The Wide-Ranging Role of Microbes in the Human Gut

New research into the microbes that live in the human gut shows they're not just along for the ride. In this week's issue of Science magazine, researchers report the findings of a genetic survey of what's living in the human digestive system. What they found is a thriving community of micro-organisms that may be essential for everything from digestion to immunity.

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New research into the microbes that live in the human gut shows they're not just along for the ride. In this week's issue of Science Magazine, researchers report the findings of a genetic survey of what's living in the human digestive system. What they found is a thriving community of micro-organisms that may be essential for everything from digestion to immunity.

NPR's Allison Aubrey reports.

ALLISON AUBREY reporting:

Everyone's heard of e-coli or salmonella, the famous bad bacteria that make people sick. But what's rarely considered are the millions of anonymous good bugs that live in our bellies.

Professor DAVID RELMAN (Stanford): And they're not simply passive bystanders. They're actually beneficial in many cases. So the relationships are mutualistic, as we say.

AUBREY: David Relman is a professor of microbiology, immunology and medicine at Stanford. He says many of the bacteria and bacteria-like microbes that thrive in the body seem to serve us well. It's almost a you scratch my back, I'll scratch yours.

Prof. RELMAN: So we give them a home that they can call their own, and they give us a whole list of capabilities.

AUBREY: Some evidence of those benefits comes from a study published this week using genome sequencing technology. Scientists took snippets of the microbes DNA extracted from people's poop and analyzed the gene content.

Prof. RELMAN: As one example, we found a representation of genes that we think encode enzymes that make what's called a short chain fatty acid.

AUBREY: A technical finding, but the significance is that this very fatty acid is known to be an important energy source to the cells that line the colon.

Prof. RELMAN: The net results of the finding is the suggestion that our bacterial communities are spending a great deal of time and effort to make us something that our own colon requires for health and growth.

AUBREY: The idea that some of the millions of microbes harbored in our guts are essential to good health is not entirely new. But this is the broadest look yet at what precisely is there. Scientists expected to find a whole mix of microbial genes, which they did, but the high concentrations of certain genes turn out to be quite telling.

Steven Gill of the University of Buffalo is lead author of the paper. He says in addition to the fatty acid precursors, they also identified genes that serve as pathways for vitamin production.

Mr. STEVEN GILL (Researcher, University of Buffalo): Some of the B vitamins. That's a good example.

AUBREY: Gill says the bacteria found in the gut contain precursors to vitamin B1. Without the microbes, our bodies would not be able to synthesize the vitamins.

All of this suggests that the type of organisms which populate our guts are important. The question is, how do the microbes get there? And is there anything we can do as humans to make sure the right ones stay there?

Some people eat yogurt to promote good bacteria.

Mr. GILL: So that's a good example of those bacteria that we eat in the yogurt, that are viable cultures, actually do repopulate our gut.

AUBREY: The challenge is that the microbes in the gut must compete. Some arrive from the outside, say the cultures in the yogurt, and may adapt quite well. But they're always up against the organisms that are already established, the ones we've picked up from our mothers during birth or perhaps from the things we touch or eat in the early years of life.

How these populations of organisms assemble is an area of active research, as is the role of yogurts and pro-biotic supplements. Stanford's David Relman says in theory probiotics should be useful since scientists think they contain species of beneficial microbes.

Prof. RELMAN: But we don't know for sure that we have picked the right species or certainly the right strains. And we don't know that we've chosen a strategy for administering these organisms that allows them to really establish themselves.

AUBREY: Given these questions, Relman says, it's too soon to say how much we can optimize or manipulate the flora in our bodies, but he's optimistic that this field of research will eventually find the answers.

Allison Aubrey, NPR News, Washington.

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