Molecular characterization of novel Bradyrhizobium strains nodulating Eriosema chinense and Flemingia vestita, important unexplored native legumes of the sub-Himalayan region (Meghalaya) of India.

Root nodule bacterial strains were isolated from the little-studied legumes Eriosema chinense and Flemingia vestita (both in tribe Phaseoleae, Papilionoideae) growing in acidic soil of the sub-Himalayan region of the Indian state of Meghalaya (ME), and were identified as novel strains of Bradyrhizobium on the basis of their 16S rRNA sequences. Seven isolates selected on the basis of phenotypic characters and assessment of ARDRA and RAPD patterns were subjected to multilocus sequence analysis (MLSA) using four protein-coding housekeeping genes (glnII, recA, dnaK and gyrB). On the basis of 16S rRNA phylogeny as well as a concatenated MLSA five strains clustered in a single separate clade and two strains formed novel lineages within the genus Bradyrhizobium. The phylogenies of the symbiotic genes (nodA and nifH) were in agreement with the core gene phylogenies. It appears that genetically diverse Bradyrhizobium strains are the principal microsymbionts of these two important native legumes. The novel genotypes of Bradyrhizobium strains isolated in the present study efficiently nodulate the Phaseoloid crop species Glycine max, Vigna radiata and Vigna umbellata. These strains are genetically different from strains of Bradyrhizobium isolated earlier from a different agro-climatic region of India suggesting that the acidic nature of the soil, high precipitation and other local environmental conditions are responsible for the evolution of these newly-described Bradyrhizobium strains. In global terms, the sub-Himalayan region of India is geographically and climatically distinct and the Bradyrhizobium strains nodulating its legumes appear to be novel and potentially unique to the region.

Multi locus sequence analysis and symbiotic characterization of novel Ensifer strains nodulating Tephrosia spp. in the Indian Thar Desert.

Phylogenetically diverse Ensifer strains associated with five species of Tephrosia growing in alkaline soils of semi-arid regions of the Thar Desert were characterized using multi locus sequence analysis. Based on 16S rRNA and four protein-coding housekeeping gene (recA, atpD, glnII and dnaK) sequences, the Tephrosia-Ensifer strains were genetically different from the type strains of Ensifer saheli, Ensifer kostiensis, Ensifer terangae (African origin) and Ensifer psoraleae (Asiatic origin). One strain, Ensifer sp. TL4, showed maximum similarity (99%) to Ensifer adhaerens LMG 20216T and formed a separate lineage close to it. Phylogenetic incongruence between sym and housekeeping genes was observed. The monophyletic origin of symbiotic genes from Asia in the Tephrosia-Ensifer strains from the Thar Desert suggests that they might have been acquired from a common ancestor and horizontally transferred. These novel strains are promiscuous, cross-nodulating some papilionoid crop species, mimosoid trees and the caesalpinioid Chamaecrista pumila. This study improves understanding of the distribution of Ensifer in unexplored and threatened alkaline arid regions of the Thar Desert and how this relates to other similar regions in the world.