Going in Circles: Quorum sensing, small RNAs, and feedback loops

Going in Circles: Quorum sensing, small RNAs, and feedback loops

Speaker: Kim Tu

Affiliation: Laboratory of Bonnie Bassler

Department of Molecular Biology, Princeton University

 Host: Karina Xavier

Abstract

Quorum sensing is a cell-cell communication process by which bacteria assess population density through the secretion and detection of diffusible signal molecules called autoinducers, enabling groups of bacteria to synchronize their gene expression.  In the bioluminescent marine bacterium Vibrio harveyi, sensory information from three independent systems impinges on the sigma54-dependent response regulator, LuxO.  LuxO activates the expression of five small regulatory RNAs (sRNAs) called Qrr1-5.  Here, we show that the sRNAs function additively to destabilize luxR mRNA.  LuxR is the master regulator of all known quorum-sensing genes, and therefore regulation of luxR by the Qrr sRNAs provides a precise temporal control of target gene expression.  We also identify two negative regulatory feedback loops involved in the control of luxO expression.  We show that LuxO represses its own transcription independent of its phosphorylated state and that the Qrr sRNAs can post-transcriptionally repress luxO mRNA.  We propose that these dual regulatory feedback loops enable cells to communicate with high fidelity and to facilitate a precise transition between different cell density modes in the presence of large, persistent fluctuations.