Thursday, November 01, 2007

Another highly radiation-resistant bacterial species

Perhaps you recall that just about a year ago research identified some of the mechanism by which what was long thought to be unique species of bacterium – Deinococcus radiodurans – managed to survive extremes of exposure to radiation and dessication.

Now it turns out that the species isn't so unique, and a distant relative also has exceptional durability, despite significant genetic differences:

Second Extremely Resistant Bacteria Sequenced Is Surprisingly Different From First
Researchers have completed the whole-genome sequence of Deinococcus geothermalis, which is only the second extremely radiation- and desiccation-resistant bacterium to be sequenced.

The first was for the Guinness World Records-holder Deinococcus radiodurans, which for 50 years has been the subject of extensive investigations aimed at solving the mystery of how this microbe and its close relatives survive immense doses of x-rays and gamma-rays.

Most surprisingly, many of the unique D. radiodurans genes that were strongly implicated in resistance over the last decade have turned out to be unrelated to its survival, and are not present in D. geothermalis.

However, now that complete genome sequences are available, it turns out that the genes they have in common to account for their durability are surprisingly few:
Using computer-based systems to compare the D. geothermalis genome sequence with the sequence of D. radiodurans, a minimal set of genes which encode extreme resistance was defined. Far fewer genes than initially believed appear to be responsible for the extreme resistance trait.

Among other things, this finding apparently rules out one possible source of the durability:
The phenomenal resistance of Deinococcus bacteria has given rise to numerous descriptions of their origin, including that they evolved on Mars under harsh cosmic radiation. The present analysis firmly places the origin of Deinococcus bacteria on Earth, where the evolutionary steps that led to their survival mechanisms clearly occurred in their terrestrial ancestors - most likely in a desert near you.

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