Inhibition of X-ray-induced Protection ofEscherichia ColiK-12 Cells against the Lethal Effects of Ultra-violet Light by Nitrofurantoin

Abstract

Wild-type cells of E. coli K-12 showed increasing U.V. resistance if they were X-irradiated and incubated at 37 degrees C in growth medium before the U.V. exposure. Development of higher U.V. resistance could be inhibited by incubating the X-irradiated cells either at temperatures below 15 degrees C, or in the presence of 0.01 M KCN. Nitrofurantoin (NF), which was recently found specifically to inhibit inducible enzyme synthesis, had only a transient inhibitory effect on X-ray-induced U.V. resistance. Cells grown in glucose medium showed less inhibition by NF of X-radiation-induced resistance to U.V.-radiation than did cells grown in glycerol, or in glucose medium with added cyclic AMP. It is suggested that X-ray-induced U.V. resistance requires active cellular metabolism, but it is not subject to catabolite repression. The following hypothesis is offered to explain the action of NF: Under de-repressed conditions (without catabolite repression by glucose) nitrofurantoin could counteract the radiation-induced inhibition of a repair inhibitor (such as post-irradiation DNA degradation).