Radioresistant Mutants of Escherichia coli B (ORNL)

Radio-resistant mutants of E. coli B (ORNL) were isolated from among survivors of treatment with uv radiation and with 1-methyl-3-nitro-1- nitrosoguanidine. The mutants surviving uv irradiation were equally resistant to uv and x radiation but could be differentiated into four classes on the basis of their cross-resistance to radiomimetic chemicals. Two of these classes also represented all the radioresistant mutants isolated after 1-methyl-3-nitro- 1nitrosoguanidine treatment. The radioresistant mutants of B (ORNL) diifer from those isolated earlier by other investigators. They all also differ from the radioresistant mutants isolated from E. coli S, a variant of strain B. An explanation for the observed differences among radioresistant strains of B isolated at different times is presented. (auth)