The sushi factor

One of the useful roles performed by the human gut microbiota is to supply digestive enzymes missing from the human genome. For instance, polysaccharides from the terrestrial plants that have been part of the human diet throughout evolution are broken down in the gut by carbohydrate active enzymes, or CAZymes, many of them highly specific enzymes from Bacteroides spp. bacteria. Little is known about the gut enzymes acting on edible marine algae such as nori, sea lettuce and wakame, common in Japanese cuisine. Now CAZymes able to digest sulphated polysaccharides from Porphyra sp. marine red algae have been identified in marine Bacteroides isolates. And surprisingly, genome data mining reveals that this enzyme is present in gut bacteria from Japanese — but not American — individuals. This demonstrates that the gene transfer has taken place — recently in evolutionary terms — from a marine environmental bacterium to the Japanese gut bacterium Bacteroides plebeius. Porphyra are otherwise known as nori and are used traditionally in sushi, suggesting that contact with non-sterile food may be a general factor in stocking gut microbes with a varied arsenal of CAZymes. [Letter p. 908; News & Views p. 837]