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Deinococcus RadioduransDeinococcus radiodurans (former Micrococcus radiodurans) is an extremophilic bacterium, and is the most radioresistant organism known. While a dose of 10 Gy is sufficient to kill a human, and a dose of 60 Gy is sufficient to kill all cells in a culture of E. coli, D. radiodurans is capable of withstanding an instantaneous dose of up to 5,000 Gy with no loss of viability, and an instantaneous dose of up to 15,000 Gy with 37% viability. It can survive heat, cold, vacuum, and acid. Using genetic engineering Deinococcus has been given the abilities to consume and digest solvents and heavy metals, even in a highly radioactive site. It accomplishes its resistance to radiation by having multiple copies of its genome and rapid DNA repair mechanisms. As a consequence of its hardiness it has been nicknamed "Conan the Bacterium" (after Conan the Barbarian); its official name literally means "strange berry that withstands radiation". D. radiodurans was discovered in 1956 by A.W. Anderson at the Oregon Agricultural Experiment Station in Corvallis, Oregon. Experiments were being performed to determine if canned food could be sterilized using high doses of gamma radiation. A tin of meat was exposed to a dose of radiation that was thought to kill all known forms of life, but the meat subsequently spoiled. D. radiodurans was isolated from the meat. A persistent question regarding D. radiodurans is how such a high degree of radioresistance could evolve. Naturally, background radiation levels are very low -- in most places, background radiation is on the order of 0.4 mGy per year, and the highest known background radiation, near Guarapari, Brazil is only 175 mGy per year. With naturally-occurring background radiation levels so low, mechanisms specifically to ward off the effects of high radiation cannot have been selected for. The most accepted theory is that proposed by Valerie Mattimore and John R. Battista of Louisiana State University, who suggested that the radioresistance of D. radiodurans is simply a side-effect of a mechanism for dealing with prolonged cellular desiccation. To support this hypothesis, they performed an experiment in which they demonstrated that mutant strains of D. radiodurans which are highly susceptible to damage from ionizing radiation are also highly susceptible to damage from prolonged desiccation, while the wild type strain is resistant to both. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=8550493 Michael Daly of the Uniformed Services University of the Health Sciences suggests that the bacterium uses manganese to protect itself against radiation damage. http://www.nature.com/news/2004/040927/full/040927-18.html The term Deinobacter has been replaced by Deinococcus based on evaluation of ribosomal RNA sequences. Several other species within the genus have been described, and they are related to heat-resistant bacteria such as Thermus; the group is accordingly known as Deinococcus-Thermus. External links
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