Rhizobia are soil bacteria able to establish a nitrogen-fixing symbiosis with leguminous plants. Most of them belong to the Alphaproteobacteria based on the sequences of the gene coding for 16S rRNA [1,2]. However, over the last 15 years studies have reported the presence of legume-nodulating bacteria in the genera Burkholderia and Cupriavidus (Burkholderiaceae) in the Betaproteobacteria [3-21]...