Deletion of speA and aroC genes impacts the pathogenicity of Vibrio anguillarum in spotted sea bass

Vibrio anguillarum is one of the major pathogens responsible for bacterial infections in marine environments, causing significant impacts on the aquaculture industry. The misuse of antibiotics leads to bacteria developing multiple drug resistances, which is detrimental to the development of the fisheries industry. In contrast, live attenuated vaccines are gradually gaining acceptance and widespread recognition. In this study, we constructed a double -knockout attenuated strain, V. anguillarum Delta speA-aroC, to assess its potential for preparing a live attenuated vaccine. The research results indicate a significant downregulation of virulence-related genes, including Type VI secretion system, Type II secretion system, biofilm synthesis, iron uptake system, and other related genes, in the mutant strain. Furthermore, the strain lacking the genes exhibited a 67.47% reduction in biofilm formation ability and increased sensitivity to antibiotics. The mutant strain exhibited significantly reduced capability in evading host immune system defenses and causing in vivo infections in spotted sea bass (Lateolabrax maculatus), with an LD50 that was 13.93 times higher than that of the wild -type V. anguillarum. Additionally, RTqPCR analysis of immune-related gene expression in spotted sea bass head kidney and spleen showed a weakened immune response triggered by the knockout strain. Compared to the wild -type V. anguillarum, the mutant strain caused reduced levels of tissue damage. The results demonstrate that the deletion of speA and aroC significantly reduces the biosynthesis of biofilms in V. anguillarum, leading to a decrease in its pathogenicity. This suggests a crucial role of biofilms in the survival and invasive capabilities of V. anguillarum.