Respiration, Growth and Viability of Repair-deficient Mutants of<i>Escherichia Coli</i>after Ultraviolet Irradiation

Abstract

SummaryEscherichia coli WP2 (a tryptophan-requiring strain of B/r) and three mutants deficient in DNA repair processes were used for a comparative study of the effects of ultraviolet radiations on respiration. An hcr− strain behaved similarly to WP2 hcr+; respiration ceased about an hour after U.V. The doses used for stopping respiration were 55 and 520 erg/mm2 respectively; these doses reduced survival in each case to about 0·5 per cent. WP2 rec− (Rec A) and WP2 exr− strains did not cease respiring after receiving a range of doses up to 520 ergs/mm2. Following irradiation, WP2 hcr+ and WP2 hcr− cells degraded their DNA slightly if at all, but degradation was extensive in the rec− and exr− strains at doses that reduced survival to 1·0 per cent (33 and 150 ergs/mm2 respectively). We conclude that cessation of respiration of irradiated Escherichia coli is dependent on the integrity of their DNA and not on the radiation sensitivity.