A team of 200 researchers, including a professor at the University of Colorado, has mapped the dizzying diversity of microbial organisms that live in the healthy human body, including more illness-causing pathogens than scientists expected.

"I think the prevalence of genes associated with pathogens in the samples surprised everyone," said CU professor Rob Knight, of the BioFrontiers Institute.

The scientists, part of the Human Microbiome Project Consortium, collected tissues from more than a dozen sites on the bodies of 242 volunteers. Then they used a technique, developed largely at CU, that allowed them to process the microbes and human tissue together in one big lump.

The technique -- which can identify large quantities of microbes relatively quickly -- essentially uses a computer to puzzle out which small fragments of DNA in the mixture belong to human tissue and which belong to specific microbe species.

In the past, researchers have had to grow cultures of the microbes taken from the body in order to identify them, a much more time-consuming process.

"Like 15th-century explorers describing the outline of a new continent, (Human Microbiome Project) researchers employed a new technological strategy to define for the first time the microbial makeup of the human body," said Francis Collins, director of the National Institutes of Health, which provided funding for the project. "This lays the foundation for accelerating infectious disease research previously impossible without this community resource."


Despite the discovery that nearly everyone carries pathogens on or in their bodies, the pathogens do not appear to cause diseases in healthy individuals, the researchers said.

The researchers also found that the microbe communities found on different people are unique to the site -- the microbes in the mouth may differ greatly from the microbes on the elbow -- and unique to the person, a finding consistent with early research done by Knight and CU colleagues.

"What we found is that people have radically different microbes in every body habitat," Knight said. "If you look at the skin of the ear, if you look in the nostrils ... what you find is that different people have almost completely non-overlapping microbial communities."

Even so, the unique microbial communities on different individuals often serve the same purpose in the body, a phenomenon called functional redundancy.

"They do more or less the same thing, but they probably don't do exactly the same thing," Knight said.

This could serve, in the future, to help scientists better understand why people's bodies function differently -- perhaps in their metabolisms, their ability to fight off diseases or the way they process certain drugs.

Knight said he and his colleagues have just begun to explore the implications of how the diverse world of microbial species affect their hosts and that there are many opportunities for future research, including searching for endangered microbial communities that may be on the verge of disappearing because of antibiotic use or because the host species is also endangered.
