A small RNA-mediated feedback loop controls quourm-sensing dynamics in Vibrio harveyi

Department of Molecular Biology, Howard Hughes Medical Institute, Princeton, NJ 08544-1014, USA.
Molecular Microbiology (Impact Factor: 4.42). 10/2008; 70(4):896-907. DOI: 10.1111/j.1365-2958.2008.06452.x
Source: PubMed


The bioluminescent marine bacterium Vibrio harveyi uses a cell-to-cell communication process called quorum sensing (QS) to co-ordinate behaviours in response to changes in population density. QS is accomplished through the secretion and detection of extracellular signalling molecules called autoinducers. At the centre of the V. harveyi QS circuit are five small regulatory RNAs called Qrr1-5 which destabilize the mRNA of luxR, encoding LuxR, the master transcriptional regulator of QS target genes. Here we show that LuxR directly activates transcription of qrr2, qrr3 and qrr4, leading to the rapid downregulation of luxR. The LuxR-binding sites in the promoters of qrr2, qrr3 and qrr4 were identified and mutated to determine the consequences of this regulatory loop on QS dynamics. Disruption of the loop delays the transition from high to low cell density, and more significantly, decreases the cell density at which the population reaches a quorum. Our results suggest that feedback is essential for optimizing the dynamics of the transitions between individual and group behaviours.

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Available from: Sine Lo Svenningsen, Jul 10, 2014
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    • "For the quorum sensing network in Vibrio harveyi, the phosphorylation of regulator protein LuxO can be controlled by the interaction between AIs and sensors. At negligible concentrations of AIs, that is, at low cell density (LCD), these sensors act as kinases that transfer phosphate through LuxU to LuxO [3] [4]. LuxO-P activates the expression of genes encoding small RNAs which in turn posttranscriptionally repress the QS master regulatory protein LuxR. "
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    ABSTRACT: Bacterial quorum sensing (QS) is an important process of cell communication and more and more attention is paid to it. Moreover, the noises are ubiquitous in nature and often play positive role. In this paper, we investigate how the noise enhances the QS though the stochastic resonance (SR) and explain the mechanism of SR in this quorum sensing network. In addition, we also discuss the interaction between the small RNA and the other genes in this network and discover the biological importance.
    Full-text · Article · Nov 2013 · Abstract and Applied Analysis
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    • "Several feedback loops regulate the level of LuxR in the cell. These involve the autorepression of luxR[19], the induction of qrr24 transcription by LuxR [20], the autorepression of luxO[21], the down-regulation of the translation of luxO and luxMN by qrr sRNAs [21,22], and the direct repression by AphA, an antagonist of LuxR [23]. "
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    ABSTRACT: Background Vibrio harveyi and closely related species are important pathogens in aquaculture. A complex quorum sensing cascade involving three autoinducers controls bioluminescence and several genes encoding virulence factors. Single cell analysis of a V. harveyi population has already indicated intercellular heterogeneity in the production of bioluminescence. This study was undertaken to analyze the expression of various autoinducer-dependent genes in individual cells. Results Here we used reporter strains bearing promoter::gfp fusions to monitor the induction/repression of three autoinducer-regulated genes in wild type conjugates at the single cell level. Two genes involved in pathogenesis - vhp and vscP, which code for an exoprotease and a component of the type III secretion system, respectively, and luxC (the first gene in the lux operon) were chosen for analysis. The lux operon and the exoprotease gene are induced, while vscP is repressed at high cell density. As controls luxS and recA, whose expression is not dependent on autoinducers, were examined. The responses of the promoter::gfp fusions in individual cells from the same culture ranged from no to high induction. Importantly, simultaneous analysis of two autoinducer induced phenotypes, bioluminescence (light detection) and exoproteolytic activity (fluorescence of a promoter::gfp fusion), in single cells provided evidence for functional heterogeneity within a V. harveyi population. Conclusions Autoinducers are not only an indicator for cell density, but play a pivotal role in the coordination of physiological activities within the population.
    Full-text · Article · Sep 2012 · BMC Microbiology
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    • "Thus, AphA acts as a master regulator of QS behaviors at LCD, and in contrast, LuxR/OpaR is the major one operating at HCD; reciprocal gradients of AphA and LuxR/OpaR are established for controlling gene expression during transition between LCD and HCD. LuxR/OpaR is also able to activate the transcription of qrr2-4 genes, leading to rapid down-regulation of luxR/opaR [47]. It should be noted that this LuxR-qrr feedback dramatically accelerates the transition HCD to LCD, but it has no effect on QS behaviors at steady-state LCD or HCD [47].The dotted lines indicated the inhibited expression of relevant regulators or the cease of relevant regulatory cascades. "
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    ABSTRACT: AphA is the master quorum-sensing (QS) regulator operating at low cell density in vibrios. Molecular regulation of target genes by AphA has been characterized in Vibrio harveyi and V. cholerae, but it is still poorly understood in V. parahaemolyticus. The AphA proteins are extremely conserved in V. parahaemolyticus, Vibrio sp. Ex25, Vibrio sp. EJY3, V. harveyi, V. vulnificus, V. splendidus, V. anguillarum, V. cholerae, and V. furnissii. The above nine AphA orthologs appear to recognize conserved cis-acting DNA signals which can be represented by two consensus constructs, a 20 bp box sequence and a position frequency matrix. V. parahaemolyticus AphA represses the transcription of ahpA, qrr4, and opaR through direct AphA-target promoter DNA association, while it inhibits the qrr2-3 transcription in an indirect manner. Translation and transcription starts, core promoter elements for sigma factor recognition, Shine-Dalgarno sequences for ribosome recognition, and AphA-binding sites (containing corresponding AphA box-like sequences) were determined for the three direct AphA targets ahpA, qrr4, and opaR in V. parahaemolyticus. AphA-mediated repression of ahpA, qrr2-4, and opaR was characterized in V. parahaemolyticus by using multiple biochemical and molecular experiments. The computational promoter analysis indicated the conserved mechanism of transcriptional regulation of QS regulator-encoding genes ahpA, qrr4, and opaR in vibrios.
    Full-text · Article · Sep 2012 · PLoS ONE
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