Influence of plasma-generated reactive species on the plasmid DNA structure and plasmid-mediated transformation of Escherichia coli cells

The influence of plasma-generated reactive species on the conformation of plasmid DNA (pDNA) and the transformation efficiency of Escherichia coli cells were studied. An atmospheric-pressure plasma jet (APPJ) was used to generate reactive oxygen and nitrogen species (RONS) in an aqueous solution. When E. coli cells were transformed, the transformation efficiency of E. coli with the APPJ-treated plasmid was lower than with the APPJ-untreated plasmid. Transformation efficiency was reduced due to structural modification and degradation of the pDNA by the APPJ. Plasma treatment caused structural modification of the plasmid from the supercoiled form to the linear form, and also decreased the amount of plasmid by degrading the deoxyribonucleic acid (DNA) structure accompanied by disruption of nucleobases and DNA strand breakage. The formation of linear plasmid from supercoiled plasmid by the APPJ treatment was verified through electrophoretic analysis of the NdeI restriction enzyme-cut supercoiled plasmid. The structural modification and/or decrease in the amount of pDNA are attributed to the RONS from the plasma itself and to those derived from the interaction of plasma radicals with the aqueous solution. The effect of plasma treatment on the transformation efficiency of E. coli cells was more pronounced with the linear plasmid than with the supercoiled plasmid, indicating that the linear plasmid is more vulnerable to RONS. Overall, these results revealed that plasma-generated RONS can modify the structural and optical properties of bacterial pDNA, thus affecting its biological function.