POSTIRRADIATION RESPONSES OF ULTRAVIOLET IRRADIATED ESCHERICHIA COLI

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Abstract
Strains B and B/r of Escherichia coli are more resistant to the lethal effects of ultraviolet radiation (UV) in the stationary than in the logarithmic growth phase. Dark recovery from irradiation injury was observed with strain B, not with B/r. The recovery was demonstrable over a wide range of UV doses. The restoration depended on temperature and on medium composition. Potassium and phosphate ions and glucose stimulate dark reactivation. Inactivation of photoreactivated suspensions resulted from prolonged exposure to reactivating light in a solution containing only glucose and potassium phosphate, not in minimal medium with glucose. The ability to be photoreactivated was lost during prolonged incubation of UV-irradiated cells faster in media supporting growth than in media incapable of doing so. The temperature coefficient for loss of photoreactivability was larger in the B than in the B/r strain.