The Chemical Sensitization of Pseudomonas Species to Ionizing Radiation

Abstract

The sensitization of Escherichia coli and other vegetative bacteria to irradiation by N-ethylmaleimide (NEM) has been described in previous reports (1, 2), and it was suggested (2) that the effect might be explained by the hypothesis proposed by Alper and Howard-Flanders for the effect of oxygen and nitric oxide (3-6). The radiation is assumed to leave certain organic molecules in a short-lived excited state, possibly as free radicals. Under certain conditions these might be restored to their original state, but in the presence of oxygen or nitric oxide they enter into a chemical reaction which results in the impairment of their biological function. It was proposed (2) that NEM might also react with such radiationinduced reactive sites. In theory, these sites need not always be identical with those which could be inactivated by oxygen, but they might be identical in the particular case of Pseudomonas sp. where there is no sensitizing effect of NEM under aerobic conditions. The possibility that compounds other than nitric oxide might act in an oxygen-like way was discussed by Alper (5). This paper reports an investigation made into the effect of various sensitizing agents on Pseudomonas sp.