Molecular Mechanisms of Radiation-Resistance in Deinococcus radiodurans

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Deinococcus radiodurans is a Gram-positive, red-pigmented, nonmotile bacterium that was originally identified as a contaminant of irradiated canned meat at 1957. It has been isolated worldwide from locations rich in organic nutrients such as animal feces and processed meat. D.radiodurans is an extremely resistant to a number of agents and conditions that damage DNA, including ionizing and ultraviolet radiation and hydrogen peroxide. When an exponential-phase culture of D. radiodurans is exposed to 6000 Gy x-rays, more than 200 double-strand breads (DSB) are introduced into the chromosome. The DSBs are not only repaired without loss of viability, but the chromosome is also apparently resembled so that the linear continuity of the genomes is unaffected by either the damage or the repair process. The capacity of D. radioudurans to survive.DNA damage suggests that 1)they have the ability to potentiate the effectiveness of the conventional complement of DNA repair proteins, or that 2)they employ repair mechanisms that are fundamentally different from other prokaryotes. Our results indicate that 1)there are at least four identical copies of chromosome per cell, 2)they have not only Escherichia coli homologs for DNA repair, such as the recA, lexA and uvrA, but also several of DNA repair genes which have not been identified, 3)they can restore DNA structure from 200 or more DSBs within 4 hours, and for the processes, recA and unknown genes are involved, and that 4)recA deficient strains have a mutator phenotype if 5-fluorouracil-resistant mutation is monitored, suggesting the role of genome instability.