Deinococcus Radiodurans - Latest Research

Bacteria belonging to the family Deinococcaceae are some of the most radiation-resistant organisms yet discovered. Deinococcus (Micrococcus) radiodurans strain R1 (ATCC BAA-816) was first reported in 1956 by A. W. Anderson and coworkers of the Oregon Agricultural Experimental Station, Corvalis, Oregon. This obligate aerobic bacterium typically grows in rich medium as clusters of two cells (diplococci) in the early stages of growth, and as clusters of four cells (tetracocci) in the late stages of growth, is non-pathogenic, and best known for its ability to survive extremely high doses of acute ionizing radiation (10,000 Gy) without cell-killing. For comparison, 5 Gy is lethal to the average human, and 2,000 Gy can sterilize a culture of Escherichia coli. D. radiodurans is capable of growth under chronic radiation (60 Gy/hour) and resistant to other DNA damaging conditions including exposure to desiccation, UV light, and hydrogen peroxide. The genes and cellular pathways underlying the survival strategies of D. radiodurans are under investigation, and its resistance characteristics are being exploited in the development of bioremediation processes for cleanup of highly radioactive US Department of Energy waste sites.

Modern radiation toxicity models are based on the tacit assumption that exposure of organisms to ionizing radiation (IR) indiscriminately damages cellular macromolecules. Because individual proteins in a cell are typically present at much higher levels than their corresponding genes, IR-induced cell death has been attributed mainly to DNA damage. However, recent investigations demonstrate that acquisition of extreme IR resistance among bacteria coincides with an increase in manganese content and a greatly diminished susceptibility to IR-induced protein oxidation. For a review, see Nat Rev Microbiol, 2009; 7(3):237-45.

Results of a recent study titled "Deinococcus geothermalis: The Pool of Extreme Radiation Resistance Genes Shrinks," was published in the Sept. 26, 2007 edition of PLoS ONE. The study reports the whole-genome sequence of D. geothermalis (image), which is only the second for an extremely radiation- and desiccation-resistant bacterium. D. geothermalis has also been engineered for bioremediation of radioactive waste sites. In a related paper, published in the ISME Journal in February 2008, we present evidence supporting that protein protection is key to surviving extreme desiccation, with interesting connections to "Extreme resistance of bdelloid rotifers to ionizing radiation" by Gladyshev & Meselson in Proc Natl Acad Sci U S A, 2008;105(13):5139-44.

One original goal of radiobiology was to explain why cells are so sensitive to ionizing radiation (IR). Early studies in bacteria incriminated DNA as the principal radiosensitive target, an assertion that remains central to modern radiation toxicity models. More recently, the emphasis has shifted to understanding why bacteria such as Deinococcus radiodurans are extremely resistant to IR (1), by focusing on DNA repair systems expressed during recovery from high doses of IR (2). Unfortunately, as key features of DNA-centric hypotheses of extreme resistance have grown weaker (3), the study of alternative cellular targets has lagged far behind, mostly because of their relative biological complexity. Recent studies have shown that extreme levels of bacterial IR resistance correlate with high intracellular Mn(II) concentrations (4), and resistant and sensitive bacteria are equally susceptible to IR-induced DNA damage. Our most recent work has established a mechanistic link between Mn(II) and protection of proteins from radiation damage (5). In contrast to resistant bacteria, naturally sensitive bacteria are highly susceptible to IR-induced protein oxidation. We propose that sensitive bacteria sustain lethal levels of protein damage at radiation doses that elicit relatively little DNA damage, and that extreme resistance in bacteria is dependent on protein protection (6).

Image overlay of transmission electron microscopy, light microscopy, and x-ray fluorescence microprobe analyses of Deinococcus radiodurans. Depth-average abundance of Mn (blue, green, pink) and Fe (red) are shown within a single D. radiodurans diplococcus.

Conan the Bacterium by Patrick Huyghe

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Last updated: July 21, 2009.