Plasmid Interactions in Rhizobium; Incompatibility Between Symbiotic Plasmids

Plasmid profiles were determined for twenty four strains of R. trifolii. All the strains harboured at least three plasmids and as many as eight were present in some strains. Southern hybridisation with cloned R. meliloti nif genes was used to identify indigenous Nif plasmids. Each strain carried a single Nif plasmid and these plasmids varied in size from 112 Mdal to at least 300 Mdal.