The human body is teeming with more than 35 trillion bacteria, coexisting in microbiomes inside the gut, mouth, lungs, skin and urogenital tract. While it’s now clear these microbes are associated with health and disease, scientists have only begun to uncover the full scale of their biology and functions.

In a striking example of just how much is still unknown, a new University of Michigan study overturns a 100-year-old assumption about one common bacterial resident of the lungs, Prevotella melaninogenica. The research is published in the Journal of Bacteriology.

The lab led by Ariangela Kozik, Ph.D., assistant professor of internal medicine at U-M Medical School and assistant professor of molecular, cellular and developmental biology at U-M, is interested in Prevotella because the bacteria are commonly found in the respiratory tract and reportedly associated with all manner of chronic conditions, yet are also found in healthy people. The genus is also widely thought to be an obligate anaerobe, incapable of surviving in the presence of oxygen.