Unprecedented N 2 O production by nitrate-ammonifying Geobacteraceae with distinctive N 2 O isotopocule signatures

作者：Zhenxing Xu, Shohei Hattori, Yoko Masuda, Sakae Toyoda, Keisuke Koba, Pei Yu, Naohiro Yoshida, Zong‐Jun Du, Keishi Senoo · 发表于：mBio · 年份：2024 · DOI：10.1128/mbio.02540-24 · 被引用次数：17 · 研究领域：Wastewater Treatment and Nitrogen Removal、Microbial Community Ecology and Physiology、Plant nutrient uptake and metabolism

ABSTRACT Dissimilatory nitrate reduction to ammonium (DNRA), driven by nitrate-ammonifying bacteria, is an increasingly appreciated nitrogen-cycling pathway in terrestrial ecosystems. This process reportedly generates nitrous oxide (N 2 O), a strong greenhouse gas with ozone-depleting effects. However, it remains poorly understood how N 2 O is produced by environmental nitrate-ammonifiers and how to identify DNRA-derived N 2 O. In this study, we characterize two novel enzymatic pathways responsible for N 2 O production in Geobacteraceae strains, which are predominant nitrate-ammonifying bacteria in paddy soils. The first pathway involves a membrane-bound nitrate reductase (Nar) and a hybrid cluster protein complex (Hcp–Hcr) that catalyzes the conversion of NO 2 − to NO and subsequently to N 2 O. The second pathway is observed in Nar-deficient bacteria, where the nitrite reductase (NrfA) generates NO, which is then reduced to N 2 O by Hcp–Hcr. These enzyme combinations are prevalent across the domain Bacteria. Moreover, we observe distinctive isotopocule signatures of DNRA-derived N 2 O from other established N 2 O production pathways, especially through the highest 15 N-site preference (SP) values (43.0‰–49.9‰) reported so far, indicating a robust means for N 2 O source partitioning. Our findings demonstrate two novel N 2 O production pathways in DNRA that can be isotopically distinguished from other pathways. IMPORTANCE Stimulation of DNRA is a promising strategy to improve ...