Cell Survival and X-Ray-Induced DNA Degradation in Micrococcus radiodurans

Oxidative Stress Resistance inDeinococcus radiodurans

“…According to data reported previously by Moseley and Laser (442), cells recovered from the initial irradiation damage are again as resistant to X-ray radiation as unirradiated cells, whereas Driedger et al (161) reported a slight increase in the radiation sensitivity of the progeny of irradiated cells, possibly due to a higher dose of irradiation of the parental cells. In other bacteria, one or more doses of radiation can cause an increase in radiation resistance (132,358,481), an increase in antibiotic resistance (498), morphological changes (173,358), biochemical changes (173), and decreased pathogenicity (180,498).…”

“…The multicellularity of D. radiodurans, which forms tetrads during exponential growth, does not contribute to its radiation resistance, judging by the high survival rate of single cells observed by microscopic examination, as opposed to the CFU scores on agar plates (161). However, cell clumping signifi-cantly increases survival as a result of the shielding of cells inside a cluster from oxygen effects (416).…”

“…Microscopic observation of dying cells revealed that only about 10% of the cells that fail to give rise to a colony after 7 to 10 kGy of radiation do not divide at all, while the majority undergo between one and six divisions, after which the entire microcolony lyses (161). The phenomenon of abortive colony formation suggests that the DNA repair is either incomplete, with an inaccurate partitioning of genetic material to the progeny upon division, or inaccurate, with the production of mutations (161).…”

“…In other bacteria, one or more doses of radiation can cause an increase in radiation resistance (132,358,481), an increase in antibiotic resistance (498), morphological changes (173,358), biochemical changes (173), and decreased pathogenicity (180,498). Irradiated or chemically treated D. radiodurans cells usually give rise to colonies identical to those of unirradiated bacteria, although some colonies are smaller, pigmentless, and rough with irregular edges (161,434). This may result from a partial defect in recombination-type repair, which is presumably required for the regulation of cell division (438).…”

“…A dose of 6 kGy induces approximately 200 DSBs (79), over 3,000 SSBs (65,79), and many more sites of base damage per D. radiodurans genome (236). D. radiodurans survives 5 kGy of ionizing radiation without lethality or mutagenesis (135,161,597) (Fig. 3A).…”