E.coli Cajoled to Resists Radiation Damage in the Lab

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According to a recent study, researchers have managed to exploit the ability of an organism to evolve in reaction to punishment from a volatile environment. The researchers have cajoled the model bacterium Escherichia coli to significantly resist ionizing radiation and, in the process, reveal the genetic mechanisms that make the accomplishment possible.

The study, published in the online journal eLife, provides evidence that just a handful of genetic mutations give E.coli the ability to endure doses of radiation that would otherwise eradicate the microbe.

The findings are important due to their implications for better understanding how organisms can resist radiation damage to cells and repair damaged DNA.

"What our work shows is that the repair systems can adapt and those adaptations contribute a lot to radiation resistance," said University of Wisconsin-Madison biochemistry and senior author of the eLife report, Professor Michael Cox.

In earlier work, Cox and his group, in collaboration with John R. Battista, a professor of biological sciences at Louisiana State University, demonstrated that E. coli could in fact evolve to resist ionizing radiation by exposing cultures of the bacterium to the intensely radioactive isotope cobalt-60.

"We blasted the cultures until 99 percent of the bacteria were dead. Then we'd grow up the survivors and blast them again. We did that twenty times," explains Cox.

The result were E. coli capable of withstanding as much as four orders of magnitude more ionizing radiation, making them comparable to Deinococcus radiodurans, a desert-dwelling bacterium found in the 1950s discovered to be extraordinarily resistant to radiation.

"That bacterium is capable of surviving more than one thousand times the radiation dose that would kill a human. Deinococcus evolved mainly to survive desiccation, not radiation; so when conditions are right, it can repair damage very quickly and start growing again," noted Cox.

Comprehending the molecular machinery that enables some organisms to survive what would otherwise be fatal doses of radiation is significant because the same bacterial machinery that repairs DNA and protects cells in microbes exists in humans and other organisms.

While turning the new findings into practice is in the works for the near future, the results could ultimately contribute designer microbes able of helping clean radioactive waste sites or making probiotics that could aid patients undergoing radiation therapy for some cancers.

The new study shows that organisms can dynamically repair genetic damage from ionizing radiation. Prior to the new work, researchers initially thought the ability of cells to resist radiation was rooted exclusively from their ability to detoxify the reactive oxygen molecules created by radiation within cells.

"That passive detoxification approach, is most likely working in tandem with active mechanisms such as the mutations found by the Wisconsin group as well as other, yet-to-be-discovered mechanisms. This extreme resistance we're looking at is a complicated phenotype. There are likely additional mechanisms buried in this data and we're working to pull those out," said Cox.

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