Phylogenetic relationships and diversity of β-rhizobia associated with Mimosa species grown in Sishuangbanna, China

In order to investigate the genetic diversity of rhizobia associated with various exotic and invasive species in tropical mainland China, 116 bacterial isolates were obtained from Mimosa root nodules collected from Sishuangbanna and Yuanjiang districts of Yunnan province. Isolated rhizobia were characterized by RFLP analysis of 16S rRNA genes, SDS-PAGE of whole-cell proteins and BOX-PCR. Most of the isolated strains were identified as beta-rhizobia belonging to diverse populations of Burkholderia and Cupriavidus, and the phylogenetic relationships of their 16S rRNA gene sequences showed that they were closely related to one of four beta-rhizobia species: Burkholderia phymatum, B. mimosarum, B. caribensis or Cupriavidus taiwanensis. Additionally, among the 116 isolates, 53 different whole-cell SDS-PAGE profiles and 30 distinct BOX-PCR genotypic patterns were detected, which demonstrated the genetic and phenotypic diversity found within these Burkholderia and Cupriavidus strains. To the best of our knowledge, this is the first report that beta-rhizobia are extant and possibly widespread on the Chinese mainland and nodulate easily with Mimosa plants. We also find it especially interesting that this appears to be the first report from mainland China of Cupriavidus symbionts of Mimosa. These records enrich our knowledge and understanding of the geographical distribution and diversity of these bacteria.