We're mostly nonhuman, after all: Scientists begin census of microbes: the trillions that live in or on us

…Only about 10 percent of the trillions of cells that make up a person are truly human, researchers say. The other 90 percent are bacteria, viruses and other microbes swarming in your gut and on your skin. "We really are a superorganism," Brett Finlay, a microbiologist at the University of British Columbia in Vancouver, said in an e-mail. "From the moment we are born until we die, we live in a symbiotic relationship with our microbes." …  

The National Institutes of Health has launched a $115 million, five-year project to identify, analyze and catalog hundreds of microbial species resident in or on the human body. Called the Human Microbiome Project, it's modeled after the Human Genome Project, which decoded most of the human genes in the 1990s. The first 35 microbiome research grants took effect this summer.

"The composition of the complex microbial communities inhabiting the human body has a tremendous influence on human health and disease," said Richard Gibbs, a leading human genome researcher at the Baylor College of Medicine in Houston. Gibbs received a grant to sequence the genes of 400 bacterial strains by 2011.

The goal of the Microbiome project, which is international in scope, is to identify which microbes are harmful and to figure out ways to prevent or treat diseases they cause.

It's a bewildering task because scientists estimate there are about 1,000 different species of microbes living in the human gut and about as many more separate species on human skin. The microbes form tiny colonies of bacteria that settle in different areas of the body. Jeffrey Gordon, a microbiologist at the University of Washington in St. Louis, likened them to "ecosystems," similar to those that plants and animals form on islands on Earth.

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