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We’re not alone: healthy humans have more microbes than cells

U.S. Department of Agriculture

Researchers have completed the first comprehensive census of the human “microbiome” — the trillions of bacteria, viruses, and other microorganisms that live in and on our bodies.

The associate director of Washington University’s Genome Institute, George Weinstock, was one of the project’s lead researchers. He says we have about ten times more microbial cells in our body than we have human cells.

“If we add up all the genes in those microbes, there’s probably a hundred times or more microbial genes in our body than there are genes in our human genome,” Weinstock said. “So the microbes, they’re not just a small little part of us, they’re really a very, very large, perhaps almost dominant part of our body.”

Researchers used DNA sequencing techniques to identify more than 10,000 species of microbes in five main areas of the body: the skin, the mouth, the nose, the vagina, and the lower intestine.

Weinstock says they focused on the microbiomes of healthy people.

“This is all the precursor to being able to do clinical studies where you compare healthy and diseased people, and now you want to try to see what’s different between them,” Weinstock said. “The first thing you have to do is see how much variability there is just among healthy people all by themselves.”

Weinstock says we still don’t know what most of the microorganisms are doing in our bodies, but that many are beneficial, helping us digest our food or protecting us from disease.

He says one unexpected finding was that healthy people were infected with low levels of viruses — without getting sick.

The five-year, $153 million Human Microbiome Project was funded by the National Institutes of Health. The results are published in the journal Nature and several journals of the Public Library of Science (PLoS ONE, PLoS Genetics, and PLoS Computational Biology).

Follow Véronique LaCapra on Twitter: @KWMUScience

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