Burkholderia and Cupriavidus spp. are the preferred symbionts of Mimosa spp. in Southern China

Rhizobia were isolated from invasive Mimosa spp. (M.similar to diplotricha and M.similar to pudica) in Dehong district of the province of Yunnan in subtropical southern China. Almost all of the 98 isolates were beta-rhizobia in the genera Burkholderia and Cupriavidus. These strains were analysed for their distribution characteristics together with strains from a previous study from Sishuangbanna. The proportion of nodules containing each beta-rhizobial genus varied between Mimosa species, with Cupriavidus being predominant in M.similar to diplotricha nodules (63.3% compared to 36.7% occupation with Burkholderia), but with M.similar to pudica showing a slight preference for Burkholderia over Cupriavidus, with them occupying 56.5% and 43.5% of nodules, respectively. The symbiosis-essential genes nodA and nifH were present in all the Burkholderia and Cupriavidus strains tested, and their phylogenies indicated that these Mimosa symbionts share symbiotic genes with native South American rhizobia. The evolutionary discrepancies among 16S rRNA genes, nodA and nifH of Mimosa spp. symbionts, suggests that the nod and nif genes of beta-rhizobia evolved independently.