Lethal and Sublethal Effects of X-Rays on Escherichia coli as Related to the Yield of Biochemical Mutants

Abstract

Cell suspensions of E. coli were uniformly irradiated with X-rays. The log of the survival ratio decreased linearly with time of irradiation, down to a survival ratio of 10-5. This is in accordance with the "one-hit-to-kill" theory of the bactericidal effects of X-rays. From this the authors derive an equation showing that the greater the % of cells killed by X-rays, the greater will be the % of mutant cells among the survivors. With more extensive X-ray treatment the death rate increases, and this ratio apparently does not hold. The yield of mutant cells may be increased by improved exptl. conditions which permit a greater number of the injured cells to grow into colonies. 4,420 colonies were isolated from plates poured shortly after X-ray treatment. 61 growth factor-requiring mutant cultures were obtained.