A novel Schinkia sp. respires nitrous oxide over a broad pH range

Known bacteria reduce the climate-active gas nitrous oxide (N₂O) to dinitrogen (N₂) over narrow pH ranges, limiting their efficacy in pH heterogeneous soil environments. A dual pH (pH 4.5 → 7.0 → 4.5) enrichment strategy with N₂O as electron acceptor yielded a novel Schinkia isolate, strain CFF1, capable of N₂O reduction over broad pH (4.5-8.5) and salinity (1-20 g L^-1 NaCl) ranges. Strain CFF1 couples complete fumarate oxidation with N₂O respiration and produces 10.2 ± 2.4 mg of biomass (dry weight) per mmol N₂O consumed. Fumarate, succinate, lactate, pyruvate, and propionate, but not acetate, formate, or hydrogen, support N₂O respiration. N₂O reduction rates of 6.13 ± 0.30 µmol N₂O (mg biomass hour)^-1 were measured at pH 7.5, with ~30% lower rates observed at pH 4.5 and 8.5. Acetylene (33%, vol/vol), a potent inhibitor of N₂O reductase (NosZ), had no impact on the growth of strain CFF1 with N₂O. Alternate growth-supporting electron acceptors include nitrate, nitrite, and O₂. Genomic investigations revealed four distinct clade II nosZ genes, and proteomic measurements demonstrated the synthesis of the same two NosZ under both acidic and alkaline growth conditions. Physiological characterization and phylogenomic analysis indicate the isolate represents a new species in the genus Schinkia, for which the name Schinkia acidoalkalinis strain CFF1 is proposed. A soil isolate capable of reducing N₂O over a broad pH range expands our understanding of the ecophysiology of N₂O-reducing bacteria and N₂O turnover in environments where pH varies across space and time.IMPORTANCEDissimilatory N₂O reduction catalyzed by the N₂O reductase NosZ is the major process consuming the climate-active gas N₂O. Known N₂O-reducing microorganisms operate within narrow pH windows, potentially limiting N₂O turnover in heterogeneous soil environments. We isolated Schinkia acidoalkalinis strain CFF1 capable of reducing N₂O at similar rates over a broad pH range spanning pH 4.5-8.5. The discovery of an N₂O-reducing pH generalist expands opportunities for developing robust biotechnologies to enhance N₂O consumption in natural and engineered systems characterized by pH heterogeneity.