Transfer and maintenance of IncP and IncW group plasmids into and between extra-slow-growing Bradyrhizobium japonicum strains

IncP group plasmid pRL180 was conjugally transferred from Agrobacterium tumefaciens LBA928 into extra-slow-growing (ESG) Bradyrhizobium japonicum strains and between ESG strains, RJ17W and RJ12S. pRL180 was integrated into the chromosome of RJ12S, RJ17W and RJ19FY. ESG strains efficiently transferred pRL180 into Escherichia coli at about a 3 × 10−5 frequency. IncW group plasmid pTY97 was transferred in intergeneric matings from E. coli into ESG strains at a high frequency of 2.5 × 10−3; between RJ17W and RJ12S transfer was about 5.6 × 10−4. pTY97 was maintained as an R′ plasmid in RJ12S. The R′ plasmid was resolved upon transfer into E. coli C where only pTY97 was autonomously replicated.