Loss of transforming activity of plasmid DNA (pBR322) in E. coli caused by singlet molecular oxygen

Plasmid DNA pBR322 in aqueous solution was exposed to singlet molecular oxygen (1O2) generated by microwave discharge. DNA damage was detected as loss of transforming activity of pBR322 in E. coli (CMK) dependent on the time of exposure. DNA damage was effectively decreased by singlet-oxygen quenchers such as sodium azide and methionine. Replacement of water in the incubation buffer by D2O led to an increase in DNA damage. 9,10-Bis(2-ethylene)anthracene disulfate was used as a chemical trap for 1O2 quantitation by HPLC analysis of the endoperoxide formed.