f 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.slu09T), isolated from activated sludge, was characterized by a polyphasic approach to clarify its taxonomic position. Strain A.slu09T was observed to grow optimally at 30 °C and at pH 7.0 on R2A agar medium. Strain A.slu09T showed β-glucosidase activity, converting the major ginsenoside Rd to ginsenoside F2. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain A.slu09T belongs to the genus Ciceribacter of the family Rhizobiaceae and was most closely related to Ciceribacter lividus MSSRFBL1T (97.8 % similarity). The DNA G+C content was 67.2 mol%. The DNA–DNA hybridization value between strain A.slu09T and C. lividus KCTC 32403T 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 C_19 : 0 cyclo ω8c, C_18 : 1ω7c and/or C_18 : 1ω6c (summed feature 8) and C_18 : 0, a profile that supported the affiliation of A.slu09T 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.slu09T from the recognized species of the genus Ciceribacter . Therefore, strain A.slu09T represents a novel species of the genus Ciceribacter , for which the name Ciceribacter azotifigens sp. nov. is proposed. The type strain is A.slu09T (=KACC 19080T=LMG 29962T).