Scientists have discovered that bacteria inhabiting the intestines of Japanese sushi-eaters have picked up seaweed-digesting genes from marine microbes!
Writing in Nature, University of Victoria, British Columbia, researcher Gurvan Michel and his colleagues explain how they first identified, in a marine bacterium called Zobellia galactanivorans (a member of the Bacteroidetes family), a new class of enyzmes called porphyranases. These break down sugar-based molecules called porphyrans, which are present in large amounts in certain seaweeds, including the one used to wrap up sushi.
Having identified the gene sequences encoding the enzymes, the team then searched the international DNA databases for any other similar genes.
Surprisingly, the same sequences turned up a having been found in bacterial samples from human intestines. In this case the organism harbouring them was part of the normal human flora and known as Bacteroides plebeius.
But, intriguingly, the samples in which these bacteria had been identified were all from Japanese people; the genes are absent from the guts of people in America.
This suggests that the Japanese liking for seaweed (the average daily consumption is 14.2g per person) has at some point carried the DNA from a marine bacterium with seaweed-digesting genetic know-how into the guts of aJapanese sushi-eaters whereupon their own bacterial flora have grabbed the genes and incorporated them into their own metabolic repertoire.
In this way they've equipped themselves with the chemical equivalent of a new knife and fork to help them to deal with an unusual fodstuff.
As Stanford scientist Justin Sonnenburg puts in in commenting on the paper, - "next time you take a bite of an unfamiliar food, think about the microbial inhabitants you may be ingesting, and the possibility that you will beproviding one of your ten trillion closest friends with a new set of utensils..."
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