Two-step method for curing Escherichia coli of ColE1-derived plasmids

To cure Escherichia coli for plasmids derived from the ColE1 replicon advantage is taken of the fact that maintenance of this replicon requires a wild-type allele of polA, encoding DNA polymerase I. Curing is achieved by cotransduction of a mutant polA allele with metE::Tn10, fadAB::Tn10 or other transposon insertions near polA. Reciprocal transduction to Met+ Pol+ or to Fad+ Pol+ ensures reestablishment of the original genotype except for loss of the plasmid. A set of useful bacterial strains is provided.