TABLE 2.

Level of mutations in DPA-less sleB spoVF spores exposed to various treatments

Treatment	Level of killing (%)	No. of colonies tested	No. of mutationsa			%b
			aux	spo	aux and spo
70°C, 30 min	85	416	0	1	0	0.2
H2O2, 20 min	94	416	1	0	0	0.2
Four freeze-dry cycles	95	432	8	20	1	6.7 (<0.2)
None	0	355	0	0	0	0

^aSpores of strain FB122 prepared on plates without DPA were treated in various ways, and survivors were tested for mutations to auxotrophy (aux) or asporogeny (spo) as described in Materials and Methods. One colony surviving freeze-drying was both auxotrophic and asporogenous (aux and spo). Spores treated with wet heat at an OD₆₀₀ of 2 and with hydrogen peroxide at an OD₆₀₀ of 1 were decoated prior to treatment and recovered by lysozyme germination in hypertonic medium. Samples subjected to no treatment or to freeze-drying were not decoated and were recovered by Ca²⁺-DPA treatment.

^bThis value is the percentage of mutants in the survivors and was calculated as: 100 × (the number of colonies with mutations/the total number of colonies tested). The value in parentheses is the percentage of mutations in DPA-replete FB122 spores given four cycles of freeze-drying.