Rhizobium chutanense sp. nov., isolated from root nodules of Phaseolus vulgaris in China

Two Gram-stain-negative, rod-shaped bacterial strains (C5(T) and C16), isolated from root nodules of Phaseolus vulgaris L. in Jiangxi Province, PR China, were characterized by using a polyphasic taxonomical approach. The phylogenetic analysis of the 16S rRNA gene and three concatenated housekeeping genes (recA-glnll-atpD) revealed that C5(T) and C16 were members of the genus Rhizobium, yet were distinct from known species. The case for strain C5(T) representing a novel species was supported by genomic results. Pairwise digital DNA-DNA hybridization and average nucleotide identity values were much lower than the proposed and generally accepted species boundaries. The genome-based phylogenetic tree reconstructed by using the up-to-date bacterial core gene set consisting of 92 genes showed that the strains formed a monophyletic branch, further supporting this result. The symbiotic genes of nodC and nifH were identified in both strains; each could nodulate Phaseolus vulgaris and Glycine max but not Leucaena leucocephala, Pisum sativum or Medicago sativa plants. Major cellular fatty acids of C5(T) were summed feature 8 (C-18:(1) omega 7c/(C)(18)(:1) omega 6c; 58.8 %), C-18:(1) omega 7c 11-methyl (14.2 %) and C-18(:0) (8.1 %). The DNA G+C content of C5(T) was 61.4 mol%. Based on these genomic, chemotaxonomic and phenotypic characteristics, we propose a novel species: Rhizobium chutanense sp. nov. The type strain is C5(T) (=CCTCC AB 2018143(T) =LMG 30777(T)).