Scientists Just Overturned a 100-Year-Old Belief About Bacteria in the Lungs

New findings raise questions about the role of microbes living in the lungs.

More than 35 trillion bacteria live throughout the human body, forming microbiomes in the gut, mouth, lungs, skin, and urogenital tract.

Researchers increasingly recognize that these microbial communities are connected to both health and disease, but much about what individual microbes do and how they survive remains unknown.

A University of Michigan study now challenges a 100-year-old assumption about Prevotella melaninogenica, a common bacterial resident of the lungs.

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, leads a laboratory that studies Prevotella. The bacteria are commonly found in the respiratory tract and have been associated with numerous chronic conditions, yet they also live in healthy people. Scientists have long classified P. melaninogenica as an obligate anaerobe, meaning it cannot survive in the presence of oxygen.

That raised a fundamental mystery about how it persists in the lungs.

Kozik, an asthma researcher, notes that Prevotella occurs at different levels in the respiratory tracts of both healthy people and people with asthma and COPD. They make up roughly 10% of microbial populations in healthy lungs and as much as 13% on average in people with respiratory disease.

Prevotella survives far more oxygen than expected

To investigate the contradiction, Kozik’s team exposed cultures of P. melaninogenica to progressively higher concentrations of oxygen and measured their growth and survival.

The bacteria were able to grow at oxygen concentrations between 5 and 8% and briefly survived exposure to levels as high as 21%.

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,” said Kozik.

Oxygen tolerance may be more flexible

Kozik notes that a bacterium’s ability to tolerate oxygen may fall along a spectrum rather than fitting neatly into the traditional categories scientists have used.

Her laboratory next plans to investigate how the immune system responds to Prevotella and examine lung bacteria more closely to determine how these microbes interact with the body.

“We need to work to look at the bacterial community and ask, how does this community function currently? What metabolites are they making, what signals are they sending to the immune system? How’s the immune system responding to it? How does this activity differ in health versus in the context of chronic lung diseases?” said Kozik.

A clearer picture of how the body’s microbiomes function could eventually contribute to more targeted therapies, Kozik added.

“Those kinds of questions about the relationships between bacteria and the body are what is a big black box right now.”

Reference: “Aerotolerant capacity of the lung symbiont Prevotella melaninogenica” by Claire Albright, Gouri Anil, Jacob Evans, Souzane Ntamubano and Ariangela Kozik, 14 July 2026, Journal of Bacteriology.
DOI: 10.1128/jb.00142-26