Deinococcus radiodurans
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| Deinococcus radiodurans |
Description and significance
Deinococcus radiodurans, meaning "strange berry that withstands radiation", is a non-pathogenic, Gram-positive aerobic bacteria classified as a member of the family Deinococcaceae. Reddish-pink in color due to the presence of carotenoid pigment, the bacterium has a roughly spherical shape, taking the diplococci form (clusters of two cells) in early growth stages and the tetracocci form (clusters of four cells) in later stages of growth. Nicknamed, "superbug" and "Conan the Bacterium" and was named "the world's strongest (by Guinness World Book or Records), D. radiodurans is the most radiation-resistant vegetative cell, resisting radiation in the megarad range. D. radiodurans was discovered and subsequently isolated in 1956 by Arthur W. Anderson during a laboratory experiment at the Oregon Agriculture Experiment Station (Corvalis, Oregon, US). While seeking new methods for preserving package meat, Anderson noticed bacterial growth after ground meat had been sterilized with radiation.
Biologists consider it a polyextremophile, meaning that it can thrive in a very diverse range of extreme habitats, although no one has been able to identify its natural habitat. D. radiodurans has been located everywhere from cow dung to granite in Antartica’s dry valleys. D. radiodurans' ability to endure environmental conditions far more extreme that those presently found on Earth leads Scientists to believe that it evolved and existed during the planet's primitive stages when it was unshielded by a protective ozone layer and when it was exposed to extreme conditions such as Ionic Radiation (IR) and Ultra Violet (UV) rays from the sun.
In addition to high levels of ionizing and ultraviolet radiation, D. radiodurans can also withstand other extreme stresses such as genotoxic chemicals, oxidative damage, electrophilic mutagens, desiccation, and dehydration. In order to gauge how resistant D. radiodurans is to radiation in comparison to other life forms, consider that, while 5 units of gamma radiation is lethal to humans and 2,000 units of gamma radiation is enough to stop all cell activity for E. Coli, D. radiodurans can be exposed to 10,000 units of gamma radiation without dying or mutating. It can continue to survive despit exposure to small amounts of chronic radiation, for example, 6 kilorads/hr as well as large doses of acute radiation exceeding 1500 kilorads/hr. Although biologists do not yet fully understand why or how, D. radiodurans growing in the tetracocci stage are better able to tolerate radiation than the those growing in the diplococci.
Typically, life forms exposed to extreme stresses such as dehydration, IR or UV, or desiccation experience oxidizing DNA damage in which radiation energizes an atom enough to break a chemical bond (such as in a DNA strand) and then act like an atom of oxygen and bind with another atom, ultimately enabling free radicals to cause genetic mutations or DNA breakage. D. radiodurans, however, demonstrates a unique ability to effectively repair broken DNA. Several factors contribute to this ability, including additional genomes, redundancy in genetic code, protiens, and DNA-repair pathways.
Genome structure
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Cell structure and metabolism
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Ecology
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Pathology
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Application to Biotechnology
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Current Research
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