Defining the requirements for the conjugative transfer of plasmid pRleVF39b.

strain VF39 contains a plasmid, pRleVF39b, which encodes a distinctive type of conjugation system (rhizobial type IVa) that is relatively widespread among rhizobial genomes. The cluster of genes encoding the transfer functions lacks orthologs to genes such as , and , but contains 15 conserved genes of unknown function. We determined the importance of these genes in conjugation by constructing marked and unmarked mutations in each gene, and established that six genes, now designated , played a significant role in plasmid transfer.

Counter-transcribed RNAs of Rhizobium leguminosarum repABC plasmids exert incompatibility effects only when highly expressed.

The six plasmids of Rhizobium leguminosarum VF39SM comprise nearly 35% of the bacterium's genome and are all repABC replicons. The repABC operons of the three largest plasmids of VF39SM were found to have strong incompatibility determinants in the non-protein coding regions. However, in all three repABC operons, the intergenic region between repB and repC was the strongest incompatibility factor; this intergenic region has been shown, for most repABC plasmids, to encode a counter-transcribed RNA (ctRNA) that regulates RepC abundance and therefore also rate of initiation of replication.

Genetic characterization of a novel rhizobial plasmid conjugation system in Rhizobium leguminosarum bv. viciae strain VF39SM.

Rhizobium leguminosarum strain VF39SM contains two plasmids that have previously been shown to be self-transmissible by conjugation. One of these plasmids, pRleVF39b, is shown in this study to carry a set of plasmid transfer genes that differs significantly from conjugation systems previously studied in the rhizobia but is similar to an uncharacterized set of genes found in R. leguminosarum bv.

Glycerol utilization by Rhizobium leguminosarum requires an ABC transporter and affects competition for nodulation.

Plasmid curing has shown that the ability to use glycerol as a carbon source is plasmid-encoded in Rhizobium leguminosarum. We isolated the locus responsible for glycerol utilization from plasmid pRleVF39c in R. leguminosarum bv.