Deinococcus radiodurans is an extremophilic bacterium (a category of baterium which we will further discuss in the next posting) and it is the most radioresistant organism known to mankind. Radioresistant organisms is defined as organisms which are capable of living in enviroments with very high levels of ionizing radiation. A dose of 10 Gray or Gy, which is the SI unit of energy for the absorbed dose of radiation and one gray is the absorption of one joule of radiation energy by one kilogram of matter, is sufficient to kill a human. A dose of 60 Gy is sufficient to kill all cells in a culture of E. coli. However, Deinococcus 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 is not entirely clear as to how Deinococcus radiodurans could have developed naturally such a high degree of radioresistance. 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, which is 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 during evolution.
Using genetic engineering, Deinococcus radiodurans has been given the abilities to consume and digest solvents and heavy metals, even in highly radioactive sites. It is now known that Deinococcus radiodurans accomplishes its resistance to radiation by having multiple copies of its genome and rapid DNA repair mechanisms.
When a creature gets hit by a high dose of radiation, the intense energy causes the large DNA molecule in each cell to fall apart. No creature can survive without its genes in working order. Most microbes have tools they can use to repair occasional damage to their DNA. The Deinococcus radiodurans, unlike other bacteria, has lots of extra copies of its genes. Deinococcus radiodurans cells have four to ten copies of their DNA molecule. Most bacteria have only one copy. These copies serve as back-ups, and when radiation hits and the Deinococcus radiodurans’ DNA becomes damaged, the bacterium has a lot more chances of finding an intact copy of each gene to use as it stitches its DNA back together.
In addition to the above, it also appears that Deinococcus radiodurans may have more of the cell repair tools that most bacteria have. Other microbes have many of the same kind of tools, although not in as high numbers and variety as Deinococcus radiodurans does. Michael Daly of the Uniformed Services University of the Health Sciences also suggested that the bacterium uses manganese to protect itself against radiation damage.
As a consequence of its hardiness, Deinococcus radiodurans has been nicknamed "Conan the Bacterium" (after Conan the Barbarian) and its official latin name literally means "strange berry that withstands radiation".
In addition to high levels of ionizing and ultraviolet radiation, it can also survive, and acid genotoxic chemicals, oxidative damage, extreme temperatures and vacuum. It also turns out that Deinococcus radiodurans is also able to live through extensive periods with absolutely no water. It was hypothesized that the bacterium’s radiation resistance could be a lucky side effect of the ability the bacterium evolved to withstand long periods without water, which is a more common natural occurrence than being exposed naturally to incredibly high radiation blasts. This is because dehydration causes the same kinds of breaks in DNA as radiation does and requires the same stitching process to fix these breaks.
Deinococcus 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 and Deinococcus radiodurans was isolated from the meat.