Bradyrhizobium hardenbergiae sp. nov., isolated from Hardenbergia violacea in Australia, represents a novel basal lineage of the B. elkanii supergroup

Abstract

Bradyrhizobia are widespread across the Australian continent, where they are essential to Australian ecosystems by helping legumes to compensate nutrient deficiencies and low fertility of Australian soils. Among the Bradyrhizobium genospecies identified during a survey of Australian native rhizobia communities in 1994-1995, genospecies L appeared to be only distantly related to any Bradyrhizobium lineages known at the time. We take advantage of the recent sequencing of the genome of strain BDV5419, the original strain corresponding to Bradyrhizobium genospecies L, to re-assess this lineage taxonomic status. We characterized further strain BDV5419 based on morpho-physiological traits and determined its phylogenetic relationships with the type strains of the 88 currently known Bradyrhizobium species based on sequence comparisons of SSU rRNA genes and complete genomes. The digital DNA-DNA hybridization relatedness with any type strain was less than 33% and both SSU rRNA gene and genome phylogenies confirmed that this strain does not belong to any formerly described species within the Bradyrhizobium genus. Whereas its position within the lineage encompassing the B. elkanii and B. jicamae supergroups is unresolved in the SSU rDNA phylogeny, strain BDV5419 appears to be one of most basal lineages of the B. elkanii supergroup in the genome comparison. All data thus support the description of the novel species Bradyrhizobium hardenbergiae sp. nov. which type strain is BDV5419T (= CFBP 9111T = LMG 32897T), isolated from a nodule of Hardenbergia violaceae in Black Mountain Nature Reserve, in Canberra, ACT, Australia.