Deinococcus radiodurans-World's Toughest Bacteria

What's All The Fuss About?

Deinococcus radiodurans  is infamous for its resistance to high levels of radiation and long periods of desiccation.  Upon learning of D.radiodurans' viability, it was surprising to find that it does not produce a spore.  Its mechanisms of surviving utilize a different mechanism of resistance. 


Which Came First, the Chicken Or the Egg?

It was particularly perplexing to consider how D. radiodurans evolvedPhoto Copyright and Permission by Dennis Kunkel Microscopy, Inc. such a strong resistance to radiation.  The average level of naturally occurring radiation measured on Earth is 5x10-8 Gy per hour, compared to the 5,000 Gy that D. radiodurans can survive without a loss of viability. It is thought instead, the radiation resistance is a byproduct of D. radiodurans' tolerance to desiccation. It turns out that prolonged exposure to extremely dry conditions causes double stranded DNA breaks, similar to those caused by radiation. In developing a mechanism to combat desiccation, it also developed a way to cope with the effects of ionizing radiation. A study completed by John Battista and Valerie Mattimore published in 1996 tested 41 strains of radiation sensitive Deinococcus radiodurans mutants and discovered that all of the strains were also sensitive to desiccation.



It is estimated that each cell of D. radioduDNA Cartoon From Microsoft Clip Artrans contains approximately four copies of its genetic material.  The genome is contained in a circular chromosome that condenses to a ring structure compared to other bacteria that have their DNA scattered throughout the cell.  Previously, it was thought that the key to radiation resistance was in the DNA.  However, recent research has revealed that the key does not lie in the DNA but in the ability to maintain the proteins in the cell instead.  Now, they believe that extra copies of DNA serve as reservoir of genetic information instead of the main player in the mechanism. 


Well If It's Not DNA What Is It?

Instead current research indicates that the key to rManganese metal photo from Wikipedia Commonsadiation resistance is due to the presence of the manganese II cation which is in particularly high concentrations in the cells of D. radiodurans.  This cation acts to oxidize species such as free radicals.  It also acts as a unique cofactor in the ligase enzymes, an enzyme that repairs DNA.  In one experiment, they added manganese ions to the cells of Eschericia coli and found that it increased the cells viability when exposed to radiation.  Even though it is still in question what role the manganese ion plays, it is certainly important.


The Big Picture

It is thought that in the case of both radiation and desiccation, the organism acquires double stranded breaks like any other organism.  D. radiodurans does not protect its DNA but its proteins.  By protecting the proteins, it enables the bacteria to fix its DNA efficiently and grow in the presence of ionizing radiation. 

Photo of a Desiccator from Wikipedia CommonsRadiation Sign from Microsoft Clip Art

Woa... That's some pretty cool stuff but what can this adaptation do for YOU?

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