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Background  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.    Results  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.    Conclusion  The data are consistent with those of fully sequenced bacterial genomes and show that the potential for  lu xS 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.

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