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Potential for luxS related signaling in marine bacteria and production of autoinducer-2 in the genus Shewanella

Helmholtz-Center for Infection Research, Group Microbial Communication, Division of Cell Biology, Inhoffenstr, 7, 38124 Braunschweig, Germany.
BMC Microbiology (Impact Factor: 2.98). 02/2008; 8:13. DOI: 10.1186/1471-2180-8-13
Source: PubMed

ABSTRACT The autoinducer-2 (AI-2) group of signalling molecules are produced by both Gram positive and Gram negative bacteria as the by-product of a metabolic transformation carried out by the LuxS enzyme. They are the only non species-specific quorum sensing compounds presently known in bacteria. The luxS gene coding for the AI-2 synthase enzyme was found in many important pathogens. Here, we surveyed its occurrence in a collection of 165 marine isolates belonging to abundant marine phyla using conserved degenerated PCR primers and sequencing of selected positive bands to determine if the presence of the luxS gene is phylogenetically conserved or dependent on the habitat.
The luxS gene was not present in any of the Alphaproteobacteria (n = 71) and Bacteroidetes strains (n = 29) tested; by contrast, these bacteria harboured the sahH gene, coding for an alternative enzyme for the detoxification of S-adenosylhomocysteine (SAH) in the activated methyl cycle. Within the Gammaproteobacteria (n = 76), luxS was found in all Shewanella, Vibrio and Alteromonas isolates and some Pseudoalteromonas and Halomonas species, while sahH was detected in Psychrobacter strains. A number of Gammaproteobacteria (n = 27) appeared to have neither the luxS nor the sahH gene. We then studied the production of AI-2 in the genus Shewanella using the Vibrio harveyi bioassay. All ten species of Shewanella tested produced a pronounced peak of AI-2 towards the end of the exponential growth phase in several media investigated. The maximum of AI-2 activity was different in each Shewanella species, ranging from 4% to 46% of the positive control.
The data are consistent with those of fully sequenced bacterial genomes and show that the potential for luxS related signalling is dependent on phylogenetic affiliation rather than ecological niche and is largest in certain groups of Gammaproteobacteria in the marine environment. This is the first report on AI-2 production in Shewanella species; its signalling role in these organisms remains to be elucidated.

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    • "One hypothesis to explain this observation is that cells might form aggregates at high cell concentration that are more resistant to pressure than cells alone (Furukawa et al., 2002). The presence of quorum sensing in Shewanella has been suggested by the presence of signaling molecules in several Shewanella species, including marine species and strain MR-1 (Bodor et al., 2008). In Sp LT13a, high CFU concentrations could induce changes in the metabolic state of cells, for example by channeling most energy produced via Fe(III) reduction to cell-maintenancerelated processes, as opposed to growth. "
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    • "These results indicate that the SSO are able to produce AI-2. The production of AI-2 in Shewanella has been previously reported by Bodor et al. (2008). When the ethyl acetate extract from SA02 was analyzed by GC–MS, one peak was identified as cyclo-(L-Pro-L-Leu) (Fig. 3c and d), while no DKPs were identified in the ethyl acetate extracts from SS01 and the negative control (data not shown). "
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    • "Most researchers have worked with the AHLmediated QS systems of Gram-negative human and plant pathogens. AI-2, which is common to both Gram-positive and Gram-negative bacteria (Bodor et al. 2008), is a target that offers an opportunity to discover compounds that inhibit population densitydependent gene regulation in a wide range of bacterial species. Additionally, the GacS/GacA system (Teplitski and Ahmer 2005), which is universal for all g-Proteobacteria, offers unique opportunities to find QS inhibitors controlling all g-Proteobacteria. "
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