The relationship between survival and mutagenesis in Escherichia coli after fractionated ultraviolet irradiation.

The relationship between survival and mutagenesis in Escherichia coli after fractionated ultraviolet (UV) irradiation was studied. The cells were incubated either in buffer or nutrient media. Regardless of incubation conditions, greater survival is observed after fractionated irradiation than after acute irradiation. When the cells are incubated in buffer, UV mutagenesis decreases with an increase in the number of dose fractions. However, when the cells are cultivated in nutrient media, the increased survival (i.e., the enhanced capacity for repair) is coupled with the enhanced capacity for UV mutagenesis. We, therefore, assume that during incubation in nutrient media, fractionated irradiation leads to full and prolonged expression of all UV-inducible (SOS) genes, including those required for mutagenesis.