We inherit every one of our genes, but we leave the womb without a single microbe. As we pass through our mother’s birth canal, we begin to attract entire colonies of bacteria. By the time a child can crawl, he has been blanketed by an enormous, unseen cloud of microorganisms—a hundred trillion or more. They are bacteria, mostly, but also viruses and fungi (including a variety of yeasts), and they come at us from all directions: other people, food, furniture, clothing, cars, buildings, trees, pets, even the air we breathe. They congregate in our digestive systems and our mouths, fill the space between our teeth, cover our skin, and line our throats. We are inhabited by as many as ten thousand bacterial species; these cells outnumber those which we consider our own by ten to one, and weigh, all told, about three pounds—the same as our brain. Together, they are referred to as our microbiome—and they play such a crucial role in our lives that scientists like Blaser have begun to reconsider what it means to be human.
“I love genetics,” Blaser said. “But the model that places our genes at the root of all human development is wrong. By itself, it simply cannot explain how rapidly the incidence of many diseases has risen.” He stressed that genes matter immensely, but that one must take into account more than just the twenty-three thousand genes we inherit from our parents. The passengers in our microbiome contain at least four million genes, and they work constantly on our behalf: they manufacture vitamins and patrol our guts to prevent infections; they help to form and bolster our immune systems, and digest food. Recent research suggests that bacteria may even alter our brain chemistry, thus affecting our moods and behavior.
Human Microbiome Project
Within the body of a healthy adult, microbial cells are estimated to outnumber human cells ten to one. This community, however, remains largely unstudied, leaving their influence upon human development, physiology, immunity, and nutrition almost entirely unknown. To take advantage of recent technological advances and to develop new ones, the NIH Common Fund Human Microbiome Project (HMP) was established with the mission of generating resources enabling comprehensive characterization of the human microbiota and analysis of their role in human health and disease.
Traditional microbiology has focused on the study of individual species as isolated units. However the vast majority of microbial species have never been successfully isolated as viable specimens for analysis, presumably because their growth is dependent upon a specific microenvironment that has not been, or cannot be, reproduced experimentally. Advances in DNA sequencing technologies have created a new field of research, called metagenomics, allowing comprehensive examination of microbial communities, even those comprised of uncultivable organisms. Instead of examining the genome of an individual bacterial strain that has been grown in a laboratory, the metagenomic approach allows analysis of genetic material derived from complete microbial communities harvested from natural environments. In the HMP, this method will complement genetic analyses of known isolated strains, providing unprecedented information about the complexity of human microbial communities.
The NIH Human Microbiome Project is one of several international efforts designed to take advantage of metagenomic analysis to study human health. The HMP expects to continue the practice established by the Human Genome Project of international collaboration to generate a rich, comprehensive, and publicly available data set. This information will be available worldwide for use by investigators and others in efforts to understand and improve human health. For more information on the Human Microbiome Project, e-mail HMPinformation@mail.nih.gov or visit http://www.hmpdacc.org .
microbes, their genetic elements (genomes), and environmental interactions in a particular environment. The term "microbiome" was coined by Joshua Lederberg, who argued that microorganisms inhabiting the human body should be included as part of the human genome, because of their influence on human physiology. The human body contains over 10 times more microbial cells than human cells, although the entire microbiome only weighs about 200 grams (7.1 oz).
Microbiomes are being characterized in many other environments as well, including soil, seawater and freshwater systems.