Integration Host Factor positively regulates virulence gene expression in Vibrio cholerae

Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, New Hampshire 03755

^* To whom correspondence should be addressed. Email: Karen.A.Skorupski{at}Dartmouth.edu.

	Abstract

Virulence gene expression in Vibrio cholerae is dependent upon a complex transcriptional cascade that is influenced by both specific and global regulators in response to environmental stimuli. Here we report that the global regulator IHF positively affects virulence gene expression in V. cholerae. Inactivation of ihfA or ihfB, the genes encoding the IHF subunits, decreased expression of the two main virulence factors tcpA and ctx and prevented TCP and CT production. IHF was found to directly bind to and bend the tcpA promoter region at an IHF consensus site centered at -162 using gel mobility shift assays and DNase I footprinting experiments. Deletion or mutation of the tcpA IHF consensus site resulted in the loss of IHF binding and additionally disrupted the binding of the repressor H-NS. DNase I footprinting revealed that H-NS protection overlaps with both the IHF and ToxT binding sites at the tcpA promoter. In addition, disruption of ihfA in an hns or toxT mutant background had no effect on tcpA expression. These results suggest that IHF may function at the tcpA promoter to alleviate H-NS repression.