Our own microbe catalogue

MICROBES are everywhere—on our skin, inside the nose and in the gut. In fact, each one of us carries more microbes in and on our bodies than cells. But scientists have mostly studied microbes that cause diseases. There are others that do not need to be eliminated and are a fundamental part of what makes us human. Together they constitute the microbiome.

After five years of intensive research scientists have produced the first comprehensive genetic map of the microbes that live in and on a healthy body. The study was part of the Human Microbiome Project, kicked off by the National Institutes of Health in the US.

Samples were collected from 242 healthy adults living around Houston and St Louis in the US. The microbes were collected from 15 sites in males and 18 sites in females such as skin, nose, mouth, throat, vagina and face. Over 22 months, the teams collected a total of 11,174 samples. In some of the samples the researchers obtained the nucleotide sequence of 16S, a small-subunit ribo¬somal RNA found in all cellular life, to infer the relationships between these organisms. In other samples, the teams looked at random sequences from a complex pool of DNA. These were then reconstructed according to the similarity in genetic sequence. This allowed the researchers to identify genes.

They found there are more than 10,000 types of microbes on and in the body, many times more than the few hundred estimated earlier through culture techniques. Two studies were published in Nature and 12 studies in PLoS on June 14. These studies have set a baseline for future studies on diseases.

While such projects yield results, caution is needed on the representativeness of the people. In this project samples were taken from adults in developed countries who had similar lifestyles. Studies have shown that people living in less-developed areas have different microbiomes, comments David Relman, professor at the department of medicine at Stanford University, in Nature. He adds that future studies of the microbiome should investigate factors like rising obesity, chronic use of prescription drugs and urbanisation which influence our microbial inhabitants.