Experimental and theoretical cross sections for Escherichia coli mutants B, B/r, and Bs-1 after heavy-ion irradiation.

Data for the inactivation of three Escherichia coli mutants by energetic heavy ions are fitted by the track theory of a one-hit detector in an extended target mode. The respective E0's are 46, 36.5, and 12.6 Gy for E. coli B, B/r, and Bs-1 and a0, the assumed target radius, is 0.5 microns for all three. The parameter E0, the D37 with gamma rays, is measured directly, while a0 is fitted to the data. It is significant that neither a point target model nor calculations with a0 = 0.2 and 1.0 micron fit the data. Our fitted target radius, a0, approximates the size of the bacterium. These results raise questions as to why the E. coli mutants are one-hit detectors, and concerning the differences in the E0's in relation to a mechanistic interpretation of cell killing.