A transcription factor-sRNA-mediated double-negative feedback loop confers pathogen-specific control of quorum-sensing genes

The cell-to-cell communication process called quorum sensing enables bacteria to synchronize collective behaviors. Quorum sensing relies on the production, release, and detection of signaling molecules called autoinducers. In Vibrio cholerae, the VqmA transcription factor, following binding of the DPO autoinducer, activates the expression of the gene encoding the VqmR small regulatory RNA. VqmR controls traits including biofilm formation. Here, we identify repressors of DPO-VqmA-VqmR signaling. We focus on one identified repressor, the LuxT transcription factor. We show that LuxT represses vqmR transcription. VqmR post-transcriptionally represses luxT translation. This arrangement forms a double-negative feedback loop between the two regulators. Reciprocal control hinges on the N-terminal eight amino acids of LuxT. The nucleotide sequence encoding this LuxT region serves as the VqmR binding site in the luxT mRNA and the amino acids specified by this same N-terminal region are required for LuxT to bind the vqmR promoter. This same LuxT N-terminal region also expands the DNA motifs to which LuxT can bind. We show this regulatory circuit is unique to V. cholerae and closely related species and absent from other vibrios. We define the set of LuxT-controlled genes in V. cholerae and show that LuxT promotes biofilm formation, a key requirement for successful colonization of eukaryotic hosts.