Ciceribacter azotifigens sp. nov., a nitrogen-fixing bacterium isolated from activated sludge

A Gram-reaction-negative, catalase- and oxidase-positive, aerobic, transparent, motile and rod-shaped bacterium that was capable of fixing dinitrogen (designated strain A.slu09^T), isolated from activated sludge, was characterized by a polyphasic approach to clarify its taxonomic position. Strain A.slu09^T was observed to grow optimally at 30 °C and at pH 7.0 on R2A agar medium. Strain A.slu09^T showed β-glucosidase activity, converting the major ginsenoside Rd to ginsenoside F2. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain A.slu09^T belongs to the genus Ciceribacter of the family Rhizobiaceae and was most closely related to Ciceribacter lividus MSSRFBL1^T (97.8 % similarity). The DNA G+C content was 67.2 mol%. The DNA-DNA hybridization value between strain A.slu09^T and C. lividus KCTC 32403^T was 16.9±1.17 %. The major polar lipids were phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine, aminophospholipid and two glycolipids, and one unknown phospholipid as a minor lipid. The predominant quinone was ubiquinone-10 (Q-10). The major fatty acids were C19 : 0 cyclo ω8c, C18 : 1 ω7c and/or C18 : 1ω6c (summed feature 8) and C18 : 0, a profile that supported the affiliation of A.slu09^T to the genus Ciceribacter. Moreover, the physiological and biochemical characteristics and low level of DNA-DNA relatedness allowed the phenotypic and genotypic differentiation of strain A.slu09^T from the recognized species of the genus Ciceribacter. Therefore, strain A.slu09^T represents a novel species of the genus Ciceribacter, for which the name Ciceribacter azotifigens sp. nov. is proposed. The type strain is A.slu09^T (=KACC 19080^T=LMG 29962^T).