Studies with RP1 deletion plasmids: Incompatibility properties, plasmid curing and the spontaneous loss of resistance.

Four deletion plasmids, pHH301, pHH302, pHH303 and pHH401, obtained from RP1 DNA-transformed bacterial clones, were shown to be incompatible with three Ρ plasmids in Escherichia coli K12 strains. Kinetic experiments and colony tests were used to verify the position of these R plasmids. Pseudomonas aeruginosa and Ε. coli strains, harbouring deletion plasmids, could be cured by using two mutagens, acriflavine and mitomycin C, which affect a percentage of the cell population. The deletion plasmid-positive strains could also be induced at an elevated temperature to spontaneously loose their plasmids.