Modification of radiation resistance of Bacillus spores by water

Spores of Bacillus subtilis, containing plasmid (B. subtilis ED 366(pUB110, Trp C2 thr 5)), were prepared free of additives and the effect of water on their radiation sensitivity under aerobic condition was investigated. The moisture content of spores was controlled by (i) drying over CaCl2 (Aw = 0. 0), (ii) equilibrating with the vapor of saturated aqueous NaCl solution (A w = 0.7), or (iii) suspending in water (Aw = 1.0). The resistance of spores to radiation increased with increasing moisture content. The analysis of s pore DNA by agarose gel electrophoresis showed that DNA damage (strand brea ks) decreased with increasing water activity of the spores, a finding conco mitant with the observed survival rates. (C) 2000 Elsevier Science Ltd. All rights reserved.