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Some Japanese Harbor Seaweed-Eating Microbes

Only some people have gut microbes capable of digesting nori, the seaweed that wraps sushi.
April 8, 2010

Some Japanese people are endowed with a unique power to digest carbohydrates in seaweed, thanks to their gut microbes. The accidental finding–French scientists were studying enzymes that digest red algae when a genetic database revealed that the same gene could be found in some humans–hints at regional differences in our intestinal bacteria that may have allowed different groups to adapt to their local diets. And it’s just the latest example of nutritional advantages derived from microbes, which give us the ability to digest foods whose nutrients would otherwise be lost to us and make essential vitamins and amino acids that our bodies can’t.

As I wrote in a feature on our microbial menagerie in 2008,

New ultrafast DNA-sequencing technologies allow scientists to study the genetic makeup of entire microbial communities, each of which may contain hundreds or thousands of different species. For the first time, microbiologists can compare genetic snapshots of all the microbes inhabiting people who differ by age, origin, and health status. By analyzing the functions of those microbes’ genes, they can figure out the main roles the organisms play in our bodies.

In the new study, published today in the journal Nature, researchers searched for the gene within bacteria living in the guts from 18 North Americans and from 13 Japanese. They found it in 5 of the Japanese but none of the Americans. The gene was probably transferred to human gut microbes when people ate seaweed–and the microbes that live on it. According to a piece in Nature,

Although gene transfer to gut microbes is suspected in other cases, this is the first clear-cut example in which a gut microbe has gained a new biological niche by snatching genes from an ingested bacterium, says Mirjam Czjzek, a chemist at the Pierre and Marie Curie University in Paris, one of the two researchers who led the study. “Probably there are many more examples,” she says. “It’s only because of this exotic niche and the very rare specificity of this enzyme that we were able to pinpoint where it came from.”

As our food becomes increasingly sterile, our exposure to this genetic treasure chest is dwindling, Justin L. Sonnenburg, a Stanford University microbiologist told the journal. “We’ve gone to great lengths in the developed world to decrease the microbial burden of food, and in doing so we have decreased food-borne illness,” says Sonnenburg, who wrote a commentary in Nature accompanying the study. “This is good, but it comes at a cost. We’ve eradicated this potentially beneficial microbial component.”

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