Scientists Create Radiation Resistant E.Coli To Learn How Bacteria Develop Antibiotic Resistance

By Shweta Iyer on March 15, 2014 4:31 PM EDT

E. coli
As antibiotic-resistant bacteria become stronger, scientists are trying to learn how they are able to mutate and develop resistance. (Photo: Mattosaurus, CC BY 2.0)

Many disease-causing bacteria have been mutating, becoming antibiotic resistant, and forcing us to find new ways to fight them. How do organisms achieve this feat to survive the hostile environments created by drugs and other factors such as radiation? Scientists attempted to analyze this with the help of Escherichia coli and its ability to resist ionizing radiation.

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The experiment, which involved exposing cultures of E.coli to high doses of radiation, was conducted by Professor Michael Cox from the University of Wisconsin-Madison and John R. Battista from Louisiana State University. Their results were published online in the journal eLife. E.coli, which is typically very sensitive to radiation, developed a resistance to it after undergoing genetic mutations.

Understanding E.coli's radiation resistance and its ability to repair damaged DNA is a huge step toward identifying approaches to facilitate recovery from radiation in other organisms, including human beings. "What our work shows is that the repair systems can adapt and those adaptations contribute a lot to radiation resistance," Cox said in a statement.

In earlier experiments, Cox and his team exposed strains of E.coli to cobalt-60, a highly radioactive isotope. "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," Cox said.

The bacteria soon became resistant to the ionizing radiation and could survive up to four times more radiation than normal. This made them similar to the bacteria Deinococcus radiodurans, one of the most radioresistant organisms ever known - it can endure a thousand times more radiation than humans. "Deinococcus evolved mainly to survive desiccation, not radiation," Cox said, "so when conditions are right, it can repair damage very quickly and start growing again."

Understanding the mechanism that allows some organisms to survive otherwise highly toxic and potentially lethal doses of ionizing radiation is important, since the same genetic, biochemical, and physiological processes involved in the repair and regeneration of DNA and cells in bacterium occur in humans. Knowing how these organisms survive radiation can help scientists create microbes capable of clearing toxic waste, or probiotics that could help patients undergoing radiation therapy for some cancers.

Discovering that these organisms can repair the radiation damage in their cells is relatively new. Scientists used to believe that cells resisted radiation by detoxifying the oxygen molecules as they reacted to radiation within the cell. But Cox noted that these bacteria were using this passive process along with active mechanisms, such as mutation and recombinational DNA repair, and other undiscovered processes. "This extreme resistance we're looking at is a complicated phenotype," Cox said in the statement. "There are likely additional mechanisms buried in this data and we're working to pull those out." 

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