Transfer of plasmid pRD1 from Escherichia coli to Azospirillum brasilense

Data are presented which indicate that plasmid pRD1 can be transferred from Escherichia coli to strains of Azospirillum brasilense with a frequency of about 10(-7). The reverse was also possible; in this case the frequency of transfer appeared to be much higher, about 5 x 10(-1). Transfer of the plasmid was also obtained between strains of A. brasilense; in this cross the transfer frequency was very high (about 10(-1)). Moreover the pRD1 plasmid seems very stable in A. brasilense cells.