Two components in the radiation sensitization of bacterial spores by p-nitroacetophenone: the -OH component.

Abstract

p-Nitroacetophenone (PNAP) sensitizes Bacillus megaterium spores under anoxic conditions to the lethal effects of 50 kVp X-rays. Concentrations between approximately 5 X 10(-4) M and 3-8 X 10(-3) M produce the maximum effect, an increase of about 30 per cent over the anoxic response when the spores are irradiated in water. Compounds that scavenge -OH decrease, but cannot completely eliminate, this maximum amount of sensitization. These results indicate that PNAP acts to increase spores' radiation sensitivity through two separable types of chemical reactions: one which involves -OH and one which does not. Possible mechanisms responsible for these two components of damage are discussed. In these experiments 1/15 M phosphate buffer acts in several unexpected ways. This concentration itself increased the anoxic spore response by about 9 per cent (relative to the anoxic response in water). In addition, although the maximum amounts of sensitization were the same, the amounts of sensitization from lower PNAP concentrations differed when the suspending fluid was buffer instead of water. An interaction was also seen during the PNAP-t-butanol experiments; again, the responses at low PNAP concentrations were different in buffer and in water. No mechanisms for these actions of this buffer were suggested, although somewhat similar effects may occur with other organisms. Clearly, such effects must be recognized and evaluated before quantitative analyses of the actions of sensitivity-modifying agents can be completed.