Non-coding small RNAs regulate multiple mRNA targets to control the Vibrio cholerae quorum sensing response
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The waterborne bacterial pathogen Vibrio cholerae uses a process of cell-to-cell communication called quorum sensing (QS) to coordinate transcription of four sRNAs (Qrr1-4; quorum regulatory RNAs) in response to changes in extracellular QS signals that accumulate with cell density. The Qrr sRNAs are predicted to negatively control translation of several mRNAs, including hapR, which encodes the master QS transcription factor that controls genes for virulence factors, biofilm formation, protease production, and DNA uptake. The Qrr sRNAs are also predicted to positively control vca0939, which encodes a GGDEF family protein that promote biofilm formation by elevating intracellular levels of the second messenger molecule c-di-GMP. Using complementary in vivo, in vitro, and bioinformatic approaches, I showed that Qrr sRNAs base-pair with and repress translation of the mRNA encoding HapR. A single nucleotide mutation in Qrr RNA abolishes hapR pairing and thus prevents cholera toxin production and biofilm formation that are important in disease, and also alters expression of competence genes required for uptake of DNA in marine settings. I also demonstrated that base-pairing of the Qrr sRNAs with vca0939 disrupts an inhibitory structure in the 5' UTR of the mRNA. Qrr-activated translation of vca0939 was sufficient to promote synthesis of c-di-GMP and early biofilm formation in a HapR-independent manner. Thus, these studies define the non-coding Qrr sRNAs as a critical component allowing V. cholerae to sense and respond to environmental cues to regulate important developmental processes such as biofilm formation.