Nitrite is a central molecule in the nitrogen cycle because nitrite oxidation to nitrate (an aerobic process) retains fixed nitrogen in a system and its reduction to dinitrogen gas (anaerobic) reduces the fixed nitrogen inventory. Despite its acknowledged requirement for oxygen, nitrite oxidation is observed in oxygen-depleted layers of the ocean’s oxygen minimum zones (OMZs), challenging the current understanding of OMZ nitrogen cycling. Previous attempts to determine whether nitrite-oxidizing bacteria in the anoxic layer differ from known nitrite oxidizers in the open ocean were limited by cultivation difficulties and sequencing depth. Here, we construct 31 draft genomes of nitrite-oxidizing bacteria from global OMZs. The distribution of nitrite oxidation rates, abundance and expression of nitrite oxidoreductase genes, and relative abundance of nitrite-oxidizing bacterial draft genomes from the same samples all show peaks in the core of the oxygen-depleted zone (ODZ) and are all highly correlated in depth profiles within the major ocean oxygen minimum zones. The ODZ nitrite oxidizers are not found in the Tara Oceans global dataset (the most complete oxic ocean dataset), and the major nitrite oxidizers found in the oxygenated ocean do not occur in ODZ waters. A pangenomic analysis shows the ODZ nitrite oxidizers have distinct gene clusters compared to oxic nitrite oxidizers and are microaerophilic. These findings all indicate the existence of nitrite oxidizers whose niche is oxygen-deficient seawater. Thus, specialist nitrite-oxidizing bacteria are responsible for fixed nitrogen retention in marine oxygen minimum zones, with implications for control of the ocean’s fixed nitrogen inventory.

中文翻译：

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适应低氧条件的亚硝酸盐氧化细菌在海洋最低氧区中主导亚硝酸盐氧化


亚硝酸盐是氮循环中的中心分子，因为亚硝酸盐氧化成硝酸盐（需氧过程）将固定氮保留在系统中，而其还原成氮气（厌氧）会减少固定氮库存。尽管公认需要氧气，但在海洋最低氧区 (OMZ) 的缺氧层中观察到亚硝酸盐氧化，这挑战了当前对 OMZ 氮循环的理解。先前试图确定缺氧层中的亚硝酸盐氧化细菌是否与公海中已知的亚硝酸盐氧化细菌不同，但受到培养难度和测序深度的限制。在这里，我们构建了来自全球 OMZ 的 31 个亚硝酸盐氧化细菌基因组草图。同一样品中亚硝酸盐氧化速率的分布、亚硝酸盐氧化还原酶基因的丰度和表达以及亚硝酸盐氧化细菌草图基因组的相对丰度都在缺氧区（ODZ）的核心显示出峰值，并且在主要海洋含氧最低区的深度剖面。 Tara Oceans 全球数据集（最完整的含氧海洋数据集）中未发现 ODZ 亚硝酸盐氧化剂，并且含氧海洋中发现的主要亚硝酸盐氧化剂也不出现在 ODZ 水域中。泛基因组分析表明，与含氧亚硝酸盐氧化剂相比，ODZ 亚硝酸盐氧化剂具有不同的基因簇，并且具有微需氧性。这些发现都表明亚硝酸盐氧化剂的存在，其利基是缺氧海水。因此，专门的亚硝酸盐氧化细菌负责海洋氧气最低区的固定氮保留，这对控制海洋固定氮库存具有影响。