Rhizobium helianthi sp. nov., isolated from the rhizosphere of sunflower

A Gram-stain-negative, non-spore-forming, rod-shaped and aerobic bacterium, designated Xi19^T, was isolated from a soil sample collected from the rhizosphere of sunflower (Helianthus annuus) in Wuyuan county of Inner Mongolia, China and was characterized taxonomically by using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the novel isolate was related to species of the genus Rhizobium, sharing the greatest 16S rRNA gene sequence similarity with Rhizobium rhizoryzae J3-AN59^T (98.4 %), followed by Rhizobium pseudoryzae J3-A127^T (97.4 %). There were low similarities (<91 %) between the atpD, recA and glnII gene sequences of the novel strain and those of members of the genus Rhizobium. DNA-DNA hybridization values between strain Xi19^T and the most related strain Rhizobium rhizoryzae J3-AN59^T were low. The major cellular fatty acids of strain Xi19^T were C₁₆ :₀, summed feature 8 (C₁₈ :₁ω7c and/or C₁₈ :₁ω6c) and C₁₉:₀ cyclo ω8c. Q-10 was identified as the predominant ubiquinone and the major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and phosphatidylcholine. The DNA G+C content of strain Xi19^T was 60.2 mol%. On the basis of physiological and biochemical characteristics, coupled with genotypic data obtained in this work, strain Xi19^T represents a novel species of the genus Rhizobium, for which the name Rhizobium helianthi is proposed. The type strain is Xi19^T (=CGMCC 1.12192^T=KCTC 23879^T).