The temperature-dependent expression of type II secretion system controls extracellular product secretion and virulence in mesophilic Aeromonas salmonida SRW-OG1

Aeromonas salmonicida is a typical cold water bacterial pathogen that causes furunculosis in many freshwater and marine fish species worldwide. In our previous study, the pathogenic A. salmonicida (SRW-OG1) was isolated from a warm water fish, Epinephelus coioides was genomics and transcriptomics analyzed. Type II secretion system was found in the genome of A. salmonicida SRW-OG1, while the expressions of tatA, tatB , and tatC were significantly affected by temperature stress. Also, sequence alignment analysis, homology analysis and protein secondary structure function analysis showed that tatA , tatB , and tatC were highly conservative, indicating their biological significance. In this study, by constructing the mutants of tatA, tatB , and tatC , we investigated the mechanisms underlying temperature-dependent virulence regulation in mesophilic A. salmonida SRW-OG1. According to our results, tatA , tatB , and tatC mutants presented a distinct reduction in adhesion, hemolysis, biofilm formation and motility. Compared to wild-type strain, inhibition of the expression of tatA , tatB , and tatC resulted in a decrease in biofilm formation by about 23.66%, 19.63% and 40.13%, and a decrease in adhesion ability by approximately 77.69%, 80.41% and 62.14% compared with that of the wild-type strain. Furthermore, tatA , tatB , and tatC mutants also showed evidently reduced extracellular enzymatic activities, including amylase, protease, lipase, hemolysis and lecithinase. The genes affecting amylase, protease, lipase, hemolysis, and lecithinase of A. salmonicida SRW-OG1 were identified as cyoE , ahhh1 , lipA , lipB , pulA , HED66_RS01350, HED66_RS19960 , aspA , fabD , and gpsA , which were notably affected by temperature stress and mutant of tatA, tatB , and tatC . All above, tatA, tatB and tatC regulate the virulence of A. salmonicida SRW-OG1 by affecting biofilm formation, adhesion, and enzymatic activity of extracellular products, and are simultaneously engaged in temperature-dependent pathogenicity.