Abstract:Chinese cabbage clubroot is a common soil-borne disease caused by Plasmodiophora brassicae Woron, which mainly damages the roots of Chinese cabbage. Rhizosphere is the most active key micro-domain of plant-soil-microbiome interaction, and the microbial imbalance in rhizosphere is a primary factor leading to soil-borne diseases. Deciphering the interaction mechanism between rhizosphere micro-ecology and soil-borne diseases is beneficial for finding safe and effective ways for the control of soil-borne diseases by rhizosphere microorganisms, disease-inhibiting substances, and functional metabolism. This paper introduced the relationship between rhizosphere micro-ecology and the occurrence of Chinese cabbage clubroot and expounded the mechanism of rhizosphere microorganisms in regulating the occurrence of clubroot disease in Chinese cabbage from the harm of the disease, rhizosphere microecology, and biocontrol strains. This review is expected to provide a theoretical basis for the control of clubroot disease in Chinese cabbage, improve soil health, and maintain the rhizosphere microecosystem stability.

Abstract:In recent years, continuous cropping obstacles have become increasingly serious, leading to adverse impacts on agricultural production and sustainable development. The causes of these obstacles are complex, in which phenolic acid toxicity is a key factor. The most economical, environmentally friendly, and effective method for removing phenolic acids is biological control. In this review, the microorganisms involved in phenolic acid degradation and their phenolic acid substrate ranges were investigated. The metabolic pathways, key enzymes, and molecular mechanisms of ferulic, vanillic, syringic, and protocatechuic acid degradation were reviewed, which enriched the knowledge of the degradation process. Furthermore, we discussed the application of phenolic acid-degrading microorganisms in improving crop rhizosphere and alleviating continuous cropping obstacles and presented the existing problems and prospects, aiming to provide a theoretical reference for further research and development. This review provides a knowledge base for the application of microbial resources in addressing continuous cropping obstacles and promoting the sustainable development of modern agriculture.

Abstract:[Background] The marine pathogenic bacterium, Photobacterium damselae, causes various diseases in marine organisms and humans. Therefore, it is of great significance to investigate the approaches for the biocontrol of P. damselae. [Objective] To investigate the activity and mechanism of bacilosarcin B from Bacillus subtilis in inhibiting P. damselae.[Methods] Bacilosarcin B was prepared from the fermentation broth of B. subtilis fmb60 by high-performance liquid chromatography. The minimum inhibitory concentration of bacilosarcin B against various pathogenic bacteria and the time-kill curve against P. damselae were determined using a spectrophotometer. The impacts of bacilosarcin B on the biofilm, extracellular nucleic acids, proteins, and intracellular alkaline phosphatase content of P. damselae were assessed. Fluorescence microscope, scanning electron microscope, and transmission electron microscope were employed to examine the cell membrane permeability and cell wall integrity of P. damselae. Finally, the effects of bacilosarcin B on bacterial motility and intracellular DNA were studied. [Results] The minimum inhibitory concentration of bacilosarcin B against P. damselae was 8 μg/mL. Bacilosarcin B disrupted the integrity of bacterial cell walls and cell membranes and increased membrane permeability to cause the leakage of cellular components. Additionally, it bound to intracellular DNA by the manner similar to the insertion of ethidium bromide into DNA. [Conclusion] Bacilosarcin B exhibits a significant inhibitory effect on P. damselae and has the potential to be developed as a novel antibacterial agent, which is of significance for the healthy development of marine aquaculture.

Abstract:[Background]The biocontrol bacteria Bacillus nematicida B16 and B. subtilis 168 present different perceptions for nematodes and have significant differences in the expression of the nematode attractant 2-heptanone.[Objective] To investigate the key factor, the thioesterase Ynep, involved in methyl ketone synthesis in B. nematicida B16 and B. subtilis 168, and compare the heterologous expression, structure, and activity of this enzyme between the two strains. [Methods] Quantitative polymerase chain reaction (qPCR) was employed to examine the transcriptional levels of thioesterase in the two Bacillus strains. Bioinformatics analysis was conducted to compare the structural differences of this enzyme. Furthermore, the heterologous expression level and activity of this protein were compared between the two strains. [Results] The transcription level of ynep in B. nematicida B16 was 1.428 and 0.991 folds of that in B. subtilis 168 at the time points of 12and 72 h, respectively. Bioinformatics analysis indicated an amino acid sequence identity of 97.12% between the two enzymes. The two enzymes were predicted to have the molecular weights of 15 993.35 Da and 16 007.42 Da and the isoelectric point (pI) values of 7.06 and 7.82, respectively. They possessed the transcriptional enhancer (TE) domain with the conserved catalytic triad Asp16-His23-Tyr26. Homology modeling revealed that both Ynep enzymes presented the typical "hot dog" fold, a common structure in the TE superfamily. Four residue differences existed between the two enzymes, potentially influencing the formation of the thioesterase tetramer. The Ynep in B. nematicida B16 and B. subtilis 168 showed the binding energy of -5.47 kcal/mol and -6.95 kcal/mol, respectively, with the substrate β-ketoacyl-CoA. The purified recombinant enzymes of B. nematicida B16 and B. subtilis 168 demonstrated the activities of 1.243 U/mL and 1.233 9 U/mL, respectively. Both enzymes exhibited optimal reaction temperatures of 30 and optimal pH 8.0 and 9.0, respectively. Both enzymes demonstrated good stability within the temperature range from 10 to 30 and at pH 7.0-8.0. Moreover, the Ynep in B. subtilis 168 had stronger thermal tolerance than that in B. nematicida B16. [Conclusion] The thioesterase Ynep in the two Bacillus strains shows differences in heterologous expression, structure, and enzyme activity, which lead to variations in the synthesis of 2-heptanone. The findings contribute to the understanding of the molecular mechanisms underlying the different perceptions of nematodes by different Bacillus strains, providing new insights for the development of efficient biocontrol products against nematodes.

Abstract:[Background] Xanthomonas campestris pv. campestris (Xcc) is the pathogen of black rot in cruciferous plants, causing immense economic losses worldwide. Therefore, it is urgent to study the pathogenic mechanism of this pathogen and develop novel methods to control this disease. The bacterial fatty acid synthesis system provides not only substrates for cell membrane synthesis but also the intermediates to be used as precursors for the synthesis of bioactive molecules. With important functions, the fatty acid synthesis system is a promising target for the screening of antibacterial agents. [Objective] To investigate the effects of Xcc fabZ on the diffusible signal factor (DSF) family signals production, pathogenicity, extracellular enzymes, extracellular polysaccharides, and motility of Xcc. [Methods] The yields of DSF family signals produced by different strains were estimated by the bioassay method with the DSF reporter strain. The replacement mutants were established from the DSF family signals high yield strain based on homologous recombination. Then, the yields of DSF family signals were determined by high performance liquid chromatography (HPLC). The pathogenicity of different strains to the host plant Brassica oleracea L. was examined by the leaf-clipping method, and the production of exopolysaccharides (EPS), extracellular enzymes, and motility were compared among different strains. [Results] The DSF family signals produced by the Escherichia coli fabZ replacement mutant (Xcc ΔfabZ/pSRK-EcfabZ) decreased sharply. Moreover, the mutant presented attenuated pathogenicity to the host plant, slow growth in the plant extract, reduced extracellular enzyme production, and weakened motility. The production of DSF family signals by the Xcc fabZ replacement mutant was restored to the level of the wild-type strain, and excessive production of EPS enhanced the pathogenicity and restored the extracellular enzymes and motility. [Conclusion] FabZ affects the production of DSF family signals and extracellular enzymes, pathogenicity, and motility of Xcc.

Abstract:[Background] Endophytic fungi capable of promoting plant growth, enhancing plant tolerance to drought, and improving plant resistance to diseases have significant research and utilization values, especially for the growth of orchid plants. [Objective] To systematically analyze the diversity and reveal the community structure of fungi in the roots and rhizosphere soil of Dactylorhiza hatagirea, so as to provide a reference for further exploring the associations between D. hatagirea and fungi. [Methods] The Illumina Miseq high-throughput sequencing was employed to analyze the diversity of fungi in the roots and rhizosphere soil of D. hatagirea. [Results] The endophytic fungi in the roots of D. hatagirea belonged to 89 genera of 7 phyla, with the dominant genera being Epulorhiza (16.93%), Cephaliophora (10.41%), Saccharomyces (5.73%), Ceratobasidium (5.32%), and Fusarium (5.12%), among which Epulorhiza and Ceratobasidium were mycorrhizal fungi in orchid plants. The fungi in the rhizosphere soil belonged to 269 genera of 11 phyla, with the dominant genera being Fusarium (8.09%), Neonectria (6.79%), Plectosphaerella (3.39%), and Mortierella (3.01%). The diversity of fungi in the rhizosphere soil of D. hatagirea was significantly higher than that in the roots. [Conclusion] This study revealed the fungal composition in the roots and rhizosphere soil of D. hatagirea in Inner Mongolia, enriching the endophytic fungi resources of this medicinal plant. The findings help to promote the research on endophytic microorganisms in the medicinal plants with limited resources, alleviate the shortage of Chinese medicinal herb resources, and protect and reasonably develop wild medicinal plant resources.

Abstract:[Background] Fusarium head blight (FHB) caused by Fusarium graminearum has caused serious economic losses to the wheat industry in China.[Objective] To isolate and screen out the Streptomyces strains with inhibitory activity on F. graminearum and provide a theoretical basis for the development and application of biocontrol strains. [Methods]A plate confrontation experiment was conducted to screen out the strain with antagonistic effects on F. graminearum. The strain was identified based on morphological, physiological, and biochemical characteristics and sequence analysis of the 16S rRNA gene. The antagonistic activity of the fermentation broth was evaluated based on the mycelial growth, conidiation, and germination of F. graminearum. The biocontrol effect of the fermentation broth was evaluated by an artificial inoculation experiment. [Results] A Streptomyces strain 21-1 showed antagonistic effect on F. graminearum, with the inhibition rate of 59.5%, and it was identified as Streptomyces flavotricini. The fermentation broth of the strain inhibited the mycelial growth, conidiation, and germination of F. graminearum. Moreover, it decreased the content of soluble protein and increased the content of malondialdehyde in the mycelia of F. graminearum. Strain 21-1 had the ability to produce protease and cellulase. The control effect of the 10-fold diluted fermentation broth of the strain on FHB was 70.1%. In addition, the fermentation broth showed antagonistic activity against eight plant pathogens. [Conclusion] Strain 21-1 has a promising prospect in the biocontrol of F. graminearum.

Abstract:[Background] Single biocontrol agents have unstable and poor lasting biocontrol effects. It is one of the effective ways to control plant diseases to develop composite microbial agents for biocontrol by studying the synergistic effect of different functional microorganisms. [Objective] To explore the biocontrol effects of different functional microbial combinations on rice blast, and develop an efficient composite microbial agent. [Methods] The biocontrol effects of Streptomyces combined with bacteria on rice blast were studied by pot and field experiments. [Results] The combination of Streptomyces Ahn75 and Bacillus amyloliquefaciens CWJ2 had the best effect, which, combined with adjuvants, showed the potting control effects of 65.07% and 63.00% on rice blast in the leaves and panicles, respectively. The combination had significantly higher biocontrol effect than the single strain Ahn75 or CWJ2 and other combinations. Moreover, this composite microbial agent can promote the growth of rice plants, increasing the number of tillers and plant height in pots by 93.33% and 9.83%, respectively. Similarly, the results of field experiments showed that this composite microbial agent reduced the incidence of rice blast, with the maximum control effect of 52.16%, which was comparable to that (52.97%) of tricyclazole. In addition, the inhibition rates of Ahn75 and CWJ2 against 14 and 16 races of Magnaporthe oryzae were higher than 50%, indicating that the composite microbial agent possessed broad-spectrum resistance to rice blast. [Conclusion] The composite microbial agent (Ahn75+CWJ2) has a promising prospect in the control of rice blast and can be used in the development and application of biopesticides.

Abstract:[Background] Pleurotus abieticola is a new species of edible and medicinal fungus with a potential economic value. [Objective] To well develop and utilize the polysaccharides in P. abieticola and develop potential functional foods. [Methods] The response surface methodology was employed to optimize the extraction process of P. abieticola polysaccharide. Furthermore, the in vitro antioxidant activities of the polysaccharide at different concentrations and Vc (positive control) were evaluated by measuring the activities in scavenging 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH), 2,2'-azinobis-3-ethylbenzthiazoline-6-sulphonate (ABTS), hydroxyl radicals (·OH) and reducing iron ions. [Results] The extraction process was optimized as extraction at a liquid-to-solid ratio of 28.87:1 (mL:g) and 60.27℃ for 122.62 min, under which the extraction rate of pure polysaccharide from P. abieticola reached a maximum value of 2.39%. The polysaccharide at the concentration of 1 mg/mL showed the DPPH, ABTS, and ·OH scavenging rates of 49.42%, 88.37%, and 19.87%, respectively, and the iron ion reducing power of 0.273. [Conclusion] This study provides a theoretical basis for the efficient development and utilization of P. abieticola polysaccharide and lays a foundation for further research on the polysaccharide bioactivity and development of polysaccharide products.

Abstract:[Background] Ectomycorrhizal fungi (ECMF) can promote plants to absorb insoluble phosphorus in the soil. [Objective] To study the mycelial growth and phosphorus solubilization of Entoloma clypeatum with different insoluble phosphorus sources, so as to provide a basis for further research and application of the fungus. [Methods] An ECMF strain was isolated by the tissue culture method and identified based on the internal transcribed spacer (ITS) sequence. The effects of lecithin, aluminum phosphate, calcium phytate, and iron phosphate on the mycelial growth, available phosphorus content, phosphorus solubility, pH, citric acid content, and acid phosphatase content of the strain were determined under pure culture conditions. [Results] The strain was identified as E. clypeatum, and its mycelia grew normally in solid and liquid media with different phosphorus sources. The mycelial growth was slow in the solid media, and the dry weight of mycelial pellets in the liquid medium supplemented with lecithin was the highest. The available phosphorus content (75.029 mg/L) and phosphorus-solubilizing rate (9.31%) of the strain were the highest in the medium containing calcium phytate and the lowest (25.880 mg/L and 0.55%, respectively) in the medium supplemented with lecithin. The pH of each fermentation broth decreased over time. The citric acid content was the highest (19.4 mmol/L) in the medium supplemented with phytic acid calcium and the lowest (12.4 mmol/L) in the medium supplemented with lecithin, which were 1.9-5.1 times that of the control group. The acid phosphatase content in the media supplemented with different insoluble phosphorus sources was 1.3-3.2 times that of the control. It was the highest (0.006 7 U/mL) in the medium with calcium phytate as the insoluble phosphorus source, with significant differences from that in the other three treatments (P<0.05). The available phosphorus content was positively correlated with phosphorus-solubilizing rate (P<0.05) and citric acid content (P<0.01) and negatively correlated with pH and mycelial pellet dry weight. [Conclusion] E. clypeatum capable of solubilizing insoluble phosphorus serves as an excellent choice to reduce the use of phosphate fertilizer. The findings provide a reference for the development and utilization of E. clypeatum and further research on the phosphorus-solubilizing mechanism of ECMF.

Abstract:[Background] Actinomycetes are a kinds of important biocontrol bacteria with strong metabolic activity, which can produce natural products such as antibiotics, enzymes, enzyme inhibitors, and hormones to inhibit the growth of pathogens. [Objective] To study the activities of the actinomycetes isolated from the rhizosphere soil of tea plants against Colletotrichum camelliae (pathogen of tea anthracnose) and Fusarium solani (pathogen of konjac stem rot) and evaluate the biocontrol potential of the isolates.[Methods] The antagonistic actinomycetes strains against C. camelliae and F. solani were isolated and screened from the rhizosphere soil of tea plants the plate dilution method, plate confrontation method, and mycelial growth assay. The isolates were identified based on the morphological characteristics, physiological and biochemical properties, and phylogenetic relationship. Furthermore, the abilities of actinomycetes to produce growth-promoting substances and secrete cell wall hydrolase were determined. [Results] A total of 14 actinomycete strains were isolated. Among them, the isolate A-dyzsc04-2, identified as Streptomyces diastatochromogenes, presented the inhibition rates of 66.71%±1.23% and 71.59%±2.46% against C. camelliae and F. solani, respectively. The 10-fold dilution of the cell-free fermentation filtrate of this strain presented the inhibition rates over 90% against the two pathogens. In addition, A-dyzsc04-2 was capable of producing siderophore and glucanase and dissolving inorganic phosphorus. [Conclusion] A-dyzsc04-2 serves as an elite biocontrol strain with a high development and utilization value. The results provide theoretical support for the application of A-dyzsc04-2 in the prevention and treatment of tea anthracnose and konjac stem rot.

Abstract:[Background] Fusarium oxysporum f. sp. niveum (Fon) is the causal agent of watermelon wilt, seriously threatening the production of watermelon in continuous cropping. [Objective] To screen out the antagonistic strain against Fon and identify the antifungal components in the cell-free supernatant (CFS), providing a theoretical basis for application of the strain in agricultural production. [Methods] Plate confrontation was employed to screen the antagonistic strain against Fon. Pot experiments were conducted to verify the control effect of the antagonistic strain on watermelon wilt. Scanning electron microscopy and confocal microscopy were employed to observe the conidial morphology and membrane integrity of Fon. The activities of antioxidant enzymes were determined to evaluate the oxidative damage. Whole genome sequencing through second-generation Illumina Hiseq combined with third-generation PacBio Sequel sequencing platform, LC-MS-based non-target metabolomics, and ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UHPLC-ESI-MS/MS) were employed to identify the antifungal substances in the secondary metabolites of the strain. [Results] An antagonistic strain J4 was screened out from the rhizosphere soil of healthy watermelon. The pot experiments showed that its control effect against watermelon wilt was 72.6%. The strain was identified as Bacillus methylotrophicus J4 by whole genome sequencing, and it could produce protease, amylase, glucanase, cellulose, and siderophores. The CFS of J4 in the decline stage presented the inhibition rate of 71.87% on the growth of Fon. Moreover, it led to the collapsing of Fon spore surface, destroyed the integrity of the cell membrane, and caused cell death. Strain J4 induced the accumulation of reactive oxygen species (ROS) in the mycelia of Fon. The CFS of strain J4 significantly increased the activities of superoxide dismutase, catalase, peroxidase, and glutathione reductase and the content of soluble protein and malondialdehyde in the mycelia of Fon. The genome of strain J4 carried 13 gene clusters for the synthesis of secondary metabolites with antimicrobial functions. The CFS of strain J4 contained three peptides, which were proved to inhibit the growth of Fon. It was hypothesized that the antifungal functional substances in the CFS of strain J4 were iturin A, fengycin, and surfactin. [Conclusion] Strain J4 had a strong control effect on watermelon wilt and could be used to control watermelon wilt in the future.

Abstract:[Background] Environmental factors affect the microbial growth and metabolism. Therefore, understanding their influences on microbial community succession in the semi-open fermentation process is of great significance for the production regulation of light flavor Baijiu. Distilled grains play a role in regulating the fermentation speed of Baijiu, while their effects on microbial community succession are still unclear. [Objective] To reveal the effects of distilled grains fermented for different time periods on the environmental factors and microbial community succession during light flavor Baijiu fermentation. [Methods] The high-throughput sequencing on PacBio platform and multivariate statistical analysis were performed to reveal the microbial community structures in two different groups of fermented grains. Monte Carlo permutation tests were conducted to determine the effects of environmental factors on microorganisms. [Results] The fermented grains prepared with distilled grains produced in extended fermentation period (EG) had lower water content and higher acidity, amino acid nitrogen, total free amino acids, reducing sugar, and residual starch than those prepared with distilled grains produced in normal fermentation period (NG). The fermented grains with EG had higher bacterial alpha diversity (P<0.001) and lower fungal alpha diversity than those with NG (P<0.05, P<0.001). A total of 28 differential bacterial indicator species and 15 differential fungal indicator species between groups were identified. Water content, acidity, amino acid nitrogen, reducing sugar, residual starch, and total free amino acids had effects on the microbial community structure (P<0.05). Among them, water content, acidity, amino acid nitrogen, and total free amino acids were associated with the microbial community of fermented grains with EG, and reducing sugar and residual starch were the main driving factors for the microbial community succession of fermented grains with NG. [Conclusion] The effects of environmental factors on microbial community assembly in the fermentation process of light flavor Baijiu with distilled grains produced in different fermentation periods were revealed, laying a foundation for the controlled brewing of light flavor Baijiu.

Abstract:[Background] Seneca valley virus (SVV) can cause severe blistering in pigs. Due to the lack of commercial vaccines, it is essential to probe into the interactions of SVV with host antiviral molecules. [Objective] To investigate the role of the E3 ubiquitin ligase, F-box and WD repeat domain containing 7 (FBXW7), in anti-SVV infection. [Methods] The small interfering RNA (siRNA) was employed to knock down FBXW7. RT-qPCR, TCID₅₀, and Western blotting were employed analyze the effect of FBXW7 on SVV replication and cytokines in PK-15 cells. [Results] Western blotting results showed that SVV infection down-regulated the expression of FBXW7 in PK-15 cells. The knockdown of FBXW7 promoted SVV replication and down-regulated the mRNA levels of interleukin-6 (IL-6), interferon-β (IFN-β), and tumor necrosis factor-α (TNF-α). When ATG5 was knocked down to inhibit autophagy, FBXW7 protein degradation was inhibited and SVV replication decreased. [Conclusion] FBXW7 has an inhibitory effect on the replication of SVV which mediates FBXW7 degradation by activating autophagy. The finding provides a new strategy for the development of antiviral targets.

Abstract:[Background] Pasteurella multocida can cause various diseases such as porcine pulmonary disease, bovine hemorrhagic sepsis, and rabbit hemorrhagic sepsis, posing a serious threat to the healthy development of the animal husbandry in China. [Objective] A rabbit farm in Chongqing sent a batch of sick and dead rabbits for examination. To study their pathogens and treatment methods, we carried out microbial isolation and whole genome sequencing for the pathogens. [Methods] The bacterial isolation and purification, biochemical testing, 16S rRNA gene identification, capsule serotyping, drug susceptibility testing, and virulence gene testing were conducted with the diseased rabbit samples from a rabbit farm in Chongqing, 2022. The whole genome sequencing results were employed to annotate the virulence genes and drug resistance genes and build the phylogenetic tree. [Results] The isolate was identified as a rabbit-derived type A Pasteurella multocida strain belonged to the sequence type ST74 and named LXSS001. The genome sequence was uploaded to NCBI (collection number:CP119523.1). The strain was resistant to tetracycline, compound sulfamethoxazole, and sulfamethoxazole, while it was sensitive to cefotaxime, cefoperazone, and amikacin and so on. The strain had the whole genome length of 2 480 671 bp and carried 58 virulence genes and resistance genes for 9 classes of antibiotics. The phylogenetic tree showed that LXSS001 had the highest homology with the 3480 strain. [Conclusion] This study completed the isolation, identification, and whole genome sequencing of a type A P. multocida strain and revealed its phylogenetic relationship with other isolates, providing a basis for the subsequent research on P. multocida.

Abstract:[Background] The irregular use of antimicrobials and disinfectants in quail breeding has exacerbated the spread of drug-resistant strains between animals, premises, and food. So it is important to understand the drug-resistant status of pathogenic strains of farmed animals. [Objective] To detect the drug resistance characteristics and the prevalence of drug resistance genes in the pathogenic strains derived from quail eggs in the quail farms around Beijing. [Methods] The samples of quail cloacal feces, quail egg surface, breeding environment, and quail drinking water were collected from some quail farms in Wuqing District, Tianjin. A strain was isolated and identified by colony morphology observation, staining microscopy, and biochemical tests. Serotyping and invA sequencing were carried out for this strain. Furthermore, the mouse challenge test was performed to determine the median lethal dose (LD₅₀), and the drug susceptibility test and PCR were employed to detect the drug resistance phenotypes and genes and the virulence genes of the isolates. [Results] The colony color, microscopic morphology, and biochemical properties of the isolates were consistent with those of Salmonella. The invA sequencing results showed that the strain had 99.44% homology with the reference strain of Salmonella Typhimurium, and thus it was identified as S. Typhimurium, with the serotype being 1,4,[5],[12]:i:l,2. The strain had pathogenic effect on mouse, with the LD₅₀ of 2.10×10⁷ CFU/mL. It was resistant to ampicillin, amoxicillin/clavulanate, ceftiofur, streptomycin, sulfamethoxazole, sulfafurazole, norfloxacin, and ciprofloxacin and sensitive to ten antibiotics such as cefazolin. The strain presented enhanced resistance to cationic surfactants and peroxide disinfectants. It carried four resistance genes such as bla_TEM and thirteen virulence genes such as mogA. [Conclusion] A pathogenic Salmonella Typhimurium strain was isolated from a quail farm. It has multi-drug resistance and carries multiple virulence genes. The results provide a reference not only for the hazard assessment but also for the formulation of prevention and control measures of Salmonella from quails.

Abstract:[Background] In fungi, chitin is an important component of the cell wall and synthesized under the catalysis of chitin synthase (CS). Its presence and expression pattern in Flammulina filiformis remain unclear. [Objective] To investigate the number of CS genes and their expression patterns in F. filiformis at different development stages, so as to provide a basis for revealing the roles of these genes in the growth and development of macrofungi. [Methods] The genome data of F. filiformis L11 and the CS sequences of other fungi in the NCBI database were employed to identify the CS genes in F. filiformis. Bioinformatics analysis and phylogenetic analysis were then carried out for these genes. Furthermore, the transcriptome data of F. filiformis F19 and RT-qPCR were employed to analyze the expression patterns of the CS gene family in F. filiformis. [Results] In the genome of the single-spore strain L11 of F. filiformis, nine chitin synthase genes were identified. Phylogenetic analysis revealed that they belong to four distinct classes. The expression patterns of these genes during fruiting body development can be classified into four categories (Pearson correlation coefficient=0.85). [Conclusion] The expression patterns of the CS gene family in F. filiformis show variations at different growth and developmental stages, indicating their potential involvement in morphogenesis of different tissues and developmental stages in the fruiting body formation of F. filiformis.

Abstract:[Background] Bacillus thuringiensis (Bt) LM1212 with a unique differentiation phenotype has been identified. It carries 14 insecticidal genes, which comprise 10 transcription units. With the crystal producing cell regulator (CpcR) derived from the LM1212 strain and the cry35-like gene promoter activated by CpcR, the non-sporulating expression system of insecticidal protein has been successfully established in the typical Bt strain HD73. [Objective] To compare the transcriptional activities of different insecticidal gene promoters of strain LM1212, identify the promoters with high transcriptional activity and activated by the transcription factor CpcR, and optimize the non-sporulating expression system. [Methods] Ten promoter regions were respectively fused with lacZ reporter gene on the pHT304-18Z vector, and 10 recombinant plasmids were obtained. The cpcR gene and its promoter (P_cpcR-cpcR) were reversely integrated in the upstream region of each selected promoter region and the lacZ reporter gene, and 10 recombinant plasmids capable of expressing CpcR and corresponding to the above construction were obtained. Subsequently, these recombinant plasmids were separately transferred into the HD73 strain without CpcR, and thus 20 recombinant strains were obtained for the determination of β-galactosidase activity. The expression of insecticidal protein was determined by microscope observation and SDS-PAGE. [Results] In HD73 strain, the transcription of the promoters P₁, P₃, P₄, P₅, P₆, P₇, and P₈ could be activated by CpcR, while that of the promoter P₁₀ was inhibited by CpcR. In the presence of CpcR, P₇ and P₈ showed high transcriptional activities. Vip3Aa11 protein with strong activity against Spodoptera frugiperda was successfully expressed by CpcR combined with P₇ and P₈. [Conclusion] The screened promoter with high transcriptional activity can be used to optimize the non-sporulating expression system of insecticidal protein, so as to construct novel bacteria for the biocontrol of S. frugiperda.

Abstract:[Background] Candida albicans is a conditional pathogenic fungus capable of causing severe mucosal and systemic fungal infections and one of the major fungi leading to high morbidity and mortality in patients. [Objective] To study the inhibitory activity and mechanism of thyme essential oil against C. albicans. [Methods] The inhibitory zone diameters of 5 thyme essential oils against C. albicans were determined, and the components of the essential oils with high inhibitory activity were identified. Scanning electron microscope (SEM) was employed to observe the effect of essential oils on the morphology of C. albicans. The alkaline phosphatase (AKP) content and extracellular solution conductivity were determined, and propyl iodide (PI) staining was performed, on the basis of which the effects of essential oil on the biofilm formation and adhesion and the phospholipase activity of C. albicans were determined. In addition, real-time fluorescence quantitative PCR was conducted for the lectin-like sequence gene ALS4 involved in the biofilm formation, HWP1 involved in the switch from yeast growth to hyphal growth, and the phospholipase gene PLB1 to reveal the inhibitory mechanism of this essential oil on C. albicans. [Results] The Organic Thymus vulgaris CT borneol essential oil (TBEO) with the strongest inhibitory effect on C. albicans was selected, which showed the inhibition zone diameter was (36.0±4.8) mm. The main components of TBEO were α-terpineol (43.43%), camphene (8.97%), caryophyllene (7.70%), carvacrol (5.81%), and linalool (5.19%), which accounted for about 70% of the total TBEO. The results of SEM showed that TBEO caused concave surface and distorted cells of C. albicans. TBEO increased the permeability of the cell membrane and cell wall of C. albicans, causing the leakage of intracellular substances. TBEO inhibited the biofilm formation and exerted a scavenging effect on the formed biofilm of C. albicans. TBEO reduced mycelium formation, affected adhesion, and decreased phospholipase activity. Real-time fluorescence quantitative PCR results showed that TBEO significantly down-regulated the expression levels of HWP1, ALS4, and PLB1. [Conclusion] TBEO exerts an inhibitory effect on C. albicans. This study provides a theoretical basis for the application of TBEO in the prevention and control of C. albicans infection.

Abstract:The stringent response refers to a process in which bacteria respond to nutrient deprivation and environmental stress by synthesizing the alarmones guanosine tetra- and penta-phosphate (collective referred to as (p)ppGpp) under the catalysis of the RelA/SpoT enzyme, which induces the shut-down of the transcription of rRNAs, tRNA, and ribosomal protein genes, thereby halting the translation of proteins and tightly controlling most metabolic activities. Stringent response is a key mechanism employed by the majority of bacteria to cope with adversity. The Chinese publications have inconsistent translations of "stringent response". In view of this problem, we analyzed and discussed the regulatory mechanism, physiological function, and literal meaning of stringent response, and determined a more reasonable and accurate Chinese translation of this term.

Abstract:“Biofilm” refers to an aggregated bacterial film in which bacterial cells wrap themselves by secreting extracellular polymeric substances (EPS) after attaching to abiotic or biotic surfaces. The formation of a biofilm includes five stages:attachment, colonization, development, maturation, and active dispersal. A biofilm is a dynamic bacterial community with a complex structure and multiple functions, so the bacteria in a relatively stable microenvironment have stronger resistance to stress, which makes pathogens more difficult to be eliminated and promotes the survival and colonization of probiotics in the host. At present, there is confusion in the Chinese translation of "biofilm", and no clear conclusion as to which usage is more appropriate. In view of this problem, this paper analyzed the formation process, physiological functions, and current usage of "biofilm", and finally determined the most appropriate Chinese translation of this word.

Abstract:[Background] The recent years have witnessed the increasing incidence of Clostridium difficile infection (CDI) in patients with inflammatory bowel disease (IBD), which has attracted widespread attention from scholars. China started the research late in this field, while there were a large number of patients. Learning from international research on IBD combined with CDI is of great significance for improving China's research in this field. [Objective] To help researchers grasp the research topics, directions, hotspots, and frontiers in the correlation between IBD and CDI by bibliometric and visual analysis. [Methods] The articles about CDI and IBD were searched against the Science Citation Index-Expanded (SCI-E) in the Web of Science (WOS) and CNKI. CiteSpace 6.2.2r was employed to analyze the authors, research institutions, countries, and keyword co-occurrence, citations, and journal co-citation, and the results were visualized. [Results] After data retrieval and duplicate checking, 1 030 articles published by WOS and 80 articles by CNKI were included for analysis. On a global scale, the United States was the country with the most publications. The major research institutions included Harvard University, University of California System, and Mayo Clinic. The prolific authors included Khanna S, Shen B, and Ananthakrishnan AN. High-frequency keywords included Inflammatory bowel disease, Ulcerative colitis, Clostridium difficile, Clostridium difficile infection, and Crohn's disease. The articles were clustered into the categories of Diarrhea, Ulcerative colitis, Probiotics, Pouchitis, Gut microbiota, Fecal microbiota transplantation, Depression, Entamoeba histolytica, Pseudomembranous colitis, Clostridium difficile, and Clindamycin. In China, the major research institutions included Southern Medical University and Hebei Medical University, and the prolific authors included WANG Pu and WANG Siqi. The high-frequency keywords included Fecal bacteria transplantation, Clostridium difficile, Gut microbiota, Risk factors, and Crohn's disease. The articles in Chinese were clustered into the categories of Clostridium difficile, Probiotics, Risk factors, Diarrhea, and Fecal bacteria transplantation. [Conclusion] The CiteSpace-based visual analysis of the correlation between CDI and IBD shows that this research direction still receives the attention from medical institutions and researchers worldwide. The keywords of Diarrhea and Fecal microbiota transplantation represent the research hotspots in the WOS and CNKI, respectively.