Figure 6.

Spontaneous and H₂O₂‐ or 4‐NQO‐ induced mutation frequencies of outgrown spores of different B. subtilis strains. Dormant spores of different strains were heat shocked and germinated, and 15 min after the initiation of germination cultures were left untreated (a), made 0.5 mmol L^‐1 in H₂O₂ (b) or 2 μmol L^‐1 in 4‐NQO (c). After 180 min of incubation the Rif^r mutation frequency in the cultures was determined as described in Materials ad Methods. Each bar represents the mean of data collected from three independent experiments with different lots of spores, and error bars represent the standard deviation. **, p < .01 (by the Mann‐Whitney U)