DNA strand scission in E.coli by electronically excited state molecules generated by enzymatic systems

$\text{E.}\text{coli}$ containing pAT 153 plasmid undergoes strand scission when exposed to the indole-3-acetic acid/peroxidase/D₂ system. Neither the initial components of this reaction nor the final stable products are responsible for this effect. Indole-3-aldehyde in its triplet state and singlet oxygen have been recently identified in this system. That singlet oxygen is one of the species acting on the plasmid in $\text{E.}\text{coli}$ cells was suggested by protective effect of histidine and guanosine which are singlet oxygen quenchers. Similar effect on plasmid with malonaldehyde/peroxidase/O₂ system was observed, which is an excellent singlet oxygen generator. This is the first report of a biological system where it is possible to detect a DNA scission in the intact cell by a bioenergized process. This presumably is related to spontaneous mutagenesis.