Selection of strains cured of theRhizobium leguminosarumSym-plasmid pRL1JI by using small bacteriocin

Fast growing Rhizobia are usually insensitive to a low Mr (small) bacteriocin. Introduction of the Sym-plasmid pRL1JI into these strains results in sensitivity towards small bacteriocin. Of such strains, small bacteriocin insensitive mutants (Sbs−) were selected. A high percentage of these Sbs− mutants appeared to be cured of pRL1JI. This selection of cured strains was feasible as well for the wild-type plasmid pRL1JI, as for a variety of transposon marked derivatives in several bacterial backgrounds.