The chemical reversal of ultraviolet effects on bacteria.

It is now well established that the effects of ultraviolet radiations on a variety of cells and cell process can be reversed in part by exposure to strong illumination in the visble or near ultraviolet range (Kelner, 1949; Errara, 1953). Both lethal and mutagenic effects on bacteria are photoreversible although to different degrees. When high ultraviolet dosages are employed, induced mutations are photostable although reactivation still occurs in the expected manner (Newcombe and Whitehead, 1951). Heinmets and his co-workers have shown that the inactivation of E. coli strain B/r by ultraviolet radiation (Heinmets, 1953; Heinmets et al., 1954b) and by other physical or chemical agents (Heinmets et al., 1954a) could be reversed to a significant degree by certain metabolites related to the citric acid cycle. These authors found it necessary to suspend the irradiated culture in buffer containing the metabolite prior to plating; they were unable to obtain reactivation by plating directly in a defined medium supplemented by the chemicaLs employed. The results reported below demonstrate that both the lethal and the mutagenic effects of ultraviolet radiation can be reversed by plating in nutrient agar containing acetate.