Isolation and characterization of vicH, encoding a new pleiotropic regulator in Vibrio cholerae

During the last decade, the has gene and its product, the H-NS protein, hav e been extensively studied in Escherichia coli. H-NS-like proteins seem to be widespread in gram-negative bacteria. However, unlike in E. coli and in Salmonella enterica serovar Typhimurium, little is known about their role i n the physiology of those organisms. In this report, we describe the isolat ion of vicH, an hns-like gene in Vibrio cholerae, the etiological agent of cholera. This gene was isolated from a V. cholerae genomic library by compl ementation of different phenotypes associated with an hns mutation in E. co li. It encodes a 135-amino-acid protein showing approximately 50% identity with both H-NS and StpA in E. coli. Despite a law amino acid conservation i n the N-terminal part, VicH is able to cross-react with anti-H-NS antibodie s and to form oligomers in vitro. The vicH gene is expressed as a single ge ne from two promoters in tandem and is induced by cold shock. A V; cholerae wild-type strain expressing a vicH Delta 92 gene lacking its 3' end shows pleiotropic alterations with regard to mucoidy and salicin metabolism. More over, this strain is unable to swarm on semisolid medium. Similarly, overex pression of the vicH wild-type gene results in an alteration of swarming be havior. This suggests that VicH could be involved in the virulence process in V. cholerae, in particular by affecting flagellum biosynthesis.