HIGH-RESISTANCE OF SOME OLIGOTROPHIC BACTERIA TO IONIZING-RADIATION

The resistance of seven cultures of eutrophic and oligotrophic bacteri a to gamma radiation (at doses up to 360 Gy) was investigated. The bac teria under study were divided into three groups according to their su rvival ability after irradiation. Methylobacterium organophilum and '' Pedodermatophilus halotolerans'' (LD50 = 270 Gy) were highly tolerant. By their tolerance, these organisms approached Deinococcus radioduran s. Aquatic ring-shaped (toroidal) bacteria Flectobacillus major and '' Arcocella aquatica'' (LD50 = 173 and 210 Gy, respectively) were modera tely tolerant. Eutrophic Pseudomonas fluorescens and Escherichia coli (LD50 = 43 and 38 Gy, respectively) were the most sensitive. X-ray mic roanalysis showed that in tolerant bacteria the intracellular content of potassium increased and the content of calcium decreased after irra diation. No changes in the element composition of the eutrophic bacter ium E. coli were detected. Possible mechanisms of the resistance of ol igotrophic bacteria to gamma radiation are discussed.