Scientists have revealed that 100 trillion good bacteria live in healthy bodies. Illustration by Bryan Christie.

Scientists provide first census of the human microbiome

MSU News, Jun 14 2012

Through genome sequencing, scientists have created the first census for microbes living with healthy adults, according to a series of coordinated scientific papers appearing in Nature and the Public Library of Science journals.

Michigan State University, part of the Human Microbiome Project Consortium that conducted the research, revealed that part of each person's collection of microbes includes 100 trillion good bacteria living in or on the human body, creating their own unique microbiome. Moreover, researchers calculate that they have identified between 81 to 99 percent of all microbial species in the human body.

Thomas SchmidtBacteria inhabit nearly every part of the body, including on the skin, in the gut, and up the nose. Sometimes they cause sickness, but most of the time, these microbes live in harmony with their human hosts, providing vital functions essential for human survival, said Tom Schmidt, MSU professor of microbiology and molecular genetics.

“We have evolved in a sea of microbes, and so perhaps it is not surprising that there are so many intimate and beneficial associations between microbes and humans,” he said. “Understanding the microbes associated with the human body is crucial to understanding human health and disease.”

The human genome carries a mere 22,000 protein-coding genes. However, there are 8 million -- 360 times more bacterial genes. This means that there are more bacterial genes than human genes. Or, in different terms, there are more genes responsible for human survival than humans contribute.

Another interesting finding is that nearly everyone carries pathogens, which cause illnesses. In healthy people, they don’t cause disease but rather coexist peacefully. Researchers must now figure out why some pathogens turn deadly. These findings provide the foundation for accelerating infectious disease research that was previously impossible, said Francis Collins, National Institutes of Health (NIH) director.

Schmidt’s contributions focused on microbes in the gut. Genes carried by bacteria in the gut are critical for human survival as they allow humans to digest foods and absorb nutrients that otherwise would be unavailable.

His future work will focus on microbes closely affiliated with the tissue lining the GI tract. Schmidt is testing the hypothesis that these microbes inhabit this environment due to their ability to harvest low levels of oxygen from the host tissue into the colon.

The Human Microbiome Project is managed by National Human Genome Research Institute, in partnership with the NIH Office of the Director, the National Institute of Allergy and Infectious Diseases, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Cancer Institute, National Institute of Dental and Craniofacial Research, and National Institute of Diabetes and Digestive and Kidney Diseases, all part of NIH.