THE EFFECT OF X-RAYS ON THE SURVIVAL OF BACTERIA AND YEAST

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Abstract
Dose-survival curves were determined for 6 microorganisms irradiated in physiological buffer under standardized conditions with 250 kvcp X-rays. Survival was judged by macrocolony formation on yeast or yeast-glucose agar. Survival was an exponential function of dose in the case of P. fluorescens, R. spheroides, and S. cerevisiae (haploid) for which LD50 values of 0.95, 1.8 and 1.9 kr, respectively, were found. Data for E. coli, W-1485, were fitted by a complex function which was the sum of 2 exponential curves. It appeared that 66% of the cells (sensitives) had an LD50 of 1.2 kr and 34% (resistants) had an LD50 of 3.5 kr. Subculturing either the resistant or a mixture of resistant and sensitive cells gave rise to the original type of mixed population. The results for A. agile and S. cerevisiae (diploid) were fitted by multihit curves. The LD50''s were 8.5 and 24 kr, respectively.

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