Unlocking N2O respiratory pathways in Stutzerimonas stutzeri PRE-2: Implications for reducing N2O emissions from estuaries

Abstract

Although nitrogen cycling in nitrogen-enriched estuaries is highly active, the reported nitrous oxide (N₂O) emission factor (EF_5e) values for N₂O emissions in estuarine environments are usually low. Therefore, biological or abiotic mechanisms control the emission of N₂O from estuarine ecosystems. In this study, a pure culture of N₂O-reducing bacteria was isolated from Pearl River Estuary surface sediment and identified as Stutzerimonas stutzeri PRE-2. This strain displayed a high N₂O reduction capability, and the average N₂O reduction rate was 17.93 ± 0.43 μmol h⁻¹ under anoxic conditions. This reduction of N₂O was coupled with the stoichiometric consumption of acetate or lactate as electron donors, suggesting that microbial N₂O reduction involves electron transport. Furthermore, N₂O reduction can yield energy that supports microbial growth. Genomic analysis demonstrated that the strain Stutzerimonas stutzeri PRE-2 contains a complete pathway for the reduction of N₂O to N₂. Typical respiratory chain inhibitors did not significantly inhibit N₂O reduction activity, demonstrating that the electron transfer pathway involved in N₂O reduction is unique compared to the classic respiratory chain. The integrated evidence suggests that microbial N₂O reduction by Stutzerimonas stutzeri PRE-2 involves N₂O respiration and may play an important role in reducing N₂O emissions in estuarine ecosystems.