Deletion of hemolysis-related genes attenuates the pathogenicity of Vibrio anguillarum to Lateolabrax maculatus

Lateolabrax maculatus is an important mariculture fish in China. In recent years, fishery losses caused by diseases have become more and more serious. Vibrio anguillarum is a gram-negative pathogenic bacterium widely distributed in seawater and marine organisms, and it is one of the important sources of bacterial diseases in mariculture and can cause serious infections in fish. Hemolysin is an essential component of virulence factor of V. anguillarum, which causes hemorrhagic septicemia in the host. However, very little information is available about hemolysin in L. maculatus. To explore the role of hemolysin in V. anguillarum infection of the fish, 5.0×10⁵ CFU V. anguillarum wild strain or △vah1-vah4-rtxA was immunized by intraperitoneal injection, and the colonization ability of bacteria in L. maculatus, histopathological changes and immune response of L. maculatus after deletion of hemolysis-related genes were evaluated. The results showed that the virulence of V. anguillarum decreased by 8.74 times after the deletion of hemolysis-related genes, and the LD₅₀ of wild strain or △vah1-vah4-rtxA was 2.103×10⁵ CFU/mL and 1.837×10⁶ CFU/mL, respectively. The intestine and gill were the main colonization sites of V. anguillarum, which were seriously damaged after infection. After the deletion of hemolysis-related genes, the colonizing ability of V. anguillarum and the damage degree of intestinal mucosa vacuolation and gill necrosis was reduced. The KEGG pathway enrichment analysis showed that the differentially expressed genes were significantly enriched into hematopoietic cell lineage, antigen processing and presentation, cell adhesion molecules and intestinal immune network for IgA production signal pathways related to immune response. The above results showed that deletion of hemolysis-related genes attenuated the pathogenicity of V. anguillarum to L. maculatus. The results of this study will help to further understand the pathogenic mechanism of V. anguillarum and provide a basis for the development of anti-Vibrio immune enhancer or attenuated vaccine for L. maculatus.