The Chemical Protection of Pseudomonas Species against Ionizing Radiation

Abstract

Many compounds have been reported to protect bacteria against ionizing radiation, and the most widely studied have been organic sulfhydryl compounds. In many instances the effect can be shown to be due to depletion of dissolved oxygen by autoxidation (1, 2), but there are at least two other ways in which organic sulfhydryl compounds can protect. Firstly, at low concentrations (0.001 M) they may exert a protective effect which is completely abolished by bubbling with air during irradiation (3). While this is also an oxygen-depletion effect, it is not, however, due to autoxidation but to a radiation-induced reaction involving the sulfhydryl compound in which oxygen is consumed.2 Secondly, some sulfhydryl compounds at high concentrations may afford protection which is not due to oxygen depletion (2, 4-6). With Escherichia coli this type of protection by cysteine needs a temperature-dependent period of incubation before irradiation (2). The aliphatic alcohols (e.g., glycerol) and, more recently, dimethyl sulfoxide (DMS) have also been shown conclusively to protect vegetative bacteria under controlled gas conditions (7-10). The present paper describes a similar action of thiourea and reports some experiments designed to indicate whether or not all the compounds mentioned protect against the same component of radiation damage.