The human body is host to trillions of microbes. A majority of these microorganisms are known to play an important role in our lives, say from dental health to digestion to strengthening our immune system. But little was understood about which microbes reside in specific sites of the body up until yesterday.
Now, a consortium of 200 U.S. scientists, from nearly 80 research institutions, working on the Human Microbiome Project, have mapped the human body's bacterial ecosystem, in what could be the first and the most comprehensive census of the microbial make-up of healthy humans.
The findings were arrived at by sampling 242 healthy U.S. volunteers (129 male, 113 female), collecting tissues from 15 body sites in men and 18 body sites in women namely from the mouth, nose, skin (two behind each ear and each inner elbow), lower intestine (stool) and three vaginal sites.
Previously, only a few hundred microbial species were known to live on humans. But new research has identified more than 10,000 species of microbes that occupy the human ecosystem.
According to the researchers, even healthy people harbor harmful bacteria in and on their bodies, but in low levels. These harmful microorganisms coexist with beneficial microbes within a healthy immune system. However, when a person gets sick or takes antibiotics, there may be substantial shift in the species that make up the microbiome.
Different microbial communities are know to inhabit different body parts. For example, the microbes that live on the teeth are different from those in saliva, while the skin, being the body's barrier to the outside world, is said to host the most diverse collection of microbes.
Having an idea about which microbes live in various ecological niches in healthy people will help scientists better understand how changes in the microbiome are associated with, or even cause, illnesses, such as ulcerative colitis, Crohn's disease and psoriasis, to name a few, say the researchers.
Some of the other significant findings of the Human Microbiome Project include:
* About 8 million unique protein-coding genes are contributed by human microbiome whereas the human genome carries only 22,000 protein-coding genes. That represents 360 times more bacterial genes than human genes. The bacterial genes are critical for human survival. Digestion of foods and absorption of nutrients would otherwise be impossible without the genes carried by bacteria in the gastro-intestinal tract because humans do not have all the enzymes needed for the digestion of diet.
* The vaginal microbiome of pregnant women is different from that of women who are not pregnant as the former is principally characterized by decreased species diversity.
* It is not necessary that the same bacterial species are needed to carry out a certain metabolic activity. "In the healthy gut, for example, there will always be a population of bacteria needed to help digest fats, but it may not always be the same bacterial species carrying out this job".
Commenting on the findings, co-investigator Mark Watson, Washington University School of Medicine said, "Data generated from this study has the added potential to provide scientists with new insights into how local environments shape the composition of microbes that are found in healthy individuals."
The research findings are published June 14 in Nature and in several Public Library of Science journals.
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June 05, 2026 16:18 ET A busy week for economic news flow saw a slew of reports being released that reflected the trends in the U.S. labor market. In Europe, economic growth and inflation data gained attention as the European Central Bank and Bank of England head for policy session later in the month. In Asia, the monetary policy session of the Indian central bank was in focus as the country, a major oil importer, reels under the pressures of a weaker rupee and rising inflation.