Novel strains of nodulating Burkholderia have a role in nitrogen fixation with papilioniod herbaceous legumes adapted to acid infertile soils

We investigated the taxonomic position and symbiotic capabilities of two root-nodule bacterial strains
isolated from the South African herbaceous, papilionoid legume Rhynchosia ferulifolia. The 16S rRNA gene
sequence of the two strains was determined along with intragenic sequences of nodA and nifH, together
with their symbiotic capabilities when inoculated onto the papilionoid legumes R. ferulifolia, Rhynchosia
caribaea, Rhynchosia minima and Macroptilium atropurpureum (Siratro). Burkholderia phymatum STM815T,
Cupriavidus taiwanensis LMG 19424T and root-nodule bacteria isolated from R. minima and Rhynchosia
totta were included in the study. Root-nodule bacteria isolated from R. ferulifolia, WSM3937 and
WSM3930, belong to the genus Burkholderia and are most closely related to Burkholderia terricola (98.8%
similarity). The phylogenetic analysis of nodA and nifH revealed substantial similarity of the novel strains
with Burkholderia tuberum STM678T, a b-rhizobium also originated from South Africa, and only a distant
relationship with South American Mimosa-nodulating b-rhizobia. R. ferulifolia was effectively nodulated
only by Burkholderia sp. WSM3937 and WSM3930 and not by bradyrhizobia isolated from Rhynchosia
minima and Rhynchosia totta or STM815 and LMG 19924. Nodules induced by the novel strains were
determinate and hosted well organized symbiosomes within infected cells. In this study we describe
a new symbiotic N-fixing relationship between Burkholderia sp. and the South African legume R. ferulifolia.
This is the first report of N-fixation between b-rhizobia and an herbaceous, papilionoid legume
from which the strains were originally isolated. The level of N-fixation in this symbiosis approached that
achieved by effectively nodulated Medicago sativa and suggests that the b-rhizobia may have a role in Nfixation
in agricultural systems.