The cyclic AMP receptor protein modulates quorum sensing, motility and multiple genes that affect intestinal colonization in Vibrio cholerae.

Vibrio cholerae is the causative agent of cholera, which continues to be a major public health concern in Asia, Africa and Latin America. The bacterium can persist outside the human host and alternates between planktonic and biofilm community lifestyles. Transition between the different lifestyles is mediated by multiple signal transduction pathways including quorum sensing. Expression of the Zn-metalloprotease haemagglutinin (HA)/protease is subject to a dual regulation which involves the quorum-sensing regulator HapR and the cAMP receptor protein. In a previous study, we observed that a mutant defective in the cAMP-receptor protein (CRP) expressed lower levels of HapR. To further investigate the role of CRP in modulating HapR and other signal transduction pathways, we performed global gene expression profiling of a Deltacrp mutant of El Tor biotype V. cholerae. Here we show that CRP is required for the biosynthesis of cholera autoinducer 1 (CAI-1) and affects the expression of multiple HapR-regulated genes. As expected, the Deltacrp mutant produced more cholera toxin and enhanced biofilm. Expression of flagellar genes, reported to be affected in DeltahapR mutants, was diminished in the Deltacrp mutant. However, an epistasis analysis indicated that cAMP-CRP affects motility by a mechanism independent of HapR. Inactivation of crp inhibited the expression of multiple genes reported to be strongly induced in vivo and to affect the ability of V. cholerae to colonize the small intestine and cause disease. These genes included ompU, ompT and ompW encoding outer-membrane proteins, the alternative sigma factor sigma(E) required for intestinal colonization, and genes involved in anaerobic energy metabolism. Our results indicate that CRP plays a crucial role in the V. cholerae life cycle by affecting quorum sensing and multiple genes required for survival of V. cholerae in the human host and the environment.