CYCLIC-AMP AND ITS RECEPTOR PROTEIN NEGATIVELY REGULATE THE COORDINATE EXPRESSION OF CHOLERA-TOXIN AND TOXIN-COREGULATED PILUS IN VIBRIO-CHOLERAE

Insertion mutations in two Vibrio cholerae genes, cya and crp, which e ncode adenylate cyclase and the cyclic AMP (cAMP) receptor protein (CR P), respectively, derepressed the expression of a chromosomal cholera toxin (CT) promoter-lacZ fusion at the nonpermissive temperature of 37 degrees C. In the classical biotype strain O395, the crp mutation inc reased the production of both CT and toxin-coregulated pilus (TCP) in vitro under a variety of growth conditions not normally permissive for their expression. The most dramatic increase in CT and TCP was observ ed with the crp mutant in Luria-Bertani (LB) medium pH 8.5, at 30 degr ees C. El Tor biotype strains differ from classical strains in that th ey do not produce CT or TCP when grown in LB media. Incorporation of t he crp mutation into El Tor strain C6706 permitted production of these proteins in LB medium pH 6.5, at 30 degrees C. In the infant mouse ch olera model, the crp mutation decreased colonization in both biotypes at least 100-fold relative to the wild-type strains. The data presente d here suggest a model whereby cAMP-CRP negatively regulates the expre ssion of CT and TCP in both classical and El Tor biotypes under certai n environmental conditions and also influences pathogenesis by regulat ing other processes necessary for optimal growth in vivo.