You'll Never Walk Alone

The Human Genome Project was launched to map the DNA sequences carried inside every human cell. Now that the HGP is largely complete, biologists are working to map the DNA of our closest and most intimate companions, the bacteria carried in and upon every human body. The Human Microbiome Project seeks to identify and describe the complement of microbes that inhabit healthy humans, and to see how changes in that biota correlate with disease and other environmental disruptions. The project subdivides the body into biomes. In ecology, biomes are geographic regions characterized by distinct climate patterns and plant and animal communities. In the microbiome project, biomes are body regions distinguished by their physical and chemical conditions and their bacterial communities. The first steps in HMP research are sampling various biomes, such as the skin, digestive tract, nose and mouth and identifying and comparing their bacterial inhabitants.

Biologists have known for a long time that our skin teems with microbial life. But most of these bacteria don’t grow well in petri dishes, so it’s been very difficult to study them in any detail. DNA sequencing has provided a new way of exploring the microbiota. Ribosomal RNA is extracted from swab samples taken from a biome, sequenced, and analyzed to determine the diversity and composition of the bacterial community. The results of such a study of the skin have just been released. Samples collected from 20 places on the skin of each of 10 volunteers yielded over 1000 species from 200 different genera and 12 phyla. Samples from the same site on different people were far more similar than those from different spots on the same person, suggesting that the biota of human biomes do represent real communities. The forearm bacteria were the most diverse, averaging 44 species, with a paltry 19 found behind the ear.

Researchers now plan to gather samples from volunteers with skin disorders such as psoriasis, eczema, acne, and skin infections. They hope that differences in the bacterial communities between healthy and sick people will provide insights into the development and progression of disease and suggest new treatments.

As an active area of research and a novel way of approaching human health, the Human Microbiome Project has a lot of natural hooks for biology education. There’s something very charming and at the same time slightly unsettling about thinking of your body as a complex and crowded ecosystem, isn’t there? I find myself giving my forearms a lot of sidelong glances lately. Just what is going on over there?

Illustration: Skin sample sites for a study of bacterial diversity. Credit: Jane Ades, NHGRI