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

Publisher Website
Google Scholar
Abstract
The effect of cell concentration on sensitivity to X-rays and the relation of this effect to endogenous respiration were investigated with Escherichia coli, Pseudomonas fluorescens, Rhodopseudomonas speroides, Azotobacter agile, and Saccharomyces cerevisiae (haploid and diploid). Washed cells suspended in buffer were irradiated with 250 kvcp X-rays and survival determined by macrocolony counts. Only S cerevisiae (haploid) had the same sensitivity at all concentrations (2 x 102 to 2 x 109 cells/ml. That of the other strains was constant at low concentrations (2 x 102 to 2 x 107 cells/ml) but above a critical value the sensitivity decreased. Critical cell concentration depended on the strain and varied from 2 x 10 cells/ml with S cerevisiae (diploid to 2 x 1010 cells/ml with E coli. It was concluded that O2 depletion resulting from endogenous respiration caused the decrease in sensitivity, for the following reasons: (1) Shaking the suspension in air or O2 during irradiation eliminated the concentration effect. (2) The critical cell concentration and the Q02 (cell) of the various strains are inversely related.