DNA repair in the extremely radioresistant bacterium Deinococcus radiodurans

Abstract

Deinococcus radiodurans and other members of the same genus share extraordinary resistance to the lethal and mutagenic effects of ionizing and u.v. radiation and to many other agents that damage DNA. While it is known that this resistance is due to exceedingly efficient DNA repair, the molecular mechanisms responsible remain poorly understood. Following very high exposures to u.v. irradiation (e.g. 500 J m-2, which is non-lethal to D. radiodurans), this organism carries out extremely efficient excision repair accomplished by two separate nucleotide excision repair pathways acting simultaneously. One pathway requires the uvrA gene and appears similar to the UvrABC excinuclease pathway defined in Escherichia coli. The other excision repair pathway is specific for u.v. dimeric photoproducts, but is not mediated by a pyrimidine dimer DNA glycosylase. Instead, it is initiated by a second bona fide endonuclease that may recognize both pyrimidine dimers and pyrimidine-(6-4)pyrimidones. After high doses of ionizing-radiation (e.g. 1.5 Mrad), D. radiodurans can mend > 100 double-strand breaks (dsb) per chromosome without lethality or mutagenesis. Both dsb mending and survival are recA-dependent, indicating that efficient dsb mending proceeds via homologous recombination. D. radiodurans contains multiple chromosomes per cell, and it is proposed that dsb mending requires extensive recombination amongst these chromosomes, a novel phenomenon in bacteria. Thus, D. radiodurans may serve as an easily accessible model system for the double-strand-break-initiated interchromosomal recombination that occurs in eukaryotic cells during mitosis and meiosis.

Repair of extensive ionizing-radiation DNA damage at 95 degrees C in the hyperthermophilic archaeon Pyrococcus furiosus

“…1). Compared to D. radiodurans, which can sustain up to 15,000 Gy without loss of viability, P. furiosus cells are 7 times less resistant to ionizing radiation, but they are 10 times more resistant than E. coli cells (17). At higher doses, the survival rate decreased very rapidly as reported for other microorganisms ( Fig.…”

Deinococcus geothermalis sp. nov. and Deinococcus murrayi sp. nov., Two Extremely Radiation-Resistant and Slightly Thermophilic Species from Hot Springs

“…Gamma irradiation of exponential-phase cultures of strains of Deinococcus radiodurans shows that there is virtually no decrease in viable counts at doses of 4 to 5 kGy (33), and survivors are routinely recovered from cultures exposed to as much as 20 kGy (1,20). The extreme gamma radiation resistance of the species of this genus is due to a very efficient repair system for double-strand breaks in the DNA, while the UV resistance is conferred by two nucleotide excision repair pathways acting simultaneously (31).…”

Ionizing Radiation and Life

“…Organisms exhibit varying degrees of resilience to ionizing radiation, with the Gram-negative (the classification of bacteria with a kind of cell wall that does not retain crystal violet dye in the Gram staining protocol) nonsporulating bacterium Deinococcus radiodurans being the most radioresistant organism known (Minton, 1994;Battista, 1997;Cox and Battista, 2005). Gamma-irradiated populations of D. radiodurans can survive a dose of 5 kGy without measurable loss of viability despite massive DNA fragmentation, and 1% survival is still found after 10 kGy (Cox and Battista, 2005).…”