Theoretical survival curves for radiation damage in bacteria

Abstract It has been suggested that killing of bacteria by irradiation with ultraviolet light may occur when portions of opposite strands of the DNA molecule excised by the cell's own repair mechanism happen to overlap, so that the structural integrity of the molecule is lost. It has also been suggested that, in cells actively synthesizing DNA, lethality might result if the moving replication centre encounters the site of a damage that has not yet been repaired, or is actively under repair. In the present theoretical study, it is shown that using only these two concepts, one may construct a mathematical model which, for appropriate values of model parameters representing details of treatment and cell condition, will predict not only the usual exponential and “multi-hit” survival curves, but also various other observed types involving multiple shoulders, plateaus and inflections. In particular, it is here demonstrated that the common “inflected” survival curve can be predicted by considering the distribution through the replication cycle of cells in logarithmic growth, and that no appeal to a further heterogeneity of the population is necessary.