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Applied and Environmental Microbiology, November 2007, p. 7482-7487, Vol. 73, No. 22
0099-2240/07/$08.00+0 doi:10.1128/AEM.01564-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Department of Microbiology, Biochemistry and Immunology, Morehouse School of Medicine, 720 Westview Dr. SW, Atlanta, Georgia,1 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, People's Republic of China2
Received 10 July 2007/ Accepted 21 September 2007
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 cyclic AMP (cAMP) receptor protein (CRP) produce very little HapR, which results in elevated expression of Vibrio exopolysaccharide (vps) genes and biofilm compared to the 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 a smooth one. The smooth
hapR
crp and
hapR
cya 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. Ectopic expression of VpsR in smooth
hapR
crp and
hapR
cya double mutants restored rugose colonial morphology. Lowering intracellular cAMP levels in a
hapR mutant by the addition of glucose diminished VpsR expression and colonial rugosity. On the basis of our results, we propose a model for the regulatory input of CRP on exopolysaccharide biosynthesis.
Published ahead of print on 5 October 2007.
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