Effect of ozone on plasmid DNA of Escherichia coli in situ

The cell suspension of Escherichia coli HB101 harboring pBR322 plasmid DNA was exposed to ozone, and the damage of plasmid DNA in vivo and also cell survival were investigated. Closed circular plasmid DNA (ccDNA) converted to open circular DNA (ocDNA) by ozone treatment. The mechanism of the conversion seemed to be similar to that observed in vitro ozone treatment of plasmid DNA [Sawadaishi et al. (1985) Nucleic Acids Res. 13, 7183; idem. (1986) ibid. 14, 1159]. These findings indicate that ozone penetrates cell membrane and reacts with cytoplasmic substances. Therefore, chromosomal DNA may be one of targets of the ozone degradation, and its damage may be one of the factors responsible for the cell killing.