In the search for new life, scientists have studied the depths of the ocean and the lips of steaming volcanoes. They've looked on Mars and the moons of Jupiter, and even planets beyond this solar system.
Dr. David Relman went searching inside his own mouth. On a routine dental visit in 1998, Relman, a Stanford infectious disease expert, brought along a test tube. When the dentist scraped the plaque off his teeth, Relman asked for a sample of it.
What he discovered back in his lab was, at the time, shocking. Using relatively new DNA sequencing technology, he found 31 bacteria that had never been seen before.
"As a clinician, I can tell you, my colleagues were not looking for new things to worry about from the microbial world," Relman said. "Some of them believed that sure, there may be some really weird microbes in soil or in the ocean, but the human body is something we understand.