Transfer of R1drd19 plasmid from Escherichia coli J53 to Rhizobium trifolii by conjugation.

Rldrd19 plasmid was transferred by conjugation from Escherichia coli J53 to Rhizobium trifolii T24, T26 and 24XSM strains with frequency 10(-3) to 10(-5). The R. trifolii exconjugants carrying Rldrd19 were in turn able to transfer the R factor by conjugation to other R. trifolii strains. Rldrd19 was maintained stably in R. trifolii. R. trifolii 24XSM, T26 and 14M were also found to harbor an endogenous plasmid (molecular weight 5.5 megadaltons) with undetermined as yet properties. Ridrd19 could be stably maintained in the same cell together with the endogenous plasmid.