Molecular mechanism of the reuterin-producing pathway in lactobacilli

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Probiotics are live microorganisms that confer health benefits on the host. A great deal of interest has been focused on some members of lactobacilli and bifidobacteria with regard to their use as probiotics. To elucidate the molecular basis on the probiotic property exhibited by Lactobacillus reuteri, we determined the complete genome sequences of L. reuteri and non-probiotic L. fermentum that is phylogenetically closest to L. reuteri in the Lactobacillus. Comparative analysis of both genomes showed that L. reuteri harbors the unique 48 kb genomic island containing the genes necessary for the biosynthesis of a reactive 3-hydroxypropionaldehyde (reuterin) and vitamin B_<12>, both of which may influence the microflora balance in the gut. These findings suggest the lateral gene transfer was involved in the acquisition of the probiotic property in L. reuteri.As mentioned above, vitamin B_<12>-dependent dehydratase seems a crucial enzyme for the reuterin production in L. reuteri, while it … More is known to be an enzyme that exclusively acts to metabolize 1,2-propanediol but not glycerol in several bacteria such as Salmonella spp. This difference on the substrate selectivity may come from the reason why the degradation of glycerol results in producing reuterin naturally toxic to the bacteria. L. reuteri is resistant to reuterin probably because of the high tolerance of ribonucleotide reductase against reuterin, which allows the accumulation and release of reuterin in and from cells. These mechanisms characterize the glycerol degradation by B_<12>-dependent dehydratase encoded by gupCDE and the subsequent reuterin production correlating with the probiotic property in L. reuteri. Furthermore, vitamin B_<12> is produced in L. reuteri, which may have a nutrient effect to host cells and the capability of controlling balance of microflora in gut as well as reuterin. In conclusion, L. reuteri has evolved to a probiotic lactic acid bacterium through lateral transfer of the probiotic gene sets into the genome. Less