Production of single- and double-strand breaks in plasmid DNA by ozone

Agarose gel electrophoresis and electron microscopy were used to determine the type of lesions produced in DNA by ozone. This strong oxidizing agent was found to relax, linearize, then degrade native plasmid (pAT153) DNA molecules in solution. Ozone, like ionizing radiation, thus produced DNA breakage. To ascertain this point, wild-type and radiosensitive strains of Escherichia coli were transfected with control or ozonated plasmid DNA, and the host cells were selected for antibiotic resistance. A significant reduction in the transforming ability of pAT153 was observed following ozonation. Mutants deficient in the repair of DNA single-strand breaks yielded less ampicillin- or tetracycline-resistant clones than repair-proficient strains. In E. coli, the same gene products are probably involved in the repair of both radiation- and ozone-induced DNA breaks.