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.

This study investigates the water-saving and emission-reduction effects of biofilm technology on the pond culture of largemouth bass (Micropterus pallidus) and Japanese eel (Anguilla japonica) using a combination of biofilm water purification grids and a complex microbial preparation. The results show that during the 150-day largemouth bass aquaculture trial, the TN, TAN, TP, nitrite, and LP in the treatment group were significantly lower than those in the control group by 26.2%, 74.7%, 53.9%, 30.7%, and 59.1% (p < 0.01), respectively. During the 145-day aquaculture trial of Japanese eel, the TN, TAN, and TP levels in the treatment group were significantly lower than those in the control group by 30.1%, 68.6%, and 18.7% (p < 0.01), respectively. The nitrite and COD levels were also significantly lower in the treatment group than in the control group by 18.3% and 16.0% (p < 0.05). In addition, largemouth bass and Japanese eel tailwater nitrogen and phosphorus discharges were significantly reduced and culture yields were significantly increased. This biofilm pond culture technology has advantages such as low cost, water saving and emission reduction, increased production, ease of operation, and a wide range of applications.

Background: The cytokine Macrophage migration inhibitory factor (MIF) is involved in inflammatory diseases. The objective of the present study was to measure the expression levels of MIF in the tissues of Epinephelus awoara (E. awoara). mRNA levels of MIF were investigated in the tissues including spleen, liver, brain, head kidney, stomach, gill, heart, intestine and muscle of E. awoara. Methods: In the experiment, E. awoara were infected with V. alginolyticus and then they were analyzed by ELISA to confirm the mRNA levels of MIF, TNF-α and IL-1 in the many tissues in diseased fishes were higher than those in healthy fishes. Result: The mRNA levels increased significantly in treatment groups. Likewise, E. awoara with V. alginolyticus infections showed significant increases in IL-1 and TNF-α tissues content of intestine, head kidney, liver, muscle and spleen, respectively. There was evidence that MIF stimulates the release of TNF-á and IL-1. The results have the potential to perpetuate that MIF is connected with the inflammatory process in V. alginolyticus infectious diseases.