Microorganisms possessing N₂O reductases (NosZ) are the only known environmental sink of N₂O. While oxygen inhibition of NosZ activity is widely known, environments where N₂O reduction occurs are often not devoid of O₂. However, little is known regarding N₂O reduction in microoxic systems. Here, 1.6-L chemostat cultures inoculated with activated sludge samples were sustained for ca. 100 days with low concentration (<2 ppmv) and feed rate (<1.44 µmoles h⁻¹) of N₂O, and the resulting microbial consortia were analyzed via quantitative PCR (qPCR) and metagenomic/metatranscriptomic analyses. Unintended but quantified intrusion of O₂ sustained dissolved oxygen concentration above 4 µM; however, complete N₂O reduction of influent N₂O persisted throughout incubation. Metagenomic investigations indicated that the microbiomes were dominated by an uncultured taxon affiliated to Burkholderiales, and, along with the qPCR results, suggested coexistence of clade I and II N₂O reducers. Contrastingly, metatranscriptomic nosZ pools were dominated by the Dechloromonas-like nosZ subclade, suggesting the importance of the microorganisms possessing this nosZ subclade in reduction of trace N₂O. Further, co-expression of nosZ and ccoNO/cydAB genes found in the metagenome-assembled genomes representing these putative N₂O-reducers implies a survival strategy to maximize utilization of scarcely available electron acceptors in microoxic environmental niches.

拥有 N ₂ O 还原酶 (NosZ) 的微生物是唯一已知的 N ₂ O 环境汇。虽然氧对 NosZ 活性的抑制是众所周知的，但发生 N ₂ O 还原的环境通常并非没有 O ₂。然而，关于微氧系统中 N ₂ O 的减少知之甚少。在这里，接种活性污泥样品的 1.6 L 恒化器培养物持续了约 10 年。通过定量 PCR (qPCR) 和宏基因组/宏转录组分析对低浓度 (<2 ppmv) 和进料速率 (<1.44 µmoles h ^-1 ) 的 N _{2 O 进行 100 天分析，并分析由此产生的微生物群落。O 2}的意外但量化的入侵持续溶解氧浓度高于 4 µM；然而，在整个孵化过程中，流入的 N 2 O_完全减少了 N _{2 O。}宏基因组研究表明，微生物组主要由隶属于伯克霍尔德氏菌目 (Burkholderiales) 的未培养分类群主导，并且与 qPCR 结果一起，表明进化枝 I 和进化枝 II N ₂ O 还原剂共存。相比之下，元转录组nosZ池由脱氯单胞菌样nosZ亚枝主导，表明拥有该nosZ亚枝的微生物在减少痕量 N ₂ O 方面的重要性。此外，nosZ的共表达在代表这些推定的 N ₂ O 还原剂的宏基因组组装基因组中发现的和ccoNO / cydAB基因暗示了一种生存策略，以最大限度地利用微氧环境生态位中稀缺的电子受体。