Renee Bina

My research centers on the molecular mechanisms of Vibrio cholerae pathogenesis with a specific focus on the role of the RND (resistance-nodulation-division) efflux systems in V. cholerae pathogenesis. Previously we reported that the V. cholerae RND efflux systems were required for colonization of the small intestine and the optimal production of two important virulence factors: cholera toxin (CT) and the toxin-coregulated pilus (TCP). The TCP is a type IV bundle-forming pilus that is essential for V. cholerae to colonize the intestinal tract, whereas CT is an enterotoxin that is responsible for the profuse diarrhea that is characteristic of cholera. The expression of the genes encoding for CT and TCP production are under the control of a hierarchical regulatory pathway that consists of the ToxT, TcpPH, ToxRS and AphAB transcriptional regulatory proteins. In response to unknown environmental stimuli, ToxRS and TcpPH, which are membrane associated transcriptional regulators, activate the transcription of the toxT gene. ToxT is a transcriptional regulator of the AraC family that then directly activates the transcription of the genes encoding for CT and TCP.  AphAB are cytoplasmic proteins that function as activators for tcpPH gene expression.

We have shown that mutation of the RND efflux systems in V. cholerae results in significantly reduced amounts of CT and TCP while blocking colonization of the small intestine. The decreased CT and TCP production in the RND mutant was due to reduced tcpPH and toxT transcription.  Applying genomic approaches (e.g. DNA microarrays and RNAseq) combined with biochemical analysis to define genes linking RND efflux and the tcpPH transcription, we have identified a new transcriptional regulator that regulates tcpPH gene expression, and thus virulence factor production, in V. cholerae. This transcriptional regulator serves to link the RND efflux systems and CT and TCP production. We are now investigating the role of small molecules as effectors of this phenotype. In addition, we are using luminescent-based reporters to investigate the in vivo expression of V. cholerae genes in real-time during colonization of the small intestines.