Protection of Escherichia coli against ultraviolet irradiation by catalase and related enzymes.

The addition of the enzyme catalase to cells of certain strains of E8cherichia coli strain K 12, after exposure to ultraviolet light (2537A), has been found to increase the survival ratio (Monod et al., 1949; Latarjet et al., 1954; Miletic, 1954; Teti, 1954). Catalase has also been found to counteract the biological effects produced in Micrococcus pyogenes var. aureus, either by ultraviolet irradiation of nutrient broth or by the addition of hydrogen peroxide to the broth (Wyss et al., 1948). Latarjet and Caldas (1952) extended the study of the restorative action of catalase on ultraviolet-irradiated cells and found that small doses of visible light enhanced the action of this enzyme. Clark (1952) has suggested that part of the resistance exhibited by E. coli strain B/r to substrates that are irradiated with ultraviolet light or treated with hydrogen peroxide could be due to its high catalase activity. Wagner et al. (1950) found that when inhibitors of catalase and the cytochromes were incorporated into irradiated medium, there was an increase in the mutation rate of Neurospora. Giese et al. (1955) compared the order of hydrogen peroxide and ultraviolet sensitivity in a large group of protozoans and, based on differences in the order of sensitivity, questioned the importance of the effect of hydrogen peroxide produced during ultraviolet irradiation. They also studied the effect of catalase added to protozoan suspensions before, during, and after irradiation but were unable to show any clear-cut results. Since this work included a large group of organisms representing different genera, it is likely that some factors, such as permeability differences and differences in the lability and importance of various enzyme systems, were involved. It would obviously be of value to study the ultraviolet irradiation resistance of a single