By one reckoning, we are about 10 percent human. The prodigious number and variety of microbes in and on our bodies outnumber our human cells about 10:1. (Don’t take this news too hard. Since bacterial cells are so tiny in comparison to our cells, by volume, we are still mostly human.)
In recent years, it has become clear that our microbial companions are not just passive travelers with us on our journey through life. There is evidence that the particular complement of bacteria, fungi and viruses we harbor might affect our propensity to get sick or become obese, and determine how we smell, which in turn helps determine our attractiveness to other people.
As a first step in better understanding the role of microbes in and on our bodies in health and disease, scientists for the past several years have been engaged in a massive research undertaking called the Human Microbiome Project. Using newly developed techniques, scientists read genetic “bar codes” to decipher the collection of microbes found at 15 or 18 different sites on the body of more than 200 different people. They also probed more deeply and identified all the genes present in some of the microbes located in different sites on the body.
Altogether, the project generated 3,500,000,000 pieces of genetic information. (This is equivalent to about 3500 sets of the Encyclopedia Britanica.) Based on the researchers’ analysis, about 50,000 different kinds of bacteria were found in or on the subjects’ bodies.
One of the key findings from this massive project was that each person tested had a unique bacterial flora — no two people harbored the same collection of microbes. In spite of these differences, it appeared that microbes in a given site in the body had a similar function. For example, the collection of bacteria in the mouth appeared to have a common function of breaking down sugars and starches, regardless of the specific actors found in an individual. The researchers also found that many healthy people harbored potentially harmful bacteria. For example, about a third of people in the sample had Staphylococcus aureus in their nostrils, a microbe that can potentially cause serious, even fatal, infections.
This research will provide a baseline for better understanding the role of our microbial companions in health and disease. By understanding the microbes that make a living in and on our bodies, we will gain insight into the complex ecosystem that is a human being. Ultimately, this work could have profound effects on the way we think about and treat many human ailments.
More information is available in: Li K, Bihan M, Yooseph S, Methé BA (2012) Analyses of the Microbial Diversity across the Human Microbiome. PLoS ONE 7(6): e32118. doi:10.1371
Huse SM, Ye Y, Zhou Y, Fodor AA (2012) A Core Human Microbiome as Viewed through 16S rRNA Sequence Clusters. PLoS ONE 7(6): e34242. doi:10.1371
Pennisi, E. Microbial Survey of Human Body Reveals Extensive Variation. Science 336: 1369-1370 June, 2012.
PATRICK GUILFOILE has a Ph.D. in bacteriology and is currently an interim associate vice president at Bemidji State University.