Tianxiang Xu’s research while affiliated with Tokyo University of Agriculture and Technology and other places

Nitrous oxide-reducing bacteria (N2ORB) are generally considered the only biological sink for the potent greenhouse gas N2O. Although N2O consumption activities by diverse heterotrophic N2ORB have been detected, knowledge gaps remain about the phylogenies, physiologies, and activities of N2ORB. Here, we successfully enriched a methylotrophic N2ORB consortium under intermittent oxygen and N2O supplies. 15N tracer analysis showed that the N2O consumption activity of the enriched consortium was higher than its N2O production activity in the presence of either a single or multiple electron acceptors (i.e., nitrogen oxides). The observed maximum N2O consumption was 80.7 μmol·g-biomass–1·h–1. Quantitative PCR results showed that clade I nosZ bacteria overwhelmed clade II nosZ bacteria at high (0.41 mmol·min–1) and low (0.08 mmol·min–1) N2O loading rates. The dilution rate and N2O loading rate affected the microbial community composition and activity. A higher N2O loading rate stimulated active and oxygen-tolerant N2ORB that boosted N2O consumption by approximately 50% in the presence of oxygen. Metagenomic analysis unraveled the predominance of a novel methylotrophic N2ORB, possessing entire denitrifying genes and high-affinity terminal oxidase genes, from the reactor with a high N2O loading rate. The unique physiological traits of the consortium enriched by methanol shed light on a novel function─aerobic N2O consumption by N2ORB─and pave the way for innovative N2O mitigation strategies applying powerful N2O sinks in engineered systems.