The human genome codes for approximately 23,000 genes, yet some experts have suggested that the total information coded by the human genome alone is not enough to carry out all of the body's biological functions. A growing number of studies suggest that part of what determines how the human body functions may be not only our own genes, but also the genes of the trillions of microorganisms that reside on and in our bodies.
The genomes of the bacteria and viruses of the human gut alone are thought to encode 3.3 million genes. "The genetic richness and complexity of the bugs we carry is much richer than our own," says Jayne Danska, an immunologist at the Hospital for Sick Children Research Institute in Ontario, Canada. "They serve as a buffer and interpreter of our environment. We are chimeric organisms."
A role for gut microbes in gastrointestinal function has been well documented since researchers first described differences in the fecal bacteria of people with inflammatory bowel disease. The molecular mechanisms responsible for the gut microbiome's impact on metabolism and diseases throughout the body remain largely unknown. However, researchers are beginning to decipher how the microorganisms of the human intestinal tract influence biological functions beyond the gut and play a role in immunological, metabolic, and neurological diseases.