Methanotrophic bacteria play a key role in limiting methane emissions from lakes. It is generally assumed that methanotrophic bacteria are mostly active at the oxic‐anoxic transition zone in stratified lakes, where they use oxygen to oxidize methane. Here, we describe a methanotroph of the genera Methylobacter that is performing high‐rate (up to 72 μM day⁻¹) methane oxidation in the anoxic hypolimnion of the temperate Lacamas Lake (Washington, USA), stimulated by both nitrate and sulfate addition. Oxic and anoxic incubations both showed active methane oxidation by a Methylobacter species, with anoxic rates being threefold higher. In anoxic incubations, Methylobacter cell numbers increased almost two orders of magnitude within 3 days, suggesting that this specific Methylobacter species is a facultative anaerobe with a rapid response capability. Genomic analysis revealed adaptations to oxygen‐limitation as well as pathways for mixed‐acid fermentation and H₂ production. The denitrification pathway was incomplete, lacking the genes narG/napA and nosZ, allowing only for methane oxidation coupled to nitrite‐reduction. Our data suggest that Methylobacter can be an important driver of the conversion of methane in oxygen‐limited lake systems and potentially use alternative electron acceptors or fermentation to remain active under oxygen‐depleted conditions.

中文翻译：

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添加硝酸盐和硫酸盐刺激缺氧湖水中的甲烷氧化。


甲烷营养菌在限制湖泊甲烷排放方面发挥着关键作用。一般认为，甲烷营养菌主要活跃在分层湖泊的缺氧过渡带，利用氧气氧化甲烷。在这里，我们描述了甲基杆菌属的甲烷氧化菌，在硝酸盐和硫酸盐添加的刺激下，在温带拉卡马斯湖（美国华盛顿）的缺氧低层中进行高速率（高达 72 μM 天^-1 ）甲烷氧化。好氧和缺氧培养均显示出甲基杆菌属物种的活跃甲烷氧化作用，缺氧率高出三倍。在缺氧培养中，甲基杆菌细胞数量在 3 天内增加了近两个数量级，表明这种特定的甲基杆菌是一种具有快速反应能力的兼性厌氧菌。基因组分析揭示了对氧限制的适应以及混合酸发酵和 H ₂生产的途径。反硝化途径不完整，缺乏基因narG/napA和nosZ ，仅允许甲烷氧化与亚硝酸盐还原相结合。我们的数据表明，甲基杆菌可以成为限氧湖泊系统中甲烷转化的重要驱动力，并可能使用替代电子受体或发酵在缺氧条件下保持活性。