Abstract:
The root-nodule bacteria of legumes endemic to the Cape Floristic Region are largely understudied, even though recent
reports suggest the occurrence of nodulating Burkholderia species unique to the region. In this study, we considered the
diversity and evolution of nodulating Burkholderia associated with the endemic papilionoid tribes Hypocalypteae and
Podalyrieae. We identified distinct groups from verified rhizobial isolates by phylogenetic analyses of the 16S rRNA and recA
housekeeping gene regions. In order to gain insight into the evolution of the nodulation and diazotrophy of these rhizobia
we analysed the genes encoding NifH and NodA. The majority of these 69 isolates appeared to be unique, potentially
representing novel species. Evidence of horizontal gene transfer determining the symbiotic ability of these Cape Floristic
Region isolates indicate evolutionary origins distinct from those of nodulating Burkholderia from elsewhere in the world.
Overall, our findings suggest that Burkholderia species associated with fynbos legumes are highly diverse and their
symbiotic abilities have unique ancestries. It is therefore possible that the evolution of these bacteria is closely linked to the
diversification and establishment of legumes characteristic of the Cape Floristic Region.
