Deinococcus radiodurans
Bailey Callahan

Discovered in 1956 by A. W. Anderson when trying to completely sterilize food through radiation, Deinococcus radiodurans (ATCC number 13939) is one of the extremophilic bacterium of the world. Though it was first called Micrococcus radiodurans, the genus Micrococcus did not quite match all of the characteristics that this microbe exhibited, therefore it was placed in its own genus Deinococcus which most closely matches the genus Thermus. The Greek phrase deino kokkus means “terrible berry” while the Latin words radius and durare means “radiation surviving” producing the name Deinococcus radiodurans.

A. W. Anderson and his coworkers were working on a way to sterilize food by using high doses of gamma radiation. They exposed a tin can of meat to a dose of radiation that was thought to be strong enough to kill all known forms of life. However, the meat still spoiled.  Puzzled that anything could survive such a dose, they investigated only to find that the microbe D. radiodurans was the cause. This rather large nonmotile bacterium shaped like a red berry with a diameter of about 1.5 to 3.5 µm usually forms in groups of two in its early stages of growth where it will then create a cluster of four in later growth stages. D. radiodurans does not produce spores and is a nonpathogenic obligate aerobe. It stains Gram positive though its cell envelope is unusual and suggests a relationship to the cell walls of Gram negative bacteria. Growth conditions for this chemoorganotroph are nutrient agar with 1% glucose at a temperature of 30 degrees Celsius and can be purchased for $205 with the right permits.

D. radiodurans can survive just about anything including drought conditions, lack of nutrients, cold, acid, vacuum, and thousands times more radiation than a person can. It is no wonder that this little guy was named “the world’s toughest bacterium” by Guinness Book of World Records and given the nickname Conan the Bacterium. Some of its secrets to being able to survive as a polyextremophile are its unique layering that can be thought of as a lead vest, its ability to have multiple copies of its genome, and a mechanism that can repair its DNA in a two step process that takes 12-24 hours. This process starts by reconnecting some chromosome fragments through single-strand annealing followed by a protein that mends double-strand breaks through homologous recombination. With these two steps D. radiodurans can withstand up to 10,000 Gy, where a human can only survive 5 Gy and it takes about 1,000 Gy to sterilize an entire culture of E. coli in moments. It can also take a constant dose of 60 Gy in an hour.

Then what on Earth could be the reason for such a will to survive when radiation is not found at these levels? The origins of D. radiodurans are unknown since it has been isolated in locations that differ from anywhere between animal feces to hot springs. Some suggest that it may be an alien from one of Jupiter’s moon Europa because of an unusual spectrum found there that may be caused by something like D. radiodurans while more would argue that its ability to survive such high doses of radiation is just a side effect for something else it had to live through. There are also many who would say that they are just characteristics that came from its ancestors that were able to withstand the harsh climate of early Earth. Whatever the reason that Deinococcus radiodurans can live the way it does they all say that this microbe deserves the nickname Conan the Bacterium.

Figure 1 by Superbug Gifts for Geeks & Science Tees

References

Conan the Bacterium: The Ancient Microscopic Hero.” Chaotic Utopia. 2006. 16 Feb 2007. <http://chaoticutopia.com/wp/?p=254 >

Deinococcus radiodurans.” Wikipedia: The Free Encyclopedia. 2007. 16 Feb 2007.
<http://en.wikipedia.org/wiki/Deinococcus_radiodurans>

Stone, Marcia. “Metal Balance Helps Explain Survival of Microbial ‘Superhero’.” Microbe. 2009. 16 Feb 2010.

<http://www.usuhs.mil/pat/deinococcus/index_20.htm >

*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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