Deinococcus radiodurans is the most radiation-resistant organism that has ever been discovered. D. radiodurans is a Gram-positive, non-motile, non-sporulating bacterium that was discovered in 1956 by Arthur W. Anderson at Oregon Agricultural Experiment Station in Corvallis. Many characteristics of D. radiodurans include an extreme resistance to: genotoxic chemicals, oxidative damage, and high levels of ionizing and ultraviolet radiation. It is known that heat, dehydration and radiation causes double-strand breaks in chromosomal DNA. D. radiodurans will repair these chromosome fragments, usually within 12-24 hours. D. radiodurans can survive blasts of radiation thousands of times greater than the level that would kill a human being. Radiation is measured in units called rads. A dose of 500 to 1,000 rads is enough to kill a person. D. radiodurans thrives even after being hit by up to 1,500,000 rads.
The reason that D. radiodurans can survive these extreme conditions is that it has lots of extra copies of its genes. D. radiodurans cells have four to ten copies of their DNA molecule. Most bacteria have only one copy. These copies serve as back-ups. When radiation hits the D. radiodurans, their DNA gets damaged, and it needs to be repaired. D. radiodurans has a better chance of finding an intact copy of each gene as it stitches its DNA back together, since it has four to ten copies of each gene. Some researchers think that D. radiodurans’ radiation resistance is a side effect of its ability to withstand long periods without water, a common natural occurrence. This is because dehydration causes the same kinds of breaks in DNA as radiation does and requires the same patching process to fix these breaks.
Scientists that studyD. radiodurans have come up with the "Lifesaver" hypothesis to help explain its repair mechanism. The hypothesis states, that in order to speed homologous recombination, D. radiodurans align copies of its genome so that identical DNA sequences are near each other. This proposal is now entirely possible due to the verification that D. radiodurans genes come packaged in four distinct circular chromosomes, thus giving stacked loops of DNA and resembling a Life Saver.
D. radiodurans are currently being studied in the field of bioremediation. Researchers put some genes from a strain of E. coli bacteria that are resistant to particularly toxic forms of mercury into the Deinococcus radiodurans's genome. The genetically altered D. radiodurans was able to transform toxic mercury commonly found at nuclear weapons production sites into less harmful forms. Researchers are currently looking for ways to customize D. radiodurans to break down heavy metals, radioactive wastes and other substances that pollute the soil and groundwater at nuclear production sites.
from:http://science.nasa.gov/newhome/headlines/images/conan/D_rad_dish.jpg
Sources:
http://www.microbe.org/microbes/Deinococcus.asp
http://deinococcus.allbio.org/
http://web.umr.edu/~microbio/BIO221_2000/Deinococcus_radiodurans.html
*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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