Radiation survival of bacterial spores in neutral and alkaline ice

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Abstract
The effect of pH values ranging from 6 to 12 on spores of Clostridium botulinum 33A exposed to 0.6–0.9 Mrad Co-60 resulted in a complex wavelike pattern of survival which was influenced by pH, temperature, and dose of radiation. Within the experimental pH range three typical survival patterns could be recognized. Pattern A (at −190 °C) showed peaks of high survival at pH 7 and 9.5 and troughs of low survival at pH 8 and 10–11. Pattern B (at −50 °C) showed a single broad peak of high survival at pH 8.5 to 9 and troughs of low survival at pH 7 and 10. Pattern C (at 0 °C) showed peaks of high survival at pH 7.5 and 10 and troughs of low survival at pH 6,9, and 11. Between the temperatures showing typical A, B, and C patterns the survival profiles indicated various degrees of transition from A to B and from B to C.These results can be tentatively explained in terms of indirect effects, viz. maximum activity of radicals such as ∙OH in the troughs and extinction of ∙OH by reaction with eaq− or H∙ at the peaks.

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