IAI Accepts, published online ahead of print on 26 October 2009

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Infect. Immun. doi:10.1128/IAI.00590-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Quorum sensing negatively regulates hemolysin transcriptionally and post-translationally in Vibrio cholerae

Amy M. Tsou and Jun Zhu^*

Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104

^* To whom correspondence should be addressed. Email: junzhu{at}mail.med.upenn.edu.

Recent work has shown that in addition to Cholera Toxin (CT) and the Toxin Coregulated Pilus (TCP), other cytotoxic proteins in Vibrio cholerae also cause disease symptoms, and this is particularly evident in strains lacking CT. One such protein is the hemolysin encoded by hlyA. Here, we show that, like CT and TCP, HlyA is repressed by the quorum sensing-regulated transcription factor, HapR. This repression occurs on two levels: one at the transcriptional level that is independent of the metalloprotease, HapA, and one at the post-translational level that is mediated by HapA. The transcriptional regulation is significantly more apparent on solid media than in liquid cultures. This is the first time that hemolysis has been shown to be directly regulated by quorum sensing in V. cholerae, and it is interesting that, like other virulence factors, HlyA is also repressed by HapR, which is expressed late in infection.