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J. Bacteriol. doi:10.1128/JB.01766-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Growth phase regulation of Vibrio cholerae RTX toxin export

^* To whom correspondence should be addressed. Email: k-satchell{at}northwestern.edu.

	Abstract

Vibrio cholerae, the causative agent of the severe diarrheal disease cholera, secretes several "accessory" toxins including RTX toxin, which causes cross-linking of the actin cytoskeleton. RTX toxin is exported to the extracellular milieu by an atypical Type I secretion system (T1SS), and we previously noted that RTX-associated activity is only detectable in supernatant fluids from log phase cultures. Here, we investigate the mechanisms for regulating RTX toxin activity in supernatant fluids. We find that exported proteases are capable of destroying RTX activity and may therefore play a role in the growth phase regulation of toxin activity. We determined that the absence of RTX toxin in stationary phase culture supernatant fluids is also due to a lack of toxin secretion and not solely attributable to proteolytic degradation. We ascertained that the T1SS apparatus is regulated at the transcriptional level by growth phase control that is independent of quorum sensing, unlike other virulence factors of V. cholerae. Additionally, in stationary phase cultures, all RTX toxin activity is associated with bacterial membranes or outer membrane vesicles.

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