Deinococcus radiodurans is an extremophilic bacterium, one of the most radioresistant organisms known. It can survive cold, dehydration, vacuum, and acid, and is therefore known as a polyextremophile and has been listed as the world’s toughest bacterium in The Guinness Book Of World Records.
The name Deinococcus radiodurans derives from the Ancient Greek δεινός (deinos) and κόκκος (kokkos) meaning “terrible grain/berry” and the Latin radius and durare, meaning “radiation surviving”. The species was formerly called Micrococcus radiodurans. As a consequence of its hardiness, it has been nicknamed Conan the Bacterium.
Initially, it was placed in the genus Micrococcus. After evaluation of ribosomal RNA sequences and other evidence, it was placed in its own genus Deinococcus, which is closely related to the genus Thermus of heat-resistant bacteria; the group consisting of the two is accordingly known as Deinococcus-Thermus.
Ionizing radiation resistance
D. radiodurans is capable of withstanding an acute dose of 5,000 Gy (500,000 rad) of ionizing radiation with almost no loss of viability, and an acute dose of 15,000 Gy with 37% viability. A dose of 5,000 Gy is estimated to introduce several hundred double-strand breaks (DSBs) into the organism’s DNA (~0.005 DSB/Gy/Mbp (haploid genome)). For comparison, a chest X-ray or Apollo mission involves about 1 mGy, 5 Gy can kill a human, 200-800 Gy will kill E. coli, and over 4,000 Gy will kill the radiation-resistant tardigrade.
Several bacteria of comparable radioresistance are now known, including some species of the genus Chroococcidiopsis (phylum cyanobacteria) and some species of Rubrobacter (phylum actinobacteria); among the archaea, the species Thermococcus gammatolerans shows comparable radioresistance. Deinococcus radiodurans also has a unique ability to repair damaged DNA. It isolates the damaged segments in a controlled area and repairs it. This bacteria can also repair many small fragments from an entire chromosome.