Some Japanese Harbor Seaweed-Eating Microbes
Only some people have gut microbes capable of digesting nori, the seaweed that wraps sushi.
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.
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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.”
