Xenobacteria contains two classes: Deinococci and Thermi. Deinococcus radiodurans was first isolated from a can of beef that had been irradiated to sterilize it. Normally, bacteria do not withstand the radiation processing. Deinococcus radiodurans is able to withstand 1.5 million rad of gamma irradiation (3000 times the lethal dose to humans). Many deinoccocci are resistant to ultraviolet radiation and are able to tolerate dissication. Dissicated Deinococci can endure for years, and if blown by winds through the atmosphere would survive and land worldwide. Some become encased in ice, and some entombed in soil in dry desert soils.

The bacterium is also resistant to high doses of ionizing radiation. The radiation damaged the bacterium's genetic material by breaking each of the chromosomes into more than on hundred pieces. Due to a unique repair system which efficiently repairs the damage to its DNA this hardy fighter managed to stitch its genome together within a few hours. It is affectionately known among scientists as Conan the Bacterium as it can survive cold, dehydration, vacuum, and acid. It is known as polyextremophile and has been listed as the world's toughest bacterium. It is hoped that these bacteria may prove useful to break down toxic organic chemicals at hazardous waste sites. Perhaps if we understood why D. radiodurans is so resistant, we could find ways to protect people from atomic radiation and live longer.

Deinococcus radiodurans
Deinococcus radiodurans

Thermus aquaticus, first found in hot springs Yellowstone National Park, was one of the first extreme thermophilic organism discovered. It has also been found in hot water heaters.


  1. Environmental Biology for Engineers and Scientists. David A. Vaccari, Peter F. Strom, James E. Alleman
  2. Radioactivity Radionuclides Radiation. Joseph Magill, Jean Galy
  3. Alcamo's Microbes and Society. CTI Reviews
  4. Extremophiles Handbook. edited by Koki Horikoshi, Garabed Antranikian, Alan T. Bull, Frank T. Robb, Karl O. Stetter



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