[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] 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] 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.

[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] 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.

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.

[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] 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] 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.

[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.