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Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
Quorum Signaling and Symbiosis in the Marine Luminous Bacterium Vibrio fischeri, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815578/9781555814045_Chap15-1.gif /docserver/preview/fulltext/10.1128/9781555815578/9781555814045_Chap15-2.gifAbstract:
This chapter reviews the role of quorum sensing in Vibrio fischeri, focusing on recent developments in one's understanding of the genetics and physiology of cell-cell signaling by populations of these bacteria, both in culture and in their light-organ symbioses. Particular emphasis is placed on outlining the regulatory factors and pathways by which quorum sensing coordinates the biological activities of this bioluminescent microbe. Early work showed that V. fischeri strains native to Euprymna scolopes were especially well adapted to this host and that nonnative strains such as MJ1 did not colonize juvenile squid well; thus, MJ1 was not an appropriate strain for studying the symbiosis between V. fischeri and E. scolopes. Production of N-octanoyl-homoserine lactone (C8-HSL) initiates stimulation of the lux operon at moderate cell densities; if ES114 had relatively low expression of AinS and low C8-HSL output, this deficiency could potentially explain why ES114 is so much dimmer than MJ1. Most likely, then, the large difference in the levels of N-3-oxo-hexanoyl-homoserine lactone (3-O-C6-HSL) production and luminescence seen between cultures of ES114 and MJ1 is due to external regulatory influences on the autoinducer synthase genes, and such regulation may be multifactorial. Biochemical and genetic studies of Acyl-homoserine lactone (AHL) signaling in Vibrio harveyi have shown that, in the presence of an inducing concentration of the LuxM-synthesized AHL, the receptor, LuxN,participates in a phosphorelay cascade by stimulating the relative dephosphorylation of LuxU.
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Specific luminescence (luminescence per A595) of ES114 (A) or MJ1 (B) grown at 24°C in 250-ml flasks, shaken at 200 rpm, in 50 (diamonds), 100 (squares), or 200 (triangles) ml of SWTO, a rich nutrient medium ( 7 , 66 ). Bacterial cell density was measured by absorbance of the culture at 595 nm (A 595).
Model of quorum sensing in V. fischeri ES114. Each gene is indicated by a labeled open arrow with the open reading frame designation from the V. fischeri genome database provided underneath in parentheses (e.g., luxI is designated VFA924). The structures of three autoinducer molecules are presented underneath their respective synthases, and a “?” by AI-2 indicates that its structure is inferred but has not been identified in V. fischeri. Interactions between autoinducers, proteins, genes, and small RNAs (designated “sRNAs”) are indicated, and dotted lines around sRNA or protein components indicate that these have been identified in the genome database but not functionally confirmed in ES114 experimentally.
Output of HSL autoinducers by V. fischeri strains ES114 and MJ1
Presence of homologous quorum-sensing systems in some Vibrio species a