Vibrio cholerae requires rpoS for efficient intestinal colonization

Vibrio cholerae is a facultative intestinal pathogen that lives in aquatic environments, often in association with planktonic species. In the suckling mouse, oral inoculation with V; cholerae leads to intestinal colonization and symptoms of diarrheal disease. Results reported here indicate a role fo r the alternative sigma factor, RpoS, in intestinal colonization in this mo del of cholera. We constructed within rpoS multiple independent mutations w hich consistently resulted in a fivefold decrease in colonization ability a s assessed by competition assays. These mutations had no detectable effect on the in vitro growth of V. cholerae in a rich medium. The occurrence of s pontaneous suppressor mutations potentially required for viability of rpoS strains was ruled out by determination of the frequency of insertional inac tivation of rpoS in comparison to two of her nonessential loci. Finally, bo th the in vitro and in vivo mutant phenotypes of rpoS strains were fully co mplemented by providing rpoS in trans or by allelic reversion, indicating t hat the observed decrease in colonization fitness was indeed due to the los s of functional RpoS.