Physiologic determinants of radiation resistance in Deinococcus radiodurans

Immense volumes of radioactive wastes, which were generated during nuclear weapons production, were disposed of directly in the ground during the Cold War, a period when national security priorities often surmounted concerns over the environment, The bacterium Deinococcus radiodurans is the most rad iation-resistant organism known and is currently being engineered for remed iation of the toxic metal and organic components of these environmental was tes. Understanding the biotic potential of D. radiodurans and its global ph ysiological integrity in nutritionally restricted radioactive environments is important in development of this organism for in situ bioremediation, We have previously shown that D. radiodurans can grow on rich medium in the p resence of continuous radiation (6,000 rads/h) without lethality. In this s tudy we developed a chemically defined minimal medium that can be used to a nalyze growth of this organism in the presence and in the absence of contin uous radiation; whereas cell growth was not affected in the absence of radi ation, cells did not grow and were killed in the presence of continuous rad iation. Under nutrient-limiting conditions, DNA repair was found to be limi ted by the metabolic capabilities of D. radiodurans and not by any nutritio nally induced defect in genetic repair. The results of our growth studies a nd analysis of the complete D. radiodurans genomic sequence support the hyp othesis that there are several defects in D, radiodurans global metabolic r egulation that limit carbon, nitrogen, and DNA metabolism. We identified ke y nutritional constituents that restore growth of D. radiodurans in nutriti onally limiting radioactive environments.