Rhizobium zhangyense sp. nov., a Novel Species Isolated from a Root Nodule of Hedysarum multijugum in Northwestern China

A Gram-negative motile strain, designated a22-2T, was isolated from a nodule of Hedysarum multijugum grown in sandy soil in Northwest China. Phylogenetic analysis of the 16S rRNA gene sequence showed that the strain was closely related to Rhizobium tumefaciens (98.37%), R. arsenijevicii (98.37%), R. radiobacter (98.22%), R. nepotum (98.1%) and R. vaccinii (98.17%). Phylogenetic analysis based on the protein-coding genes recA, glnA and atpD suggested that the strain a22-2T represents a distinctly delineated species of the genus Rhizobium, with sequence similarities less than 78.8% (recA), 89.4% (glnA) and 89.2% (atpD) with the defined reference species of Rhizobiaceae. The DNA–DNA relatedness with the most closely related reference strains was below 48%. The genome sequence of the isolate was determined. The average nucleotide identity (ANI) between the a22-2T genome and the most closely related type strain, Rhizobium selenitireducens ATCC BAA-1503, was 78.5%, and genomic phylogeny based on at least 100 core genes supported that strain a22-2T was a novel branch within the Rhizobium cluster. Its G+C content was 61.74%. The strain a22-2T could grow at temperatures between 20 and 40 °C (optimum, 28 °C) and at pH between 5.0 and 10.0 (optimum, pH 6.0–7.0). The cells contained ubiquinone Q-10 as the sole respiratory quinone and had 18:1 ω7c (43.8%) as the major cellular fatty acid. 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). Note: The genome record is automatically labelled as ‘Agrobacterium sp.’ by NCBI based on sequence similarity; in the present polyphasic study, strain a22-2T is assigned to the genus Rhizobium as discussed below.