Radiation survival of bacterial spores in neutral and acid ice

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Abstract
Spores of C. botulinum 33A were irradiated at pH 2, 3, 4, 5, 6, and 7 to 0.6, 0.7, and 0.9 Mrad cobalt-60. Temperatures were controlled at −196 °C to 0 °C in distinct intervals. The survival data presented a complex wave-like pattern which appeared to be influenced by pH, temperature, and dose of radiation. Three typical survival patterns could be recognized. Pattern A (at −190 °C) showed peaks of high survival at pH 4 and 7 and low survival at pH 2 and 6. Pattern B (at −50, −40, and −30 °C) showed peaks of high survival at pH 3 and 6 and low survival at pH 2, 4–5, and 7.0. Pattern C (at 0 °C) was similar to pattern A but had generally higher peaks and deeper troughs. Between the temperatures showing typical A, B, and C patterns, the survival profiles indicated various degrees of transition from A to B or from B to C.The effect of pH appears to be related to its influence on yield of radicals in water such as, for example, ∙OH, which may result in highly lethal conditions within the region of low spore survival, and extinction of ∙OH by reaction with H∙ at the peaks of spore survival.

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