Search

Vibrio alginolyticus is a common opportunistic pathogen of fish, shrimp, and shellfish, and many diseases it causes can result in severe economic losses in the aquaculture industry. Causing host disease was confirmed by several virulence factors of V. alginolyticus. To date, there have been no reports on the effect of the pstS gene on its virulence regulation of V. alginolyticus. The virulence mechanism of target genes regulating V. alginolyticus is worthy of further study. Previous studies found that Fructus schisandrae (30 mg/mL) inhibited the growth of V. alginolyticus ND-01 (OD600 = 0.5) for 4 h, while the expressions of pstS and pstB were significantly affected by F. schisandrae stress. So, we speculated that pstS and pstB might be the virulence genes of V. alginolyticus, which were stably silenced by RNAi to construct the silencing strains pstS-RNAi and pstB-RNAi, respectively. After the expression of pstS or pstB gene was inhibited, the adhesion capacity and biofilm formation of V. alginolyticus were significantly down-regulated. The chemotaxis and biofilm formation ability of pstS-RNAi was reduced by 33.33% and 68.13% compared with the wild-type strain, respectively. Sequence alignment and homology analysis showed that pstS was highly conserved, which suggested that pstS played a vital role in the secretion system of V. alginolyticus. The pstS-RNAi with the highest silencing efficiency was selected for transcriptome sequencing. The Differentially Expressed Genes (DEGs) and GO terms were mapped to the reference genome of V. alginolyticus, including 1055 up-regulated genes and 1134 down-regulated genes. The functions of the DEGs were analyzed by GO and categorized into different enriched functional groups, such as ribosome synthesis, organelles, biosynthesis, pathogenesis, and secretion. These DEGs were then mapped to the reference KEGG pathways of V. alginolyticus and enriched in commonalities in the metabolic, ribosomal, and bacterial secretion pathways. Therefore, pstS and pstB could regulate the bacterial virulence of V. alginolyticus by affecting its adhesion, biofilm formation ability, and motility. Understanding the relationship between the expressions of pstS and pstB with bacterial virulence could provide new perspectives to prevent bacterial diseases. [ABSTRACT FROM AUTHOR]

Aeromonas hydrophila infections are common in aquaculture. Our previous studies found that the A. hydrophila B11 strain can survive in fish macrophages for at least 24 h and the two‐component system EnvZ/OmpR may be involved in intracellular survival. To reveal the role and mechanism of the two‐component system EnvZ/OmpR in intracellular survival of A. hydrophila, the genes of envZ/ompR were silenced by shRNAi. The results showed that the survival rates of the envZ‐RNAi and ompR‐RNAi strains were only 2.05% and 3.75%, respectively, which were decreased by 91% and 83.6% compared with that of the wild‐type strain. The escape ability of envZ‐RNAi and ompR‐RNAi was also decreased by 51.4% and 19.7%, respectively. The comparative transcriptome analysis revealed that the functional genes directly related to bacterial intracellular survival mainly included the genes related to anti‐stress capacity, and the genes related to Zn2+ and Mg2+ transport. Further research confirmed that two‐component system EnvZ/OmpR can regulate the expression of the important molecular chaperones, such as groEL, htpG, dnaK, clpB and grpE. The expression of these molecular chaperones in wild‐type strain was up‐regulated with the increase in H2O2 concentrations, while the expression of these molecular chaperones in silent strains did not change significantly. Cells that phagocytosed wild‐type strain had higher ROS content than cells that phagocytosed silent strains. Two‐component system EnvZ/OmpR could also regulate zinc transporter (znuA, znuB, znuC) and zinc efflux protein (zntA) to maintain zinc homeostasis in cells, thus affecting the ability of bacteria to survive in phagocytes. Moreover, two‐component system EnvZ/OmpR could affect the growth and intracellular survival of A. hydrophila by regulating the expression of MgtA, MgtC and MgtE and participating in bacterial Mg2+ homeostasis in fish macrophages. [ABSTRACT FROM AUTHOR]

• A significant decrease in gene expression of adhesion-deficient V. harveyi. • fliA , fliR , and flrB were responsible for flagellation and silenced via RNAi. • fliA , fliR , and flrB have important roles in the adhesion of V. harveyi. • fliA , fliR , flrB regulate bacterial adhesion by affecting its motility, biofilm formation. • fliA , fliR , flrB regulate adhesion ability of V. harveyi in different environments. Bacteria adhesion to fish mucus is a crucial virulence mechanism. As the initial step of bacterial infection, adhesion is impacted by bacterial motility and environmental conditions. However, its molecular mechanism is yet unclear. In this study, a significant decrease in gene expression of adhesion-deficient Vibrio harveyi was observed when the bacteria were subjected by Cu2+(50 mg/L), Pb2+(100 mg/L), Hg2+(25 mg/L), and Zn2+(50 mg/L). The genes fliA , fliR , and flrB were responsible for flagellation; being crucial for adhesion, these genes were identified and silenced via RNAi. After silencing of these genes by RNAi technology, the ability of adhesion, biofilm formation, motility, and flagella synthesis of V. harveyi were considerably reduced. Compared with the control group, it was observed that the expression levels of fliS , fliD , flgH , and flrC were significant down-regulated in fliR -RNAi, flrB -RNAi, and fliA -RNAi. This data indicates that the expression levels of most virulence genes are affected by fliA , fliR , and flrB. Also, the expression of fliA , fliR , and flrB can be influenced by the salinity, temperature, and pH. The results show that: (1) fliA , fliR , and flrB have important roles in the adhesion of V. harveyi ; (2) fliA , fliR , and flrB can regulate bacterial adhesion by affecting its motility, and biofilm formation; (3) fliA , fliR , and flrB can regulate adhesion ability of V. harveyi in different environments. [ABSTRACT FROM AUTHOR]