IscR Is a Global Regulator Essential for Pathogenesis of Vibrio vulnificus and Induced by Host Cells

A mutant that exhibited less cytotoxic activity toward INT-407 human intestinal epithelial cells than the wild type was screened from a random transposon mutant library of Vibrio vulnificus, and an open reading frame encoding an Fe-S cluster regulator, IscR, was identified using a transposon-tagging method. A mutational analysis demonstrated that IscR contributes to mouse mortality as well as cytotoxicity toward the INT-407 cells, indicating that IscR is essential for the pathogenesis of V. vulnificus. A whole-genome microarray analysis revealed that IscR influenced the expression of 67 genes, of which 52 were upregulated and 15 were downregulated. Among these, 12 genes most likely involved in motility and adhesion to host cells, hemolytic activity, and survival under oxidative stress of the pathogen during infection were selected and experimentally verified to be upregulated by IscR. Accordingly, the disruption of iscR resulted in a significant reduction in motility and adhesion to INT-407 cells, in hemolytic activity, and in resistance to reactive oxygen species (ROS) such as H2O2 and tert-butyl hydroperoxide (t-BOOH). Furthermore, the present study demonstrated that iscR expression was induced by exposure of V. vulnificus to the INT-407 cells, and the induction appeared to be mediated by ROS generated by the host cells during infection. Consequently, the combined results indicated that IscR is a global regulator that contributes to the overall success in the pathogenesis of V. vulnificus by regulating the expression of various virulence and survival genes in addition to Fe-S cluster genes.