SOME NUTRITIONAL ASPECTS OF BACTERIAL RECOVERY FROM IONIZING RADIATIONS

Abstract

Survival of X-or gamma-irradiated Escherichia coli B/r is dependent on the post-irradiation incubation temperature and plating medium as well as the medium from which the cells are harvested prior to irradiation. Cells grown in nutrient broth require after irradiation some nutritional factors contained in complex extracts of yeast or tissues. Nonirradiated cells show no such medium effect. The effect cannot by explained on the basis of satisfying the requirements of stable, radiation-induced auxotrophs. A chemically defined medium was found which will substitute for natural materials in increasing survival of such cells. The required components of this chemically defined medium are resolved to glutamic acid, guanine and uracil plus inorganic salts and glucose. Reduced incubation temperatures are conducive to recovery in such cells. The optimal post-irradiation incubation temperature for this strain on all media studied is 18[degree]C. The temperature and medium effect are additive in promoting recovery. An investigation of the effect of the medium on which cells are cultured before irradiation indicates that only cells harvested from a medium rich in amino acids show the requirements following irradiation. The data indicate that recovery in this strain may involve new enzyme synthesis.