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Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
Acylated Homoserine Lactone Signaling in Marine Bacterial Systems, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815578/9781555814045_Chap16-1.gif /docserver/preview/fulltext/10.1128/9781555815578/9781555814045_Chap16-2.gifAbstract:
This chapter reviews the current understanding of acylated homoserine lactone (AHL) signaling in marine bacterial systems outside of the well-described Vibrio fischeriand Vibrio harveyi models. AHL production has far only been documented in proteobacterial groups. Representatives of these taxa, however, constitute one of the most numerous and functionally diverse classes of microorganisms, and they are particularly abundant in marine environments. Direct chemical analyses, such as those employed by Wagner- Dobler et al., do not have intrinsic biases but are currently at least 10-fold less sensitive than the best biosensors. AHL synthesis is often strongly regulated by other environmental conditions, and these activating conditions may not be recapitulated in standard laboratory culture. The surveys discussed in the chapter should be considered as conservative estimates of AHL production capacity among cultivatable marine bacteria and should be integrated with emerging genomic information on marine bacteria. The Roseobacteria are one of the dominant microbial groups in the ocean, and several subgroups are also the most common AHL signal producers. Ulva zoospores preferentially settled on top of bacteria, suggesting a direct interaction between the bacteria and zoospores and providing evidence that attachment is not a random process. This work led to the discovery that bacterial quorum-sensing molecules, specifically AHLs, are involved in zoospore settlement. The marine environment is a source of abundant materials and resources across the globe. The oceans are sources of diverse and complex quorum-sensing signal molecules produced by many of their endogenous proteobacteria.
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AHL production in the Roseobacter lineage. Phylogram of bacteria within the Roseobacter group adapted with permission from Buchan et al. ( 10 ). Robust phylogenetic lineages are indicated with filled ovals at branch nodes and vertical black lines. The numbers of clone and isolate sequences representing each cluster are provided in brackets. The tree was constructed using a neighbor-joining method. The bar represents Jukes-Cantor evolutionary distances. Bootstrap values of greater than 50% are shown at branch nodes (100 iterations). AHL+ indicates that representatives of these isolates and subgroups have been reported to produce AHL activities.
Genetic organization and context of roseobacterial LuxI-LuxR systems. LuxI homologues are dark gray arrows, LuxR homologues are light gray arrows, and all flanking genes are black arrows. In most cases, labels above genes indicate a reference homologue or, in the cases of certain sequences, the genetic ID from Roseobase (www. roseobase. org). Maps are drawn roughly to scale. Abbreviations: CoA, crotonyl CoA reductase; DBP, DNA-binding protein; HK, histidine kinase; HK/RR, hybrid histidine kinase/response regulator; HK/PAS, histidine kinase with PAS domain; Hyp, hypothetical protein; RND, resistance, nodulation, cell division multidrug efflux pump homologue; RR, response regulator; SigB, sigma B.
Model for quorum-sensing regulation in V. anguillarum. Depicts current understanding of quorum-sensing mechanisms in V. anguillarum relative to the cell exterior and interior.
Settlement of Ulva zoospores. Processes and signals that attract Ulva zoospores to surfaces in the marine environment, including AHL signaling.
Milky seas off the coast of Africa. Satellite imagery of a milky sea. Study areas (Top) corresponding to unfiltered (A–C) and filtered (D–F) images over three successive days: (A and D) Jan. 25, 1995, 1836 GMT; (B and E) Jan. 26, 1995, 1804 GMT; and (C and F) Jan. 27, 1995, 1725 GMT. Arrowheads in F indicate low signal-to-noise ratio artifacts. Shown in D are the track of a ship (dashed line) and positions at time of first sighting on the horizon (point a) and exit from the glowing waters (point b), based on details of the ship report. Reprinted from reference 50 . Copyright 2007 National Academy of Sciences, USA.
LuxI-LuxR homologues in the Roseobacteria