Scientists map microbes in healthy humans

Will help in diagnosis and treatment of diseases

By Sonal Matharu
Published: Thursday 14 June 2012

After five years of intensive research, scientists have produced the first comprehensive genetic map of the microbes that live in or on a healthy human body. The development paves the way for new advances in research and diagnosis and treatment of diseases.

Each individual carries microbiomes, groups of microorganisms, which outnumber the human cells by 10 to 1. Because of their small size microorganisms make up only about one to three per cent of the body’s mass, but play a vital role in human health. For example, bacteria in the gastrointestinal tract of humans help in digesting foods and absorption of nutrients.

To find out what these microbiomes are and what they do in healthy individuals, over 200 scientists of the Human Microbiome Project (HMP) from nearly 80 multidisciplinary research institutions carried extensive studies. Their findings were published in Nature and 12 journals in PLoS on June 14.
For the study, samples of microbes were collected from 18 body parts including nose, skin, mouth, gut and vagina from over 242 healthy individuals aged between 18 and 40 years.

The HMP researchers found that this plethora of microbes contribute more genes responsible for human survival than humans themselves. While the human genome carries some 22,000 protein-coding genes that carry out metabolic activities, microbiome contributes eight million unique protein-coding genes or 360-times more bacterial genes than human genes.

The scientists found that the microbial communities were diverse and abundant. In addition, microbes varied widely not just from site to site on a single person but also from person to person. People living in the same community had similar kinds of microbes in their saliva. In contrast, the bacteria found on skin showed greater differences between people. Interestingly, despite differences in the microbes present on the same body site among different people, the overall collection of organisms performed similar metabolic tasks, such as breaking down energy sources.

“Although everybody understands that our microbes make important contributions to our own biology, this is the first time we have attempted a comprehensive survey of what’s there,” says Bruce Birren, co-author of the study.

The team also found that the disease-causing microbiomes co-exist peacefully with the humans. For example, Staphylococcus aureus, strains of which are linked to the drug-resistant infection called MRSA, was found in the noses of about 30 per cent of the people. The scientists, however, still have not found what factors can tip them towards disease.
“It remains an open question how individual variation in the types of bacteria within healthy people influences disease development,” says Anthony Fodor, another co-author of the paper. “It will be really interesting to see how this question is resolved as we learn more about the contribution of the microbiome to specific diseases such as obesity, cancer, fatty liver and inflammatory bowel disease,” he adds.


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