Knight (left) and Bucheli take soil samples from beneath one of the decomposing bodies. Katie Hayes Luke for NPR hide caption

itoggle caption Katie Hayes Luke for NPR

Billie Iverson, 86, of Cranston, R.I., recently underwent a transplant of intestinal microbes that likely saved her life. Ryan T. Conaty for NPR hide caption

itoggle caption Ryan T. Conaty for NPR

We may not see them, but we need them. iStockphoto.com hide caption

itoggle caption iStockphoto.com

It's busy down there: a gut bacterium splits into two, becoming two new cells. Centre For Infections/Science Photo Library/Corbis hide caption

itoggle caption Centre For Infections/Science Photo Library/Corbis

Bad bug: The bacterium Clostridium difficile kills 14,000 people in the United States each year. Janice Carr/CDC/dapd hide caption

itoggle caption Janice Carr/CDC/dapd

Sucking may be one of the most beneficial ways to clean a baby's dirty pacifier, a study found iStockphoto.com hide caption

itoggle caption iStockphoto.com