CONTROL OF THE TOXR VIRULENCE REGULON IN VIBRIO-CHOLERAE BY ENVIRONMENTAL STIMULI

Many bacterial pathogens regulate the expression of virulence genes in a co-ordinate manner in response to changes in the environment, For e xample, the human pathogen, Vibrio cholerae, possesses a virulence reg ulon composed of over 20 genes involved in colonization, toxin product ion and bacterial survival within the host, which are co-ordinately re gulated by external stimuli, such as temperature, pH and osmolarity. A lthough the expression of the regulon is dependent upon the transcript ional activator ToxR, most of these genes are controlled by a second t ranscriptional activator, ToxT, which is itself positively regulated b y ToxR. The mechanisms by which environmental stimuli influence the To xR regulon are not yet understood, but ToxR-mediated control over the expression of toxT clearly plays a role, The recent finding that the g lobal regulator cAMP-CRP also influences the expression of the ToxR re gulon under various environmental conditions raises new issues regardi ng the pathways and mechanisms by which this regulation is achieved an d indicates that multiple overlapping systems are involved.