10,000 germ species live in and on healthy people
Our bodies are a witch’s brew of microbes. It’s true. Miss Perfect, despite a lifetime of shampoos and facials, you are a walking bacterial zoo. And you, the guy who brushes and flosses his teeth every couple of hours in the men’s room, you’re crawling with literally trillions of microorganisms.
All those bacteria and fungi colonizing our saliva, skin and intestinal tracts have been the subject of a massive quest by scientists seeking to understand both the workings of the human body and a host of diseases inflicted on it by microbes.
On Wednesday, officials offered an early progress report on the Human Microbiome Project, an effort that has drawn researchers from nearly 80 universities and attracted $173 million in funding from the National Institutes of Health since its launch in 2007.
The project, like the Human Genome Project completed in 2003, adds a potentially large piece to the puzzle of human health. Just as the genome project mapped thousands of genes, helping scientists begin to look at how those genes work together, the microbiome project maps the large number of different microbes, offering a starting point to study how they function in ecosystems. Understanding these ecosystems may lead to new strategies for fighting diseases caused by microbes, everything from the flu and chickenpox to the common cold and athlete’s foot.
John Baker, a professor of surgery at the Medical College of Wisconsin, called the project and the preliminary findings “a revelation.”
“I think until five years ago we really were not thinking about the microbiome in terms of health and disease,” Baker said. “As this project evolves, it’s going to give us so much more information about what it means to be human.”
The scientists involved in the project examined microbes drawn from the noses, mouths, lower intestines and other regions of 300 healthy American volunteers from two cities: St. Louis and Houston. They identified more than 10,000 different species of microbes and sequenced those to determine their genetic makeup, providing a wealth of previously unknown information.
Broad outlines of the work were described in a pair of articles published Thursday in the journal Nature.
The Nature articles, Baker said, “are giving us for the first time this map in terms of microbes, who’s there, who’s living on our skin, who’s living in our intestines. Then, when we know who’s there, we can start to ask what they’re doing.”
Figuring out what’s normal
This map gives scientists a window into what’s normal, what microbes are present in healthy humans and what happens when they are missing or not functioning as they should.
Perhaps as significant, the findings indicate that a traditional plank of medicine may need to be reconsidered. From the time of Louis Pasteur, there has been an assumption that one germ causes one disease.
“Now we have to say, ‘OK pathogens happen, but (disease) may happen because germs are not in a healthy ecosystem,’ ” said Phillip Tarr, a professor of pediatrics at Washington University School of Medicine in St. Louis and one of the project’s researchers.
On the human body, microbes outnumber human cells by 10 to 1, but they are many times smaller. In all, these microorganisms make up only 1% to 3% of our body mass – that’s about 2 to 6 pounds of bacteria on a 200-pound man. While the term “microbe” conjures images of unseen invaders and agents of disease, many play a positive role in the body and are even critical to our survival.
In the gastrointestinal tract, for example, genes carried by bacteria help us to digest food and absorb nutrients. Scientists have learned that some bacteria even appear to “pinch hit” for others. This indicates that what’s of greatest importance is the jobs the microbes do rather than which ones do them.
In addition to the broad findings detailed in the Nature papers, the project resulted in a series of papers in the Public Library of Science journals describing new insights that address more specific aspects of the role microbes play in human health.
Researchers from the Baylor College of Medicine in Houston learned that pregnant women experience a dramatic reduction in the diversity of different microbes found in the vaginal microbiome. This seems to be an evolutionary advantage that eases the passage of an infant from the sterile womb to a world teeming with microbes.