Regulation of rugosity and biofilm formation in Vibrio cholerae: Comparison of VpsT and VpsR regulons and epistasis analysis of vpsT, vpsR and hapR

Department of Environmental Toxicology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA

^* To whom correspondence should be addressed. Email: yildiz{at}etox.ucsc.edu.

	Abstract

Vibrio cholerae undergoes phenotypic variation that generates two morphologically different variants termed smooth and rugose. The transcriptional profiles of the two variants differ greatly and many of the differentially regulated genes are controlled by a complex regulatory circuitry that includes the transcriptional regulators VpsR, VpsT and HapR. In this study, we identified the VpsT regulon and compared VpsT and VpsR regulons to elucidate the contribution of each positive regulator to the rugose variant transcriptional profile and associated phenotypes. We have found that although VpsT and VpsR regulons are very similar, the magnitude of gene regulation by each regulator is different. We also determined that cdgA, which encodes a GGDEF domain protein, is partially responsible for the altered vps gene expression between the vpsT and vpsR mutants. Analysis of epistatic relationships among hapR, vpsT and vpsR with respect to whole genome expression profile, colony morphology and biofilm formation revealed that vpsR is epistatic to hapR, and vpsT. Expression of virulence genes was increased in vpsRhapR double mutant relative to hapR mutant, suggesting that VpsR negatively regulates virulence gene expression in hapR mutant. These results show that a complex regulatory interplay among VpsT, VpsR, HapR and GGDEF/EAL family proteins controls transcription of the genes required for Vibrio polysaccharide and virulence factor production in V. cholerae.