Bradyrhizobium ontarionense sp. nov. isolated from Aeschynomene indica (Indian jointvetch) harbours photosynthesis, nitrogen fixation and nitrous oxide reductase genes.

Abstract

Bacterial strain A19T was previously isolated from a root-nodule of Aeschynomene indica (Indian jointvetch) and assigned to a new lineage in the genus Bradyrhizobium. Here data are presented for the detailed phylogenomic and taxonomic characterisation of strain A19T. Phylogenetic analysis of whole genome sequences as well as 51 concatenated core gene sequences placed strain A19T in a highly supported lineage that was distinct from described Bradyrhizobium species; B. oligotrophicum, a symbiont of A. indica, was the most closely related species. The digital DNA-DNA hybridization and average nucleotide identity values for strain A19T in pair-wise comparisons with close relatives were far lower than the respective threshold values of 70% and ~96% for definition of species boundaries. The complete genome of strain A19T consists of a single 8.44 Mbp chromosome (DNA G+C content, 64.9 mol%) and contains a photosynthesis gene cluster, nitrogen-fixation genes and genes encoding a complete denitrifying enzyme system including nitrous oxide reductase. Nodulation and type III secretion system genes, needed for nodulation by most rhizobia, were not detected in the genome of A19T. Data for multiple phenotypic tests complemented the sequence-based analyses. Strain A19T elicits nitrogen-fixing nodules on stems and roots of A. indica plants but not on soybeans or Macroptilium atropurpureum. Based on the data presented, a new species named Bradyrhizobium ontarionense sp. nov. is proposed with strain A19T (= LMG 32638T = HAMBI 3761T ) as the type strain.