Genetic transformation of Rhizobium leguminosarum by plasmid DNA

We demonstrated the genetic transformation of Rhizobium leguminosarum by R68.45 plasmid DNA by freezing and thawing cell suspensions in the presence of R68.45 plasmid DNA and 20 mM MgCl2. Clones resistant to kanamycin and tetracycline were recovered at a frequency of 10(-8) per recipient cell. No colonies that were doubly drug resistant were recovered in parallel control experiments.