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 Latinradius and durare, meaning “radiation surviving”.
The name Deinococcus radiodurans derives from the Ancient Greek δεινός (deinos) and κόκκος (kokkos) meaning “terrible grain/berry” and the Latinradius 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 genusDeinococcus, which is closely related to the genus Thermus of heat-resistant bacteria; the group consisting of the two is accordingly known asDeinococcus-Thermus.
Deinococcus is the only genus in the order Deinococcales. D. radiodurans is the type species of this genus, and the best studied member. All known members of the genus are radioresistant: D. proteolyticus, D. radiopugnans, D. radiophilus, D. grandis, D. indicus, D. frigens, D. saxicola, D. marmoris,D. deserti, D. geothermalis and D. murrayi; the latter two are also thermophilic.
D. radiodurans is a rather large, spherical bacterium, with a diameter of 1.5 to 3.5 µm. Four cells normally stick together, forming a tetrad. The bacteria are easily cultured and do not appear to cause disease. Colonies are smooth, convex, and pink to red in color. The cells stain Gram positive, although its cell envelope is unusual and is reminiscent of the cell walls of Gram negative bacteria.
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.
Deinococcus has been genetically engineered for use in bioremediation to consume and digest solvents and heavy metals, even in a highly radioactive site. For example, the bacterial mercuric reductase gene has been cloned from Escherichia coli into Deinococcus to detoxify the ionic mercury residue frequently found in radioactive waste generated from nuclear weaponsmanufacture. Those researchers developed a strain of Deinococcus that could detoxify both mercury and toluene in mixed radioactive wastes.
The Craig Venter Institute has used a system derived from the rapid DNA repair mechanisms of D. radiodurans to assemble synthetic DNA fragments into chromosomes, with the ultimate goal of producing a synthetic organism they call Mycoplasma laboratorium.
In 2003, U.S. scientists demonstrated D. radiodurans could be used as a means of information storage that might survive a nuclear catastrophe. They translated the song It’s a Small World into a series of DNA segments 150 base pairs long, inserted these into the bacteria, and were able to retrieve them without errors 100 bacterial generations later. However, since only a small portion of the information can be stored in DNA of D. radiodurans, several species had to be created, each holding a different part of the song and species needed to be kept segregated over time. If species are evolving together after a number of generations certain species will emerge dominant and others will become extinct and parts of the encoded message which were stored in extinct species will be lost.