Rhizobium acidisoli sp. nov., isolated from root nodules of Phaseolus vulgaris in acid soils

Two Gram-negative, aerobic, non-motile, rod-shaped bacterial strains, FH13^Tand FH23, representing a novel group of Rhizobium isolated from root nodules of Phaseolus vulgaris in Mexico, were studied by a polyphasic analysis. Phylogeny of 16S rRNA gene sequences revealed them to be members of the genus Rhizobium related most closely to ‘Rhizobium anhuiense’ CCBAU 23252 (99.7% similarity), Rhizobium leguminosarum USDA 2370^T(98.6%), and Rhizobium sophorae CCBAU 03386T and others (≤98.3%). In sequence analyses of the housekeeping genes recA, glnII and atpD, both strains formed a subclade distinct from all defined species of the genus Rhizobium at sequence similarities of 82.3-94.0%, demonstrating that they represented a novel genomic species in the genus Rhizobium. Mean levels of DNA-DNA relatedness between the reference strain FH13T and the type strains of related species varied between 13.0±2.0 and 52.1±1.2%. The DNA G+C content of strain FH13T was 63.5 mol% (Tm). The major cellular fatty acids were 16: 0, 17: 0 anteiso, 18: 0, summed feature 2 (12: 0 aldehyde/unknown 10.928) and summed feature 8 (18: ω7c). The fatty acid 17: ω5c was unique for this strain. Some phenotypic features, such as failure to utilize adonitol, L-arabinose, D-fructose and D-fucose, and ability to utilize D-galacturonic acid and itaconic acid as carbon source, could also be used to distinguish strain FH13T from the type strains of related species. Based upon these results, a novel species, Rhizobium acidisoli sp. nov., is proposed, with FH13^T(=CCBAU 101094^T=HAMBI 3626T=LMG 28672^T) as the type strain.