If you want to shell a walnut, it helps to have a nutcracker. And if you want to digest seaweed, it helps to have the right enzymes. Now, a study in the journal Nature shows that Japanese people—but not North Americans—have what it takes to eat their sushi, and digest it, too. [Jan-Hendrik Hehemann et al, http://bit.ly/bqsLjS]

The scientists were studying a particular marine bacterium, which makes enzymes that break down the kind of seaweed used to wrap sushi. In searching the public databases, they discovered, to their surprise, that the enzymes was not just confined to ocean organisms. They also turned up in bacteria that live in the human gut.

Our intestines are teeming with trillions of bacteria from hundreds of different species. By sequencing the genomes of the microbial tenants from 30 volunteers, the scientists found that the Japanese harbor bugs with seaweed-eating enzymes. Not so the North Americans.

The enzymes were most likely gifts from a marine microbe, eaten along with some seaweed a long time ago. The marine microbe happened to transfer some of its enzyme genes to gut microbes. And with seaweed a staple in the Japanese diet, the genes stuck around. So it was a good bargain between man and microbe. Not a raw deal.

—Karen Hopkin

[The above text is an exact transcript of this podcast.]