Microbial enzymes often occur as distinct variants that share the same substrate but differ in substrate affinity, sensitivity to environmental conditions, or phylogenetic ancestry. Determining where variants occur in the environment helps identify thresholds that constrain microbial cycling of key chemicals, including the greenhouse gas nitrous oxide (N₂O). To understand the enzymatic basis of N₂O cycling in the ocean, we mined metagenomes to characterize genes encoding bacterial nitrous oxide reductase (NosZ) catalyzing N₂O reduction to N₂. We examined data sets from diverse biomes but focused primarily on those from oxygen minimum zones where N₂O levels are often elevated. With few exceptions, marine nosZ data sets were dominated by ‘atypical’ clade II gene variants. Atypical nosZ has been associated with low oxygen, enhanced N₂O affinity, and organisms lacking enzymes for complete denitrification, i.e., non‐denitrifiers. Atypical nosZ often occurred in metagenome‐assembled genomes (MAGs) with nitrate or nitrite respiration genes, although MAGs with genes for complete denitrification were rare. We identified atypical nosZ in several taxa not previously associated with N₂O consumption, in addition to known N₂O‐associated groups. The data suggest that marine environments generally select for high N₂O‐scavenging ability across diverse taxa and have implications for how N₂O concentration may affect N₂O removal rates.

中文翻译：

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非脱氮剂一氧化二氮还原酶主导海洋生物群落

微生物酶通常以不同的变体形式出现，它们共享相同的底物，但底物亲和力，对环境条件的敏感性或系统发生学上的差异。确定环境中变体的位置有助于确定限制关键化学物质（包括温室气体一氧化二氮（N ₂ O））的微生物循环的阈值。为了了解海洋中N ₂ O循环的酶基础，我们开发了元基因组来表征编码细菌一氧化二氮还原酶（NosZ）催化N ₂ O还原为N _2的基因。我们检查了来自不同生物群落的数据集，但主要集中在那些经常升高N ₂ O水平的最低氧区域的数据集。除少数例外，海洋nosZ数据集以“非典型”进化枝II基因变异为主导。非典型的nosZ与低氧，增强的N ₂ O亲和力以及缺乏用于完全反硝化的酶的生物（即非脱氮剂）有关。非典型号ž常发生于宏基因组组装基因组（MAG的）与硝酸盐或亚硝酸盐呼吸的基因，虽然与基因完全脱硝的MAG是罕见的。除了已知的与N ₂ O相关的基团，我们还发现了一些先前与N ₂ O消耗无关的分类单元中的非典型Z号。数据表明，海洋环境通常会选择高N ₂跨不同分类单元的O清除能力，并影响N ₂ O浓度如何影响N ₂ O去除率。