| Summary: | <p>Abstract</p> <p>Background</p> <p><it>Vibrio cholerae </it>is the causative agent of cholera. Extensive studies reveal that complicated regulatory cascades regulate expression of virulence genes, the products of which are required for <it>V. cholerae </it>to colonize and cause disease. In this study, we investigated the expression of the key virulence regulator ToxR under different conditions.</p> <p>Results</p> <p>We found that compared to that of wild type grown to stationary phase, the <it>toxR </it>expression was lower in an <it>aphB </it>mutant strain. AphB has been previously shown to be a key virulence regulator that is required to activate the expression of <it>tcpP</it>. When expressed constitutively, AphB is able to activate the <it>toxR </it>promoter. Furthermore, gel shift analysis indicates that AphB binds <it>toxR </it>promoter region directly. We also characterize the effect of AphB on the levels of the outer membrane porins OmpT and OmpU, which are known to be regulated by ToxR.</p> <p>Conclusions</p> <p>Our data indicate that <it>V. cholerae </it>possesses an additional regulatory loop that use AphB to activate the expression of two virulence regulators, ToxR and TcpP, which together control the expression of the master virulence regulator ToxT.</p>
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