The bacterium Deinococcus radiodurans was discovered in 1957 in a can of meat that had been irradiated in order to sterilize it for longer shelf life. Typically, cultures of Deinococcus (whose name comes from the Greek for "terrible berry that withstands radiation", and has been nicknamed "Conan the Bacterium" by scientists who study it) can withstand up to a million Rads (10,000 Grays) of ionizing radiation, roughly 2000 times the dose that would be expected to kill 50% of a population of humans exposed to it. Exactly what mechanisms Deinococcus radiodurans uses to repair all the breaks in its DNA caused by radiation at this dose level remains poorly understood but recent work by Michael Daly, of the Uniformed Services University of the Health Sciences in Bethesda, MD, is providing some intriguing clues. In work supported by the Office of Biological and Environmental Research's (BER) Natural and Accelerated Bioremediation Research and Microbial Genome Programs, and grounded in the availability of the complete genome sequence of this bacterium (determined by The Institute for Genomic Research with BER funding), Daly and collaborators find that Deinococcus radiodurans cells accumulate very high intracellular levels of manganese (Mn) but display extremely low levels of iron (Fe), suggesting a protective role for the Mn and a deleterious role for the Fe. Furthermore, a similar profile of levels of these elements is found in other relatively radioresistant bacteria. This work suggests that radiation resistance could be altered by adjusting intracellular Mn and/or Fe levels. In human cancer therapies, treatments with agents reducing Mn or increasing Fe potentially could increase the radiosusceptibility of targeted cells thus improving prospects for survival. This work was published in the online version of Science Magazine on Sept. 30, 2004.







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9/27/04