In this project, we have been investigating the physiological, regulatory, and mechanistic underpinnings of quorum sensing (QS) and virulence gene expression in Vibrio cholerae. Using a combination of genetic and biochemical methods, we have explored the regulatory principles of QS-mediated signaling in vibrio species and discovered several new regulators involved in this process. Specifically, we have discovered that the recently discovered AI molecule DPO (3,5-dimethylpyrazin-2-ol) affects biofilm formation and virulence expression in V. cholerae and that this function critically depends on the regulatory roles of the VqmR small RNA (sRNA), which base-pairs with and inhibits the production of the major virulence determinant AphA. We further showed that DPO works in concert with other signaling molecules and that full QS behavior requires the combined activity of at least three signaling molecules.
These findings prompted us to search for additional sRNAs regulators controlling QS and/or virulence. Indeed, we discovered three additional sRNAs (FarS, VcdRP, and VadR) involved in these processes, however, their exact regulatory functions differed. For example, FarS controls fatty acid metabolism, which is key for host colonization, whereas VcdRP modulates cholera toxin production in response to changes in carbohydrate metabolism. In contrast, VadR modulates biofilm formation and antibiotic tolerance in V. cholerae. Taken together, these results suggest that post-transcriptional regulation is fundamental for QS signaling (incl. DPO-mediated signaling) and virulence in V. cholerae, and thus could be exploited as a potential drug target. Of note, all of these sRNAs are conserved in other pathogenic vibrio species suggesting that our findings could be relevant beyond the realm of a single organism.
Recently, we further expanded our research into QS regulation in V. cholerae and discovered a novel regulatory module consisting of the transcription factor, QrrT, and the non-coding regulator, QrrX. We showed that both, QrrT and QrrX, are required for rapid conversion from one QS state to another and that this function relies on inactivation of key QS regulators by the QrrX transcript. Interestingly, QrrX does not function as a typical sRNA controlling the expression of mRNAs, but rather base-pairs with other non-coding regulators to control their function. This type of regulation was previously unknown in vibrio species and studying their functions could help to improve our general understanding of QS pathway architectures in bacteria.
