Plasmid-instability in acrA Mutants of Escherichia coli K12

SUMMARY: The effect of a mutation at acrA, which alters the bacterial membrane, on plasmid stability was studied. F-gal + residing in the mutant was remarkably unstable in the presence of acridine dyes or at high temperature (42°C) as compared with wild-type (acrA +) strains. Following suppression or back-mutation to acridine resistance, cells became capable of stably hosting the plasmid in the presence of acridine. Lipophilic substances, such as phenethyl alcohol and sodium dodecylsulphate, enhanced the curing-action of acridine in the F/acrA strain. Certain fatty acids promoted curing of the mutant bacteria in the absence of acridines. It is suggested that the stability of F-gal + may depend on some feature of the plasma membrane.