Methane is produced microbially in vast quantities in sediments throughout the world’s oceans. However, anaerobic oxidation of methane (AOM) provides a near-quantitative sink for the produced methane and is primarily responsible for preventing methane emissions from the oceans to the atmosphere. AOM is a complex microbial process that involves several different microbial groups and metabolic pathways. The role of different electron acceptors in AOM has been studied for decades, yet large uncertainties remain, especially in terms of understanding the processes in natural settings. This study reports whole-core incubation methane oxidation rates along an estuarine gradient ranging from near fresh water to brackish conditions, and investigates the potential role of different electron acceptors in AOM. Microbial community structure involved in different methane processes is also studied in the same estuarine system using high throughput sequencing tools. Methane oxidation in the sediments was active in three distinct depth layers throughout the studied transect, with total oxidation rates increasing seawards. We find extensive evidence of non-sulphate AOM throughout the transect. The highest absolute AOM rates were observed below the sulphate-methane transition zone (SMTZ), strongly implicating the role of alternative electron acceptors (most likely iron and manganese oxides). However, oxidation rates were ultimately limited by methane availability. ANME-2a/b were the most abundant microbial phyla associated with AOM throughout the study sites, followed by ANME-2d in much lower abundances. Similarly to oxidation rates, highest abundances of microbial groups commonly associated with AOM were found well below the SMTZ, further reinforcing the importance of non-sulphate AOM in this system.

中文翻译：

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电子受体可用性和微生物群落结构对北方河口沉积甲烷氧化的影响

甲烷是在全世界海洋的沉积物中大量通过微生物产生的。然而，甲烷的厌氧氧化 (AOM) 为产生的甲烷提供了近乎定量的汇，主要负责防止甲烷从海洋排放到大气中。AOM 是一个复杂的微生物过程，涉及几种不同的微生物群和代谢途径。几十年来，人们一直在研究不同电子受体在 AOM 中的作用，但仍然存在很大的不确定性，尤其是在理解自然环境中的过程方面。这项研究报告了沿河口梯度从近淡水到微咸水条件的全核孵化甲烷氧化率，并研究了不同电子受体在 AOM 中的潜在作用。还使用高通量测序工具在同一河口系统中研究了涉及不同甲烷过程的微生物群落结构。沉积物中的甲烷氧化在整个研究断面的三个不同深度层中活跃，总氧化率向海方向增加。我们在整个横断面上发现了大量非硫酸盐 AOM 的证据。在硫酸盐 - 甲烷过渡区 (SMTZ) 下方观察到最高的绝对 AOM 率，强烈暗示替代电子受体（最有可能是铁和锰氧化物）的作用。然而，氧化速率最终受到甲烷可用性的限制。ANME-2a/b 是整个研究地点与 AOM 相关的最丰富的微生物门，其次是 ANME-2d，其丰度要低得多。与氧化速率类似，