Sushi arms the guts of the Japanese with new digestive powers. A seaweed-eating enzyme seems to have jumped from marine bacteria to the harmless bugs that call the intestines of sushi-eaters home.
This is the first evidence that food bacteria can transfer genes to our own gut bacteria, and could help us extract more energy from food, says at the National Centre for Scientific Research (CNRS) in Roscoff, France.
Czjzek鈥檚 group uncovered the genetic swap while hunting the genes for certain enzymes produced by bacteria. These enzymes break down carbohydrates in the cell walls of the algae that the bacteria feed on.
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One enzyme, porphyranase, breaks down a polysaccharide that makes up around 40聽per cent of the cell walls of , a red alga used to make the nori sheets that wrap around sushi. The carbohydrate is rare in most other marine plants, however.
The enzyme turned up in samples of marine bacteria, but also, curiously, the gut of a Japanese person. 鈥淲e thought this was a funny coincidence, especially as Porphyra is used in sushi,鈥� says Czjzek.
The guts for sushi
To see if a gene for the enzyme was present in the microflora of other Japanese people, Czjzek鈥檚 team looked up a previous study of Japanese and North American guts. The gene was not found in any North American, but the group found porphyranase genes in 5 of the 13 Japanese.
鈥淭he number is low,鈥� says Czjzek. 鈥淏ut we can say that apparently this enzyme is present only in Japanese and not in [North] Americans.鈥� She thinks the difference is due to the seaweed-rich diet of Japanese people, who eat an average of 14.2聽grams of the stuff a day.
Genes regularly shuttle between different bacteria, offering each other new traits such as drug resistance. But this is the first time a gut bacterium has been found to have got new genes from its host鈥檚 food. In theory, Japanese people with the porphyranase enzyme can digest seaweed, while it passes straight through the North American gut.
鈥淚t鈥檚 a really nice demonstration of genetic variation of microbiota between individuals,鈥� says , a microbiologist at Stanford University in California. He agrees that the gut bacteria from the Japanese people probably use the enzyme to break down seaweed carbs.
But non-Japanese readers shouldn鈥檛 rush off for a sushi fix to 鈥済row your own鈥� porphyranase enzymes just yet. Supermarket seaweeds are commonly roasted to sterilise them, Czjzek says. 鈥淚f the algae are roasted before preparing sushi, the microbes are destroyed, and the genes are not transferred.鈥�
Journal reference: , DOI: 10.1038/nature08937
