Bacterium Induced to Resist Radiation Damage in the Lab

By exploiting the ability of an organism to evolve in response to punishment from a hostile environment, scientists have coaxed the bacterium Escherichia coli to drastically resist ionizing radiation, and at the same time, reveal the genetic mechanisms that make the feat possible.

The study, published March 4, 2014, in the online journal eLife, provides evidence that only several genetic mutations give E. coli the capacity to tolerate doses of radiation that would otherwise kill the microbe. The findings are important because they have implications for better determination of 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 (USA) biochemistry Prof. Michael Cox, the senior author of the report.

Prof. Cox and his group, working with John R. Battista, a professor of biological sciences at Louisiana State University (Baton Rouge, USA), in earlier research demonstrated that E. coli could evolve to resist ionizing radiation by exposing cultures of the bacterium to the highly radioactive isotope cobalt-60. “We blasted the cultures until 99% of the bacteria were dead. Then we’d grow up the survivors and blast them again. We did that 20 times,” explained Prof. Cox.

The outcome was E. coli capable of enduring as much as four orders of magnitude more ionizing radiation, making them similar to Deinococcus radiodurans, a bacterium that lives in the desert found in the 1950s to be incredibly 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,” Prof. Cox said, “so when conditions are right, it can repair damage very quickly and start growing again.”

Determining the molecular machinery that allows some organisms to survive what would otherwise be deadly doses of radiation is significant because the same bacterial processes that repairs DNA and protects cells in microbes exists in humans and other organisms. Although turning the new findings into application is in the distant future, the new findings could eventually contribute engineered microbes capable of helping clean radioactive waste sites or making probiotics that could aid patients undergoing radiation therapy for some cancers.

The new study showed that organisms can actively repair genetic damage from ionizing radiation. Before this new research, scientists believed the ability of cells to resist radiation originated mostly from their ability to detoxify the reactive oxygen molecules created by radiation within cells.

That passive detoxification approach, noted Dr. Cox, is in all probability working in tandem with active processes such as the mutations found by these investigators as well as other, yet-to-be-discovered mechanisms. “This extreme resistance we’re looking at is a complicated phenotype,” said Dr. Cox. “There are likely additional mechanisms buried in this data and we're working to pull those out.”

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