Abstract
Spores formed by members of the genus Bacillus exhibit two types of radiation inactivation curves: Bacillus subtilis, B. brevis, and B. mesentericus are inactivated in a "single hit" fashion, whereas B. megaterium, B. cereus, and B. mycoides are inactivated in a "multiple hit" fashion. In all cases there is no effect on spore survival if the post-irradiation medium is changed from yeast extract medium to a chemically defined medium. Implication of the radiation results is discussed.