A Microbe Census of the Human Body

About ten thousand species of microbes inhabit the human body, many of which are critical to our health and survival. Our bodies are actually their own microbial ecosystems comprising bacteria, virus and fungi populations in the trillions.

There are ten times as many microbe cells found on surfaces in and on the human body as human cells.
There are ten times as many microbe cells found on surfaces in and on the human body as human cells.

Until recently, researchers did not know in detail how microbes are distributed throughout the human body. The five-year long National Institutes of Health’s Human Microbiome Project (HMP) has taken a “microbe census” of these invisible populations, characterizing the inhabitants of the nasal passages, oral cavity, skin and gastrointestinal and urogenital tracts. The resulting “census data” will help researchers understand not only which microbes are where, but how changes in their populations affect human health.

The HMP will catalogue 3,000 microbes and their genes.  It is a complementary activity to the Human Genome Project, which identified all 23,000 genes in human DNA, according to a BBC Audio Interview.  The human microbiome contains many more genes than our human DNA–some ten to twenty million.  The genes found in the microbial populations we support help us digest foods, absorb nutrients, and produce vitamins and compounds that naturally suppress inflammation in the intestine.  These genes also may hold clues to curing certain diseases.

Humans as “Super-organisms”

The scientists working on the HMP tell us that our human genetic content should be thought of holistically as the sum total of the genes we inherit in our DNA plus the genes of the microbial populations with which we coexist.  Dr. Julie Segre, senior investigator in the HMP said in the BBC interview, “We need to start thinking of ourselves as super-organisms”.

There is evidence that Crohn’s Disease and obesity are linked to microbial populations inhabiting the body.  Additionally, bacteria in the human body may play a role in the development of Alzheimer’s disease, autism and rheumatoid arthritis.  If these linkages are confirmed, it is possible that microbial populations in humans will one day be manipulated through personalized treatment to prevent or mitigate diseases.

We look forward to a period of exciting medical developments as scientists detail the full genetic makeup of the human super-organism!

Joan B. Rose, PhD, is the Homer Nowlin Chair in Water Research at Michigan State University and a member of the Water Quality and Health Council.