| Quorum sensing (QS) is a cell-to-cell communication mechanism used by bacteria to determine their population density and to regulate genes involved in group behaviors. The human pathogen Vibrio cholerae contains two distinct QS systems that converge into a shared phosphorelay pathway. The cholera-specific pathway is composed of the autoinducer CAI-1, which is produced by the synthase CqsA and recognized by the membrane-bound histidine kinase CqsS. The universal QS pathway is composed of the autoinducer AI-2, which is produced by the autoinducer synthase LuxS and binds to the receptor LuxPQ. Here, we investigate regulation of the V. cholerae autoiducer synthases and receptors. We discovered that the LuxS/PQ system exhibits no regulation under conditions examined, whereas the CqsA/S system contains an auto-regulatory positive feedback loop. We characterized feedback in the CqsA/S by identifying the Qrr sRNAs as the source of feedback, and that they act via indirect repression of CqsA/S through an unknown intermediate. Additionally, we showed that regulation of cqsA and cqsS occurs at the post-transcriptional level. We further investigated growth phase regulation of cqsA, and discovered DctD as a potential regulator of the Qrr sRNAs. |
