Radiosensitization of Bacillus megaterium Spores by Combinations of Oxygen and Misonidazole

Abstract

Misonidazole sensitized anoxic spores of Bacillus megaterium against the lethal action of gamma radiation to an extent amounting to about 30% of the level achieved by O₂. An enhancement by misonidazole, equal in magnitude to that occurring in anoxia, was seen in spores at an O₂ concentration obtained by equilibrating with 1.2 or 2.2% O₂ in N₂ gas. At these two concentrations of 02 the enhancing actions of O₂ and misonidazole were additive. No effect of misonidazole was observed with spores equilibrated with 3.0 or 4.1% O₂ in N₂ gas. At high O₂ concentrations (equilibration with air or 100% O₂) misonidazole protected the spores to a small extent against lethal action of radiation. The mechanistic implications of the enhancing action of O₂ in spores are given.