[Objective] To understand the microbial community structure and its relationship with soil quality in the rhizosphere of the dominant plant Xanthium sibiricum in the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir. [Methods] We collected the rhizosphere soil samples of X. sibiricum exposed to different flooding stress conditions in a typical WLFZ in Yunyang County, the heart of the Three Gorges Reservoir area. High-throughput sequencing was carried out to analyze the microbial diversity and community structure, and the redundancy analysis was then conducted. [Results] Proteobacteria was the dominant bacterial phylum in the rhizosphere bacteria of X. sibiricum under strong flooding stress (XaRLL) and weak flooding stress (XaRHL), while Ascomycota and Basidiomycota were the dominant fungal phyla in the two types of soil, respectively. Regardless of bacteria or fungi, the linear discriminant analysis effect size (LEfSe) showed that XaRLL always had more key biomarkers than XaRHL. Functional prediction revealed that PWY-3781 associated with aerobic respiration was a dominant metabolic pathway enriched by microorganisms from both XaRLL and XaRHL. Overall, the bacteria and fungi in the rhizosphere of X. sibiricum had strong responses to changes in soil physicochemical properties and enzyme activity. [Conclusion] The results provide a theoretical basis for understanding the relationship between plants and their rhizosphere microorganisms in the WLFZ, as well as their adaptability to strong flooding stress.

[Objective] To isolate and identify actinomycetes from two mangrove soil samples in Quanzhou Bay as well as secondary metabolites from the target strain Streptomyces sp. W444 with antifungal activity. [Methods] The rhizosphere soil samples of two different mangrove plants were collected from Luoyang River in Quanzhou Bay. Actinomycetes were isolated from the soil samples by the dilution plating method. The isolates were classified by the phylogenetic tree constructed based on 16S rRNA gene sequences. The antifungal activities of the isolates were examined by the agar diffusion method. The target strain Streptomyces sp. W444 was subjected to fermentation scale-up for the isolation of secondary metabolites. Furthermore, the biosynthetic gene clusters were analyzed to deduce the biosynthetic pathway of staurosporine. [Results] A total of 56 strains of actinomycetes were isolated from mangrove soil samples and categorized into 8 genera belonging to 6 families of 6 orders. Among them, Streptomyces and Micromonospora were dominant, with the relative abundance of 41.0% and 33.9%, respectively. Strain Streptomyces sp. W444 exhibited excellent antifungal activity, and three indoles (staurosporine, K252c, and streptochlorin) were isolated and identified from this strain. The biosynthetic gene cluster of staurosporine was localized in the genome of Streptomyces sp. W444 by bioinformatics analysis. The biosynthetic pathway of staurosporine was then proposed. [Conclusion] Actinomycetes in the rhizosphere soil of mangrove plants in Quanzhou Bay had high diversity and contained potential natural product resources. Staurosporine, K252c, and streptochlorin were isolated from strain W444. These findings lay a solid foundation for studying the diversity and secondary metabolites of cultivable actinomycetes in mangrove forests in Quanzhou Bay.

[Objective] To isolate the strain for solubilizing both inorganic and organic phosphorus (P) from the rhizosphere of Moso bamboo (Phyllostachys edulis) and mine the related genes, laying a foundation for activating the soil P pool and improving P bioavailability by P-solubilizing microorganisms (PSM). [Methods] High-throughput screening was employed to isolate PSM strains from the rhizosphere of Moso bamboo, an important economic plant in subtropical regions. The P-solubilizing activities of the strain under various carbon sources and soil P levels were investigated by microplate culture and soil inoculation experiments, respectively. The genes involved in P solubilizing of the strain were mined by whole-genome sequencing. [Results] The strain zafu-3 (Achromobacter xylosoxidans) capable of solubilizing P via multiple pathways was isolated from the rhizosphere of Moso bamboo. The strain solubilized Ca₃(PO₄)₂, FePO₄, AlPO₄, lecithin, and calcium phytate by using four carbon sources such as glucose and citric acid, with the highest P-solubilizing activity of 32.75 mg/(L·d). Compared with the control group, the zafu-3 inoculation group showed increases of 4.21%-33.88% and 13.54%-112.06% in activities of acid phosphatase and alkaline phosphatase, respectively. In the high P-level soil, inoculation of the strain decreased the soil pH by 0.04 and increased the available P content by 16.32%. The whole genome of strain zafu-3 contained 35 genes encoding phosphohydrolases and 53 genes involved in organic acid metabolisms. Furthermore, strain zafu-3 carried the genes associated with the production of indole-3-acetic acid and siderophores, and the degradation of lignin. [Conclusion] Strain zafu-3 directly solubilized inorganic and organic P by secreting diverse organic acids and phosphatases, and indirectly activated soil P pools by promoting plant growth. These findings provide an important microbial resource and theoretical foundation for the development of multifunctional biofertilizers.

[Objective] To explore the role of VraSR in regulating the biological functions of Staphylococcus epidermidisvia the CidA-LrgAB system. [Methods] The recombinant plasmid pKOR1-ΔlrgAB was constructed and then electroporated into SE1457 ∆vraSR to delete lrgAB from the genome of ∆vraSR by homologous recombination. The suspected mutant ∆vraSR-lrgAB was verified by PCR, RT-PCR, and sequencing. The growth, drug susceptibility, autolysis, and biofilm formation of ∆vraSR-lrgAB were determined. [Results] The S. epidermidis mutant ∆vraSR-lrgAB was successfully constructed. Compared with SE1457, ∆vraSR, and ∆lrgAB, ∆vraSR-lrgAB exhibited retarded growth, especially at 25 ℃ and 40 ℃ (P<0.001), increased drug susceptibility (P<0.01), enhanced autolysis (P<0.001), and reduced biofilm formation (P<0.01). [Conclusion] VraSR may regulate the growth, drug susceptibility, autolysis, and biofilm formation of S. epidermidis partly via the LrgAB system.

Salmonella as common zoonotic pathogens can cause a variety of foodborne diseases. Salmonella Typhimurium (STM) is one of the key serotypes, and the research, prevention, and control of STM are of great significance to public health. [Objective] To investigate the effects of greA and greB on the biological characteristics and pathogenicity of STM. [Methods] Red homologous recombination was employed to construct the greA- and greB-deleted STM strains well as the complemented strains. The strains were then characterized in terms of growth characteristics, biofilm formation, and adhesion and invasion in Caco-2 cells. Mouse models were used to evaluate the effects of greA and greB deletion on STM pathogenicity. [Results] The mutant strains STM LT2ΔgreA and STM LT2ΔgreB were successfully constructed. Compared with the wild-type strain, the deletion of greA and greB did not affect the cell growth rate, while inhibiting the biofilm formation, adhesion, and invasion of STM. In addition, the deletion of greA and greB decreased the colonization of STM in the liver and spleen of mice, increasing the LD₅₀ of STM by 39.81 times and 2.5 times, respectively. [Conclusion] The deletion of greA and greB could reduce the pathogenicity of STM. This finding provides a theoretical basis for further revealing the pathogenicity of Salmonella.

Galacto-oligosaccharides (GOS) as prebiotics can regulate gut microbiota to improve brain development, whereas antibiotics can affect the nervous system by interfering with gut microbiota. The mechanisms of antibiotics and GOS in regulating brain neurotransmitters and animal behaviors remain unknown. [Objective] To investigate the effects of antibiotics and GOS on the behaviors and neurotransmitters in weaned Sprague-Dawley (SD) rats. [Methods] Forty 3-week-old male SD rats were selected and assigned into four groups: control (CON, sterilized water), antibiotics (ABX), GOS (5 g/L), and antibiotics+GOS (AG). The antibiotics used in the experiment were composed of ampicillin, vancomycin, ciprofloxacin hydrochloride, imipenem, and metronidazole. The experiment lasted for 16 days. [Results] The body weight of rats in the ABX group was lower than that in the GOS group (P<0.05), and the liver index in the ABX, GOS, and AG groups was lower than that in the CON group (P<0.05). Compared with the CON group, the ABX group showcased decreased phototaxis index (percentage of time in bright during bright-dark box test) and reduced times of self-grooming (P<0.05), and the GOS group had reduced times of self-grooming (P<0.05). The AG group had longer resting time in the open field than the other three groups (P<0.05) and shorter distance, shorter time, and slower movement than ABX and GOS groups (P<0.05). Compared with the CON group, the ABX group showcased elevated level of norepinephrine and lowered level of levodopa in the hippocampus (P<0.05). Compared with the CON group, the GOS and AG groups demonstrated elevated levels of norepinephrine and declined levels of levodopa and epinephrine (P<0.05). Compared with the CON group, the ABX and AG groups presented decreased microbial diversity (P<0.05), where Escherichia_Shigella became dominant. The Chao1 index in the GOS group was lower than that in the CON group (P<0.05). The dominant bacteria in the GOS group were Firmicutes and Bacteroidota. Compared with that in the ABX group, the relative abundance of Lactobacillus increased in the AG group (P<0.05). [Conclusion] ABX decreased anxiety-like behaviors compared with CON, while reducing levodopa and increasing norepinephrine in the hippocampus and enriching potentially pathogenic bacteria. GOS improved growth without influencing the behaviors of rats, and meanwhile it increased the relative abundance of Lactobacillus and decreased levodopamine and norepinephrine in the hippocampus. The combined use of ABX and GOS decreased the locomotor activity and increased the anxiety-like behaviors of rats.

The antibiotic resistance and virulence of Acinetobacter baumannii are increasingly serious. Studies have shown that the CRISPR-Cas system in A. baumannii attenuates the antibiotic resistance and virulence, while the effects of CRISPR-Cas system components on A. baumannii remain unclear. [Objective] Investigation of the role of components of the CRISPR-Cas system in the modulation of bacterial drug resistance and virulence in A. baumannii. [Methods] The impact of cas1 overexpression on bacterial growth, serum resistance, bacterial drug resistance, biofilm formation ability, and survival rate of mice in a mouse model of bacterial infection was investigated by constructing cas1 overexpression strains and corresponding with them to detect the aforementioned changes. [Results] The resistance of the bacterial strain AB26::cas1 to 22 commonly used antibiotics was determined using the paper diffusion method. Of these antibiotics, six were found to have an effect on the strain, causing it to change from resistant to sensitive. The capacity of the bacterial strain AB26::cas1 to form biofilms was evaluated through the use of crystal violet staining, which revealed a reduction in biofilm formation ability when compared to the AB26 strain. The intraperitoneal injection of the infected mice model demonstrated that no mortality occurred in the AB26::cas1 strain in vivo infected group in comparison to the AB26 strain in vivo infected group. The fluorescence quantitative PCR assay demonstrated a reduction in mRNA expression of the majority of resistance and toxicity genes. The survival assay, which involved incubating normal human serum with inactivated serum, revealed no statistically significant difference in serum resistance between the wild strains and the overexpression strains. [Conclusion] The cas1 gene, derived from strain AB43, was observed to exert an inhibitory effect on the drug resistance and biofilm-forming ability of A. baumannii, as well as the pathogenicity of the bacteria in mice.

[Objective] To investigate the invitro inhibitory activity of Gan Dan oral liquid (GD) against Vibrioparahaemolyticus and decipher the inhibition mechanism at the transcriptome level. [Methods] The invitro inhibitory activity of GD against V. parahaemolyticus was evaluated based on the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and growth curve. Scanning electron microscopy and transmission electron microscopy were employed to analyze the effect of GD on the cellular structure of V. parahaemolyticus. Transcriptome sequencing coupled with bioinformatics methods were employed to investigate the effect of GD at 1/4MIC on the transcriptome of V. parahaemolyticus, and the obtained results were examined by real-time quantitative reverse transcription PCR (RT-qPCR). [Results] GD exhibited high invitro inhibitory activity against V. parahaemolyticus, with the MIC and MBC of 7.6 mg/mL and 15.2 mg/mL, respectively. The GD treatment at a concentration of 1/4MIC disrupted the cell wall integrity and increased cell membrane permeability of the pathogen, and leading to the leakage of intracellular macromolecules. The results of transcriptome sequencing showed that GD treatment significantly altered the transcriptome profile of V. parahaemolyticus, resulting in significant upregulation of 1 074 genes and significant downregulation of 1 179 genes. The downregulated genes were mainly enriched in pathways related to the synthesis of inosinate and ribonucleoside, whereas the upregulated genes were primarily categorized into pathways associated with transcription factor activity and cell wall synthesis. [Conclusion] GD may inhibit V. parahaemolyticus by disrupting cell structure and inhibiting cellular energy metabolism and biosynthesis.

[Objective] In view of the difficulty in the culture of chemoautotrophic bacteria, this study analyzed the reasons for the difficulty based on the theory of electron distribution and explored the feasibility of using the electron distribution strategy for increasing the biomass of chemoautotrophic bacteria based on pure culture. [Methods] From the perspective of maintaining intracellular pH balance and optimal energy metabolism, we calculated the optimal distribution ratios of electrons produced by the sulfur-oxidizing bacterial strain Halothiobacillus sp. DCM-3, nitrite-oxidizing bacterial strain Nitrobacter sp. N1, and ammonia-oxidizing bacterial strain Nitrosomonas sp. SCUT-1 to O₂ and CO₂ by oxidizing corresponding substrates. Furthermore, different molar ratios of O₂ to HCO₃^- (CO₂) were set respectively to form different electron distribution ratios for pure culture verification of the strains. Substrate and product concentrations were measured by ion chromatography and ultraviolet spectrophotometry, and cell density was measured by the dilution coating method. [Results] The optimal electron distribution ratios of strains DCM-3, N1, and SCUT-1 were 0.733:0.267, 0.867:0.133, and 0.6:0.4, respectively. Based on the optimal electron distribution ratios, strains DCM-3, N1, and SCUT-1 could synthesize 3.967 ATP/S₂O₃^2-, 0.433 ATP/NO₂^-, and 1.35 ATP/NH₃, respectively. According to the calculation results, the main reasons for the difficulty in culture were the small amount of ATP synthesized with the energy provided by per unit substrate and the need to control a low oxygen concentration and supplement an appropriate amount of inorganic carbon. The results of pure culture verification showed that the biomass of DCM-3 under the optimal ratio was 6.5×10⁷ CFU/mL, which was 2.2 times that of the control group. The biomass of N1 under the optimal ratio was 7×10⁶ CFU/mL, which was not significantly different from that of the control group. However, the HCO₃^- concentration (0.4 mmol/L) of the optimal ratio of strain N1 was significantly lower than that (2.5 mmol/L) of the control group, which meant that the strain showed a growth characteristic of tending to higher oxygen concentration but lower CO₂ demand, which was consistent with the calculated optimal ratio. The biomass accumulation per unit NH₄⁺ concentration of SCUT-1 strain in the group with controlled O₂ and CO₂ was more than 1.3×10⁶ CFU/(mL·(mmol/L)), which was 25%-40% higher than that obtained under sufficient O₂ and CO₂. [Conclusion] The culture strategy of chemoautotrophic bacteria based on electron distribution restricts the culture conditions of electron distribution by limiting the molar amounts and forming a certain ratio of O₂ and CO₂, which helps to improve the biomass accumulation under the same substrate condition and provides certain strategic reference for the culture of chemoautotrophic bacteria.

[Objective] To develop a rapid detector for biochemical oxygen demand (BOD) in the wastewater from ships entering ports in response to the stringent mandates of the International Maritime Organization (IMO). The objective is to facilitate swift detection of domestic wastewater produced by the multitude of vessels arriving at the port. [Methods] When testing the BOD standard solution, Clostridium butyricum and Bacillus subtilis were used to manufacture the biosensitive elements inducing electron transfer during the consumption of dissolved oxygen (DO), which led to a change in electrical conductivity (COND). By treating dissolved oxygen as a pivotal indicator and an intermediary in the monitoring process, this study explored the correlation between changes in electrical conductivity and sample concentration. Through the development of a quadratic polynomial fitting model that correlates electrical conductivity with dissolved oxygen levels, and by establishing a connection between dissolved oxygen and sample concentration, this research delves into the correlation between variations in electrical conductivity and the concentration of the sample. [Results] The changes in electrical conductivity exhibited by different solutions enabled the detector to rapidly distinguish between the wastewater with a BOD concentration higher than 25 mg/L (the slope of the COND variation value is less than -0.01) and that below 25 mg/L (the slope of the COND variation value is greater than -0.01). By establishing a highly correlated fitting curve between dissolved oxygen and electrical conductivity (coefficient of determination R²=0.977 83), this study achieved precise reading of samples within the ultra-low concentration range (BOD<25 mg/L). The accuracy rate of the measurements exceeded 85% in the in-suit tests conducted in Qinhuangdao, Hebei, China. [Conclusion] The measurement data read by the rapid detector for BOD is highly consistent with the results obtained by the dilution inoculation method. Moreover, the detector is capable of performing rapid quantitative analysis of BOD in domestic wastewater from ships entering ports within 30 min, demonstrating high detection efficiency.