Title: How nitrifiers denitrify?
Kaihang Zhang, Lei Cheng
Abstract
The sources of nitrous oxide (N2O), a potent and long-lived greenhouse gas, remain highly uncertain. This uncertainty arises largely from limited understanding of nitrifier denitrification, the reduction of nitrite by ammonia oxidizing bacteria (AOB) (Zhu et al., 2013). Here, we propose a novel conceptual framework to address the long-standing question of whether AOB could persist via nitrifier denitrification under hypoxic and/or anoxic conditions. We present an analysis of recent advances in nitrite and nitric oxide (NO) reductase enzymology (Murali et al., 2024) which suggests that AOB could utilize heme-copper-containing NO reductase (sNOR)-mediated nitrifier denitrification to generate proton motive force and conserve energy during anaerobic respiration. Our phylogenetic analysis further shows that sNOR is present in nearly 96 % of sequenced AOB genomes. We therefore suggest that sNOR-mediated nitrifier denitrification may represent a substantial, and likely increasing, contribution to global N2O emissions, particularly in aquatic and lowland ecosystems under future climate change-induced global deoxygenation conditions.
Link:https://doi.org/10.1016/j.soilbio.2026.110098
