Tuesday, January 18, 2011

Deinococcus radiodurans

This organism was first noticed in 1956 when it spoiled a can of meat that had been irradiated.[1] It was subsequently determined that it can withstand 15,000 Grays of radiation. To put that in perspective, 10 Grays of radiation will kill a human being and a little over 60 will kill a cockroach.[2] It is able to do this through two adaptations not normally seen in bacteria.[3] First, it has four copies of its genome (mouse over for definition), rather than one. So if any gene is mutated by the radiation, it still has several good copies to keep it alive until it has time to repair the damaged gene. Second, it repairs DNA damage more quickly than other bacteria. Because it is such a tough organism (it can also withstand extreme cold, dehydration, vacuum, and acid), it has been nicknamed 'Conan the Bacterium'.

We can't really be thrilled that Deinococcus radiodurans will survive irradiation and continue to spoil our food, but it does have some uses for human beings. Because it can withstand radiation, it can actually be used in the treatment of radioactive waste.[4] It has also been proposed that Deinococcus radiodurans could be used to store information in the event of a global nuclear catastrophe.[5] That assumes, of course, that extraterrestrials 1. would be interested in visiting a radioactive planet with no visible signs of life and 2. would be able to decipher English messages encoded into DNA.[6]


[1] See http://en.wikipedia.org/wiki/Deinococcus_radiodurans#Name_and_classification.

[2] See http://en.wikipedia.org/wiki/Radioresistant#Radioresistance_comparison.

[3] There are also three fungi (Cladosporium sphaerospermum, Cryptococcus neoformans, and Wangiella dermatitidis), found growing in Chernobyl, which not only are resistant to radiation, but actually harness the radiation (the beta radiation) for their energy needs. They're able to do this by using the pigment molecule melanin, which is also a component of skin color in humans. See http://en.wikipedia.org/wiki/Radiotrophic_fungus.

[4] It can't eliminate the radioactivity, but it can remove other toxins from the waste, like degrading toluene or reducing ionic mercury to a less toxic form. See Brim, H. et al. (2000) "Engineering Deinococcus radiodurans for metal remediation in radioactive mixed waste environments." Nature Biotechnology 18:85–90.

[5] Scientists translated the song "It's a Small World After All" into DNA code (well, amino acid code, actually) and inserted it into D. radiodurans. 100 generations later the inserted DNA was still intact. See McDowell, Natasha. (2003) "Data stored in multiplying bacteria." New Scientist.

[6] Hopefully the message will include a disclaimer like:

"And now, behold, we have written this record according to our knowledge, in the characters which are called among us the genetic code, being handed down and altered by us, according to our manner of speech.

"And if our DNA alphabet had been sufficiently large we should have written in English; but the English hath been altered by us also; and if we could have written in English, behold, ye would have had no imperfection in our record."

Image attribution:

False-color electron micrograph of Deinococcus radiodurans is by Michael Daly, available at http://commons.wikimedia.org/wiki/File:Deinococcus radiodurans.jpg.

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