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Superbug Survives Radiation and Imperviously Eats Waste
Conan the Bacterium
Although scientists now find it in many different soil and water sites around the world, D. radiodurans was not identified until 1956. It was isolated from a can of ground beef that had been radiation sterilized but had spoiled nonetheless. Perhaps because it can efficiently repair radiation breakage of its own DNA, D. radiodurans can endure 1.5 million rads of radiation, a dose 3,000 times higher than would kill organisms from microbes to humans. Scientists are unsure how this resistance evolved, although they suspect it may be a side effect of the microbe’s ability to survive periods of severe dehydration, which also fragments DNA.
Recognition of D. radiodurans’ resistance to radiation led DOE Microbial Genome Program (MGP) managers to believe the microbe could be useful in cleaning up mixed-waste sites contaminated with toxic chemicals as well as radiation. They began to fund projects to decipher the microbe’s genome and alter it to detoxify the most common chemical contaminants at these sites. Such detoxification functions might include concentrating heavy metals and breaking down organic solvents such as trichlorethylene.
In the Nature Biotechnology article, Daly and Minton reported successfully altering the microbe’s genome. This was accomplished by first fusing a gene encoding toluene dioxygenase (an enzyme that degrades the organic contaminant toluene) to a D. radiodurans promoter (a site that activates the gene). This DNA was then inserted into one of the bacterium’s chromosomes. The resulting recombinant bacterium is capable of degrading toluene and other organic compounds in a high-radiation environment. It also is tolerant of toluene and trichloroethylene’s solvent effects at levels exceeding those of many radioactive waste sites.