An Aftereffect of Ionizing Radiation on a Mutant of Escherichia coli

Abstract

Many aftereffects of ionizing radiation on biological materials have been reported (for review, see ref. 1). Alper's demonstration (2, 3) that, under certain conditions, part of the inactivation of bacteriophage is an aftereffect caused by radiationproduced hydrogen peroxide is particularly pertinent to the present work. Likewise, the observations of Taylor et al. (4) that the viscosity of deoxyribonucleic acid continues to fall for many hours after X-irradiation is of particular interest. This phenomenon may also involve radiation-produced hydrogen peroxide (5). In these experiments, a mutant of the bacterium Escherichia coli Monod was studied for aftereffects of ionizing radiation. If hemin is present in the growth medium, the cells contain active catalase, cytochromes, and other porphyrincontaining enzymes. If hemin is absent, the cells show no catalase or cytochrome activity. The parent bacterium is independent of hemin.