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Gut bacteria learn to eat sushi

January 12, 2012

For this week’s final microbial snapshot: How do our gut microbes learn to eat sushi?

A study of the human gut microbiome (in other words, fecal bacteria) shows how different people with different diets carry different “enterotypes,” that is, different communities of species. For example, people who eat meat carry more species of Bacteroides, whereas vegans have more species of Prevotella. This surprises me, actually, because Bacteroides species are known for digesting complex plant components, even lignins. So it must be even more complicated than that–thousands of different species work together, fine-tuned by adapting to a particular person’s diet. I suppose in the future we’ll have a Craigslist of fecal samples from people with particularly effective digestive capabilities.

So how does a given bacterial community member “learn” to eat an exotic food such as sushi? Research shows that Japanese individuals who consume raw seaweed (nori) have a distinctive species called Bacteroides plebeius that digests the unusual sulfonated sugar chains of marine red algae. So where did B. plebeius get this ability? The bacterium possesses certain genes encoding enzymes that break down the sulfonated chains. And those genes came from plasmids or viruses–which got them from wild marine bacteria. Presumably, wild bacteria feeding on the seaweed consumed by the Japanese or their ancestors. (We pass along our gut bacteria to our children, but that’s another story.)

So the Japanese gut bacteria acquired sushi-eating genes from marine algae-eating bacteria. The result is that Japanese get more food value out of sushi than we do, since we cannot digest the sulfonated chains.

I can see the future Craigslist ad now.  “Sushi-eating fecal community. Free samples.”

  1. January 13, 2012 12:33 am

    > I can see the future Craigslist ad now. “Sushi-eating fecal community.
    > Free samples.”

    More likely, we’ll see something like. “I want to take a vacation in Louisiana, so I went to my doctor who said I really should get an inoculation of xxxxx because, as it stands, I can’t handle red beans and rice very well and would get the runs.”

    • January 13, 2012 9:01 am

      You’re right. At the same time, though, there have been kidneys on Craigslist.

  2. January 14, 2012 11:27 am

    They were removed as illegal though.
    My question is, as a descendent of Eastern Europeans , who survived on (imported) potatoes and cabbage, how is it that I happily (and I would say efficiently) eat sushi and seaweed on an extremely regular basis, for the last 40+ years> And my kids, who have eaten it since before birth (ie in the wo
    mb)- do they have these plasmids too?

    • January 14, 2012 4:34 pm

      I assume when you eat sushi, it’s the kind where a thin toasted sheet of seaweed wraps around rice, fish etc. The main calories you get are from the filling. The seaweed mostly goes through your system as “fiber.”

      When Japanese eat seaweed, in the traditional manner, it may form a larger part of the diet, so the potential caloric content of the “fiber” is more important. Their gut bacteria help them break down the fiber and release sugars for energy. Before industrialization, ability to digest seaweed probably helped the Japanese survive in a way that less crucial today.

  3. SFreader permalink
    January 15, 2012 6:15 pm

    According to Wiki, seaweed is a fairly common food among coastal peoples – including northern Europeans and North Americans. Perhaps if you’re used to one seaweed variety, then you may have the some gut bacteria that’s closely enough related to enable you to digest other varieties of seaweed. I’ve tried a Canadian Maritimes dried kelp (a local substitute for potato chips) – digestible, and not bad as taste goes but still an acquired taste.

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