had a more efficient symbiotic relationship with the host variety. [Conclusion] The isolated new species R. sesbaniae ZK1^T plays a role in promoting the growth and nodulation of S. cannabina and can tolerate severe acid, alkali, and salt stress. The findings have important theoretical significance and a practical value for the efficient improvement of plant-microorganism interactions in marginal land.

Saline-alkali stress is one of the main abiotic constraints limiting plant growth and development. Endophytic bacteria can enhance the stress tolerance of host plants by increasing osmotic adjustment substances and boosting antioxidant enzyme activities. [Objective] To isolate and identify saline-alkali tolerant endophytic bacteria from the roots of alfalfa grown in saline-alkali soil and evaluate them regarding the saline-alkali tolerance, plant growth-promoting traits, effects on alfalfa growth under saline-alkali stress, and colonization. [Methods] Saline-alkali tolerant endophytes were isolated by the tissue homogenization method from alfalfa roots. Strains were identified by morphological observation, 16S rRNA gene-based phylogenetic analysis, and physiological and biochemical assays. Multiple plant growth-promoting traits were assayed in vitro. A greenhouse pot experiment was conducted to assess the effect of the selected strain on alfalfa growth under saline-alkali conditions. Colonization of strain Z-1 in alfalfa roots was visualized by green fluorescent protein tagging and laser scanning confocal microscopy. [Results] Pseudomonas moraviensis Z-1 was successfully isolated from the roots of alfalfa growing in saline-alkali soil. The endophytic bacterial strain tolerated 4% NaCl and pH 9.0 and displayed the ability to produce 1-aminocyclopropane-l-carboxylate deaminase, siderophores, indole-3-acetic acid, and soluble phosphorus. Under saline-alkali conditions, inoculation with Z-1 significantly increased the dry weights of the aboveground parts, root vigor, and soluble protein content of alfalfa. Moreover, the strain significantly increased catalase, peroxidase, and superoxide dismutase activities and decreased the hydrogen peroxide, superoxide anion, and malondialdehyde content (P<0.05). Confocal microscopy confirmed successful colonization of Z-1 in alfalfa roots at 7.57×10⁴ CFU/g. [Conclusion] The saline-alkali tolerant endophytic bacterium Z-1 plays a vital role in promoting alfalfa growth and enhancing its tolerance to saline-alkali stress. It represents a promising candidate for developing microbial preparations to ameliorate saline-alkali soil.

[Objective] To screen and identify an endophytic bacterial strain with plant growth-promoting effects on rice from the stem of rice grown in the soda saline-alkaline soil in Daqing City, Heilongjiang Province and explore its plant growth-promoting effects and related genes, with a view to enriching and utilizing the endophytic microbial resources of rice. [Methods] An endophytic bacterial strain was isolated from rice stems via the dilution coating method, and the strain was identified by morphological observation, physiological and biochemical tests, and 16S rRNA gene sequencing. The mechanisms underlying the plant growth-promoting effects of the strain were deciphered by Illumina sequencing of the whole genome. antiSMASH was used to predict the synthetic gene clusters of secondary metabolites. The plant growth-promoting performance of the strain was evaluated by promotion performance, rice seed germination, and seedling cultivation tests. [Results] An isolated endophytic bacterial strain of rice was designated as J-7, and the strain was identified as Acinetobacter baumannii by whole genome sequencing and ANI analysis. The strain was a mesophilic bacterium with an OD₆₀₀ value of 0.679 at pH 10.5, showcasing alkaline tolerance. The strain had an OD₆₀₀ value of 0.293 in the presence of 1.0 mol/L NaCl, exhibiting salt tolerance. The strain had the ability to solubilize inorganic and organic phosphorus, with the amounts of inorganic and organic phosphorus solubilized being (179.54±1.21) mg/L and (65.57±1.07) mg/L, respectively. In addition, the strain had the ability to produce siderophores and utilize ferric ammonium salts. The strain genome (national microbiology data center accession number: NMDC60154488) was 3 666 630 bp in length, with the G+C content of 39% and a total of 3 432 genes (including 8 potential synthetic gene clusters of secondary metabolites). The rice seed germination test results showed that the application of 1×10⁷ CFU/mL suspension of the strain significantly increased the radicle length and stem base width by 13.02% and 17.68%, respectively, compared with the control group. The rice seedling cultivation test results showed that the application of 2×10⁹ CFU/mL suspension of the strain significantly increased the plant height and root length by 32.69% and 36.55%, respectively, compared with the control group. [Conclusion] Strain J-7 has a good growth-promoting effect on rice, showing application potential in agriculture as a microbial strain resource. Whole genome sequencing provides a theoretical basis for in-depth study of the plant growth-promoting mechanism of A. baumannii.

[Objective] Both no-tillage with straw mulching and combined application of organic and inorganic fertilizers can effectively enhance soil fertility. However, the mechanisms by which they influence microbial carbon and nitrogen turnover remain unclear. [Methods] Soil samples included conventional tillage (CK) as the control, along with two management treatments: soils under combined application of organic and inorganic fertilizers (CM) and no-tillage with straw mulching (CT). By employing DNA-stable isotope probing (DNA-SIP) with ¹³C-glucose in a laboratory microcosm incubation experiment, we investigated the responses of microbial activities in black soil to exogenous glucose and urea addition. Key processes examined included respiration, mineralization, dissimilatory decomposition (measured by ¹³C-CO₂), assimilatory formation of stable organic carbon (measured by ¹³C-SOC), priming effects, N₂O emissions, carbon neutrality, and active microorganisms. [Results] In the control treatment with water addition, soil microbial respiration and mineralization intensity followed the order of CK<CM<CT, which showed the maximum CO₂ emission rates of 0.413, 0.589, and 0.615 µmol/(g⋅d), respectively. Exogenous carbon and nitrogen addition induced positive priming effect, with the intensity ranking as simultaneous carbon and nitrogen addition (Glu+N)>carbon-only addition (Glu)>nitrogen-only addition (N). However, the priming effect did not continuously enhance with the increase in the total amount of exogenous organic matter. Dissimilatory decomposition enhanced as the amount of exogenous addition increased, with cumulative ¹³C-CO₂ emissions following the trend of CK (97.0 nmol/g)>CM (90.4 nmol/g)>CT (81.9 nmol/g). The content of stable ¹³C-SOC produced by microbial assimilation in CT was 296.4 nmol/g, higher than that in CM (263.5 nmol/g). The carbon use efficiency of soil in the three groups was approximately 80%, and about 30% of N₂O emissions were offset by the formation of ¹³C-SOC. Carbon neutrality analysis revealed that the net CO₂ emissions from CK and CT soil samples were 50% higher than those from the CM soil sample. Additionally, under the addition of exogenous carbon and nitrogen, the active ammonia-oxidizing microorganisms during microbial proliferation were primarily ammonia-oxidizing bacteria, specifically Nitrosospira. [Conclusion] CT demonstrates higher respiration, mineralization, and carbon sequestration capabilities and lower dissimilatory decomposition capability in enhancing soil fertility than CM, while it results in higher net CO₂ emissions.

[Objective] To explore the mechanism by which biochar alters the soil bacterial community structure and thereby affects the availability of soil phosphorus. [Methods] This study employed metagenomic techniques to investigate the soil bacterial communities and microbial functional genes involved in the phosphorus cycle after the application of biochar at different doses (CK: 0 kg/hm², T1: 300 kg/hm², T2: 600 kg/hm², and T3: 900 kg/hm²). [Results] The application of biochar significantly increased inorganic phosphorus, microbial biomass phosphorus, and alkaline phosphatase activity, which showed the increases of 21.75%, 699.39%, and 34.00%, respectively, under T2 treatment. Furthermore, the application of biochar changed the diversity and richness of soil microorganisms, especially bacteria, mainly enriching Actinobacteriota, Acidobacteria, Chloroflexota, Thermoproteota, Gemmatimonadota, Nocardioides, and Sphingobium. Soil pH, water content, organic matter, inorganic phosphorus, microbial biomass phosphorus, and available phosphorus were important factors influencing soil microbial communities. In addition, biochar significantly increased the abundance of the organic phosphorus mineralization-associated gene phoD, T2 increased by 9.28% compared with CK, and the abundance of phoD was significantly affected by total phosphorus, available phosphorus, and microbial biomass phosphorus content in the soil. [Conclusion] The application of biochar can enhance phosphorus availability by regulating soil bacterial community structure. The findings provide a theoretical basis for the application of biochar in improving phosphorus availability in farmland soil.

[Objective] Black soil acidification may exacerbate the soil degradation processes and reduce microbial functions, thus threatening the crucial role of the northeast region in guaranteeing the food security of China. Unraveling the impacts of soil acidification on the soil microbial community and its underlying mechanisms can help clarify the relationship between soil organic carbon (SOC) stabilization and soil acidification. [Methods] Soil samples with different acidification degrees were collected from the corn belts of black soil regions. The changes of living microbial groups in the soil samples with different pH were investigated by the phospholipid fatty acid (PLFA) analysis. Additionally, the relationship between changes in the soil physicochemical properties and microbial community composition was analyzed. [Results] A threshold effect of black soil acidification on SOC was identified in the corn belts. Moderate acidification did not cause significant changes in SOC. However, when pH dropped below a certain threshold (6.75), further acidification resulted in a significant loss of SOC. The cation buffering effect in soil changed significantly with different acidification degrees. Calcium ion was primarily responsible for buffering black soil acidification, while when the pH fell below 6.00, both calcium and magnesium ions buffered the acidification. Soil acidification imposed noticeable stress on soil microorganism growth. Different microbial groups exhibited an S-shaped response pattern, with PLFA content initially decreasing, remaining stable within the range of pH 5.25-6.25, and subsequently declining as acidification progressed. However, different microbial groups exhibited varying sensitivities to soil acidification. Gram-negative bacteria were the most sensitive, followed by Gram-positive bacteria and arbuscular mycorrhizal fungi. Fungi, particularly arbuscular mycorrhizal fungi, may play a crucial role in stabilizing SOC during soil acidification. [Conclusion] Soil acidification significantly alters the structure of the living microbial community, primarily through changes in cation exchange capacity and substrate availability, which further affect SOC accumulation. These findings provide scientific support for developing management strategies to alleviate black soil degradation and acidification.

[Objective] The conversion of upland to paddy fields and increased fertilizer application have significantly altered soil properties. However, the dynamic evolutionary characteristics and response mechanisms of microbial communities during habitat evolution different years after conversion remain unclear. [Methods] Soil samples were collected from the paddy fields converted from upland fields for different years (0, 3, 8, 15, 20, and 30). Soil physicochemical analysis, real-time quantitative PCR, and high-throughput sequencing were employed to investigate the dynamic changes in soil chemical and biological properties, microbial community composition and asynchrony characteristics, and the interrelationships among these indicators during the habitat evolution following conversion. [Results] As the years after conversion increased, soil organic carbon, total nitrogen, total phosphorus, ammonium nitrogen, and microbial biomass carbon content gradually increased (by 3 to 4 folds), while pH (decreased by up to 0.80) and nitrate content gradually decreased. However, soil potassium content, microbial abundance, and microbial diversity showed no consistent trends. Microbial community analysis revealed that as the years after conversion increased, stress-tolerant genera (Balneola, Flavobacterium, Myxococcus, and Nitrospira) presented enhanced asynchrony and divergence. This optimized interspecies interactions and functional division, thereby improving ecosystem stability. Conversely, increased convergence in genera such as Liberibacter and Variovorax weakened soil functions such as plant growth promotion and pathogen suppression. Correlation analysis indicated that soil pH, organic carbon, and total nitrogen acted as key environmental drivers. Through synergistic and antagonistic interactions, they governed microbial community succession and exerted decisive influences on changes in community asynchrony. [Conclusion] As the years after upland-to-paddy conversion increased, the microbial community asynchrony became enhanced, which improved system stability and reduced carbon losses while compromising soil capacities of plant growth promotion and disease suppression. In the future, strategies such as water management, organic amendment regulation, precision fertilization, and application of synthetic microbial consortia could be employed to directionally enhance microbial divergence and improve ecosystem functional stability.

Saline-alkali land is a common type of degraded soil with wide distribution across the globe. Among all types of saline-alkali land, soda saline-alkali land, characterized by the coexistence of high salinity and alkalinity, is particularly difficult to be managed and represent a major obstacle to the effective utilization of soil resources. Arbuscular mycorrhizal fungi (AMF) enhance plant growth and survival by improving nutrient uptake and increasing stress resistance, offering promising potential for the reclamation and utilization of saline-alkali land. [Objective] To explore how the structures and diversity of the AMF community vary along a soda saline-alkaline stress gradient in response to stress and other environmental factors. [Methods] We collected soil samples subjected to varying levels of soda saline-alkaline stress from Changling County and Da’an City in Jilin Province. The sampling sites included Suaeda glauca-covered wildland (pH 10.0-10.5), unvegetated bare land (pH 9.5-10.0), and maize (Zea mays L.) farmlands under varying levels of stress (pH 8.5-10.0). The structures and diversity of AMF communities in these soil samples were analyzed by Illumina-based 18S rRNA gene sequencing. [Results] AMF communities were predominantly composed of Entrophospora, Funneliformis, Rhizoglomus, and Dominikia. The relative abundance of AMF was significantly positively correlated with soil total carbon, total nitrogen, total phosphorus, and available nitrogen, and it was significantly negatively correlated with soil pH, electrical conductivity, and salt content. The AMF community structure was significantly associated with soil total carbon and pH. The Shannon diversity (alpha diversity) of AMF showed significantly positive correlations with total phosphorus and salt content, while the AMF community structure dispersion (beta diversity) was significantly negatively correlated with electrical conductivity. Moreover, the alpha diversity and beta diversity of AMF had a significantly negative correlation. [Conclusion] Saline-alkaline stress exerted homogeneous selection on the AMF community, leading to reduced community size, decreased beta diversity, increased alpha diversity, and altered community composition.

Nitrogen fertilizer is an important chemical fertilizer for agricultural planting and an important fertility factor for increasing crop yields. Lack or excess of nitrogen fertilizer in soil will lead to soil acidification, soil consolidation, low crop yields and so on. Nitrogen-fixing bacteria can reduce nitrogen in the air to ammonia that is beneficial to crops through the action of nitrogenase. This process helps improve soil quality and subsequently promote crop growth. [Objective] To obtain nitrogen-fixing bacteria from the black soil of northeast China and explore the effects of nitrogen-fixing bacteria on soil quality and maize growth, thus providing excellent strain sources for the development of microbial agents suitable for the environment of black soil in northeast China. [Methods] We employed microbial isolation, culture, and functional characterization to measure the nitrogen fixation, phosphorus solubilization, and indole-3-acetic acid (IAA) secretion of the screened nitrogen-fixing bacteria. Pot experiments and soil physical and chemical tests were carried out to evaluate the effects of nitrogen-fixing bacteria on soil quality and maize growth. [Results] Three strains of nitrogen-fixing bacteria were obtained from the black soil of northeast China. Among them, Paenibacillus sp. AHC-20 had higher nitrogen-fixing ability, while Raoultella sp. Z93 and Paraburkholderia sp. W22 were multifunctional strains capable of fixing nitrogen, solubilizing phosphorus, and producing IAA at the same time. The three nitrogen-fixing strains were then applied to the black soil planted with maize. The plant height, biomass, and chlorophyll content of maize significantly increased in the chemical fertilizer reduction+AHC-20 group compared with those in the control group with application of only chemical fertilizer. In addition, the content of inorganic carbon, organic carbon, organic matter, ammonium nitrogen, and nitrate nitrogen in black soil also increased significantly, which indicated that the efficient nitrogen-fixing bacterial strain AHC-20 promoted maize growth upon chemical fertilizer reduction and improved the fertility of black soil. [Conclusion] Nitrogen-fixing bacteria in black soil can effectively promote the growth of maize and improve the quality of black soil to achieve fertilizer reduction without compromising crop yields, showing the potential for the development of nitrogen-fixing microbial agents.

[Objective] Black soil regions are globally critical for grain production, with their soil health directly impacting world food security and ecological stability. These regions hold significant strategic importance for sustainable agriculture and human health. In recent years, rapid advancements in microbiome research methodologies have highlighted the pivotal role of soil microorganisms in the sustainable utilization and health management of black soil. [Methods] To systematically summarize the research status and trends in black soil microorganisms, we employed “bibliometrix” R package and VOSviewer to conduct bibliometric analysis. We quantitatively analyzed the literature from the Web of Science core collection (2014-2024) and manually screened the abstracts. [Results] The results revealed a surge in the research on black soil microorganisms after 2021, with China, Russia, and the United States being the most prolific contributors. Leading institutions included the Chinese Academy of Sciences, University of Chinese Academy of Sciences, Northeast Agricultural University, Heilongjiang Academy of Agricultural Sciences, and Chinese Academy of Agricultural Sciences. Key findings were predominantly published in Applied Soil Ecology, Soil Biology & Biochemistry, and Eurasian Soil Science. Current research focuses on microbial networks, biochar applications, and rhizosphere microecology, emphasizing the roles of microorganisms in soil fertility regulation, environmental remediation, soil improvement, climate change responses, and farming system optimization. Studies also explore interactions between microorganisms and environmental factors such as soil aggregates, physicochemical properties, and enzyme activities, with a growing shift toward mechanism insights. [Conclusion] Over the past decade, research on black soil microbiota has rapidly advanced, with current focus on the role of microorganisms in soil fertility enhancement and sustainable utilization. Future studies should integrate cutting-edge technologies such as microbiomics, metagenomics, metatranscriptomics, and metabolomics to comprehensively analyze microbial community distribution, functionality, and regulatory mechanisms. Ultimately, this will provide a robust theoretical and technical foundation for the sustainable use and health enhancement of black soil resources.

Streptomyces can produce various active secondary metabolites, which can be widely used in medical, industrial, agricultural, and other fields. The secondary metabolite synthesis in Streptomyces is regulated by pathway-specific, pleiotropic, and global regulatory genes. The two-component system, as the main signal transduction system in prokaryotes, participates in various physiological and biochemical reactions of Streptomyces and can globally regulate secondary metabolites. The deletion or overexpression of specific two-component system genes can significantly affect the biosynthesis of secondary metabolites. Identifying the functions of two-component systems and elucidating their regulatory mechanisms can contribute to enhancing the production efficiency of secondary metabolites by genetic engineering. This paper reviews the research trends of two-component systems in various Streptomyces species such as Streptomyces albidoflavus in recent years and particularly summarizes and elaborates on the regulatory mechanisms of their secondary metabolite synthesis.

As a major risk factor for cardiovascular disease worldwide, hypertension poses threats that cannot be ignored. In recent years, the role of gut microbiota in the pathogenesis of hypertension has gradually become a research hotspot. This review systematically explores the relationship between gut microbiota and hypertension and elaborates on the mechanisms of gut microbiota regulation of blood pressure by mediating inflammatory responses, influencing the microbiota-gut-brain axis, and producing specific metabolites. Furthermore, this article discusses the potential application value of gut microbiota-based intervention strategies in the prevention and treatment of hypertension and reveals the potential targets and evidence of gut microbiota in the treatment of hypertension and its complications, paving a new way for the exploration of therapeutic methods.

One Health integrates the health of the environment, animals, and humans, involving food safety, environmental hygiene, and animal and human health. Currently, antibiotic resistance is exacerbating worldwide, seriously hindering the achievement of One Health. Phages, as viruses with a century-long application history and the ability to specifically kill bacteria, bring new hope for addressing antibiotic-resistant bacterial infections. This article reviews the development history, diversity, and applications of phages in food safety and the environment, animals, and humans, with the aim of providing references for the application of phages in the era of One Health.

[Objective] To investigate the mechanism of the induced cross resistance of drug-resistant mutants of Escherichia coli to tigecycline in vitro. [Methods] We used doxycycline hydrochloride and the mutation preventive concentration (MPC) method to induce the drug resistance mutation of Escherichia coli ATCC 25922, and the drug resistance spectra of the mutants were determined. Genome-wide next-generation sequencing was utilized to analyze the mutations of key differentially expressed resistance genes of ATCC 25922 and the mutant with the highest resistance index. RT-PCR was used to determine the transcription levels of the key differentially expressed resistance genes of the mutant with the highest resistance index according to the whole genome sequencing results. The expression of key differentially expressed resistance genes in the mutant with the highest resistance index was knocked down by siRNA. [Results] Three drug-resistant E. coli mutants Y_3.2-2, Y₆₄, and Y_128-2 with different degrees of resistance to tigecycline were obtained after stepwise induction of drug resistance mutation, with the resistance following the order of Y_3.2-2<Y₆₄<Y_128-2. All the mutants showed multi-drug resistance. Fourteen resistance genes were detected with varying degrees of base mutations and amino acid mutations. In the mutant Y_128-2 with the highest resistance index, the expression of acrA, acrE, acrF, acrS, plsC, rpsJ, acrB, and macA was up-regulated, while that of tolC, marA, sdiA, and macB was down-regulated. The resistance genes rpsJ and plsC in Y_128-2 were successfully interfered with at tigecycline concentrations of 1×MIC and 1/2×MIC, and the strain regained sensitivity to tigecycline. [Conclusion] Y_128-2 develops resistance to tigecycline by the overexpression of the ribosome binding site gene rpsJ and the bacterial cell membrane permeability-related resistance gene plsC.

[Objective] We employed the wild-type strain of Listeria monocytogenes, the lipoprotein gene pplA- deleted strain, and the complementary strain to investigate the role of PplA in the infection of L. monocytogenes. [Methods] We compared the hemolytic capacity, cell adhesion and invasion, intracellular proliferation, cell-to-cell migration, mouse organ colonization, transcription levels of virulence factors in mouse organs, and transcription levels of quorum sensing-related genes among wild-type, pplA-deleted, and complementary strains to explore the role of PplA in the infection of L. monocytogenes. [Results] After the deletion of pplA, L. monocytogenes showed no significant change in intracellular proliferation or cell-to-cell migration. However, its hemolytic capacity, cell adhesion and invasion, mouse organ colonization, and transcription levels of virulence factors such as plcB, hly, and prfA in mouse organs were significantly reduced. Moreover, the transcription levels of quorum sensing-related genes agrA, agrB, agrC, and luxS were altered in the pplA-deleted strain. [Conclusion] Thelipoprotein PplA is involved in the virulence regulation and affects the pathogenicity of L. monocytogenes.

[Objective] Seed endophytes are key components of the plant microbiome, and their community structure and diversity are highly susceptible to environmental changes. Revealing the effects of fencing versus grazing management on the endophytic microbial communities of Caragana korshinskii seeds is essential for elucidating the dynamic interactions among plants, soil, and microorganisms. This study also provides a theoretical foundation for ecological restoration in arid and semi-arid grasslands. [Methods] The study was conducted in Otog Front Banner, Inner Mongolia, focusing on C. korshinskii under two management practices: fencing and grazing. The physicochemical properties of soil were analyzed by high-throughput sequencing of seed endophytic microbial communities to assess shifts in their structural composition and diversity under these contrasting regimes. [Results] Fencing management decreased soil pH while increasing moisture content, total carbon, total nitrogen, and total phosphorus of soil. Grazing management increased the abundance-based coverage estimator (ACE) index of seed endophytic fungi. Fencing increased the relative abundance of Pseudomonadota and decreased the relative abundance of Bacillota in seed endophytic bacteria, while promoting the relative abundance of Pantoea. In seed endophytic fungi community, Alternaria dominated under fencing management, while Trichoderma dominated under grazing management. Additionally, grazing management increased the number of modules and complexity in seed endophytic bacterial-fungal networks. [Conclusion] The contrasting management practices of fencing and grazing in desert stepps alters soil environment, thereby shaping the diversity and community structure of both bacterial and fungal endophytes in C. korshinskii seeds. This study reveals the impact of different management measures on plant-microbe interactions in desert steppes, providing theoretical support for related research.

[Objective] Transcription is the first step in gene expression, and the mRNA abundance to a certain extent determines the final protein expression abundance. Recent studies have found that different ribosome-binding sites (RBSs) located in the 5′ untranslated region (5′-UTR) can affect the mRNA abundance of the downstream gene. From the perspective of regulatory factors in the mRNA degradation process, the effect may be attributed to the binding strength between the Shine-Dalgarno (SD) sequence and the ribosome and the local secondary structure of the 5′-UTR. [Methods] We constructed a 5′-UTR mutant library with a size of 528. High-throughput sequencing was employed to efficiently collect the information on the mRNA abundance of downstream egfp corresponding to various 5′-UTR variants. The effectiveness was verified by RT-qPCR. [Results] The association between abundance of each mRNA mutant and its corresponding 5′-UTR sequence was analyzed. The results showed that the SD sequence with moderate to strong binding strength to the ribosome was most conducive to maintaining high mRNA abundance. Too high or low binding strength will lead to a reduction in the mRNA abundance. The completely conserved core SD sequence (GGAGG) was the key to ensuring high binding strength, and the decline in conservation would cause a significant decrease in the mRNA abundance. When the SD sequence was similar among different 5′-UTR variants, i.e.,the binding strength of the SD sequence to the ribosome was comparable, the local secondary structure of the 5′-UTR was instable and the abundance of corresponding mRNA was high. [Conclusion] This study delves into the regulatory effects of 5′-UTR sequence features 5′-UTR on the mRNA abundance and establishes a qualitative model of their interrelationships, providing a reference for the rational design of regulatory elements in metabolic engineering and gene circuits.

Photobacterium damselae subsp. damselae (PDD), a pathogenic bacterium widely found in seawater, can infect a variety of economic fish and cause huge economic losses to the global aquaculture industry. The flagellar gene flgK encodes the flagellar hook protein FlgK, which is essential for the normal formation of bacterial flagella. [Objective] To systematically analyze the influencing mechanism of flgK on the virulence of PDD. [Methods] The flgK-deleted mutant of PDD (ΔflgK-PDD) was constructed by homologous recombination mediated by a high-efficiency suicide plasmid, and the mutation was confirmed by gene sequencing. The biological characteristics, virulence gene expression, and pathogenicity were compared between ΔflgK-PDD and the wild-type strain (WT-PDD). [Results] There was no significant difference in the growth ability, hemolytic activity or phospholipase activity between ΔflgK-PDD and WT-PDD. However, the motility and biofilm formation of ΔflgK-PDD were significantly lower than those of WT-PDD. Transmission electron microscopy showed that ΔflgK-PDD failed to form a flagellar structure. The artificial infection experiments showed that the LD₅₀ of ΔflgK-PDD in Sebastes schlegelii was 557% that of WT-PDD, and the pathogenicity was significantly reduced. Real-time quantitative PCR results showed that compared with WT-PDD, ΔflgK-PDD demonstrated significantly down-regulated expression of the flagellar-related genes fliK and flgL, the type II secretion system (T2SS)-related genes gspC and gspD, and the virulence gene hlyA_pl. The expression levels of flagellar-related gene fliH, T2SS-related gene gspE, outer membrane-related genes ompP, lapB, and flhB were significantly up-regulated, and those of the remaining genes did not change significantly. [Conclusion] The mutation of flgK can lead to the failure of ΔflgK-PDD to form a complete flagellar structure and significantly change the relative expression levels of flagellar-related genes, thereby reducing the motility and colonization ability and ultimately weakening the pathogenicity of PDD.

[Objective] To clarify phyllosphere microbial responses to the invasion of areca palm velarivirus 1 (APV1), a virus causing yellow leaf disease of areca (Areca catechu), and provide a theoretical basis and technical support for the study of phyllosphere micro-ecology, exploration of excellent biocontrol resources, and green prevention and control of yellow leaf disease of areca. [Methods] We collected healthy leaves, mildly diseased leaves, and severely diseased leaves of areca. The phyllosphere microbial community structure and diversity were compared by high-throughput sequencing and bioinformatics methods. Furthermore, functional differences of phyllosphere microbial communities were analyzed. [Results] The dominant bacterial phyla in the phyllosphere of areca included Actinobacteriota, Proteobacteria, Acidobacteriota, Firmicutes, and Myxococcota, while the dominant fungal phyla were Ascomycota and Basidiomycota. As the disease became increasingly severe, bacterial richness initially increased then decreased while fungal richness initially decreased then increased. However, both bacterial diversity and fungal diversity showed a trend of first increasing and then decreasing. Firmicutes and Basidiomycota served as indicators of mildly diseased areca, with the relative abundance showing consistent trends with alpha diversity. The healthy plants and the diseased plants showed different phyllosphere microbial functions. Specifically, the environmental information processing function was significantly higher in severely diseased areca plants than in healthy ones. Additionally, the relative abundance of symbiotroph fungi in the phyllosphere were significantly higher in severely diseased areca plants than in healthy ones. [Conclusion] The yellow leaf disease significantly alters the phyllosphere microbial community structure and diversity of areca, with greater changes during the early disease stage. This suggests that areca may defend against APV1 infection by recruiting beneficial microorganisms, regulating cellular metabolism and biochemical reactions, and activating autoimmunity.

Microbial deodorization is an effective technology for treating odorous waste gases, in which microbial strains play a decisive role. [Objective] To screen the strains capable of degrading dimethyl disulfide (DMDS) and investigate their degradation efficiency and ability to produce surfactants under various conditions. [Methods] DMDS, a typical sulfur-containing odorous organic compound, was selected as the sole carbon source. A strain R1 capable of simultaneously producing biosurfactants and degrading DMDS was isolated from mangrove sludge. The strain was identified based on the physiological and biochemical characteristics analysis and 16S rRNA gene sequencing. The types of self-produced biosurfactants were determined using infrared spectroscopy and nuclear magnetic resonance spectroscopy analysis. [Results] Based on physiological and biochemical characteristics and 16S rRNA gene sequence, strain R1 was identified as Achromobacter sp. The strain was capable of degrading DMDS, with optimal degradation conditions of an initial DMDS concentration of 12.49 mg/L, a system temperature of 30 ℃, and an inoculum amount of 1.0 g/L, under which the DMDS degradation rate reached 70.74%. Emulsification experiments showed that strain R1 can use DMDS as a carbon source to produce biosurfactants, which were identified as glycolipids through nuclear magnetic resonance and infrared spectroscopy. [Conclusion] The main intermediate product in the biodegradation of DMDS is methyl mercaptan, and the transformation rate of sulfur to SO₄^2- is 65.99%. Strain R1 exhibits impressive performance in degrading DMDS and producing biosurfactants.

[Objective] To study the effects of the glycosyltransferase WekO involved in O-antigen synthesis on the biological characteristics of avian pathogenic Escherichia coli (APEC). [Methods] The mutant strain ΔwekO of APEC O₁ was constructed by Red homologous recombination, and the complementary strain CΔwekO was then constructed. The lipopolysaccharide (LPS) profile of each strain was identified by silver staining. Simultaneously, the growth rate and swimming motility were measured. The reactivity of each strain with rabbit anti-O₁ serum was determined by Western blotting. The ability of ΔwekO to form biofilms was measured by the crystal violet staining method. DF-1 cells were used to evaluate the adhesion and invasion of ΔwekOin vitro. Subsequently, chicks were selected as an animal model to evaluate the pathogenicity of ΔwekO. [Results] The mutant strain ΔwekO and the complementary strain CΔwekO were constructed. The LPS profile of ΔwekO was incomplete compared with that of the wild-type strain. The mutant lacked O-antigen bands and showed no reactivity to anti-O₁ serum. There was no significant difference in growth rate between different strains (P>0.05). However, the motility and biofilm formation capabilities of ΔwekO decreased (P<0.001). Additionally, ΔwekO demonstrated weakened adhesion to DF-1 cells (P<0.001) and demonstrated weakened invasion to DF-1 cells (P<0.01). Also, ΔwekO reduced pathogenicity to 7-day-old chicks (P<0.05). [Conclusion] The deletion of wekO results in impaired O-antigen synthesis, incomplete LPS profile, loss of flagellar and biofilm formation capabilities, and reduced pathogenicity of APEC. These findings are highly significant for improving the understanding of the role of glycosyltransferases involved in APEC O-antigen synthesis.

Pseudomonas plecoglossicida is the pathogen of visceral white spot disease in large yellow croaker (Larimichthys crocea). At present, the pathogenic mechanism of P. plecoglossicida has been partially understood, and some effective vaccines have been screened, whereas no commercial vaccine has been developed. [Objective] To deepen the understanding about the pathogenic mechanism and develop efficient attenuated live vaccines of P. plecoglossicida. [Methods] We targeted luxR and the RNA polymerase σ factor gene rpoE associated with quorum sensing to construct deletion mutants of P. plecoglossicida NB2011 by double homologous recombination. In addition, the strain ΔT6SS1ΔluxR with deletion of both the type VI secretion system 1 (T6SS1) gene and luxR was constructed. The biological characteristics and virulence of the mutants were analyzed. The relative percent of survival of fish after vaccination with the double deletion mutant was investigated. [Results] We successfully constructedΔluxR, ΔT6SS1ΔluxR, and ΔrpoE. Compared with the wild type, none of the three mutants showed significant changes in the growth rate, swarming ability or swimming ability, while ΔluxR and ΔT6SS1ΔluxR showed significant decreases in biofilm formation. The internalization, adsorption, and intracellular proliferation of the mutants in mouse macrophages were observed. All the three mutants could survive in J774A.1 macrophages and showed lower proliferation capacities than the wild type. Compared with the wild type, the two single mutants showed significantly reduced virulence to goldfish (Carassius auratus) after intraperitoneal injection at a concentration of 1.0×10⁷ cells/mL. The double deletion mutant ΔT6SS1ΔluxR showed no virulence when challenging goldfish at the same dose, with the LD₅₀>10⁸ cells/mL. In the immune protection experiment, the goldfish was vaccinated with ΔT6SS1ΔluxR, and the fish was artificially challenged with the wild type 28 days later. The relative percent of survival reached 78.60%, which indicated effective protection. [Conclusion] In this study, three gene deletion mutants were successfully constructed, and the virulence of the mutants was significantly decreased. Among them, ΔT6SS1ΔluxR is expected to be a candidate strain for the development of the attenuated live vaccine against P. plecoglossicida infection.

Yeast β-glucan has been widely used as a dietary supplement for its multiple biological activities, including immune stimulation. Previous studies in our laboratory have shown that yeast chs3Δ spores exposed in the glucan layer can activate immune effects more effectively than trophoblasts. However, chs3Δ spores are formed within the ascospores and are encapsulated by the ascospore cell wall, which greatly limits their direct application. [Objective] To explore whether the lysates of chs3Δ asci have the potential to be used as novel immune-stimulating dietary supplements. [Methods] We prepared chs3Δ asci lysates by ultrasonic freeze drying, enzymatic freeze drying, and enzymatic-assisted ultrasonic freeze drying and then explored their immune effects in depth. [Results] The chs3Δ asci lysate prepared by ultrasonic freeze drying induced the highest level of inflammatory cytokines compared with the vegetative cell lysate and chs3Δ spores, and the asci lysate achieved immunostimulatory responses through activation of Dectin-1 receptor. Further studies showed that the chs3Δ asci lysate also exhibited immunostimulatory activity and trained immunity-inducing ability in mice. [Conclusion] The chs3Δ asci lysate has great potential as a highly effective immunostimulatory dietary supplement.

[Objective] To systematically investigate the substrate promiscuity and catalytic performance of three UDP-glycosyltransferases: CsUGT75L12 (Camellia sinensis), CiUGT11 (Chrysanthemum indicum), and UGT73B1 (Arabidopsis thaliana). [Methods] The recombinant proteins of plant glycosyltransferases were heterologously expressed in Escherichia coli BL21(DE3) and purified for in vitro enzymatic assays. In vitro enzymatic reactions of the purified recombinant proteins were performed with six flavonoids including flavones (apigenin and acacetin) and flavanones (naringenin, eriodictyol, isosakuranetin, and hesperetin). The enzymatic products were characterized by HPLC and LC-MS and the conversion rates were calculated through comparative HPLC peak area analysis. [Results] CsUGT75L12, CiUGT11, and UGT73B1 exhibited broad substrate promiscuity towards the six tested flavonoids. The primary products were identified as flavonoid-7-O-glucosides. Notably, CiUGT11 and UGT73B1 demonstrated exceptional catalytic efficiency, achieving >96% conversion rates for hesperetin and naringenin. Leveraging this activity, we engineered CiUGT11 and UGT73B1 with high efficiency to produce hesperetin-7-O-glucoside and naringenin-7-O-glucoside through precursor feeding in E. coli. [Conclusion] The three glycosyltransferases display remarkable versatility in flavonoid recognition, with conserved preference for the C7-OH position. CiUGT11 and UGT73B1 show high catalytic efficiency for six flavonoids. These findings provide candidate gene elements for the efficient microbial production of flavonoid glycosides.

Glutamate waste liquid is the waste produced in the production process of glutamic acid, with low pH, high ammonium, and high sulfate. The waste liquid contains glutamic acid and can be used as a raw material to produce poly-γ-glutamic acid (γ-PGA), achieving the recycling of waste liquid. [Objective] To investigate the inhibitory effect of glutamate waste liquid on γ-PGA synthesis, we used Bacillus subtilis KH2 to synthesize γ-PGA and evaluated the inhibitory effect of glutamate waste liquid on the synthesis of γ-PGA. [Methods] Comparative transcriptomics was employed to excavate the key genes and inhibitory factors involved in γ-PGA synthesis, and key gene overexpression and knockout were conducted to identify the inhibitory factors. Fermentation experiments were then performed for verification. [Results] The glutamate waste liquid as the substrate for production of γ-PGA by fermentation showed significant inhibitory effects. A total of 1 819 significantly differentially expressed genes were identified, including 952 genes with significantly up-regulated expression and 867 genes with significantly down-regulated expression. The transcript levels of 10 genes (alsS, pgsA, gltT, budA, fumC, ptsG, racE, opuAB, acoC, and rocG) involved in γ-PGA synthesis of B. subtilis KH2 changed significantly during primary fermentation and glutamate waste liquid fermentation. Eight down-regulated genes (alsS, pgsA, gltT, budA, fumC, ptsG, racE, and opuAB) were overexpressed, which increased the production of γ-PGA by 91.20%, 120.77%, 137.50%, 36.44%, 40.85%, 104.58%, 65.67%, and 69.72%, respectively. The overexpression of pgsA, gltT, ptsG, racE, and opuAB increased glutamic acid utilization by 11.57%, 35.53%, 12.83%, 21.43%, and 14.80%, respectively. The overexpression of alsS, budA, and fumC had no obvious improving effect on the utilization of glutamic acid. The knockout of two up-regulated genes (acoC and rocG) had little effect on γ-PGA production and glutamic acid utilization. [Conclusion] The downregulation of ptsG, gltT, racE, pgsA, and fumC in waste liquid fermentation has significant effects on substrate utilization, glutamic acid configuration conversion and polymerization, and TCA cycle, which reduces the synthesis efficiency of γ-PGA. This study reveals the inhibitory mechanism of glutamate waste liquid in γ-PGA synthesis and provides a sustainable biotechnology for the production of value-added biopolymers from industrial waste liquid.

[Objective] To investigate the in vitro uric acid degradation performance and physiological and biochemical characteristics of Limosilactobacillus fermentum H3260 isolated from human feces and examine the effects of this strain on the serum uric acid level and gut microbiota in the mouse model of hyperuricemia, providing scientific evidence for the development of functional food for the prevention and treatment of hyperuricemia. [Methods] HPLC and the uric acid production assay were employed to determine the abilities of the target strain to degrade uric acid, adenosine, and nucleosides and to inhibit xanthine oxidase. The probiotic characteristics of the strain were evaluated by antimicrobial sensitivity tests and in vitro tolerance tests. The uric acid-lowering effect of L. fermentum H3260 was verified by in vivo experiments. [Results] L. fermentum H3260 was screened out. The strain exhibited degradation rates of (86.84±0.03)% for uric acid, (60.84±2.21)% for adenine, and (100.00±0.00)% for nucleosides, along with an inhibition rate of 22.48% for xanthine oxidase. The strain was sensitive to seven common antibiotics, including erythromycin, ceftriaxone, penicillin G, and chloramphenicol. After treatment in 0.3% bile salt for 2.5 h, the bacterial count remained above 1.00×10⁶ CFU/mL. Animal experiments showed that the strain significantly reduced uric acid, creatinine, and blood urea nitrogen in hyperuricemic mice and regulate the gut microbiota to alleviate hyperuricemia. [Conclusion] We successfully screened out a strain L. fermentum H3260 capable of efficiently degrading uric acid, adenosine, and nucleosides. The strain exhibited good physiological and biochemical characteristics in vitro and significantly improved hyperuricemia-related indicators and regulated the gut microbiota in vivo, showing potential as an elite strain for the prevention and treatment of hyperuricemia.

The puparium of Hermetia illucens is rich in chitin and protein, while efficient and environmentally friendly utilization methods remain to be developed. [Objective] To isolate chitinolytic bacteria from the puparium pile of H. illucens and explore their potential in puparium biotransformation. [Methods] Strains were isolated by the plate screening method and identified by 16S rRNA gene sequencing. The 3,5-dinitrosalicylic acid (DNS) method was employed to determine the chitinase activity. Whole genome sequencing by PacBio HiFi was conducted to elucidate the degradation mechanism. The application potential of the strain was explored by puparium fermentation experiments. [Results] Among the seven isolated strains, Bacillus cereus BSF-CH1 showed the highest chitinase activity, reaching a maximum chitinase activity of 0.48 U/mL on the second day of fermentation. The genome of BSF-CH1 contained three chitinase genes, seven chitin deacetylase genes, and four chitodextrinase genes. Puparium biotransformation experiments showed that BSF-CH1 could degrade 47.2% of puparium mass within 7 days, with degradation rates of 64.6% and 59.1% for chitin and protein, respectively. [Conclusion] This study reports an efficient chitinolytic bacterium isolated from the puparium of H. illucens, providing new insights into the puparium biotransformation and having important implications for promoting the sustainable development of the H. illucens industry.

Root-knot nematodes(Meloidogyne spp.) are widely distributed and highly destructive, causing substantial economic losses in agricultural production. Biocontrol has been considered as an effective measure for managing these pathogens. [Objective] To explore efficient and eco-friendly biocontrol resources for controlling root-knot nematodes. [Methods] Bacillus strains were isolated from soil via the serial dilution method. Strains with strong nematicidal activity against Meloidogyne incognita second-stage juveniles (J2) were screened by in vitro bioassays. The selected strains were identified based on morphological, physiological, and biochemical characteristics, as well as molecular biological evidence. The biocontrol potential of these strains was further evaluated by egg hatching inhibition assays, phosphorus/potassium solubilization tests, enzymatic activity profiling, and antagonistic spectrum analysis. Additionally, pot and greenhouse experiments were conducted to validate the biocontrol efficacy of strains. [Results] Among 189 bacterial strains isolated from 16 soil samples, strains Sneb2550 and Sneb2556 demonstrated strong nematicidal activity against M. incognita J2, inducing the corrected mortality rates of 95.64% and 95.36%, respectively, after 24 h. Based on morphological features, physiological and biochemical characteristics, and 16S rRNA gene and gyrB sequences, strains Sneb2550 and Sneb2556 were identified as Bacillus proteolyticus and B. amyloliquefaciens, respectively. Functional characterization showed that strain Sneb2550 produced protease and inhibited Fusarium asiaticum, Trichothecium roseum,and Alternaria solani. Strain Sneb2556 produced protease and amylase, solubilized phosphate, and suppressed F. asiaticum, Aternaria alternata, Botryosphaeria dothidea, T. roseum, Colletotrichum gloeosporioides, and A. solani. Moreover, both strains did not adversely affect cucumber seed germination and significantly promoted the radicle growth. Under pot conditions, Bacillus Sneb2550 and Sneb2556 significantly reduced root galls formation, with the reduction rates of 56.02% and 50.19%, respectively, while promoting plant growth. Field experiments showed that root irrigation with Bacillus Sneb2550 and Sneb2556 effectively controlled cucumber root-knot nematodes, with the control effects of 60.90% and 52.63%, respectively, while promoting plant growth. [Conclusion] Bacillus Sneb2550 and Sneb2556 effectively controlled cucumber root-knot nematodes and promoted plant growth, providing new potential resources for the biocontrol of root-knot nematodes.

[Objective] Adipic acid is a key monomer for plastics such as nylon 66 and poly (butylene adipate-co-terephthalate) (PBAT), with a vast market potential. This study aims to explore the optimal expression levels of genes in the biosynthetic pathway of adipic acid. [Methods] We regulated the expression levels of genes in the adipic acid synthesis pathway by randomly combining gradient-strength constitutive promoters. The high-throughput screening based on an adipic acid biosensor was conducted to select the strain with the optimal combination. Subsequently, the fermentation media, carbon sources, metal ions, and precursor substance addition amounts were optimized. [Results] After screening, the optimal strain Escherichia coli MG1655 Δ8-D47 was obtained, with an adipic acid yield of 431.32 mg/L. After fermentation condition optimization, the yield of adipic acid in a shake flask reached 550.34 mg/L, which represented a 134% increase compared with that of the control strain Z1. [Conclusion] Metabolic pathway imbalance in microbial synthesis of adipic acid is the main factor limiting the increase in yield.

Streptococcus suis is a major pathogen in pigs and also a zoonotic pathogen. This bacterium has numerous serotypes, among which S. suis serotype 4 (SS4) is known to infect humans and poses a threat to public health due to its potential high pathogenicity. [Objective] To develop a multiplex PCR method based on specific virulence-associated genes of SS4 virulent strains to achieve precise identification of such strains. [Methods] Based on previous research results, four target genes specific to SS4 virulent strains—sly, igdE, tran, and sao—were selected, and the SS4 serotype-specific gene wzy was used as an internal reference gene to design a pentaplex PCR method. After optimization of the multiplex PCR amplification system, specificity and sensitivity tests were conducted. This method was then employed to detect newly isolated SS4 strains. Additionally, zebrafish virulence assays were performed to validate the accuracy of this method. [Results] The multiplex PCR method specifically amplified the target genes, effectively distinguishing SS4 virulent strains from lowly virulent strains. The method exhibited high sensitivity, with a minimum detection limit of 4.1×10² CFU or 12.5 pg of genomic DNA. Specificity validation confirmed that this method accurately identified SS4 virulent strains. This method was then employed to examine six clinically isolated SS4 strains. Three strains were identified as virulent, showing high pathogenicity in zebrafish and causing a mortality rate of 60.00%-86.67%. The other three strains were identified as lowly virulent strains, exhibiting low pathogenicity in zebrafish and causing a mortality rate of 0-6.67%. [Conclusion] A multiplex PCR method based on virulence-associated genes of S. suis was successfully developed, enabling accurate and sensitive identification of SS4 virulent strains. This method provides technical support for the early diagnosis and effective prevention and control of S. suis infections.

[Objective] To investigate the structural characteristics of microbial consortia in different concentrations of petroleum hydrocarbons, cultivate efficient petroleum hydrocarbon-degrading microbial consortia, and mine the strain resources capable of degrading petroleum hydrocarbons. [Methods] We used 0# diesel as the sole carbon source to domesticate oil-contaminated soil samples through five successive generations by gradually increasing the 0# diesel concentration. The structural changes of microbial consortia were uncovered by 16S rRNA gene amplicon sequencing. The strains with petroleum hydrocarbon-degrading potential were isolated and purified via dilution plating and streaking. Finally, the improved 2,6-dichlorophenol indophenol (DCPIP) cultivation system was employed to identify efficient degrading strains. [Results] During domestication, when the concentration of 0# diesel was raised to 7 000 mg/L, the relative abundance of petroleum hydrocarbon-degrading bacteria including Bacteroidota and Bacillota significantly increased. A total of 58 bacterial strains belonging to 25 genera, 22 families of 4 phyla were isolated, including 31 (53.45%) strains of Pseudomonadota, 13 (22.41%) strains of Actinomycetota, 11 (18.97%) strains of Bacillota, and 3 (5.17%) strains of Bacteroidota. From the isolated strains, 18 petroleum hydrocarbon-degrading strains were screened out. [Conclusion] Through gradient domestication, seven natural microbial consortia were successfully enriched, achieving over 70% degradation of petroleum hydrocarbons at 7 000 mg/L of 0# diesel. Amplicon sequencing revealed that varying 0# diesel concentrations altered the microbial consortium structure. Additionally, 18 strains capable of using 0# diesel as the sole carbon source were identified, providing potential microbial resources for the bioremediation of oil-contaminated soil.