| 1. |
- Milton, Debra L., et al.
(författare)
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The LuxM homologue VanM from Vibrio anguillarum directs the synthesis of N-(3-hydroxyhexanoyl)homoserine lactone and N-hexanoylhomoserine lactone :
- 2001
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Ingår i: Journal of Bacteriology. - 0021-9193 .- 1098-5530. ; 183:12, s. 3537-3547
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Williams, P., et al.
(författare)
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Quorum sensing and the population-dependent control of virulence
- 2000
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 355:1397, s. 667-680
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Forskningsöversikt (refereegranskat)abstract
- One crucial feature of almost all bacterial infections is the need for the invading pathogen to reach a critical cell population density sufficient to overcome host defences and establish the infection. Controlling the expression of virulence determinants in concert with cell population density may therefore confer a significant survival advantage on the pathogen such that the host is overwhelmed before a defence response can be fully initiated. Many different bacterial pathogens are now known to regulate diverse physiological processes including virulence in a cell-density-dependent manner through cell-cell communication. This phenomenon, which relies on the interaction of a diffusible signal molecule (e.g. an N-acylhomoserine lactone) with a sensor or transcriptional activator to couple gene expression with cell population density, has become known as 'quorum sensing'. Although the size of the 'quorum' is likely to be highly variable and influenced by the diffusibility of the signal molecule within infected tissues, nevertheless quorum-sensing signal molecules can be detected in vivo in both experimental animal model and human infections. Furthermore, certain quorum-sensing molecules have been shown to possess pharmacological and immunomodulatory activity such that they may function as virulence determinants per se. As a consequence, quorum sensing constitutes a novel therapeutic target for the design of small molecular antagonists capable of attenuating virulence through the blockade of bacterial cell-cell communication.
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