It's one of earth's most diverse ecosystems, teeming with so many different species that scientists have barely begun to discover them all. But to see it, don't plan on jetting off to the Galápagos or trekking to a Brazilian rain forest. Just open wide and take a look in the mirror.
That's right: your mouth is awash with bacteria. In fact, Stanford researchers led by David Relman, an assistant professor of medicine, have discovered 37 additional unique organisms, bringing to around 500 the number of living things known to be in human mouths. "Such diversity is quite reassuring because it provides for biological stability and protection," says Relman, who was lead author of the study published in December in the Proceedings of the National Academy of Sciences.
There may be a certain "ick" factor, but this discovery is actually good news. The bugs that live on our teeth and gums are mostly neighborly. A few do drive people back to the dentist more often, by fostering bad breath and cavities. But most help to digest food and fill an ecological niche that might otherwise be invaded by nastier bacteria. Discovery of these new microbes could help physicians better understand gingivitis, periodontal disease and tooth decay. The knowledge might also help in the treatment of nonmouth ailments, including some heart valve infections that have their origins in mouth bacteria.
The researchers used a combination of old and new scientific methods to find the bacteria. They started with the traditional biochemical technique: taking a scraping of plaque from the deep gum pocket cradling each tooth, growing the bugs in the laboratory, and then testing and identifying different species. They also analyzed the same samples using molecular techniques designed to tease out the unique genetic signature of undiscovered bacterial strains. This new molecular method yielded 31 of the new bacteria, while the traditional approach uncovered only six new bugs.
Even though 500 strains have been identified already, Relman believes this may be only a fraction of the organisms living in healthy human mouths. The next search may lead to other hiding places, such as the back of the tongue, the inside of the cheeks, or the roof of the mouth.
