Differences in radiation resistance of 14 strains of Clostridium botulinum spores could be correlated by computer analysis with differences in the lug or shoulder portion (L) of their respective radiation sur vival curves. The exponential decline portions (E) of the survival curves were nearly identical for all 14 strains. Autoradiographic, and diphenylamine assays indicated that strains 33A, 62A and 51B contained 1, 2 and 2 genomes per spore, respectively. However, no relationship could be detected between number of genomes and radiation resistance of the spores. Alkaline sucrose gradient sedimentation of sH-DNA indicated that L was characterized by production of D N A single-strand breaks (SSB). Radiation resistant strain 33A rejoined 50-90% of the initial SSB during irradiation or shortly thereafter, i.e. while the spores were still in the cryptobiotic dormant state. Rejoining of SSB seems to be due to high DNA-ligase activity in strain 33A. On the other hand, the radiation sensitive strain 51B showed no shoulder (L) and very little or no SSB rejoining. The exponential decline portion (E) seems to be associated with those lesions which cannot be repaired during irradiation or germination. I t is thought that repair of these lesions is attempted after germination and initiation of metabolism and may involve DNA excision-resynthesis, and recombination. These repair mechanisms are errorprone and thus f r e quently result in cell death characteristic of the E portion o f the survival curve. Journal o f Food Processing and Preservation 2 (1978) 315-337. All Rights Reserved @Copyright 1979 by Food
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