Anaerobic oxidation of methane (AOM) is a potentially important methane sink in lake sediments, but the biogeochemistry and microbial ecology of this process are understudied. Potential electron acceptors for AOM include Fe(III) and sulfate; however, it is not clear to which extent low sulfate concentrations constrain the coupling of AOM to sulfate reduction, nor if Fe(III) reduction drives AOM directly or via a cryptic sulfur cycle. We investigated AOM pathways in the sediment of iron-rich Danish Lake Ørn through anoxic sediment slurry incubations with additions of ¹³C-labeled methane as a substrate, sulfate and Fe(III) as potential electron acceptors, and molybdate as an inhibitor of sulfate reduction. The experiments demonstrated the co-occurrence of sulfate- and iron-dependent modes of AOM, with the former supported by recycling of sulfate coupled to iron reduction. Quantitative PCR analysis demonstrated the abundance of archaea of the ANME-2d clade (Ca. Methanoperedenaceae) as likely drivers of AOM. Our study demonstrates that sulfate-dependent AOM can consume methane at sulfate concentrations typical for freshwater systems and emphasizes the importance of sulfur and iron cycling in the regulation of methane emission from freshwater sediments.

中文翻译：

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淡水湖沉积物中并排发生的硫酸盐和铁依赖性厌氧甲烷氧化

甲烷的厌氧氧化 (AOM) 是湖泊沉积物中潜在的重要甲烷汇，但对该过程的生物地球化学和微生物生态学研究不足。AOM 的潜在电子受体包括 Fe(III) 和硫酸盐；然而，尚不清楚低硫酸盐浓度在多大程度上限制了 AOM 与硫酸盐还原的耦合，也不清楚 Fe(III) 还原是否直接或通过神秘的硫循环驱动 AOM。我们通过添加¹³C 标记的甲烷作为底物，硫酸盐和 Fe(III) 作为潜在的电子受体，钼酸盐作为硫酸盐还原的抑制剂。实验证明了 AOM 的硫酸盐和铁依赖性模式同时发生，前者由硫酸盐的再循环与铁还原相结合来支持。定量 PCR 分析表明 ANME-2d 进化枝 ( Ca. Methanoperedenaceae)古细菌的丰度可能是 AOM 的驱动因素。我们的研究表明，硫酸盐依赖性 AOM 可以消耗淡水系统典型硫酸盐浓度下的甲烷，并强调硫和铁循环在调节淡水沉积物甲烷排放中的重要性。