Capitalizing on the ability of an organism to evolve in response to punishment from a hostile environment, scientists have coaxed the model bacterium Escherichia coli to dramatically resist ionizing radiation and, in the process, reveal the genetic mechanisms that make the feat possible. The study, published on March 4, 2014 in an open-access article in the online journal eLife, provides evidence that just a handful of genetic mutations give E. coli the capacity to withstand doses of radiation that would otherwise doom the microbe. The findings are important because they have 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," says University of Wisconsin-Madison biochemistry Professor Michael Cox, the senior author of the eLife report. In previous work, Dr. Cox and his group, working with Dr. John R. Battista, a professor of biological sciences at Louisiana State University, showed 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 percent of the bacteria were dead. Then we'd grow up the survivors and blast them again. We did that twenty times," explains Dr. Cox. The results were E. coli capable of enduring as much as four orders of magnitude more ionizing radiation, making them similar to Deinococcusradiodurans, a desert-dwelling bacterium found in the 1950s to be remarkably 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," Dr.
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