Conservation of Plasmid-Encoded Traits among Bean-Nodulating Rhizobium Species

Rhizobium etli type strain CFN42 contains six plasmids. We analyzed the distribution of genetic markers from some of these plasmids in bean-nodulating strains belonging to different species ( Rhizobium etli , Rhizobium gallicum , Rhizobium giardinii , Rhizobium leguminosarum , and Sinorhizobium fredii ). Our results indicate that independent of geographic origin, R. etli strains usually share not only the pSym plasmid but also other plasmids containing symbiosis-related genes, with a similar organization. In contrast, strains belonging to other bean-nodulating species seem to have acquired only the pSym plasmid from R. etli .