LuxS Is Required for Persistent Pneumococcal Carriage and Expression of Virulence and Biosynthesis Genes

ABSTRACT Streptococcus pneumoniae causes several diseases, including otitis media, pneumonia, and meningitis. Although little is known about the regulation of or how individual pneumococcal factors contribute to these disease states, there is evidence suggesting that some factors are regulated by a cell-density-dependent mechanism (quorum sensing). Quorum sensing allows bacteria to couple transcription with changes in cell density; bacteria achieve this by sensing and responding to small diffusible signaling molecules. We investigated how the LuxS signaling system impacts the biology of S. pneumoniae. An analysis of the transcriptional profiles of a serotype 2 strain and an isogenic luxS deletion strain utilizing an S. pneumoniae-specific microarray indicated that LuxS regulates gene expression involved in discrete cellular processes, including pneumolysin expression. Contrary to the paradigm for quorum sensing, we observed pronounced effects on transcription in early log phase, where gene expression was repressed in the mutant. Assessing the mutant for its ability to infect and cause disease in animals revealed a profound defect in ability to persist in the nasopharyngeal tissues. Our analysis of an S. pneumoniae transcriptome revealed a function for LuxS in gene regulation that is not dependent upon high cell density and is likely involved in the maintenance of pneumococcal load in susceptible hosts.

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Regulation of rpoS Gene Expression in Pseudomonas: Involvement of a TetR Family Regulator

Journal of Bacteriology ◽

10.1128/jb.183.12.3712-3720.2001 ◽

2001 ◽

Vol 183 (12) ◽

pp. 3712-3720 ◽

Cited By ~ 55

Author(s):

Milan Kojic ◽

Vittorio Venturi

Keyword(s):

Gene Expression ◽

Gene Regulation ◽

Quorum Sensing ◽

Stationary Phase ◽

Cell Density ◽

Promoter Activity ◽

Regulatory Protein ◽

Insertion Mutant ◽

Regulatory Cascade ◽

A Cell

ABSTRACT The rpoS gene encodes the sigma factor which was identified in several gram-negative bacteria as a central regulator during stationary phase. rpoS gene regulation is known to respond to cell density, showing higher expression in stationary phase. For Pseudomonas aeruginosa, it has been demonstrated that the cell-density-dependent regulation response known as quorum sensing interacts with this regulatory response. Using therpoS promoter of P. putida, we identified a genomic Tn5 insertion mutant of P. putida which showed a 90% decrease in rpoSpromoter activity, resulting in less RpoS being present in a cell at stationary phase. Molecular analysis revealed that this mutant carried a Tn5 insertion in a gene, designatedpsrA (Pseudomonas sigma regulator), which codes for a protein (PsrA) of 26.3 kDa. PsrA contains a helix-turn-helix motif typical of DNA binding proteins and belongs to the TetR family of bacterial regulators. The homolog of thepsrA gene was identified in P. aeruginosa; the protein showed 90% identity to PsrA ofP. putida. ApsrA::Tn5 insertion mutant ofP. aeruginosa was constructed. In bothPseudomonas species, psrA was genetically linked to the SOS lexA repressor gene. Similar to what was observed for P. putida, a psrA null mutant of P. aeruginosa also showed a 90% reduction inrpoS promoter activity; both mutants could be complemented for rpoS promoter activity when thepsrA gene was provided in trans.psrA mutants of both Pseudomonas species lost the ability to induce rpoS expression at stationary phase, but they retained the ability to produce quorum-sensing autoinducer molecules. PsrA was demonstrated to negatively regulatepsrA gene expression in Pseudomonas and in Escherichia coli as well as to be capable of activating the rpoS promoter in E. coli. Our data suggest that PsrA is an important regulatory protein ofPseudomonas spp. involved in the regulatory cascade controlling rpoS gene regulation in response to cell density.

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Ethanolamine regulates CqsR quorum-sensing signaling inVibrio cholerae

10.1101/589390 ◽

2019 ◽

Cited By ~ 3

Author(s):

Samit Watve ◽

Kelsey Barrasso ◽

Sarah A. Jung ◽

Kristen J. Davis ◽

Lisa A. Hawver ◽

...

Keyword(s):

Gene Expression ◽

Quorum Sensing ◽

Vibrio Cholerae ◽

Cell Density ◽

High Cell Density ◽

Chemical Signals ◽

Communication Process ◽

Control Group ◽

Dual Function ◽

High Cell

ABSTRACTThe pathogen that causes cholera,Vibrio cholerae, uses the cell-cell communication process known as quorum sensing (QS) to regulate virulence factor production and biofilm formation in response to changes in population density and complexity. QS is mediated through the detection of extracellular chemical signals called autoinducers. Four histidine kinases, LuxPQ, CqsS, CqsR and VpsS, have been identified as receptors to activate the key QS regulator LuxO at low cell density. At high cell density, detection of autoinducers by these receptors leads to deactivation of LuxO, resulting in population-wide gene expression changes. While the cognate autoinducers that regulate the activity of CqsS and LuxQ are known, the signals that regulate CqsR have not been determined. Here we show that the common metabolite ethanolamine specifically interacts with the ligand-binding CACHE domain of CqsRin vitroand induces the high cell-density QS response through CqsR kinase inhibition inV. choleraecells. We also identified residues in the CqsR CACHE domain important for ethanolamine detection and signal transduction. Moreover, mutations disrupting endogenous ethanolamine production inV. choleraedelay the onset of, but do not abolish, the high cell-density QS gene expression. Finally, we demonstrate that modulation of CqsR QS response by ethanolamine occurs inside animal hosts. Our findings suggest thatV. choleraeuses CqsR as a dual-function receptor to integrate information from the self-made signals as well as exogenous ethanolamine as an environmental cue to modulate QS response.IMPORTANCEMany bacteria use quorum sensing to regulate cellular processes that are important for their survival and adaptation to different environments. Quorum sensing usually depends on the detection on chemical signals called autoinducers made endogenously by the bacteria. We show here ethanolamine, a common metabolite made by various bacteria and eukaryotes, can modulate the activity of one of the quorum-sensing receptors inVibrio cholerae, the etiological agent of the disease cholera. Our results raise the possibility thatV. choleraeor other quorum-sensing bacteria can combine environmental sensing and quorum sensing to control group behaviors.

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Peptide signaling without feedback in signal production operates as a true quorum sensing communication system in Bacillus subtilis

Communications Biology ◽

10.1038/s42003-020-01553-5 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Iztok Dogsa ◽

Mihael Spacapan ◽

Anna Dragoš ◽

Tjaša Danevčič ◽

Žiga Pandur ◽

...

Keyword(s):

Gene Expression ◽

Bacillus Subtilis ◽

Quorum Sensing ◽

Cell Density ◽

Communication System ◽

Communication Systems ◽

Feedback Loop ◽

Signal Molecules ◽

Specific Cell ◽

Sharp Transition

AbstractBacterial quorum sensing (QS) is based on signal molecules (SM), which increase in concentration with cell density. At critical SM concentration, a variety of adaptive genes sharply change their expression from basic level to maximum level. In general, this sharp transition, a hallmark of true QS, requires an SM dependent positive feedback loop, where SM enhances its own production. Some communication systems, like the peptide SM-based ComQXPA communication system of Bacillus subtilis, do not have this feedback loop and we do not understand how and if the sharp transition in gene expression is achieved. Based on experiments and mathematical modeling, we observed that the SM peptide ComX encodes the information about cell density, specific cell growth rate, and even oxygen concentration, which ensure power-law increase in SM production. This enables together with the cooperative response to SM (ComX) a sharp transition in gene expression level and this without the SM dependent feedback loop. Due to its ultra-sensitive nature, the ComQXPA can operate at SM concentrations that are 100–1000 times lower than typically found in other QS systems, thereby substantially reducing the total metabolic cost of otherwise expensive ComX peptide.

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Quorum Sensing Controls Biofilm Formation in Vibrio cholerae through Modulation of Cyclic Di-GMP Levels and Repression of vpsT

Journal of Bacteriology ◽

10.1128/jb.01756-07 ◽

2008 ◽

Vol 190 (7) ◽

pp. 2527-2536 ◽

Cited By ~ 266

Author(s):

Christopher M. Waters ◽

Wenyun Lu ◽

Joshua D. Rabinowitz ◽

Bonnie L. Bassler

Keyword(s):

Quorum Sensing ◽

Vibrio Cholerae ◽

Cell Density ◽

Biofilm Formation ◽

High Cell Density ◽

High Cell ◽

Chemical Signaling ◽

Signaling Systems ◽

Genes Encoding ◽

Low Cell Density

ABSTRACT Two chemical signaling systems, quorum sensing (QS) and 3′,5′-cyclic diguanylic acid (c-di-GMP), reciprocally control biofilm formation in Vibrio cholerae. QS is the process by which bacteria communicate via the secretion and detection of autoinducers, and in V. cholerae, QS represses biofilm formation. c-di-GMP is an intracellular second messenger that contains information regarding local environmental conditions, and in V. cholerae, c-di-GMP activates biofilm formation. Here we show that HapR, a major regulator of QS, represses biofilm formation in V. cholerae through two distinct mechanisms. HapR controls the transcription of 14 genes encoding a group of proteins that synthesize and degrade c-di-GMP. The net effect of this transcriptional program is a reduction in cellular c-di-GMP levels at high cell density and, consequently, a decrease in biofilm formation. Increasing the c-di-GMP concentration at high cell density to the level present in the low-cell-density QS state restores biofilm formation, showing that c-di-GMP is epistatic to QS in the control of biofilm formation in V. cholerae. In addition, HapR binds to and directly represses the expression of the biofilm transcriptional activator, vpsT. Together, our results suggest that V. cholerae integrates information about the vicinal bacterial community contained in extracellular QS autoinducers with the intracellular environmental information encoded in c-di-GMP to control biofilm formation.

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Stringent Response Activates Quorum Sensing and Modulates Cell Density-Dependent Gene Expression inPseudomonas aeruginosa

Journal of Bacteriology ◽

10.1128/jb.183.18.5376-5384.2001 ◽

2001 ◽

Vol 183 (18) ◽

pp. 5376-5384 ◽

Cited By ~ 149

Author(s):

Christian van Delden ◽

Rachel Comte ◽

And Marc Bally

Keyword(s):

Gene Expression ◽

Quorum Sensing ◽

Cell Density ◽

Stringent Response ◽

Transcriptional Regulators ◽

Homoserine Lactone ◽

Density Dependent ◽

Sensing Systems ◽

Acid Analogue ◽

Enhanced Expression

ABSTRACT During nutrient starvation, Escherichia coli elicits a stringent response involving the ribosome-associated protein RelA. Activation of RelA results in a global change in the cellular metabolism including enhanced expression of the stationary-phase sigma factor RpoS. In the human pathogen Pseudomonas aeruginosa, a complex quorum-sensing circuitry, linked to RpoS expression, is required for cell density-dependent production of many secreted virulence factors, including LasB elastase. Quorum sensing relies on the activation of specific transcriptional regulators (LasR and RhlR) by their corresponding autoinducers (3-oxo-C12-homoserine lactone [HSL] and C4-HSL), which function as intercellular signals. We found that overexpression of relA activated the expression of rpoS in P. aeruginosa and led to premature, cell density-independent LasB elastase production. We therefore investigated the effects of the stringent response on quorum sensing. Both lasR and rhlR gene expression and autoinducer synthesis were prematurely activated during the stringent response induced by overexpression of relA. Premature expression of lasR and rhlR was also observed when relA was overexpressed in a PAO1 rpoSmutant. The stringent response induced by the amino acid analogue serine hydroxamate (SHX) also led to premature production of the 3-oxo-C12-HSL autoinducer. This response to SHX was absent in a PAO1 relA mutant. These findings suggest that the stringent response can activate the two quorum-sensing systems of P. aeruginosa independently of cell density.

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Hierarchical Transcriptional Control of the LuxR Quorum-Sensing Regulon of Vibrio harveyi

Journal of Bacteriology ◽

10.1128/jb.00047-20 ◽

2020 ◽

Vol 202 (14) ◽

Author(s):

Ryan R. Chaparian ◽

Alyssa S. Ball ◽

Julia C. van Kessel

Keyword(s):

Gene Expression ◽

Transcription Factors ◽

Quorum Sensing ◽

Cell Density ◽

Regulatory Networks ◽

Vibrio Harveyi ◽

Sugar Transport ◽

Content Type ◽

Second Tier

ABSTRACT In vibrios, quorum sensing controls hundreds of genes that are required for cell density-specific behaviors including bioluminescence, biofilm formation, competence, secretion, and swarming motility. The central transcription factor in the quorum-sensing pathway is LuxR/HapR, which directly regulates ∼100 genes in the >400-gene regulon of Vibrio harveyi. Among these directly controlled genes are 15 transcription factors, which we predicted would comprise the second tier in the hierarchy of the LuxR regulon. We confirmed that LuxR binds to the promoters of these genes in vitro and quantified the extent of LuxR activation or repression of transcript levels. Transcriptome sequencing (RNA-seq) indicates that most of these transcriptional regulators control only a few genes, with the exception of MetJ, which is a global regulator. The genes regulated by these transcription factors are predicted to be involved in methionine and thiamine biosynthesis, membrane stability, RNA processing, c-di-GMP degradation, sugar transport, and other cellular processes. These data support a hierarchical model in which LuxR directly regulates 15 transcription factors that drive the second level of the gene expression cascade to influence cell density-dependent metabolic states and behaviors in V. harveyi. IMPORTANCE Quorum sensing is important for survival of bacteria in nature and influences the actions of bacterial groups. In the relatively few studied examples of quorum-sensing-controlled genes, these genes are associated with competition or cooperation in complex microbial communities and/or virulence in a host. However, quorum sensing in vibrios controls the expression of hundreds of genes, and their functions are mostly unknown or uncharacterized. In this study, we identify the regulators of the second tier of gene expression in the quorum-sensing system of the aquaculture pathogen Vibrio harveyi. Our identification of regulatory networks and metabolic pathways controlled by quorum sensing can be extended and compared to other Vibrio species to understand the physiology, ecology, and pathogenesis of these organisms.

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