A novel Schinkia sp. respires nitrous oxide over a broad pH range
Known bacteria reduce the climate-active gas nitrous oxide (N2O) over narrow pH ranges, limiting their activity in 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 (0-20 g L-1 NaCl) ranges. Strain CFF1 couples complete fumarate oxidation with N2O respiration and produces 10.2 ± 2.4 mg biomass (dry weight) mmol N2O consumed-1. Succinate, lactate, pyruvate, and propionate, but not acetate or hydrogen, support N2O respiration. N2O reduction rates of 6.13 ± 0.30 µmol N2O mg biomass-1 hour-1 were measured at pH 7.5, with 33 and 27% lower rates observed at pH 4.5 and 8.5, respectively. Acetylene (33%, v/v), a potent inhibitor of N2O reductase (NosZ), had no impact on 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 expression 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 has implication for the turnover of N2O in heterogeneous ecosystems where pH varies across space and time.