A dual regulatory role of cyclic adenosine monophosphate receptor protein in various virulence traits of Vibrio vulnificus

Vibrio vulnificus causes fatal septicemia in susceptible subjects after the ingestion of raw seafood. In the present study, the roles of cyclic adenosine monophosphate (cAMP) receptor protein (CRP) in V. vulnificus pathogenesis were investigated. A mutation in the V. vulnificus crp gene resulted in a significant down-regulation of various virulence phenotypes, except for RtxA1-mediated cytoskeletal rearrangement. Bacterial growth was impeded by the crp mutation. In addition, colony morphology was converted from opaque to translucent type by this mutation, which implies a decrease in capsule production. The crp mutant also showed significant decrease in motility and adhesion to host cells. V. vulnificus CRP positively regulated production of hemolysin and protease at transcriptional level. All these changes in the crp mutant were fully complemented in trans by a plasmid harboring the wild-type gene. In contrast, CRP negatively regulated the expression of RtxA1. The crp mutant caused the cytoskeletal rearrangement in HeLa cells, which is a hallmark activity of RtxA1 toxin. Taken together, CRP seems to play a dual regulatory role in various virulence traits of V. vulnificus.