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Results for “Quorum Sensing”

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PubMed2005

Biosynthesis of tripyrrole and beta-lactam secondary metabolites in Serratia: integration of quorum sensing with multiple new regulatory components in the control of prodigiosin and carbapenem antibiotic production.

Summary Serratia sp. ATCC 39006 (39006) uses a complex hierarchical regulatory network allowing multiple inputs to be assessed before genes involved in secondary metabolite biosynthesis are expressed. This taxonomically ill-defined Serratia sp. produces a carbapenem antibiotic (Car; a beta-lactam) and a red pigmented antibiotic, prodigiosin (Pig; a tripyrrole), which are controlled by the smaIR quorum sensing (QS) locus. SmaR is a repressor of Pig and Car when levels of N-acyl- l-homoserine lactones, produced by SmaI, are low. In this study, we demonstrate direct DNA binding of purified SmaR to the promoter of the Car biosynthetic genes and abolition of this binding by the QS ligand. We have also identified multiple new secondary metabolite regulators. QS controls production of secondary metabolites, at least in part, by modulating transcription of three genes encoding regulatory proteins, including a putative response regulator of the GacAS two-component signalling system family, a novel putative adenylate cyclase and Rap (regulator of antibiotic and pigment). Mutations in another gene encoding a novel predicted global regulator, pigP, are highly pleiotropic; PigP has a significant "master" regulatory role in 39006 where it controls the transcription of six other regulators. The PigP protein and its homologues define a new family of regulators and are predicted to bind DNA via a helix-turn-helix domain. There are regulatory overlaps between the QS and PigP regulons that enable the information from different physiological cues to be funnelled into the control of secondary metabolite production.

Amino Acid Sequence↗

PubMed1998

Construction and analysis of luxCDABE-based plasmid sensors for investigating N-acyl homoserine lactone-mediated quorum sensing.

Plasmid reporter vectors have been constructed which respond to activation of LuxR and its homologues LasR and RhlR (VsmR) by N-acyl homoserine lactones (AHLs). The expression of luxCDABE from transcriptional fusions to PluxI, PlasI and PrhlI respectively, occurs in the presence of activating AHLs. A profile of structure/activity relationships is seen where the natural ligand is most potent. The characterisation of individual LuxR homologue/AHL combinations allows a comprehensive evaluation of quorum sensing signals from a test organism.

4-Butyrolactone↗

PubMed2006

The role of quorum sensing mediated developmental traits in the resistance of Serratia marcescens biofilms against protozoan grazing.

Resistance against protozoan grazers is a crucial factor that is important for the survival of many bacteria in their natural environment. However, the basis of resistance to protozoans and how resistance factors are regulated is poorly understood. In part, resistance may be due to biofilm formation, which is known to protect bacteria from environmental stress conditions. The ubiquitous organism Serratia marcescens uses quorum sensing (QS) control to regulate virulence factor expression and biofilm formation. We hypothesized that the QS system of S. marcescens also regulates mechanisms that protect biofilms against protozoan grazing. To investigate this hypothesis, we compared the interactions of wild-type and QS mutant strains of S. marcescens biofilms with two protozoans having different feeding types under batch and flow conditions. Under batch conditions, S. marcescens forms microcolony biofilms, and filamentous biofilms are formed under flow conditions. The microcolony-type biofilms were protected from grazing by the suspension feeder, flagellate Bodo saltans, but were not protected from the surface feeder, Acanthamoeba polyphaga. In contrast, the filamentous biofilm provided protection against A. polyphaga. The main findings presented in this study suggest that (i) the QS system is not involved in grazing resistance of S. marcescens microcolony-type biofilms; (ii) QS in S. marcescens regulates antiprotozoan factor(s) that do not interfere with the grazing efficiency of the protozoans; and (iii) QS-controlled, biofilm-specific differentiation of filaments and cell chains in biofilms of S. marcescens provides an efficient mechanism against protozoan grazing.

Acanthamoeba↗

PubMed2005

Modulation of quorum sensing in Pseudomonas aeruginosa through alteration of membrane properties.

Changes in the cellular envelope are major physiological adaptations that occur when micro-organisms encounter extreme environmental conditions. An appropriate degree of membrane fluidity is crucial for survival, and alteration of membrane lipids is an essential adaptive response. Emerging data suggest that microbial cells may recognize alterations in their membrane viscosity resulting from certain environmental changes as a trigger for adaptive cellular responses. In Pseudomonas aeruginosa, the quorum-sensing (QS) system involves a complex regulatory circuitry that coordinates the expression of genes according to a critical population density. Interestingly, it has been shown that the QS system of P. aeruginosa can also be activated by nutritional stress, independently of the cell density, and therefore may be part of a more general adaptive response to stressful environmental conditions. In order to examine the proposed link between membrane properties and stress signalling, the effects of genetically engineered alterations of the membrane phospholipid composition of P. aeruginosa PAO1 on the activation of the stringent response and the QS system were examined. The lptA gene encoding a functional homologue of PlsC, an Escherichia coli enzyme that catalyses the second step of the phospholipid biosynthesis pathway, was identified and disrupted. Inactivation of lptA altered the fatty acid profile of phospholipids and the membrane properties, resulting in decreased membrane fluidity. This resulted in a premature production of the QS signals N-butanoyl- and N-hexanoyl-homoserine lactone (C4-HSL and C6-HSL) and a repression of 2-heptyl-3-hydroxy-4-quinolone (PQS) synthesis at later growth phases. The effects on C4- and C6-HSL depended upon the expression of relA, encoding the (p)ppGpp alarmone synthase, which was increased in the lptA mutant. Together, the findings support the concept that alterations in membrane properties can act as a trigger for stress-related gene expression.

Acyltransferases↗

PubMed2001

Bacterial response to siderophore and quorum-sensing chemical signals in the seawater microbial community.

BACKGROUND: Oceans are iron-deficient and nutrient-poor environments. These conditions impart limitations on our understanding of and our ability to identify microorganisms from the marine environment. However, less of knowledge on the influence of siderophores and N-acyl homoserinelactone as interspecies communication signals on the bacterial diversity of seawater has been understood. RESULTS: In the presence of 0.1 nM of the commercial siderophore desferroixamine and the known quorum-sensing chemical signals, synthetic N-(3-oxo)-hexanoylhomoserine lactone (0.1 nM) or N-octanoylhomoserine lactone (0.1 nM), the total numbers of bacteria in S9905 seawater increased nearly three-fold, and nearly eight-fold in S0011 seawater as determined by DAPI staining and counting, and increased three-fold by counting colony forming units in S9905 seawater after 7 days of incubation. Similar bacterial changes in bacterial abundance were observed when high concentration of desferroixamine (1 microM) and each of homoserine lactone compounds (1 microM) were presented in seawater samples. The number of cultivable bacterial species observed was also found to increase from 3 (without addition) to 8 (with additions) including three unknown species which were identified by phylogenetic analysis of 16S rDNA sequences. The growth of unknown species was found to be related to their siderophore production with response to the addition of desferroixamine and N-acyl homoserine lactones under iron-limited conditions. CONCLUSION: Artificial addition of siderophores and HSLs may be a possible method to aid in the identification and isolation of marine bacterial species which are thought to be unknown.

4-Butyrolactone↗

PubMed2003

Global regulation in Pseudomonas aeruginosa: the regulatory protein AlgR2 (AlgQ) acts as a modulator of quorum sensing.

The Pseudomonas aeruginosa protein AlgR2 (AlgQ) was originally identified as a regulatory protein implicated in alginate production. It also regulates the synthesis of polyphosphate as well as of a variety of secretable virulence factors, upregulating neuraminidase and siderophore synthesis and downregulating rhamnolipid biosurfactant and extracellular protease synthesis. In this study, we show that the regulatory effect of AlgR2 on elastase protease synthesis is exerted at transcriptional level on the lasB gene. We also demonstrate that AlgR2 negatively modulates the expression of quorum sensing regulatory genes lasR and rhlR. Finally, results obtained from DNA retardation assays provide evidence that AlgR2 can bind specifically to the lasR and rhlR promoters. Altogether, these data provide strong support for the hypothesis that AlgR2 is a global transcriptional regulator in P. aeruginosa.

Alginates↗

PubMed2004

Modeling a synthetic multicellular clock: repressilators coupled by quorum sensing.

Diverse biochemical rhythms are generated by thousands of cellular oscillators that somehow manage to operate synchronously. In fields ranging from circadian biology to endocrinology, it remains an exciting challenge to understand how collective rhythms emerge in multicellular structures. Using mathematical and computational modeling, we study the effect of coupling through intercell signaling in a population of Escherichia coli cells expressing a synthetic biological clock. Our results predict that a diverse and noisy community of such genetic oscillators interacting through a quorum-sensing mechanism should self-synchronize in a robust way, leading to a substantially improved global rhythmicity in the system. As such, the particular system of coupled genetic oscillators considered here might be a good candidate to provide the first quantitative example of a synchronization transition in a population of biological oscillators.

Bacterial Proteins↗

PubMed2004

Tyrosol is a quorum-sensing molecule in Candida albicans.

The human fungal pathogen Candida albicans shows a significant lag in growth when diluted into fresh minimal medium. This lag is abolished by the addition of conditioned medium from a high-density culture. The active component of conditioned medium is tyrosol, which is released into the medium continuously during growth. Under conditions permissive for germ-tube formation, tyrosol stimulates the formation of these filamentous protrusions. Because germ-tube formation is inhibited by farnesol, another quorum-sensing molecule, this process must be under complex positive and negative control by environmental conditions. The identification of tyrosol as an autoregulatory molecule has important implications on the dynamics of growth and morphogenesis in Candida.

Base Sequence↗

PubMed2000

Quorum sensing but not autoinduction of Ti plasmid conjugal transfer requires control by the opine regulon and the antiactivator TraM.

Conjugal transfer of the Ti plasmids from Agrobacterium tumefaciens is controlled by autoinduction via the transcriptional activator TraR and the acyl-homoserine lactone ligand, Agrobacterium autoinducer (AAI). This control process is itself regulated by opines, which are small carbon compounds produced by the crown gall tumors that are induced by the bacteria. Opines control autoinduction by regulating the expression of traR. Transfer of pTiC58 from donors grown with agrocinopines A and B, the conjugal opines for this Ti plasmid, was detected only after the donors had reached a population level of 10(7) cells per cm(2). Donors incubated with the opines and AAI transferred their Ti plasmids at population levels about 10-fold lower than those incubated with opines only. Transcription of the tra regulon, as assessed by monitoring a traA::lacZ reporter, showed a similar dependence on the density of the donor population. However, even in cultures at low population densities that were induced with opines and AAI, there was a temporal lag of between 15 and 20 h in the development of conjugal competence. Moreover, even after this latent period, maximal transfer frequencies required several hours to develop. This lag period was independent of the population density of the donors but could be reduced somewhat by addition of exogenous AAI. Quorum-dependent development of conjugal competence required control by the opine regulon; donors harboring a mutant of pTiC58 deleted for the master opine responsive repressor accR transferred the Ti plasmid at maximum frequencies at very low population densities. Similarly, an otherwise wild-type derivative of pTiC58 lacking traM, which codes for an antiactivator that inhibits TraR activity, transferred at high frequency in a population-independent manner in the absence of the conjugal opines. Thus, while quorum sensing is dependent upon autoinduction, the two phenomena are not synonymous. We conclude that conjugal transfer of pTiC58 is regulated in a quorum-dependent fashion but that supercontrol of the TraR-AAI system by opines and by TraM results in a complex control process that requires not only the accumulation of AAI but also the expression of TraR and the synthesis of this protein at levels that overcome the inhibitory activity of TraM.

Agrobacterium tumefaciens↗

PubMed2002

Altering plant-microbe interaction through artificially manipulating bacterial quorum sensing.

Many bacteria regulate diverse physiological processes in concert with their population size. Bacterial cell-to-cell communication utilizes small diffusible signal molecules, which the bacteria both produce and perceive. The bacteria couple gene expression to cell density by eliciting a response only when the signalling molecules reach a critical threshold (a point at which the population is said to be 'quorate'). The population as a whole is thus able to modify its behaviour as a single unit. Amongst Gram-negative bacteria, the quorum sensing signals most commonly used are N-acylhomoserine lactones (AHLs). It is now apparent that AHLs are used for regulating diverse behaviours in epiphytic, rhizosphere-inhabiting and plant pathogenic bacteria and that plants may produce their own metabolites that interfere with this signalling. Transgenic plants that produce high levels of AHLs or which can degrade bacterial-produced AHLs have been made. These plants have dramatically altered susceptibilities to infection by pathogenic Erwinia species. In addition, such plants will prove useful tools in determining the roles of AHL-regulated density-dependent behaviour in growth promoting, biological control and pathogenic plant-associated bacterial species.

4-Butyrolactone↗

PubMed2004

Quorum sensing control of lantibiotic production; nisin and subtilin autoregulate their own biosynthesis.

Lantibiotics are produced by a variety of Gram-positive bacteria. The production of these peptides appears to be regulated at the transcriptional level in a cell-density-dependent manner in various bacteria. This phenomenon has been studied in detail for the production of nisin by Lactococcus lactis, and the production of the structurally similar subtilin by Bacillus subtilis. In this paper, the molecular mechanism underlying regulation of nisin and subtilin production is reviewed. This quorum sensing, autoregulatory module includes the lantibiotics themselves as peptide pheromones, the signal transduction by the corresponding two-component regulatory systems, and the lantibiotic-responsive promoter elements in the biosynthesis gene clusters. Finally, the exploitation of these regulatory characteristics for the development of highly effective controlled gene expression systems in Gram-positive bacteria is discussed.

Amino Acid Sequence↗

PubMed2001

Quorum-sensing-dependent regulation of biosynthesis of the polyketide antibiotic mupirocin in Pseudomonas fluorescens NCIMB 10586.

Mupirocin (pseudomonic acid) is a polyketide antibiotic, targeting isoleucyl-tRNA synthase, and produced by Pseudomonas fluorescens NCIMB 10586. It is used clinically as a topical treatment for staphylococcal infections, particularly in contexts where there is a problem with methicillin-resistant Staphylococcus aureus (MRSA). In studying the mupirocin biosynthetic cluster the authors identified two putative regulatory genes, mupR and mupI, whose predicted amino acid sequences showed significant identity to proteins involved in quorum-sensing-dependent regulatory systems such as LasR/LuxR (transcriptional activators) and LasI/LuxI (synthases for N-acylhomoserine lactones--AHLs--that activate LasR/LuxR). Inactivation by deletion mutations using a suicide vector strategy confirmed the requirement for both genes in mupirocin biosynthesis. Cross-feeding experiments between bacterial strains as well as solvent extraction showed that, as predicted, wild-type P. fluorescens NCIMB 10586 produces a diffusible substance that overcomes the defect of a mupI mutant. Use of biosensor strains showed that the MupI product can activate the Pseudomonas aeruginosa lasRlasI system and that P. aeruginosa produces one or more compounds that can replace the MupI product. Insertion of a xylE reporter gene into mupA, the first ORF of the mupirocin biosynthetic operon, showed that together mupR/mupI control expression of the operon in such a way that the cluster is switched on late in exponential phase and in stationary phase.

Anti-Bacterial Agents↗

PubMed2006

A quorum-quenching approach to investigate the conservation of quorum-sensing-regulated functions within the Burkholderia cepacia complex.

Taxonomic studies of the past few years have shown that the Burkholderia cepacia complex, a heterogeneous group of B. cepacia-like organisms, consists of at least nine species. B. cepacia complex strains are ubiquitously distributed in nature and have been used for biocontrol, bioremediation, and plant growth promotion purposes. At the same time, B. cepacia complex strains have emerged as important opportunistic pathogens of humans, particularly those with cystic fibrosis. All B. cepacia complex species investigated thus far use quorum-sensing (QS) systems that rely on N-acylhomoserine lactone (AHL) signal molecules to express certain functions, including the production of extracellular proteases, swarming motility, biofilm formation, and pathogenicity, in a population-density-dependent manner. In this study we constructed a broad-host-range plasmid that allowed the heterologous expression of the Bacillus sp. strain 240B1 AiiA lactonase, which hydrolyzes the lactone ring of various AHL signal molecules, in all described B. cepacia complex species. We show that expression of AiiA abolished or greatly reduced the accumulation of AHL molecules in the culture supernatants of all tested B. cepacia complex strains. Phenotypic characterization of wild-type and transgenic strains revealed that protease production, swarming motility, biofilm formation, and Caenorhabditis elegans killing efficiency was regulated by AHL in the large majority of strains investigated.

4-Butyrolactone↗

PubMed2004

Modulation of enteropathogenic Escherichia coli virulence by quorum sensing.

Enteropathogenic Escherichia coli (EPEC) produces a lesion on epithelial cells called the attaching and effacing (AE) lesion. All genes necessary for AE are encoded within the locus of enterocyte effacement (LEE). EPEC also adheres in a characteristic pattern to epithelial cells by forming microcolonies, usually referred to as localized adherence (LA). LA is mediated by the bundle-forming pilus and flagella. The LEE genes are directly activated by the LEE-encoded regulator (Ler). Transcription of Ler is under the control of Per, integration host factor, Fis, BipA, and quorum sensing (QS), specifically through the luxS system. QS activates expression of the LEE genes in EPEC, with QseA activating transcription of ler. Here we report that transcription of the LEE genes and type III secretion are diminished in both luxS and qseA mutants. Transcription of the LEE genes is affected in both mutants mostly during the mid-exponential phase of growth. Transcription of qseA itself is diminished throughout growth in a luxS mutant and is under autorepression. Furthermore, QS activation of type III secretion is independent of per, given that QseA still activates type III secretion in a per mutant strain. Both mutants are deficient in adherence to epithelial cells and form smaller microcolonies. Several factors may contribute to this abnormal behavior: transcription of LEE genes and type III secretion are diminished, and expression of flagella and Per is altered in both mutants. These results suggest that QS is involved in modulating the regulation of the EPEC virulence genes.

Bacterial Adhesion↗

PubMed2003

Killing of Caenorhabditis elegans by Burkholderia cepacia is controlled by the cep quorum-sensing system.

Burkholderia cepacia H111, which was isolated from a cystic fibrosis patient, effectively kills the nematode Caenorhabditis elegans. Depending on the medium used for growth of the bacterium two different killing modes were observed. On high-osmolarity medium the nematodes became paralysed and died within 24 h. Using filter assays we provide evidence that this killing mode involves the production of an extracellular toxin. On nematode growth medium killing occurs over the course of 2-3 days and involves the accumulation of bacteria in the intestinal lumen of C. elegans. We demonstrate that the cep quorum-sensing system of H111 is required for efficient killing of C. elegans under both killing conditions. Using the C. elegans phm-2 mutant that has a non-functional grinder evidence is provided that the cep system is required to enter the intestinal lumen but is dispensable for the colonization of the gut. Furthermore, we demonstrate that the type II secretion machinery is not essential for nematode killing.

Animals↗

PubMed1996

Bacteriocin small of Rhizobium leguminosarum belongs to the class of N-acyl-L-homoserine lactone molecules, known as autoinducers and as quorum sensing co-transcription factors.

Small bacteriocin was isolated from the culture broth of the gram-negative bacterium Rhizobium leguminosarum, which forms symbiotic nitrogen-fixing root nodules on a number of leguminous plants. The structure of the molecule was elucidated by spectroscopic methods and identified as N-(3R-hydroxy-7-cis-tetradecanoyl)-L-homoserine lactone. The absolute configuration of both asymmetric carbon atoms in the molecule was determined by the use of the chiral solvating agents S-(+)- and R-(-)-2,2,2-trifluoro-1-(9-anthryl)-ethanol. small bacteriocin is structurally related to the quorum sensing co-transcription factors for genes from other bacteria such as Vibrio fischeri, Pseudomonas aeruginosa, Erwinia carotovora, and Agrobacterium tumefaciens which are involved in animal-microbe or plant-microbe interactions. The mechanism of regulation of such interactions by this kind of co-transcription factors is still unknown in R. leguminosarum.

4-Butyrolactone↗

PubMed2004

PI factor, a novel type quorum-sensing inducer elicits pimaricin production in Streptomyces natalensis.

A chemically novel autoinducer (PI factor) has been purified from cultures of the pimaricin producer Streptomyces natalensis ATCC27448. The chemical structure of the PI molecule was identified as 2,3-diamino-2,3-bis (hydroxymethyl)-1,4-butanediol. Pimaricin biosynthesis in S. natalensis npi287, a mutant impaired in pimaricin production, was restored by supplementation with either A-factor from Streptomyces griseus IFO13350 or with PI factor. S. natalensis did not synthesize A-factor. The PI autoinducer was active at very low concentrations (50-350 nm). A threshold level of 50 nm was required to observe the induction effect. The dose-response curve was typical of a quorum-sensing type mechanism. The biosynthesis of PI factor was associated with cell growth of S. natalensis, both in defined and complex media. Supplementation of the wild-type S. natalensis with pure PI (300 nm) resulted in a stimulation of 33% of the production of pimaricin. These results indicate that the endogenous synthesis of PI factor is limiting for pimaricin biosynthesis in the wild-type strain. This water-soluble PI factor belongs to a novel class of autoinducers in Streptomyces species different from the classical butyrolactone autoinducers. Because restoration of pimaricin production in the npi287 mutant is conferred by both A-factor and PI factor, S. natalensis appears to be able to integrate different quorum signals from actinomycetes.

Antifungal Agents↗

PubMed2003

Quorum sensing : a novel target for the treatment of biofilm infections.

Present-day treatment of chronic infections is based on compounds that aim to kill or inhibit growth of bacteria. Two problems are recognised to be intrinsically associated with this approach: (i) the frequently observed development of resistance to antimicrobial compounds; and (ii) the fact that all therapeutics are considerably less effective on bacteria growing as biofilms when compared with planktonic cells. The latter point is of particular importance as evidence has accumulated over the past few years that most chronic bacterial infections involve biofilms. The discovery of bacterial communication systems (quorum sensing systems) in Gram-negative bacteria which are believed to orchestrate important temporal events during the infectious process, including the production of virulence factors and the formation of biofilms, has afforded a novel opportunity to control the activity of infecting bacteria by other means than interfering with growth. Compounds that interfere with communication systems are present in nature. Such compounds should not only specifically attenuate the production of virulence factors but should also affect biofilm formation in a manner that is unlikely to pose a selective pressure for the development of resistant mutants.

Animals↗