Rhizobium zhangyense sp. nov., a novel species isolated from a root nodule of Hedysarum multijugum in China

Abstract

Abstract Purpose Rhizobia play an important ecological and agricultural role in the N2 cycle between atmosphere and biosphere on the earth. The taxonomy of rhizobia is in a state of flux due to discovery of many novel species, which has led to numbers of revisions in the species description. Results A Gram-stain-negative mobile strain, designated as a22-2T, was isolated from a nodule of Hedysarum multijugum grown in Northwest China. Phylogenetic analysis of 16S rRNA gene sequence, recA, glnA and atpD showed that the strain was closely related to genus Rhizobium with sequence similarities less than 98.4% (16S rRNA), 85.3% (recA), 90.9% (glnA) and 54.2% (atpD). The strain a22-2T could grow at temperatures between 20-40°C (optimum, 28°C) and at pH between 5.0-10.0 (optimum, pH 7.0). The cells contained ubiquinone Q-10 as the sole respiratory quinone and had 18:1 ω7c (43.8%) as the major cellular fatty acid. The DNA relatedness with the most closely related reference strains was below 48%. Based on the phenotypic, chemotaxonomic and phylogenetic properties, the strain a22-2T represents a novel species of the genus Rhizobium, for which the name Rhizobium zhangyense sp. nov. is proposed. The type strain of Rhizobium zhangyense sp. nov. is a22-2T (= CGMCC 1.15517T = NBRC 112336T). The genome sequence of the isolate was determined. It’s G+C content was 61.74%, and the 85% average nucleotide identity of the type strain genome to its best neighbour with a completely sequenced genome (Rhizobium selenitireducens ATCC BAA-1503) indicated low genomic relatedness.