Microorganisms acting as sinks for the greenhouse gas nitrous oxide (N2O) are gaining increasing attention in the development of strategies to control N2O emissions. Non-denitrifying N2O reducers are of particular interest because they can provide a real sink without contributing to N2O release. The bacterial strain under investigation (IGB 4-14T), isolated in a mesocosm experiment to study the litter decomposition of Phragmites australis (Cav.), is such an organism. It carries only a nos gene cluster with the sec-dependent Clade II nosZ and is able to consume significant amounts of N2O under anoxic conditions. However, consumption activity is considerably affected by the O2 level. The reduction of N2O was not associated with cell growth, suggesting that no energy is conserved by anaerobic respiration. Therefore, the N2O consumption of strain IGB 4-14T rather serves as an electron sink for metabolism to sustain viability during transient anoxia and/or to detoxify high N2O concentrations. Phylogenetic analysis of 16S rRNA gene similarity revealed that the strain belongs to the genus Flavobacterium. It shares a high similarity in the nos gene cluster composition and the amino acid similarity of the nosZ gene with various type strains of the genus. However, phylogenomic analysis and comparison of overall genome relatedness indices clearly demonstrated a novel species status of strain IGB 4-14T, with Flavobacterium lacus being the most closely related species. Various phenotypic differences supported a demarcation from this species. Based on these results, we proposed a novel species Flavobacterium azooxidireducens sp. nov. (type strain IGB 4-14T = LMG 29709T = DSM 103580T).
Keywords: Clade II nosZ; Flavobacterium azooxidireducens sp. nov.; nitrous oxide reduction; non-denitrifier; phylogenomic analysis.