N2O production using native nos-deficient denitrifying bacterial strains screened by a genome mining approach

Abstract

Although N2O is a notorious greenhouse and ozone-depleting gas, N2O is a strong oxidant and can be an energy source by combusting with methane gas. The present study screened N2O-producing denitrifying bacteria by genome mining approach, and the activity and efficiency of NO2− reduction to N2O were examined. Presence and absence of the genes encoding nitrite reductase (nir), nitric oxide reductase (nor), and nitrous oxide reductase (nos) on the 2750 prokaryotic genomes were examined to screen nos-deficient denitrifying bacteria capable of NO2− reduction to N2O. The 131 nos-deficient denitrifying bacterial genomes were screened, and Cupriavidus necator H16 and Propionibacterium freudenreichii showed high activity and efficiency of 15NO2− reduction to 15N2O. Nitrogen removal performance and N2O conversion efficiencies were further investigated in a membrane bioreactor, and C. necator H16 showed 0.18 kg-N m−3 d−1 of NO2− removal rate with 75–95% of N2O conversion efficiencies.