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.
What, they wondered, is it doing in
the lungs?
Testing a lung microbe's limits
Kozik, an asthma researcher, notes
that Prevotella are found in differing amounts inside the respiratory tract in
both healthy people and people with asthma and COPD, accounting for roughly 10%
of microbial populations in healthy lungs and up to 13%, on average, among
individuals with respiratory disease.
To unravel this paradox, Kozik's
team subjected cultures of P. melaninogenica to increasing percentages of
oxygen, comparing the rates of growth and survival.
They found that the upper threshold
for growth was between 5–8% oxygen, and the bacteria could briefly survive
oxygen levels as high as 21%.
Furthermore, the study found, using
a new real-time sensor platform and RNA sequencing, that Prevotella appear to
be consuming oxygen and dealing with oxidative stress and DNA damage
differently than 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.
The ability to exist in the
presence of oxygen may lie along a spectrum and not be as clear-cut as
scientists have traditionally defined, she notes.
Questions beyond oxygen tolerance
Kozik and her lab hope to next
interrogate how the immune system responds to Prevotella and dive deeper into
lung bacteriology to understand specifically how these microbes affect the
body.
"We need to work to look at
the bacterial community and ask, how does this community currently function?
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.
This deeper understanding of the
body's various microbiomes could help drive more targeted therapies, she adds.
"Those kinds of questions about the relationships between bacteria and the body are a big black box right now."
Source: New findings overturn 100-year-old assumption about common bacteria in the lungs
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