USC Breaks Down Bacterial Defenses
February 2, 2018
transformed into dormant spores, can survive millions of years in
extreme environments, threatening human life in the form of food
poisoning and the biological weapon anthrax. But understanding how
bacteria adapt to hostile environments has largely remained a
In a new study, USC Viterbi School of Engineering professors Priya
Vashishta, Rajiv K. Kalia and Aiichiro Nakano used computer-based models
to identify mechanisms or "strategies" used by bacterial spores to evade
attack from extreme temperatures, chemicals and radiation.
Using complex mathematical techniques to examine spores at the molecular
level, the team also determined the optimal conditions for killing
Vashishta, Kalia and Nakano have joint appointments with the USC
Viterbi's Department of Computer Science, the Mork Family Department of
Chemical Engineering and Materials Science, and the USC Dornsife's
Department of Physics and Astronomy.
"Imagine bacterial spores are like a seed with a hard coating that
preserves the DNA machinery," says Vashishta, the director of USC's
Collaboratory for Advanced Computing and Simulations.
This hard coating acts as an armor protecting the spore. In this
"freeze-dried," almost lifeless state, the spores wait for the right
conditions to bloom into harmful bacteria.
Earlier studies have shown that wet heat sterilization can destroy
disease-causing bacteria, but the mechanisms whereby spores are killed
by this treatment had not been fully revealed.
As such, optimizing the technique and assuring the destruction of
bacterial spores with any degree of certainty has been a challenge for
public health authorities and defense agencies.
Breaking down bacterial defenses
Using x-ray crystallography data, the researchers first determined the
key elements of a single bacterium--water, acid and a calcium ion. Then,
they used a supercomputer to run hundreds of thousands of simulations,
controlling the percentage of acid, water and calcium, and watched what
The simulations revealed that depending on water concentration and
temperature, the water inside the bacterial cell behaves like either
solid, gel or liquid.
"Our models showed the spores perform a kind of chemical magic trick to
intentionally freezes themselves and immobilize the water in their
cells," says Nakano, who also holds an appointment with USC's Department
of Biological Sciences.
"The frozen cells cannot be disturbed by any radiation or chemical
process and it also protects the DNA, so the spores can continue to
to the researchers' models, a combination of heat and moisture
"defrosts" the water inside the cell, returning it to a liquid form.
Without this protective barrier, the spore is more easily destroyed.
The computer models also allowed the researchers to determine the exact
temperature and water balance needed to destroy the bacteria: between
90-95 degrees Celcius with a water concentration above 30 percent.
These insights could be used to prevent microbial contamination on food
processing equipment and limit the spread of disease in the event of a
biological attack. And because the process relies on moist-heat rather
than chemical processes, the bacteria shouldn't be able to develop
The paper, entitled "Gel phase in hydrated calcium dipicolinate,"
appeared in Applied Physics Letters. The research was supported by the
Defense Threat Reduction Agency.