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Results for “Quorum Sensing”

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PubMed2001

Haemodynamic effects of the bacterial quorum sensing signal molecule, N-(3-oxododecanoyl)-L-homoserine lactone, in conscious, normal and endotoxaemic rats.

N-acylhomoserine lactones (AHLs) are small, diffusible signalling molecules, employed by Gram-negative bacteria to coordinate gene expression with cell population density. Recent in vitro findings indicate that AHLs may function as virulence determinants per se, through modification of cytokine production by eukaryotic cells, and by stimulating the relaxation of blood vessels. In the present study, we assessed the influence of AHLs on cardiovascular function in conscious rats, and draw attention to the ability of the N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C12-HSL), a signal molecule produced by P. aeruginosa, to cause marked bradycardia. This bradycardic effect was blocked by atropine and atenolol, and did not occur in vitro. Furthermore, modification of the acyl side chain length resulted in the loss of activity, whereas removal of the homoserine lactone ring, did not. The bradycardic effect of 3-oxo-C12-HSL was also observed in endotoxaemic animals, albeit attenuated. In normal rats, 3-oxo-C12-HSL caused initial mesenteric and hindquarters vasoconstriction, but only slight, and delayed signs of vasodilatation in the renal and mesenteric vascular beds. Furthermore, administration of 3-oxo-C12-HSL (pre-treatment or 2 h post-treatment) together with LPS, did not modify the established regional haemodynamic effects of the LPS, 6 h after the onset of its infusion. Our observations do not provide any clear evidence for an ability of 3-oxo-C12-HSL to modify the haemodynamic responses to LPS infusion. However, they are not inconsistent with the hypothesis that some of the cardiovascular sequelae of bacterial infection may be modulated by an influence of bacterial quorum sensing signalling molecules on the host.

4-Butyrolactone↗
PubMed2006

Autoinducer 2 controls biofilm formation in Escherichia coli through a novel motility quorum-sensing regulator (MqsR, B3022).

The cross-species bacterial communication signal autoinducer 2 (AI-2), produced by the purified enzymes Pfs (nucleosidase) and LuxS (terminal synthase) from S-adenosylhomocysteine, directly increased Escherichia coli biofilm mass 30-fold. Continuous-flow cells coupled with confocal microscopy corroborated these results by showing the addition of AI-2 significantly increased both biofilm mass and thickness and reduced the interstitial space between microcolonies. As expected, the addition of AI-2 to cells which lack the ability to transport AI-2 (lsr null mutant) failed to stimulate biofilm formation. Since the addition of AI-2 increased cell motility through enhanced transcription of five motility genes, we propose that AI-2 stimulates biofilm formation and alters its architecture by stimulating flagellar motion and motility. It was also found that the uncharacterized protein B3022 regulates this AI-2-mediated motility and biofilm phenotype through the two-component motility regulatory system QseBC. Deletion of b3022 abolished motility, which was restored by expressing b3022 in trans. Deletion of b3022 also decreased biofilm formation significantly, relative to the wild-type strain in three media (46 to 74%) in 96-well plates, as well as decreased biomass (8-fold) and substratum coverage (19-fold) in continuous-flow cells with minimal medium (growth rate not altered and biofilm restored by expressing b3022 in trans). Deleting b3022 changed the wild-type biofilm architecture from a thick (54-mum) complex structure to one that contained only a few microcolonies. B3022 positively regulates expression of qseBC, flhD, fliA, and motA, since deleting b3022 decreased their transcription by 61-, 25-, 2.4-, and 18-fold, respectively. Transcriptome analysis also revealed that B3022 induces crl (26-fold) and flhCD (8- to 27-fold). Adding AI-2 (6.4 muM) increased biofilm formation of wild-type K-12 MG1655 but not that of the isogenic b3022, qseBC, fliA, and motA mutants. Adding AI-2 also increased motA transcription for the wild-type strain but did not stimulate motA transcription for the b3022 and qseB mutants. Together, these results indicate AI-2 induces biofilm formation in E. coli through B3022, which then regulates QseBC and motility; hence, b3022 has been renamed the motility quorum-sensing regulator gene (the mqsR gene).

Biofilms↗
PubMed2005

A quorum-sensing regulator controls expression of both the type IV secretion system and the flagellar apparatus of Brucella melitensis.

Both a type IV secretion system and a flagellum have been described in Brucella melitensis. These two multimolecular surface appendages share several features. Their expression in bacteriological medium is growth curve dependent, both are induced intracellularly and are required for full virulence in a mouse model of infection. Here we report the identification of VjbR, a quorum sensing-related transcriptional regulator. A vjbR mutant has a downregulated expression of both virB operon and flagellar genes either during vegetative growth or during intracellular infection. In a cellular model, the vacuoles containing the vjbR mutant or a virB mutant are decorated with the same markers at similar times post infection. The vjbR mutant is also strongly attenuated in a mouse model of infection. As C(12)-homoserine lactone pheromone is known to be involved in virB repression, we postulated that VjbR is mediating this effect. In agreement with this hypothesis, we observed that, as virB operon, flagellar genes are controlled by the pheromone. All together these data support a model in which VjbR acts as a major regulator of virulence factors in Brucella.

4-Butyrolactone↗
PubMed2006

Ac2-DPD, the bis-(O)-acetylated derivative of 4,5-dihydroxy-2,3-pentanedione (DPD) is a convenient stable precursor of bacterial quorum sensing autoinducer AI-2.

Ac2-DPD, the bis-(O)-acetylated derivative of 4,5-dihydroxy-2,3-pentanedione (DPD), was prepared both as a racemic mixture and in the optically active form found in naturally occurring DPD. It was shown to exhibit the same ability as DPD to induce bioluminescence in Vibrio harveyi and beta-galactosidase activity in Salmonella enterica Typhimurium, both gram-negative bacteria. Likewise, it was also shown to inhibit biofilm formation in gram-positive Bacillus cereus. The most likely hypothesis is that Ac2-DPD activity is due to the release of DPD by in situ hydrolysis of the ester groups. Importantly, by contrast with DPD, Ac2-DPD proved to be a stable compound which can be purified and stored.

Acetylation↗
PubMed2007

An rhl-like quorum-sensing system negatively regulates pyoluteorin production in Pseudomonas sp. M18.

Pseudomonas sp. M18, isolated from the watermelon rhizosphere, is antagonistic against a number of soil-borne pathogens. This strain produces an uncharacterized red pigment, pyoluteorin (Plt), and two N-acylhomoserine lactones (AHLs). A previously isolated red-pigment-defective mutant, M18-T510, contains an insert within a gene similar to rhlI in P. aeruginosa PAO1. The M18 rhlI gene product is responsible for the production of two AHL signals: N-butyryl-homoserine lactone and N-hexanoylhomoserine lactone. Mutants defective in either rhlI or rhlR showed enhanced Plt biosynthesis due to loss of transcriptional repression, which was mediated, at least in part, by suppressed expression of the activator PltR. A Plt-specific ABC transporter was also upregulated in the rhl mutants in a Plt-dependent manner. In comparison with the wild-type strain, the rhl mutants survived longer during stationary-phase growth.

4-Butyrolactone↗
PubMed2004

Effects of quorum-sensing on immunoglobulin G responses in a rat model of chronic lung infection with Pseudomonas aeruginosa.

Levels of serum antibodies against Pseudomonas aeruginosa were observed for 106 days in a rat model of chronic lung infection. Significantly weaker responses of serum IgG and IgG1 and a lower ratio of IgG1/IgG2a were found in the rats infected with the quorum-signal-deficient mutant, PAO1 (rhlI, lasI), compared with the wild-type PAO1. Four out of 15 rats infected with wild-type PAO1 contained bacteria in the lungs on day 106, whereas no bacteria were found in the mutant PAO1 group. The results indicate that quorum signals contribute to the persistence of the infection and influence the immune response.

Animals↗
PubMed2000

Inducible expression and cellular location of AgrB, a protein involved in the maturation of the staphylococcal quorum-sensing pheromone.

AgrB has been suggested to be responsible for the posttranslational modification in staphylococci that leads to the production of the thiolactone-containing agr peptide pheromone. We demonstrate that AgrB is located in the cytoplasmic membrane. Vectors were constructed for the xylose-inducible overexpression of agrB, and of agrB and agrD together. A Staphylococcus epidermidis strain deleted for agr and containing these vectors was assayed for AgrB protein and pheromone production. The lack of adequate pheromone production suggests the involvement of additional factors in the production of the agr pheromone.

Bacterial Proteins↗
PubMed2005

Detection of homoserine lactone-like quorum sensing molecules in bradyrhizobium strains.

One hundred and forty-two Bradyrhizobium strains were screened for their ability to produce N-acyl homoserine lactone-like molecules (AHLs) by using an Agrobacterium tumefaciens biosensor strain containing a traI-lacZ fusion. Approximately 22% (31 of 142) of the tested strains produced AHLs that induced moderate to elevated beta-galactosidase activity levels in the biosensor strain. Bradyrhizobium japonicum and Bradyrhizobium elkanii strains were both shown to produce AHLs. Age of culture, and media composition were each shown to influence production of AHL(s), with greater production occurring in 2 day-old cultures grown in rich media. Reverse-phase high-performance liquid chromatography and thin-layer chromatography analyses indicated that the B. japonicum strain USDA 290 produced at least two types of AHLs. Our results indicate that the production AHL-like autoinducers is widespread among both B. japonicum and B. elkanii strains.

4-Butyrolactone↗
PubMed2006

Synthesis and biological evaluation of homoserine lactone derived ureas as antagonists of bacterial quorum sensing.

A series of 15 racemic alkyl- and aryl-N-substituted ureas, derived from homoserine lactone, were synthesized and tested for their ability to competitively inhibit the action of 3-oxohexanoyl-l-homoserine lactone, the natural inducer of bioluminescence in the bacterium Vibrio fischeri. N-alkyl ureas with an alkyl chain of at least 4 carbon atoms, as well as certain ureas bearing a phenyl group at the extremity of the alkyl chain, were found to be significant antagonists. In the case of N-butyl urea, it has been shown that the antagonist activity was related to the inhibition of the dimerisation of the N-terminal domain of ExpR, a protein of the receptor LuxR family. Molecular modelling suggested that this would result from the formation of an additional hydrogen bond in the protein acylhomoserine lactone binding cavity.

4-Butyrolactone↗
PubMed2006

Synthesis of Pseudomonas quorum-sensing autoinducer analogs and structural entities required for induction of apoptosis in macrophages.

The synthesis of the analogs of N-3-oxododecanoyl-L-homoserine lactone (1) and their structure-activity relationship for the apoptotic induction in macrophages, P388D1 cells, are described. It was revealed that the position of the oxo group in the acyl side chain in addition to the presence of the L-homoserine lactone unit is crucial for the apoptosis-inducing activity. Furthermore, the long acyl side chains with hydrophobic distal ends are preferable for the activity.

4-Butyrolactone↗
PubMed2006

Quorum sensing: alcohols in a social situation.

Many microbes use extracellular signals to transmit information about population density and environmental conditions. Recent evidence suggests that the budding yeast Saccharomyces cerevisiae exhibits this type of regulation and that the signals are aromatic alcohols.

Hyphae↗