The cAMP Receptor Protein Modulates Colonial Morphology Phase in Vibrio cholerae

Morehouse School of Medicine Department of Microbiology, Biochemistry and Immunology, 720 Westview Dr., SW Atlanta, Georgia; State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Communicable Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Changping, Beijing 102206

^* To whom correspondence should be addressed. Email: jbenitez{at}msm.edu.

	Abstract

Inactivation of the quorum sensing regulator HapR causes Vibrio cholerae El Tor biotype strain C7258 to adopt a rugose colonial morphology that correlates with enhanced biofilm formation. V. cholerae mutants lacking the cAMP receptor protein (CRP) produce very little HapR, which results in elevated expression of Vibrio exopolysaccharide (vps) genes and biofilm compared to wild type. However, crp mutants still exhibited smooth colonial morphology and expressed reduced levels of vps genes compared to isogenic hapR mutants. In this study we demonstrate that deletion of crp and cya (adenylate cyclase) converts a rugose hapR mutant to smooth phase. The smooth hapRcrp and hapRcya double mutants could be converted back to rugose by complementation with crp and cya respectively. CRP was found to enhance the expression of VpsR, a strong activator of vps expression, but to diminish transcription of VpsT and CytR. Ectopic expression of VpsR in smooth hapRcrp and hapRcya double mutants restored rugose colonial morphology. Lowering intracellular cAMP levels in a hapR mutant by addition of glucose diminished VpsR expression and colonial rugosity. Based on our results we propose a model for the regulatory input of CRP on exopolysaccharide biosynthesis.