151
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Hentzer M, Riedel K, Rasmussen TB, Heydorn A, Andersen JB, Parsek MR, Rice SA, Eberl L, Molin S, Høiby N, Kjelleberg S, Givskov M. Inhibition of quorum sensing in Pseudomonas aeruginosa biofilm bacteria by a halogenated furanone compound. MICROBIOLOGY (READING, ENGLAND) 2002; 148:87-102. [PMID: 11782502 DOI: 10.1099/00221287-148-1-87] [Citation(s) in RCA: 665] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Novel molecular tools have been constructed which allow for in situ detection of N-acyl homoserine lactone (AHL)-mediated quorum sensing in Pseudomonas aeruginosa biofilms. The reporter responds to AHL activation of LasR by expression of an unstable version of the green-fluorescent protein (Gfp). Gfp-based reporter technology has been applied for non-destructive, single-cell-level detection of quorum sensing in laboratory-based P. aeruginosa biofilms. It is reported that a synthetic halogenated furanone compound, which is a derivative of the secondary metabolites produced by the Australian macroalga Delisea pulchra, is capable of interfering with AHL-mediated quorum sensing in P. aeruginosa. It is demonstrated that the furanone compound specifically represses expression of a PlasB-gfp reporter fusion without affecting growth or protein synthesis. In addition, it reduces the production of important virulence factors, indicating a general effect on target genes of the las quorum sensing circuit. The furanone was applied to P. aeruginosa biofilms established in biofilm flow chambers. The Gfp-based analysis reveals that the compound penetrates microcolonies and blocks cell signalling and quorum sensing in most biofilm cells. The compound did not affect initial attachment to the abiotic substratum. It does, however, affect the architecture of the biofilm and enhances the process of bacterial detachment, leading to a loss of bacterial biomass from the substratum.
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Affiliation(s)
- Morten Hentzer
- Department of Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark1
| | - Kathrin Riedel
- Lehrstuhl für Mikrobiologie, Technische Universität München, D-85350 Freising, Germany2
| | - Thomas B Rasmussen
- Department of Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark1
| | - Arne Heydorn
- Department of Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark1
| | - Jens Bo Andersen
- Department of Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark1
| | - Matthew R Parsek
- Department of Civil Engineering, Technological Institute, North Western University, Evanston, IL 60208-3109, USA3
| | - Scott A Rice
- School of Microbiology and Immunology, University of New South Wales (UNSW), Australia 20524
| | - Leo Eberl
- Lehrstuhl für Mikrobiologie, Technische Universität München, D-85350 Freising, Germany2
| | - Søren Molin
- Department of Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark1
| | - Niels Høiby
- Department of Clinical Microbiology, University Hospital (Rigshospitalet), DK-2100 Copenhagen, Denmark5
| | - Staffan Kjelleberg
- School of Microbiology and Immunology, University of New South Wales (UNSW), Australia 20524
| | - Michael Givskov
- Department of Molecular Microbiology, BioCentrum-DTU, Technical University of Denmark, DK-2800 Lyngby, Denmark1
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152
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Abstract
Bacillus anthracis produces the anthrax toxin proteins protective antigen (PA), lethal factor (LF), and edema factor (EF) in a growth phase-dependent manner when cultured in liquid medium. Expression of the toxin genes pagA, lef, and cya peaks in late log phase, and steady-state levels of the toxin proteins are highest during the transition into stationary phase. Here we show that an apparent transition state regulator negatively regulates toxin gene expression. We identified two orthologues of the B. subtilis transition state regulator abrB in the B. anthracis genome: one on the chromosome and one on the 182-kb virulence plasmid pXO1. The orthologue located on the chromosome is predicted to encode a 94-amino-acid protein that is 85% identical to B. subtilis AbrB. The hypothetical protein encoded on pXO1 is 41% identical to B. subtilis AbrB but missing 27 amino acid residues from the amino terminus compared to the B. subtilis protein. Deletion of the pXO1-encoded abrB orthologue did not affect toxin gene expression under the conditions tested. However, a B. anthracis mutant in which the chromosomal abrB gene was deleted expressed pagA earlier and at a higher level than the parent strain. Expression of a transcriptional pagA-lacZ fusion in the abrB mutant was increased up to 20-fold during early exponential growth compared to the parent strain and peaked in mid-exponential rather than late exponential phase. In contrast to the strong effect of abrB on pagA expression, lef-lacZ and cya-lacZ expression during early-log-phase growth was increased only two- to threefold in the abrB null mutant. Western hybridization analysis showed increased PA, LF, and EF synthesis by the mutant. As is true in B. subtilis, the B. anthracis abrB gene is negatively regulated by spo0A. Our findings tie anthrax toxin gene expression to the complex network of postexponential phase adaptive responses that have been well studied in B. subtilis.
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Affiliation(s)
- Elke Saile
- Department of Microbiology and Molecular Genetics, The University of Texas-Houston Health Science Center Medical School, Houston, Texas 77030, USA
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153
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Heeb S, Haas D. Regulatory roles of the GacS/GacA two-component system in plant-associated and other gram-negative bacteria. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2001; 14:1351-1363. [PMID: 11768529 DOI: 10.1094/mpmi.2001.14.12.1351] [Citation(s) in RCA: 289] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The sensor kinase GacS and the response regulator GacA are members of a two-component system that is present in a wide variety of gram-negative bacteria and has been studied mainly in enteric bacteria and fluorescent pseudomonads. The GacS/GacA system controls the production of secondary metabolites and extracellular enzymes involved in pathogenicity to plants and animals, biocontrol of soilborne plant diseases, ecological fitness, or tolerance to stress. A current model proposes that GacS senses a still-unknown signal and activates, via a phosphorelay mechanism, the GacA transcription regulator, which in turn triggers the expression of target genes. The GacS protein belongs to the unorthodox sensor kinases, characterized by an autophosphorylation, a receiver, and an output domain. The periplasmic loop domain of GacS is poorly conserved in diverse bacteria. Thus, a common signal interacting with this domain would be unexpected. Based on a comparison with the transcriptional regulator NarL, a secondary structure can be predicted for the GacA sensor kinases. Certain genes whose expression is regulated by the GacS/GacA system are regulated in parallel by the small RNA binding protein RsmA (CsrA) at a posttranscriptional level. It is suggested that the GacS/GacA system operates a switch between primary and secondary metabolism, with a major involvement of posttranscriptional control mechanisms.
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Affiliation(s)
- S Heeb
- Laboratoire de Biologie Microbienne, Université de Lausanne, Switzerland
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154
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Riedel K, Hentzer M, Geisenberger O, Huber B, Steidle A, Wu H, Høiby N, Givskov M, Molin S, Eberl L. N-acylhomoserine-lactone-mediated communication between Pseudomonas aeruginosa and Burkholderia cepacia in mixed biofilms. MICROBIOLOGY (READING, ENGLAND) 2001; 147:3249-62. [PMID: 11739757 DOI: 10.1099/00221287-147-12-3249] [Citation(s) in RCA: 280] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Pseudomonas aeruginosa and Burkholderia cepacia are capable of forming mixed biofilms in the lungs of cystic fibrosis patients. Both bacteria employ quorum-sensing systems, which rely on N-acylhomoserine lactone (AHL) signal molecules, to co-ordinate expression of virulence factors with the formation of biofilms. As both bacteria utilize the same class of signal molecules the authors investigated whether communication between the species occurs. To address this issue, novel Gfp-based biosensors for non-destructive, in situ detection of AHLs were constructed and characterized. These sensors were used to visualize AHL-mediated communication in mixed biofilms, which were cultivated either in artificial flow chambers or in alginate beads in mouse lung tissue. In both model systems B. cepacia was capable of perceiving the AHL signals produced by P. aeruginosa, while the latter strain did not respond to the molecules produced by B. cepacia. Measurements of extracellular proteolytic activities of defined quorum-sensing mutants grown in media complemented with AHL extracts prepared from culture supernatants of various wild-type and mutant strains supported the view of unidirectional signalling between the two strains.
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Affiliation(s)
- K Riedel
- Department of Microbiology, TUM, Am Hochanger 4, D-85350 Freising, Germany
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155
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Pessi G, Williams F, Hindle Z, Heurlier K, Holden MT, Cámara M, Haas D, Williams P. The global posttranscriptional regulator RsmA modulates production of virulence determinants and N-acylhomoserine lactones in Pseudomonas aeruginosa. J Bacteriol 2001; 183:6676-83. [PMID: 11673439 PMCID: PMC95500 DOI: 10.1128/jb.183.22.6676-6683.2001] [Citation(s) in RCA: 262] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Posttranscriptional control is known to contribute to the regulation of secondary metabolism and virulence determinants in certain gram-negative bacteria. Here we report the isolation of a Pseudomonas aeruginosa gene which encodes a global translational regulatory protein, RsmA (regulator of secondary metabolites). Overexpression of rsmA resulted in a substantial reduction in the levels of extracellular products, including protease, elastase, and staphylolytic (LasA protease) activity as well as the PA-IL lectin, hydrogen cyanide (HCN), and the phenazine pigment pyocyanin. While inactivation of rsmA in P. aeruginosa had only minor effects on the extracellular enzymes and the PA-IL lectin, the production of HCN and pyocyanin was enhanced during the exponential phase. The influence of RsmA on N-acylhomoserine lactone-mediated quorum sensing was determined by assaying the levels of N-(3-oxododecanoyl)homoserine lactone (3-oxo-C12-HSL) and N-butanoylhomoserine lactone (C4-HSL) produced by the rsmA mutant and the rsmA-overexpressing strain. RsmA exerted a negative effect on the synthesis of both 3-oxo-C12-HSL and C4-HSL, which was confirmed by using lasI and rhlI translational fusions. These data also highlighted the temporal expression control of the lasI gene, which was induced much earlier and to a higher level during the exponential growth phase in an rsmA mutant. To investigate whether RsmA modulates HCN production solely via quorum-sensing control, hcn translational fusions were employed to monitor the regulation of the cyanide biosynthesis genes (hcnABC). RsmA was shown to exert an additional negative effect on cyanogenesis posttranscriptionally by acting on a region surrounding the hcnA ribosome-binding site. This suggests that, in P. aeruginosa, RsmA functions as a pleiotropic posttranscriptional regulator of secondary metabolites directly and also indirectly by modulating the quorum-sensing circuitry.
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Affiliation(s)
- G Pessi
- Laboratoire de Biologie Microbienne, Université de Lausanne, CH-1015 Lausanne, Switzerland
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156
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Huber B, Riedel K, Hentzer M, Heydorn A, Gotschlich A, Givskov M, Molin S, Eberl L. The cep quorum-sensing system of Burkholderia cepacia H111 controls biofilm formation and swarming motility. MICROBIOLOGY (READING, ENGLAND) 2001; 147:2517-2528. [PMID: 11535791 DOI: 10.1099/00221287-147-9-2517] [Citation(s) in RCA: 325] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Burkholderia cepacia and Pseudomonas aeruginosa often co-exist as mixed biofilms in the lungs of patients suffering from cystic fibrosis (CF). Here, the isolation of random mini-Tn5 insertion mutants of B. cepacia H111 defective in biofilm formation on an abiotic surface is reported. It is demonstrated that one of these mutants no longer produces N-acylhomoserine lactones (AHLs) due to an inactivation of the cepR gene. cepR and the cepI AHL synthase gene together constitute the cep quorum-sensing system of B. cepacia. By using a gene replacement method, two defined mutants, H111-I and H111-R, were constructed in which cepI and cepR, respectively, had been inactivated. These mutants were used to demonstrate that biofilm formation by B. cepacia H111 requires a functional cep quorum-sensing system. A detailed quantitative analysis of the biofilm structures formed by wild-type and mutant strains suggested that the quorum-sensing system is not involved in the regulation of initial cell attachment, but rather controls the maturation of the biofilm. Furthermore, it is shown that B. cepacia is capable of swarming motility, a form of surface translocation utilized by various bacteria to rapidly colonize appropriate substrata. Evidence is provided that swarming motility of B. cepacia is quorum-sensing-regulated, possibly through the control of biosurfactant production. Complementation of the cepR mutant H111-R with different biosurfactants restored swarming motility while biofilm formation was not significantly increased. This result suggests that swarming motility per se is not essential for biofilm formation on abiotic surfaces.
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Affiliation(s)
- Birgit Huber
- Lehrstuhl für Mikrobiologie, Technische Universität München, Am Hochanger 4, 85350 Freising, Germany1
| | - Kathrin Riedel
- Lehrstuhl für Mikrobiologie, Technische Universität München, Am Hochanger 4, 85350 Freising, Germany1
| | - Morten Hentzer
- Department of Microbiology, DTU, Building 301, 2800 Lyngby, Denmark2
| | - Arne Heydorn
- Department of Microbiology, DTU, Building 301, 2800 Lyngby, Denmark2
| | - Astrid Gotschlich
- Lehrstuhl für Mikrobiologie, Technische Universität München, Am Hochanger 4, 85350 Freising, Germany1
| | - Michael Givskov
- Department of Microbiology, DTU, Building 301, 2800 Lyngby, Denmark2
| | - Søren Molin
- Department of Microbiology, DTU, Building 301, 2800 Lyngby, Denmark2
| | - Leo Eberl
- Lehrstuhl für Mikrobiologie, Technische Universität München, Am Hochanger 4, 85350 Freising, Germany1
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157
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Gardiner SM, Chhabra SR, Harty C, Williams P, Pritchard DI, Bycroft BW, Bennett T. Haemodynamic effects of the bacterial quorum sensing signal molecule, N-(3-oxododecanoyl)-L-homoserine lactone, in conscious, normal and endotoxaemic rats. Br J Pharmacol 2001; 133:1047-54. [PMID: 11487515 PMCID: PMC1572880 DOI: 10.1038/sj.bjp.0704174] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2000] [Revised: 03/07/2001] [Accepted: 05/17/2001] [Indexed: 11/09/2022] Open
Abstract
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.
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Affiliation(s)
- S M Gardiner
- School of Biomedical Sciences, Queen's Medical Centre, University of Nottingham NG7 2UH, UK.
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158
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Milton DL, Chalker VJ, Kirke D, Hardman A, Cámara M, Williams P. The LuxM homologue VanM from Vibrio anguillarum directs the synthesis of N-(3-hydroxyhexanoyl)homoserine lactone and N-hexanoylhomoserine lactone. J Bacteriol 2001; 183:3537-47. [PMID: 11371516 PMCID: PMC95229 DOI: 10.1128/jb.183.12.3537-3547.2001] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vibrio anguillarum, which causes terminal hemorrhagic septicemia in fish, was previously shown to possess a LuxRI-type quorum-sensing system (vanRI) and to produce N-(3-oxodecanoyl)homoserine lactone (3-oxo-C10-HSL). However, a vanI null mutant still activated N-acylhomoserine lactone (AHL) biosensors, indicating the presence of an additional quorum-sensing circuit in V. anguillarum. In this study, we have characterized this second system. Using high-pressure liquid chromatography in conjunction with mass spectrometry and chemical analysis, we identified two additional AHLs as N-hexanoylhomoserine lactone (C6-HSL) and N-(3-hydroxyhexanoyl)homoserine lactone (3-hydroxy-C6-HSL). Quantification of each AHL present in stationary-phase V. anguillarum spent culture supernatants indicated that 3-oxo-C10-HSL, 3-hydroxy-C6-HSL, and C6-HSL are present at approximately 8.5, 9.5, and 0.3 nM, respectively. Furthermore, vanM, the gene responsible for the synthesis of these AHLs, was characterized and shown to be homologous to the luxL and luxM genes, which are required for the production of N-(3-hydroxybutanoyl)homoserine lactone in Vibrio harveyi. However, resequencing of the V. harveyi luxL/luxM junction revealed a sequencing error present in the published sequence, which when corrected resulted in a single open reading frame (termed luxM). Downstream of vanM, we identified a homologue of luxN (vanN) that encodes a hybrid sensor kinase which forms part of a phosphorelay cascade involved in the regulation of bioluminescence in V. harveyi. A mutation in vanM abolished the production of C6-HSL and 3-hydroxy-C6-HSL. In addition, production of 3-oxo-C10-HSL was abolished in the vanM mutant, suggesting that 3-hydroxy-C6-HSL and C6-HSL regulate the production of 3-oxo-C10-HSL via vanRI. However, a vanN mutant displayed a wild-type AHL profile. Neither mutation affected either the production of proteases or virulence in a fish infection model. These data indicate that V. anguillarum possesses a hierarchical quorum sensing system consisting of regulatory elements homologous to those found in both V. fischeri (the LuxRI homologues VanRI) and V. harveyi (the LuxMN homologues, VanMN).
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Affiliation(s)
- D L Milton
- Department of Cell and Molecular Biology, Umeå University, S-901 87 Umeå, Sweden.
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159
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Lutter E, Lewenza S, Dennis JJ, Visser MB, Sokol PA. Distribution of quorum-sensing genes in the Burkholderia cepacia complex. Infect Immun 2001; 69:4661-6. [PMID: 11402012 PMCID: PMC98545 DOI: 10.1128/iai.69.7.4661-4666.2001] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The distribution of quorum-sensing genes among strains from seven genomovars of the Burkholderia cepacia complex was examined by PCR. cepR and cepI were amplified from B. cepacia genomovars I and III, B. stabilis, and B. vietnamiensis. cepR was also amplified from B. multivorans and B. cepacia genomovar VI. bviIR were amplified from B. vietnamiensis. All genomovars produced N-octanoyl-L-homoserine lactone and N-hexanoyl-L-homoserine lactone. B. vietnamiensis and B. cepacia genomovar VII produced additional N-acyl-L-homoserine lactones.
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Affiliation(s)
- E Lutter
- Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, Alberta, Canada T2N 4N1
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160
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MDowell P, Affas Z, Reynolds C, Holden MT, Wood SJ, Saint S, Cockayne A, Hill PJ, Dodd CE, Bycroft BW, Chan WC, Williams P. Structure, activity and evolution of the group I thiolactone peptide quorum-sensing system of Staphylococcus aureus. Mol Microbiol 2001; 41:503-12. [PMID: 11489134 DOI: 10.1046/j.1365-2958.2001.02539.x] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In Staphylococcus aureus, the agr locus is responsible for controlling virulence gene expression via quorum sensing. As the blockade of quorum sensing offers a novel strategy for attenuating infection, we sought to gain novel insights into the structure, activity and turnover of the secreted staphylococcal autoinducing peptide (AIP) signal molecules. A series of analogues (including the L-alanine and D-amino acid scanned peptides) was synthesized to determine the functionally critical residues within the S. aureus group I AIP. As a consequence, we established that (i) the group I AIP is inactivated in culture supernatants by the formation of the corresponding methionyl sulphoxide; and (ii) the group I AIP lactam analogue retains the capacity to activate agr, suggesting that covalent modification of the AgrC receptor is not a necessary prerequisite for agr activation. Although each of the D-amino acid scanned AIP analogues retained activity, replacement of the endocyclic amino acid residue (aspartate) located C-terminally to the central cysteine with alanine converted the group I AIP from an activator to a potent inhibitor. The screening of clinical S. aureus isolates for novel AIP groups revealed a variant that differed from the group I AIP by a single amino acid residue (aspartate to tyrosine) in the same position defined as critical by alanine scanning. Although this AIP inhibits group I S. aureus strains, the producer strains possess a functional agr locus dependent on the endogenous peptide and, as such, constitute a fourth S. aureus AIP pheromone group (group IV). The addition of exogenous synthetic AIPs to S. aureus inhibited the production of toxic shock syndrome toxin (TSST-1) and enterotoxin C3, confirming the potential of quorum-sensing blockade as a therapeutic strategy.
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Affiliation(s)
- P MDowell
- Institute of Infections and Immunity, School of Pharmaceutical Sciences, and School of BioSciences, University of Nottingham, Nottingham NG7 2RD, UK
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161
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Winzer K, Williams P. Quorum sensing and the regulation of virulence gene expression in pathogenic bacteria. Int J Med Microbiol 2001; 291:131-43. [PMID: 11437336 DOI: 10.1078/1438-4221-00110] [Citation(s) in RCA: 157] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
For many pathogens, the outcome of the interaction between host and bacterium is strongly affected by the bacterial population size. Coupling the production of virulence factors with cell population density ensures that the mammalian host lacks sufficient time to mount an effective defence against consolidated attack. Such a strategy depends on the ability of an individual bacterial cell to sense other members of the same species and in response, differentially express specific sets of genes. Such cell-cell communication is called "quorum sensing" and involves the direct or indirect activation of a response regulator by a small diffusible signal molecule. A number of chemically distinct quorum-sensing signal molecules have been described including the N-acyl-L-homoserine lactones (AHLs) in Gram-negative bacteria and post-translationally modified peptides in Gram-positive bacteria. For example, the human pathogens Pseudomonas aeruginosa and Staphylococcus aureus employ AHLs and peptides, respectively, to control the expression of multiple virulence genes in concert with cell population density. Apart from their role in signal transduction, certain quorum-sensing signal molecules, notably N-(3-oxododecanoyl)homoserine lactone, possess intrinsic pharmacological and immunomodulatory activities such that they may function as virulence determinants per se. While quorum-sensing signal molecules have been detected in tissues in experimental animal model and human infections, the mutation of genes involved in either quorum-sensing signal generation or signal transduction frequently results in the attenuation of virulence. Thus, interference with quorum sensing represents a promising strategy for the therapeutic or prophylactic control of infection.
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Affiliation(s)
- K Winzer
- Institute of Infections & Immunity, Queen's Medical Centre, University of Nottingham, UK
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162
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Withers H, Swift S, Williams P. Quorum sensing as an integral component of gene regulatory networks in Gram-negative bacteria. Curr Opin Microbiol 2001; 4:186-93. [PMID: 11282475 DOI: 10.1016/s1369-5274(00)00187-9] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Bacterial cell-to-cell communication (quorum sensing) relies upon the interaction of a small diffusible signal molecule with a sensor or transcriptional activator to couple gene expression with cell population density. In Gram-negative bacteria, it is now clear that N-acylhomoserine lactones bind directly to LuxR homologues and can be synthesized via one of three unrelated bacterial protein families and by transgenic plants. New chemical classes of signal molecules have been identified, some of which exhibit crosstalk with N-acylhomoserine-lactone-mediated quorum sensing. As the determinant of cell population density, quorum sensing is emerging as an integral component of bacterial global gene regulatory networks responsible for facilitating bacterial adaptation to environmental stress. N-acylhomoserine lactones are produced during experimental animal and human infections, and a function beyond quorum sensing has been suggested by their intrinsic immunomodulatory and pharmacological activities.
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Affiliation(s)
- H Withers
- Institute of Infections and Immunity, Queen's Medical Centre University of Nottingham, NG7 2RD, Nottingham, UK
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163
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Abstract
Recent studies of microorganisms have revealed diverse complex social behaviors, including cooperation in foraging, building, reproducing, dispersing and communicating. These microorganisms should provide novel, tractable systems for the analysis of social evolution. The application of evolutionary and ecological theory to understanding their behavior will aid in developing better means to control the many pathogenic bacteria that use social interactions to affect humans.
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164
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Gotschlich A, Huber B, Geisenberger O, Tögl A, Steidle A, Riedel K, Hill P, Tümmler B, Vandamme P, Middleton B, Camara M, Williams P, Hardman A, Eberl L. Synthesis of multiple N-acylhomoserine lactones is wide-spread among the members of the Burkholderia cepacia complex. Syst Appl Microbiol 2001; 24:1-14. [PMID: 11403388 DOI: 10.1078/0723-2020-00013] [Citation(s) in RCA: 121] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Seventy strains of the Burkholderia cepacia complex, which currently comprises six genomic species, were tested for their ability to produce N-acylhomoserine lactone (AHL) signal molecules. Using thin layer chromatography in conjunction with a range of AHL biosensors, we show that most strains primarily produce two AHLs, namely N-octanoylhomoserine lactone (C8-HSL) and N-hexanoylhomoserine lactone (C6-HSL). Furthermore, some strains belonging to B. vietnamiensis (genomovar V) produce additional long chain AHL molecules with acyl chains ranging from C10 to C14. For B. vietnamiensis R-921 the structure of the most abundant long chain AHL was confirmed as N-decanoylhomoserine lactone (C10-HSL) by liquid chromatography-mass spectrometry (LC-MS) in combination with total chemical synthesis. Interestingly, a number of strains, most notably all representatives of B. multivorans (genomovar II), did not produce AHLs at least under the growth conditions used in this study. All strains were also screened for the production of extracellular lipase, chitinase, protease, and siderophores. However, no correlation between the AHL production and the synthesis of these exoproducts was apparent. Southern blot analysis showed that all the B. cepacia complex strains investigated, including the AHL-negative strains, possess genes homologous to the C8-HSL synthase cepI and to cepR, which encodes the cognate receptor protein. The nucleotide sequence of the cepI and cepR genes from one representative strain from each of the six genomovars was determined. Furthermore, the cepI genes from the different genomovars were expressed in Escherichia coli and it is demonstrated that all genes encode functional proteins that direct the synthesis of C8-HSL and C6-HSL. Given that cepI from the B. multivorans strain encodes a functional AHL synthase, yet detectable levels of AHLs were not produced by the wild-type, this suggests that additional regulatory functions may be present in members of this genomovar that negatively affect expression of cepI.
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Affiliation(s)
- A Gotschlich
- Lehrstuhl für Mikrobiologie, Technische Universität München, Germany
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165
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Mahan MJ, Heithoff DM, Sinsheimer RL, Low DA. Assessment of bacterial pathogenesis by analysis of gene expression in the host. Annu Rev Genet 2001; 34:139-164. [PMID: 11092824 DOI: 10.1146/annurev.genet.34.1.139] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A number of techniques have been developed to assess the expression of microbial virulence genes within the host (in vivo). These studies have shown that bacteria employ a wide variety of mechanisms to coordinately regulate the expression of these genes during infection. Two tenets have emerged from these studies: bacterial adaptation responses are critical to growth within the host, and interactions between microorganisms and the microenvironments of their hosts cannot be revealed from in vitro studies alone. Results that support these tenets include (i) the prevalent class of in vivo expressed genes are involved in adaptation to environmental stresses, (ii) pathogens recovered from host tissues (versus laboratory growth) are often more resistant to host killing mechanisms, and (iii) virulence gene expression can differ in the animal compared to laboratory media. Thus, pathogenicity comprises the unique ability to adapt to the varied host milieus encountered as the infection proceeds.
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Affiliation(s)
- M J Mahan
- Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, California 93106, USA.
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166
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Laue BE, Jiang Y, Chhabra SR, Jacob S, Stewart GSAB, Hardman A, Downie JA, O'Gara F, Williams P. The biocontrol strain Pseudomonas fluorescens F113 produces the Rhizobium small bacteriocin, N-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone, via HdtS, a putative novel N-acylhomoserine lactone synthase. MICROBIOLOGY (READING, ENGLAND) 2000; 146 ( Pt 10):2469-2480. [PMID: 11021923 DOI: 10.1099/00221287-146-10-2469] [Citation(s) in RCA: 163] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Several different species of Pseudomonas: produce N:-acylhomoserine lactones (AHLs), quorum-sensing signal molecules which are involved in the cell-density-dependent control of secondary metabolite and virulence gene expression. When Pseudomonas fluorescens F113 was cross-streaked against AHL biosensors capable of sensitively detecting either short (C(4)-C(8)) or long (C(10)-C(14)) acyl chain AHLs, no activity was detectable. However, by extracting cell-free stationary-phase culture supernatants with dichloromethane followed by reverse-phase HPLC, three distinct fractions were obtained capable of activating the AHL biosensors. Three AHLs were subsequently characterized using high-resolution MS and chemical synthesis. These were (i) N:-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone (3OH, C(14:1)-HSL), a molecule previously known as the Rhizobium leguminosarum small bacteriocin as a consequence of its growth inhibitory properties, (ii) N:-decanoylhomoserine lactone (C(10)-HSL) and (iii) N:-hexanoylhomoserine lactone (C(6)-HSL). A gene (hdtS) capable of directing synthesis of all three P. fluorescens AHLs in Escherichia coli was cloned and sequenced. In vitro transcription/translation of hdtS yielded a protein of approximately 33 kDa capable of directing the synthesis of 3OH, C(14:1)-HSL, C(10)-HSL and C(6)-HSL in E. coli. HdtS does not belong to either of the known AHL synthase families (LuxI or LuxM) and is related to the lysophosphatidic acid acyltransferase family. HdtS may therefore constitute a member of a third protein family capable of AHL biosynthesis.
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Affiliation(s)
- Bridget E Laue
- School of Pharmaceutical Sciences, University of Nottingham, Nottingham NG7 2RD, UK1
| | - Yan Jiang
- School of Pharmaceutical Sciences, University of Nottingham, Nottingham NG7 2RD, UK1
| | - Siri Ram Chhabra
- School of Pharmaceutical Sciences, University of Nottingham, Nottingham NG7 2RD, UK1
| | - Sinead Jacob
- Biomerit Research Centre, Department of Microbiology, National University of Ireland, Cork, Ireland2
| | - Gordon S A B Stewart
- School of Pharmaceutical Sciences, University of Nottingham, Nottingham NG7 2RD, UK1
| | - Andrea Hardman
- School of Pharmaceutical Sciences, University of Nottingham, Nottingham NG7 2RD, UK1
| | | | - Fergal O'Gara
- Biomerit Research Centre, Department of Microbiology, National University of Ireland, Cork, Ireland2
| | - Paul Williams
- School of Pharmaceutical Sciences, University of Nottingham, Nottingham NG7 2RD, UK1
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