Data_Sheet_1_Aerobic methanotrophy increases the net iron reduction in methanogenic lake sediments.zip

In methane (CH4) generating sediments, methane oxidation coupled with iron reduction was suggested to be catalyzed by archaea and bacterial methanotrophs of the order Methylococcales. However, the co-existence of these aerobic and anaerobic microbes, the link between the processes, and the oxygen requirement for the bacterial methanotrophs have remained unclear. Here, we show how stimulation of aerobic methane oxidation at an energetically low experimental environment influences net iron reduction, accompanied by distinct microbial community changes and lipid biomarker patterns. We performed incubation experiments (between 30 and 120 days long) with methane generating lake sediments amended with 13C-labeled methane, following the additions of hematite and different oxygen levels in nitrogen headspace, and monitored methane turnover by 13C-DIC measurements. Increasing oxygen exposure (up to 1%) promoted aerobic methanotrophy, considerable net iron reduction, and the increase of microbes, such as Methylomonas, Geobacter, and Desulfuromonas, with the latter two being likely candidates for iron recycling. Amendments of 13C-labeled methanol as a potential substrate for the methanotrophs under hypoxia instead of methane indicate that this substrate primarily fuels methylotrophic methanogenesis, identified by high methane concentrations, strongly positive δ13CDIC values, and archaeal lipid stable isotope data. In contrast, the inhibition of methanogenesis by 2-bromoethanesulfonate (BES) led to increased methanol turnover, as suggested by similar 13C enrichment in DIC and high amounts of newly produced bacterial fatty acids, probably derived from heterotrophic bacteria. Our experiments show a complex link between aerobic methanotrophy and iron reduction, which indicates iron recycling as a survival mechanism for microbes under hypoxia.

在甲烷（CH4）生成沉积物中，有研究表明，甲烷氧化与铁还原过程可能由属Methylococcales的古菌和细菌甲烷氧化菌所催化。然而，这些需氧与厌氧微生物的共存、过程之间的联系以及细菌甲烷氧化菌对氧的需求一直未明。本研究揭示了在能量低下的实验环境中，对需氧甲烷氧化的刺激如何影响净铁还原，并伴随着独特的微生物群落变化和脂质生物标志物模式。我们进行了为期30至120天的孵化实验，使用甲烷生成湖泊沉积物，并添加了13C标记的甲烷，以及赤铁矿和不同氧气水平的氮气空间，通过13C-二碳（DIC）测量来监测甲烷的周转。增加氧气暴露（高达1%）促进了需氧甲烷氧化、显著的净铁还原，以及如甲基单胞菌、地杆菌和脱硫弧菌等微生物数量的增加，后两者可能是铁循环的潜在候选者。在缺氧条件下，以13C标记的甲醇作为甲烷氧化菌的潜在底物而非甲烷的添加，表明这种底物主要促进了甲基营养性甲烷生成，这一过程以高甲烷浓度、强烈的正δ13CDIC值和古菌脂质稳定同位素数据为特征。相比之下，通过2-溴乙烷磺酸盐（BES）抑制甲烷生成导致了甲醇周转的增加，这由类似13C富集的DIC和大量新产生的细菌脂肪酸所支持，这些脂肪酸可能来源于异养细菌。我们的实验揭示了需氧甲烷氧化与铁还原之间复杂的联系，这表明铁循环是微生物在缺氧环境下的生存机制。