Regulation of the Vibrio vulnificus hupA gene by temperature alteration and cyclic AMP receptor protein and evaluation of its role in virulence.

Availability of free iron is extremely limited in the mammalian host, and the acquisition of iron in the host is essential for successful infection by pathogenic bacteria. Expression of many genes involved in acquiring iron is regulated in response to the level of iron availability, and iron regulation is mediated by Fur. In this study, cellular levels of Vibrio vulnificus HupA, a heme receptor protein, and the hupA transcript were found to increase in cells grown at 40 degrees C compared to cells grown at 30 degrees C. The results suggested that change in growth temperature, in addition to iron availability, is an environmental cue controlling the expression of the hupA gene. The influence of global regulatory proteins on the expression of hupA was examined, and the cyclic AMP receptor protein (CRP) was found to activate the expression of hupA at the transcriptional level. CRP exerts its effects by directly binding to DNA upstream of the hupA promoter P(hupA), and a CRP binding site, centered at 174 bp upstream of the transcription start site, was identified by a DNase I protection assay. Finally, a hupA mutant showed reduced virulence in mice and in tissue cultures, in which growth of the hupA mutant was impaired, indicating that HupA of V. vulnificus is essential for survival and multiplication during infection.