The phosphotransferase VanU represses expression of four qrr genes antagonizing VanO-mediated quorum-sensing regulation in Vibrio anguillarum

Abstract

Vibrio anguillarum utilizes quorum sensing to regulate stress responses required for survival in the aquatic environment. Like other Vibrio species, V. anguillarum contains the gene qrr1, which encodes the ancestral quorum regulatory RNA Qrr1, and phosphorelay quorum-sensing systems that modulate the expression of small regulatory RNAs (sRNAs) that destabilize mRNA encoding the transcriptional regulator VanT. In this study, three additional Qrr sRNAs were identified. All four sRNAs were positively regulated by σ54 and the σ54-dependent response regulator VanO, and showed a redundant activity. The Qrr sRNAs, together with the RNA chaperone Hfq, destabilized vanT mRNA and modulated expression of VanT-regulated genes. Unexpectedly, expression of all four qrr genes peaked at high cell density, and exogenously added N-acylhomoserine lactone molecules induced expression of the qrr genes at low cell density. The phosphotransferase VanU, which phosphorylates and activates VanO, repressed expression of the Qrr sRNAs and stabilized vanT mRNA. A model is presented proposing that VanU acts as a branch point, aiding cross-regulation between two independent phosphorelay systems that activate or repress expression of the Qrr sRNAs, giving flexibility and precision in modulating VanT expression and inducing a quorum-sensing response to stresses found in a constantly changing aquatic environment.

Quorum Sensing Determines the Choice of Antiphage Defense Strategy in Vibrio anguillarum

“…Since the phosphorylated VanO protein represses the QS regulator VanT at low cell densities, the Δ vanO mutant displays full expression of VanT at all densities and is therefore locked in a high-cell-density phenotype (19). By contrast, a Δ vanT mutant has lost the ability to regulate QS-associated functions and is therefore locked in a low-cell-density phenotype.…”

LuxU connects quorum sensing to biofilm formation in Vibrio fischeri

“…In this organism, VanU functions through VanO to regulate the expression of the LuxR VH homologue, VanT, by activating expression of qrr1‐4 (Croxatto et al ., ). VanU also appears to act through a VanO‐independent mechanism to inhibit the expression of qrr1‐4 (Croxatto et al ., ; Weber et al ., ). Weber et al .…”

Chemical shift assignments and secondary structure prediction of the phosphorelay protein VanU from Vibrio anguillarum

“…This pathway eventually results in the formation of biofilms to help ensure bacterial survivability (Frans et al 2011). V. anguillarum ’s quorum-sensing pathway is comprised of six main components (Croxatto et al 2004; Weber et al 2011). VanN, VanP/Q, and CqsS are hybrid histidine kinases (containing both histidine kinase and response regulator domains), all of which are able to phosphorylate the phosphotransferase protein VanU.…”

“…The phosphotransferase protein VanU is the convergence point in this quorum-sensing pathway. The independent quorum-sensing histidine kinase responses are channeled through this single protein (Weber et al 2011). VanU is of significance as this convergence point protein regulates Vibrio’s ability to survive long periods of time under harsh marine conditions through the development of biofilms.…”

“…vanU mutants have been shown to shorten the half-lives of vanT mRNA leading to a decreased VanT expression and thus biofilm formation (Weber et al 2011). Due to VanU’s critical role in the quorum sensing pathway and biofilm formation, VanU is of significant structural interest.…”