Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Quorum Sensing”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40Linked to original sources
PubMed2004

Regulation of proinflammatory mediator production in RAW264.7 macrophage by Vibrio vulnificus luxS and smcR.

Vibrio vulnificus causes fatal septicemia in human hosts, which is the consequence of raw shellfish consumption. The mortality following septicemia is dependent on the in vivo production of inflammatory mediators, including tumor necrosis factor-alpha (TNFalpha). The present study was set up to investigate the association of quorum sensing in V. vulnificus with the host immune response. The effect of quorum sensing on cytotoxicity and the production of proinflammatory mediators was examined using the murine macrophage cell-line RAW264.7. Cytotoxicity was determined by measuring lactate dehydrogenase release in the culture medium. Extracellular products from luxS- and smcR-deficient mutants exhibited weak cytotoxic effects on RAW264.7 cells. The production of the proinflammatory cytokines TNFalpha, IL-1beta and IL-6 was measured with real-time PCR and ELISA, and production was measured with Griess reagents. Mutation of both luxS and smcR delayed the transcription of TNFalpha, IL-1beta and IL-6 genes. Also, levels of both TNFalpha and nitric oxide induced by luxS- and smcR-deficient mutants were significantly lower than those induced by parent strains. These results suggest that quorum sensing could be involved in the modulation of TNFalpha and nitric oxide produced from host cells by regulating virulence factors, and that V. vulnificus facilitates its host's mortality and bacterial survival by enhancing virulence on host cells.

Animals↗
PubMed2001

Quorum signaling via AI-2 communicates the "Metabolic Burden" associated with heterologous protein production in Escherichia coli.

Recent reports have shown that bacterial cell-cell communication or quorum sensing is quite prevalent in pathogenic Escherichia coli, especially at high cell density; however, the role of quorum sensing in nonpathogenic E. coli is less clear and, in particular, there is no information regarding the role of quorum sensing in overexpression of plasmid-encoded genes. In this work, it was found that the activity of a quorum signaling molecule, autoinducer-2 (AI-2), decreased significantly following induction of several plasmid-encoded genes in both low and high-cell-density cultures of E. coli. Furthermore, we show that AI-2 signaling level was linearly related to the accumulation level of each protein product and that, in general, the highest rates of recombinant protein accumulation resulted in the greatest attenuation of AI-2 signaling. Importantly, our findings demonstrate for the first time that recombinant E. coli communicate the stress or burden of overexpressing heterologous genes through the quorum-based AI-2 signaling pathway.

Bacterial Proteins↗
PubMed2004

Use of Sinorhizobium meliloti as an indicator for specific detection of long-chain N-acyl homoserine lactones.

Population-density-dependent gene expression in gram-negative bacteria involves the production of signal molecules characterized as N-acyl homoserine lactones (AHLs). The synthesis of AHLs by numerous microorganisms has been identified by using biosensor strains based on the Agrobacterium tumefaciens and Chromobacterium violaceum quorum-sensing systems. The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti is rapidly becoming a model organism for the study of quorum sensing. This organism harbors at least three different quorum-sensing systems (Sin, Mel, and Tra), which play a role in its symbiotic relationship with its host plant, alfalfa. The Sin system is distinguished among them for the production of long-chain AHLs, including C(18)-HL, the longest AHL reported so far. In this work, we show that construction of a sinI::lacZ transcriptional fusion results in a strain that detects long-chain AHLs with exquisite sensitivity. Overexpression of the SinR regulator protein from a vector promoter increases its sensitivity without loss of specificity. We also show that the resulting indicator strain can recognize long-chain AHLs produced by unrelated bacteria such as Paracoccus denitrificans and Rhodobacter capsulatus. This S. meliloti indicator strain should serve as a tool for the specific detection of long-chain AHLs in new systems.

4-Butyrolactone↗
PubMed2006

RhlR expression in Pseudomonas aeruginosa is modulated by the Pseudomonas quinolone signal via PhoB-dependent and -independent pathways.

The expression of virulence determinants in Pseudomonas aeruginosa is coordinately regulated in response to both the social environment--commonly referred to as quorum sensing--and to environmental cues. In this study we have dissected the various independent regulation levels for pyocyanin production, which is influenced by the homoserine lactone- and Pseudomonas quinolone signal (PQS)-mediated quorum-sensing systems as well as by iron and phosphate availability. We demonstrate that the phosphate regulon is involved in the transcriptional activation of rhlR and the augmentation of PQS and pyocyanin production under phosphate limitation. However, we also observed an enhancement of rhlR transcription under low-iron medium conditions and after the addition of PQS that was independent of the phosphate regulon. These results highlight the complexity of secondary metabolite production in P. aeruginosa via environmental cues and the quorum-sensing system.

4-Butyrolactone↗
PubMed1999

RsaL, a novel repressor of virulence gene expression in Pseudomonas aeruginosa.

As components of a Pseudomonas aeruginosa quorum-sensing system, LasR and PAI-1 globally regulate expression of multiple virulence determinants, as well as the second P. aeruginosa quorum-sensing system. To date, no information exists on negative regulation of the quorum-sensing cascade in P. aeruginosa. Here we describe a novel gene, rsaL, which is located downstream from lasR and transcribed antisense relative to lasR. In P. aeruginosa, overexpression of rsaL results in reduced lasB expression and decreased elastase activity. With the use of a six-His protein fusion system, we demonstrate that rsaL encodes an 11-kDa protein. Direct quantitation of PAI-1 levels in cultures and studies utilizing Escherichia coli lambda lysogens carrying lacZ transcriptional fusions reveal that RsaL specifically represses transcription of the PAI-1 autoinducer synthase gene, lasI. RsaL's repressive effect on lasI and the associated decrease in elastase activity have important implications for the expression of all LasR-PAI-1-dependent virulence genes and the overall pathogenicity of P. aeruginosa.

Amino Acid Sequence↗
PubMed2005

Interference with AI-2-mediated bacterial cell-cell communication.

Bacteria communicate by means of chemical signal molecules called autoinducers. This process, called quorum sensing, allows bacteria to count the members in the community and to alter gene expression synchronously across the population. Quorum-sensing-controlled processes are often crucial for successful bacterial--host relationships--both symbiotic and pathogenic. Most quorum-sensing autoinducers promote intraspecies communication, but one autoinducer, called AI-2, is produced and detected by a wide variety of bacteria and is proposed to allow interspecies communication. Here we show that some species of bacteria can manipulate AI-2 signalling and interfere with other species' ability to assess and respond correctly to changes in cell population density. AI-2 signalling, and the interference with it, could have important ramifications for eukaryotes in the maintenance of normal microflora and in protection from pathogenic bacteria.

Bacteria↗
PubMed2006

Role of bacteriocin immunity proteins in the antimicrobial sensitivity of Streptococcus mutans.

Bacteria utilize quorum-sensing systems to modulate environmental stress responses. The quorum-sensing system of Streptococcus mutans is mediated by the competence-stimulating peptide (CSP), whose precursor is encoded by the comC gene. A comC mutant of strain GS5 exhibited enhanced antimicrobial sensitivity to a wide variety of different agents. Since the addition of exogenous CSP did not complement this phenotype, it was determined that the increased tetracycline, penicillin, and triclosan sensitivities resulted from repression of the putative bacteriocin immunity protein gene, bip, which is located immediately upstream from comC. We further demonstrated that the inactivation of bip or smbG, another bacteriocin immunity protein gene present within the smb operon in S. mutans GS5, affected sensitivity to a variety of antimicrobial agents. Furthermore, both the bip and smbG genes were upregulated in the presence of low concentrations of antibiotics and were induced during biofilm formation relative to in planktonic cells. These results suggest, for the first time, that the antimicrobial sensitivity of a bacterium can be modulated by some of the putative bacteriocin immunity proteins expressed by the organism. The implications of these observations for the evolution of bacteriocin immunity protein genes as well as for potential new chemotherapeutic strategies are discussed.

Anti-Bacterial Agents↗
PubMed2003

Presence of N-acyl homoserine lactones in soil detected by a whole-cell biosensor and flow cytometry.

Quorum sensing enables bacteria to regulate expression of certain genes according to population density. N-acyl homoserine lactone (AHL)-based quorum sensing is known to be widespread among gram-negative bacteria. Several bacterial whole-cell biosensors for AHL detection have been developed and some were used in in situ studies of AHL production. From these studies our knowledge of the significance of quorum sensing in various environments has been improved. However, very little is known about production of AHLs in soil environments. In the present study, an approach for detecting AHL production in bulk soil was developed. A whole-cell biosensor based on the regulatory region of the lux-operon from Vibrio fischeri fused to gfp was constructed, resulting in a luxR-PluxI-gfpmut3*-fusion in the high copy plasmid, pAHL-GFP. Escherichia coli MC4100 harboring pAHL-GFP responded to the AHL-compound N-octanoyl homoserine lactone (OHL) by expressing green fluorescence. In situ application of E. coli MC4100/pAHL-GFP was tested by adding OHL in different concentrations to sterile soil microcosms. E. coli MC4100/pAHL-GFP were incubated in the soil microcosms and extracted by an improved Nycodenz-extraction method optimized for flow cytometry. The presence of induced cells was then verified by single-cell analysis by flow cytometry. OHL concentrations between 0.5 and 50 nmol per g soil were detected. When introducing the AHL-producing Serratia liquefaciens to soil microcosms, expression of green fluorescent protein was induced in E. coli MC4100/pAHL-GFP. Thereby, the ability of this strain to detect excretion of AHLs by S. liquefaciens in sterile soil was shown. The use of an improved extraction method and a whole-cell biosensor combined with flow cytometry analysis proved to be promising tools in future studies of AHL production by microbial populations in soil environments.

4-Butyrolactone↗
PubMed2004

Towards structural determination of the ComX pheromone: synthetic studies on peptides containing geranyltryptophan.

Bacteria produce and respond to signal molecules depending on their cell density. This process is called "quorum sensing". The ComX pheromone, controlled by quorum sensing, activates natural genetic competence in Bacillus subtilis. ComX is an oligopeptide with a posttranslational modification. It has been suggested that ComX pheromone is modified with an isoprenoid at its tryptophan residue, but the complete chemical structure is unknown. We first determined the molecular formula of ComX(RO-E-2), a competence factor for B. subtilis strain RO-E-2. Then we synthesized putative pheromones with 1-, 2-, 4-, 5-, 6-, or 7-geranyl substituted tryptophan residues. The regio- and stereo-selective synthesis of the geranyl tryptophans was successful, and we prepared the six peptides with modified tryptophan residues. These peptides had the same molecular formula and showed similar hydrophobicity to the natural ComX(RO-E-2) in LC-MS analysis. But, none of them showed the same retention time as the natural pheromone and none exhibited its biological activity. These results suggest that the isoprenoid modification pattern of the tryptophan residue is more complex than postulated.

Bacillus subtilis↗
PubMed1998

Induction of microbial secondary metabolism.

Precursors often stimulate production of secondary metabolites either by increasing the amount of a limiting precursor, by inducing a biosynthetic enzyme (synthase) or both. These are usually amino acids but other small molecules also function as inducers. The most well-known are the auto-inducers which include gamma-butyrolactones (butanolides) of the actinomycetes, N-acylhomoserine lactones of Gram-negative bacteria, oligopeptides of Gram-positive bacteria, and B-factor (3'-[1-butylphosphoryl] adenosine) of Amycolatopsis mediterranei. The actinomycete butanolides exert their effects via receptor proteins which normally repress chemical and morphological differentiation (secondary metabolism and differentiation into aerial mycelia and spores respectively) but, when complexed with the butanolide, can no longer function. Homoserine lactones of Gram-negative bacteria function at high cell density and are structurally related to the butanolides. They turn on plant and animal virulence, light emission, plasmid transfer, and production of pigments, cyanide and beta-lactam antibiotics. They are made by enzymes homologous to Lux1, excreted by the cell, enter other cells at high density, bind to a LuxR homologue, the complex then binding to DNA upstream of genes controlled by "quorum sensing" and turning on their expression. Quorum sensing also operates in the case of the peptide pheromones of the Gram-positive bacteria. Here, secretion is accomplished by an ATP binding casette (ABC transporter), the secreted pheromone being recognized by a sensor component of a two-component signal transduction system. The pheromone often induces its own synthesis as well as those proteins involved in protein/peptide antibiotic (including bacteriocins and lantibiotics) production, virulence and genetic competence. The B-factor of A. mediterranei is an inducer of ansamycin (rifamycin) formation.

4-Butyrolactone↗
PubMed2005

GeneChip expression analysis of the VqsR regulon of Pseudomonas aeruginosa TB.

Two interlinked quorum sensing circuits, las and rhl, which control pathogenesis of Pseudomonas aeruginosa are further modulated by numerous regulators, including VqsR (virulence and quorum sensing regulator). High-density oligonucleotide microarrays were used to compare the global expression profile of a wild-type and VqsR mutant in ABC minimal medium. The expression of a large group of metabolic genes, ECF sigma factors as well as of many quorum-sensing genes previously not assigned to VqsR-regulon was found to be affected by the disruption of vqsR.

Culture Media↗
PubMed2002

Interspecies communication between Burkholderia cepacia and Pseudomonas aeruginosa.

Burkholderia cepacia and Pseudomonas aeruginosa are opportunistic pathogens that commonly cause pulmonary infections in cystic fibrosis patients and occasionally co-infect patients' lungs. Both organisms possess quorum-sensing systems dependent on N-acyl homoserine lactone (N-acyl-HSL). Cross-feeding assays demonstrated that P. aeruginosa and B. cepacia were able to utilize heterologous N-acyl-HSL signaling molecules. The ability of quorum-sensing genes from one species to complement the respective quorum-sensing mutations in the heterologous species was also examined. These studies suggest that B. cepacia CepR can use N-acyl-HSLs synthesized by RhlI and LasI and that P. aeruginosa LasR and RhlR can use N-acyl-HSLs synthesized by CepI. It is possible that a mixed bacterial population of B. cepacia and P. aeruginosa can coordinately regulate some of their virulence factors and influence the progression of lung disease due to infection with these organisms.

4-Butyrolactone↗
PubMed2006

N-acylhomoserine lactone-dependent cell-to-cell communication and social behavior in the genus Serratia.

Members of the genus Serratia are increasingly responsible for nosocomial infections, the treatment of which may be complicated by the appearance of multi-antibiotic-resistant strains. Some but not all Serratia strains and species produce N-acylhomoserine lactones (AHLs), and possess luxR and luxI homologous genes. Phylogenetic comparisons have provided evidence for the lateral transfer of these quorum-sensing systems, and in at least one strain of S. marcescens, transfer via a complex transposon has been experimentally demonstrated. AHL-dependent quorum sensing in Serratia controls population surface migration, biofilm development, the biosynthesis of a carbapenem antibiotic and production of the red pigment, prodigiosin. Serratia also possesses LuxS and produces autoinducer-2 (AI-2) which appears to function as a second quorum-sensing system controlling many of the same phenotypes as the LuxR/AHL systems.

4-Butyrolactone↗
PubMed2004

Inactivation of a bacterial virulence pheromone by phagocyte-derived oxidants: new role for the NADPH oxidase in host defense.

Quorum sensing triggers virulence factor expression in medically important bacterial pathogens in response to a density-dependent increase in one or more autoinducing pheromones. Here, we show that phagocyte-derived oxidants target these autoinducers for inactivation as an innate defense mechanism of the host. In a skin infection model, expression of phagocyte NADPH oxidase, myeloperoxidase, or inducible nitric oxide synthase was critical for defense against a quorum-sensing pathogen, Staphylococcus aureus, but not for defense against a quorum sensing-deficient mutant. A virulence-inducing peptide of S. aureus was inactivated in vitro and in vivo by reactive oxygen and nitrogen intermediates, including HOCl and ONOO(-). Inactivation of the autoinducer prevented both the up-regulation of virulence gene expression and the downstream sequelae. MS analysis of the inactivated peptide demonstrated that oxidation of the C-terminal methionine was primarily responsible for loss of activity. Treatment of WT but not NADPH oxidase-deficient mice with N-acetyl methionine to scavenge the inhibitory oxidants increased in vivo quorum sensing independently of the bacterial burden at the site of infection. Thus, oxidant-mediated inactivation of an autoinducing peptide from S. aureus is a critical innate defense mechanism against infection with this pathogen.

Animals↗
PubMed2001

Characterization of phenotypic changes in Pseudomonas putida in response to surface-associated growth.

The formation of complex bacterial communities known as biofilms begins with the interaction of planktonic cells with a surface. A switch between planktonic and sessile growth is believed to result in a phenotypic change in bacteria. In this study, a global analysis of physiological changes of the plant saprophyte Pseudomonas putida following 6 h of attachment to a silicone surface was carried out by analysis of protein profiles and by mRNA expression patterns. Two-dimensional (2-D) gel electrophoresis revealed 15 proteins that were up-regulated following bacterial adhesion and 30 proteins that were down-regulated. N-terminal sequence analyses of 11 of the down-regulated proteins identified a protein with homology to the ABC transporter, PotF; an outer membrane lipoprotein, NlpD; and five proteins that were homologous to proteins involved in amino acid metabolism. cDNA subtractive hybridization revealed 40 genes that were differentially expressed following initial attachment of P. putida. Twenty-eight of these genes had known homologs. As with the 2-D gel analysis, NlpD and genes involved in amino acid metabolism were identified by subtractive hybridization and found to be down-regulated following surface-associated growth. The gene for PotB was up-regulated, suggesting differential expression of ABC transporters following attachment to this surface. Other genes that showed differential regulation were structural components of flagella and type IV pili, as well as genes involved in polysaccharide biosynthesis. Immunoblot analysis of PilA and FliC confirmed the presence of flagella in planktonic cultures but not in 12- or 24-h biofilms. In contrast, PilA was observed in 12-h biofilms but not in planktonic culture. Recent evidence suggests that quorum sensing by bacterial homoserine lactones (HSLs) may play a regulatory role in biofilm development. To determine if similar protein profiles occurred during quorum sensing and during early biofilm formation, HSLs extracted from P. putida and pure C(12)-HSL were added to 6-h planktonic cultures of P. putida, and cell extracts were analyzed by 2-D gel profiles. Differential expression of 16 proteins was observed following addition of HSLs. One protein, PotF, was found to be down-regulated by both surface-associated growth and by HSL addition. The other 15 proteins did not correspond to proteins differentially expressed by surface-associated growth. The results presented here demonstrate that P. putida undergoes a global change in gene expression following initial attachment to a surface. Quorum sensing may play a role in the initial attachment process, but other sensory processes must also be involved in these phenotypic changes.

ATP-Binding Cassette Transporters↗
PubMed2003

LuxO controls luxR expression in Vibrio harveyi: evidence for a common regulatory mechanism in Vibrio.

Quorum-sensing control of luminescence in Vibrio harveyi, which involves an indirect autoinducer-mediated phosphorelay signal transduction system, contrasts with the prototypical quorum-sensing system of Vibrio fischeri, in which the autoinducer and the transcriptional activator LuxR directly activate lux operon expression. In V. harveyi, a regulator not homologous to V. fischeri LuxR and also designated LuxR (LuxRvh), binds specifically to the lux operon promoter region and activates the expression of luminescence. A direct connection has not been identified previously between V. harveyi LuxRvh and the autoinducer-mediated phosphorelay system. Here, we demonstrate by mobility shift assays and measurement of luxRvh mRNA levels with luxO+ and luxO- cells that the central response regulator of the V. harveyi phosphorelay system (LuxO) represses the level of LuxRvh. Expression of a luxRvh-bearing plasmid strongly stimulated luminescence of a luxO- mutant but had no effect on luminescence of wild-type luxO+ cells, indicating tight regulation of luxRvh by LuxO. Furthermore, luxO null mutants of V. fischeri MJ-1 and two autoinducer mutants, MJ-211 (luxI-) and MJ-215 (luxI-ainS-), emitted more light and exhibited more elevated levels of litR, a newly identified V. harveyi luxRvh homologue, than their luxO+ counterparts. These results suggest that activity of the autoinducer-mediated phosphorelay system is coupled to LuxRvh/LitR control of luminescence through LuxO in V. harveyi and V. fischeri. The presence of homologues of V. harveyi LuxRvh, LuxO and other phosphorelay system proteins in various Vibrio species and the control of LuxRvh and its homologues by LuxO identified here in V. harveyi and V. fischeri and recently in Vibrio cholerae suggest that the luxO-luxRvh couple is a central feature of this quorum-sensing system in members of the genus Vibrio.

Bacterial Proteins↗
PubMed2002

Genetic analysis of functions involved in the late stages of biofilm development in Burkholderia cepacia H111.

Burkholderia cepacia and Pseudomonas aeruginosa often co-exist as mixed biofilms in the lungs of patients suffering from cystic fibrosis (CF). Here, we report the isolation of 13 random mini-Tn5 insertion mutants of B. cepacia H111 that are defective in biofilm formation on a polystyrene surface. We show that the screening procedure used in this study is biased towards mutants defective in the late stages of biofilm development. A detailed quantitative analysis of the biofilm structures formed by wild-type and mutant strains revealed that the isolated mutants are impaired in their abilities to develop a typical three-dimensional biofilm structure. Molecular investigations showed that the genes required for biofilm maturation fall into several classes: (i). genes encoding for surface proteins; (ii). genes involved in the biogenesis and maintenance of an integral outer membrane; and (iii). genes encoding regulatory factors. It is shown that three of the regulatory mutants produce greatly reduced amounts of N-octanoylhomoserine lactone (C8-HSL). This compound serves as the major signal molecule of the cep quorum-sensing system. As this density-dependent regulatory system is involved in the regulation of biofilm maturation, we investigated the interplay between the three regulatory genes and the quorum-sensing cascade. The results of these investigations show that the identified genes encode for regulatory elements that are positioned upstream of the cep system, indicating that the quorum-sensing system of B. cepacia is a major checkpoint for biofilm formation.

4-Butyrolactone↗
PubMed1995

A second N-acylhomoserine lactone signal produced by Pseudomonas aeruginosa.

Quorum sensing systems are used by a number of Gram-negative bacterial species to regulate specific sets of genes in a cell density-dependent manner. Quorum sensing involves synthesis and detection of extracellular signals termed autoinducers. As shown in recombinant Escherichia coli, the Pseudomonas aeruginosa autoinducer (PAI) N-(3-oxododecanoyl)homoserine lactone, together with the lasR gene product, activate the P. aeruginosa lasB gene. In this study, PAI was shown to activate lasB-lacZ expression in a P. aeruginosa lasR mutant containing a plasmid with lasR under the control of the lac promoter. The concentration of PAI necessary for half-maximal activation of the lasB-lacZ fusion was approximately 1 microM, which is within the range of PAI levels found in P. aeruginosa culture fluids. The effect of PAI on a P. aeruginosa lasR mutant containing a plasmid with lasR under the control of its own promoter and containing the lasB-lacZ fusion was also tested. Although extracts of culture fluid activated the lasB promoter in this construct, concentrations of PAI as high as 10 microM did not. This indicates the presence of a second extracellular factor (factor 2) that is required for lasB activation in P. aeruginosa when lasR is controlled by its own promoter but not when lasR is controlled by a strong foreign promoter. Factor 2 was shown to be N-butyrylhomoserine lactone. Although recombinant E. coli cells containing the PAI synthase gene, lasI, produce PAI, these cells do not produce factor 2. Furthermore, a P. aeruginosa mutant that produced about 0.1% of the wild-type level of PAI made about 5% of the wild-type level of factor 2. This indicates that factor 2 synthesis results from the activity of a gene product other than PAI synthase. The role of factor 2 in virulence gene regulation remains to be determined, but this compound may affect the expression of lasR, which in turn activates transcription of numerous virulence genes in the presence of sufficient PAI. Apparently, multiple quorum sensing systems can occur and interact with each other in a single bacterial species.

4-Butyrolactone↗