A 100-Year-Old Belief About a Common Lung Bacterium Just Got Overturned

A University of Michigan study is challenging a century-old assumption about Prevotella melaninogenica, a bacterium commonly found in the lungs. The research, published July 14 in the Journal of Bacteriology, comes from a laboratory led by Ariangela Kozik, an assistant professor of internal medicine and of molecular, cellular and developmental biology at the university.

Scientists have long classified P. melaninogenica as an obligate anaerobe, meaning it was thought unable to survive in the presence of oxygen, which raised a puzzle over how it persists in the lungs at all. Kozik, an asthma researcher, noted that Prevotella makes up roughly 10% of microbial populations in healthy lungs and as much as 13% on average in people with respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD).

To investigate the contradiction, Kozik's team exposed cultures of P. melaninogenica to progressively higher oxygen concentrations and measured their growth and survival. The bacteria grew at oxygen concentrations between 5% and 8%, and briefly survived exposure to levels as high as 21%, roughly that of normal air. Using a new real-time sensor platform and RNA sequencing, the researchers also found evidence that Prevotella may consume oxygen and respond to oxidative stress and DNA damage differently from other aerobic bacteria. "Prevotella has all of these mechanisms to allow it to survive in oxygenated environments that previously were not appreciated for this organism at all, changing what we thought we knew," Kozik said.

Kozik said a bacterium's ability to tolerate oxygen may fall along a spectrum rather than fit neatly into traditional categories. Her laboratory next plans to investigate how the immune system responds to Prevotella and to examine what metabolites the bacterial community produces and what signals it sends to the immune system.