General method for the identification of plasmid species in fast-growing soil microorganisms.

Using a horizontal gel electrophoresis method, we demonstrated reproducibly the presence of indigenous plasmids in different Rhizobium, Agrobacterium, and Pseudomonas strains. The method yields a large amount of plasmid DNA and is sensitive in detecting megaplasmids with molecular weights higher than 5 x 10. In two Rhizobium meliloti strains, a megaplasmid other than the low-mobility plasmid already known was detected.