Genomic Diversity and Evolution of Rhizobia

The rhizosphere is colonized by a large variety of bacterial community and, thanks to the attractive chemical composition of the root exudates, some of them can penetrate inside the tissues and colonize the plant. The rhizobia are bacteria able to establish a mutualistic nitrogen-fixing endosymbiosis with specific legumes forming root nodules on the host plant. They are spread throughout the α- and β-subdivision (classes) of Proteobacteria, which often are united by the multipartite genome structure, consisting in a chromosome and additional plasmid, acquired later, and enriched in dispensable genes that play a key role in the determination of bacterium fitness in different ecological niches. Presently, Sinorhizobium meliloti is the main representative of α-proteobacteria for studies on multipartite genome evolution and environmental adaptation, but Burkholderia and Cupriavirus may represent a new frontier for the β-rhizobia knowledge.