Candida auris, as a multidrug-resistant fungus, pose a challenge to clinical treatment because of biofilm formation. Currently, effective intervention measures against its biofilm remain to be developed. [Objective] To explore the antifungal activity and biofilm inhibition mechanism of the Chinese medicine active compound matrine (MT) against C. auris. [Methods] The minimum inhibitory concentration (MIC), minimum fungicidal concentration (MFC), and sessile minimum inhibitory concentration (SMIC) of MT against C. auris were determined by the microdilution method. The time-growth curve and colony morphology of C. auris under the intervention of MT were observed by the plate method. The changes in the hydrolytic enzyme activity of the C. auris biofilm treated with MT were determined. The changes in cell surface hydrophobicity (CSH) of C. auris biofilm treated with MT were observed by the water-hydrocarbon two-phase method. The effects of MT on the metabolic activity and structure of C. auris biofilms were observed by the XTT method, crystal violet method, and confocal laser scanning microscopy (CLSM). The changes in the cell nucleus of C. auris in the biofilm treated with MT were detected by DAPI staining. The protective effect of MT on the host infected with C. auris was observed by the Galleria mellonella larvae infection model. [Results] The MIC of MT against C. auris was 128 μg/mL, while the MFC and SMIC were both 512 μg/mL. The inhibition mechanism of MT against the proliferation of C. auris mainly involved reducing the CSH, inhibiting the mature biofilm formation, significantly decreasing the metabolic activity, and inducing abnormal nuclear morphology. The experiments with G. mellonella larvae further confirmed that MT could alleviate the invasive damage caused by C. auris. [Conclusion] MT has a significant antifungal effect on C. auris and can effectively inhibit the biofilm formation, providing a new candidate drug and potential target for clinical treatment of multidrug-resistant C. auris infections.

[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.