Microdosimetric considerations of effects of heavy ions on E. coli K-12 mutants

The inactivation cross sections of E. coli K-12 recombination-deficient mutants, JC1553 (r ecA) and AB2470 ( recB), for several MeV/u α-particles and N ions have been successfully analyzed by Katz's target theory in which radiosensitivity parameter E 0 is assumed to be LET independent and equal to D 37 for gamma-rays. For E. coli K-12 wild type, AB1157 ( rec +, uvr +), however, it is impossible to interpret the inactivation cross section data by an LET independent E 0-value. In the latter case, as in the case of B. subtilis spore, it is necessary to assume that the radiosensitivity of the target for the core of a heavy ion is higher than that for δ-electrons. As well as Waligorski, Hamm and Katz's dose, the dose around the trajectory of an ion based on Tabata and Ito's energy deposition algorithm for electrons has been used in the course of analysis.