Measurement of growth and survival curves of microorganisms influenced by radiation

Growth curves in liquid peptone-glucose medium and survival curves of the Saccharomyces cerevisiae culture from variously irradiated inoculum were evaluated. Irradiation of yeast cells in solution physiological (salt) was performed with gamma-rays of (60)Co in Gammacell 220 or with UV-irradiation using ultraviolet lamps UVH 1016-6 and Photochemical reactors, Ltd, Sylvania for various time periods. Various dose rates of both types of radiation were used. The absorbed doses reached some hundreds Gy for both gamma and UV radiation. The growth curves were measured using the nephelometric data of yeast suspension in various time periods of growth. The results of repeated measurements showed that the slope of growth curves express relatively exactly the negative influence of irradiation when the standard and uniform method of evaluation was used. When the curves were fitted to the data points by the least-squares method, the average standard errors were found to be in the range from 0.6 to 0.8% and from 0.2 to 0.5% for gamma- and UV-irradiation, respectively. The negative effect of irradiation depended monotonously and non-linearly on the applied dose of irradiation. Quantitatively different effects were found in the case of gamma and UV irradiation.