Microbial study reveals extended lifespan of starved bacteria

Date:
August 13, 2021
Source:
Indiana University
Summary:
New research shows how bacteria can overcome starvation situations
and survive for an extended period, which has broader implications
for chronic infections.



FULL STORY ==========================================================================
A study of microbial populations under a prolonged period of starvation
by Indiana University professor Jay T. Lennon and his laboratory could
help researchers answer questions pertaining to chronic infections,
the functioning of bacteria in the environment and the persistence of
life itself.


==========================================================================
In a paper published online Aug. 12 by the Proceedings of the National
Academy of Sciencesof the United States of America, Lennon and his
colleagues explain their study of about 100 populations of different
bacteria in closed systems, which had no access to external food for
1,000 days. The team tracked how long they survived, and almost all of
them persisted.

"The larger question of how bacteria survive long periods of energy
limitation is relevant to understanding chronic infections in humans and
other hosts, and is related to how some pathogens tolerate drugs like antibiotics," said Lennon, a professor in the Department of Biology in
the College of Arts and Sciences.

Many bacterial infections are difficult to treat, in part, because drugs
are often designed to target the cellular machinery of metabolically
active cells.

Energy-limited bacteria often enter a quiescent, or dormant, state that
makes them less sensitive to drug treatments, Lennon said. Not only can
the pathogens persist under such conditions, the populations can also
evolve antibiotic resistance, making the problem worse.

Microbes also play an important role in the environment. The bacteria in
the study came from agricultural soils. In those habitats, Lennon said, microbes form symbiotic relationships with plants, and they carry out
processes that are essential for the functioning of ecosystems, such as
carbon sequestration, nutrient cycling and greenhouse gas emissions.

A major and unresolved question is how billions of microbial cells and thousands of microbial taxa coexist in a single gram of soil, often under
harsh environmental conditions. One explanation supported by the research
is that microbes seem to be well-adapted to feast-or-famine conditions,
where resources can be in short supply for extended periods. This may
help explain how complex microbial communities are maintained over time.

In the study, Lennon and his colleagues estimated that bacteria,
which are the fastest-reproducing organisms on the planet, can also be extremely long-lived.

Lennon and his team, including former Indiana University doctoral
student William Shoemaker, estimated that energy-limited bacteria can
have lifespans that rival, and in some cases exceed, those of plants
and animals. The study used survival analyses to estimate that some
populations have extinction times of up to 100,000 years.

"Obviously, these predictions extend far beyond what can be measured,"
Lennon said, "but the numbers are consistent with the ages of viable
bacteria that have been recovered from ancient materials, such as
amber, halite crystals, permafrost and sediments at the bottom of the
deepest oceans." The persistence of microbes under such conditions
likely involves dormancy and other mechanisms that conserve energy. For example, Lennon and colleagues found that the survival of cells in their
closed system was sustained by the ability of bacteria to "scavenge"
their dead relatives.

Under these lean conditions, where cells must eke out a living on
vanishingly small quantities of food, Lennon and his team were curious
about the potential for bacteria to evolve. They identified genes that
were under negative selection, but also signatures of positive selection,
which indicate cryptic growth that allowed new mutations to increase in frequency. This finding suggests that the recycling of dead cells has
the potential to fuel adaptive evolution. Such observations are relevant
for understanding the constraints on fundamental biological processes
given that large swaths of the planet are energy limited.

This work was funded by the National Science Foundation, the U.S. Army
Research Office and the National Aeronautics and Space Administration.

========================================================================== Story Source: Materials provided by Indiana_University. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. William R. Shoemaker, Stuart E. Jones, Mario E. Muscarella, Megan G.

Behringer, Brent K. Lehmkuhl, Jay T. Lennon. Microbial population
dynamics and evolutionary outcomes under extreme energy limitation.

Proceedings of the National Academy of Sciences, 2021; 118 (33):
e2101691118 DOI: 10.1073/pnas.2101691118 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210813152005.htm

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