Effects of γ-irradiation on Escherichia Coli Wild Type and Its Radiation-resistant Mutants

Summary

Exponentially growing cells of Escherichia coli wild type and three radiation-resistant mutants, E. coli 1γ, 6γ, and 12γ, derived therefrom, were exposed to γ-irradiation and DNA-synthesis after irradiation was determined by measuring [³H] thymidine incorporation. Irradiation at relatively low doses (10 to 30 krads) resulted in: (a) a permanent reduction of 70–90 per cent in the rate of DNA-synthesis in E. coli wild type (D₃₇ = 4 krads) and 1γ (D₃₇ = 20 krads); (b) temporary inhibition in E. coli 12γ(D₃₇ = 35 krads); and (c) about 20 per cent stimulation in the most radiation-resistant strain E. coli 6γ (D₃₇ = 50 krads). After higher doses (50–100 krads), synthesis of DNA in the 6γ strain was temporarily inhibited and resumed within one normal generation time at the same rate as in the unirradiated control. Resumption of DNA-synthesis in irradiated cells of E. coli 12γ was further delayed in this dose range.