State Key Laboratory of Microbial Metabolism, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China.
Department of Earth and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel.
Sci Total Environ. 2022 Nov 20;848:157590. doi: 10.1016/j.scitotenv.2022.157590. Epub 2022 Jul 25.
Intermittent increases of dissolved ferrous iron concentrations have been observed in deep marine methanic sediments which is different from the traditional diagenetic electron acceptor cascade, where iron reduction precedes methanogenesis. Here we aimed to gain insight into the mechanism of iron reduction and the associated microbial processes in deep sea methanic sediment by setting up long-term high-pressure incubation experiments supplemented with ferrihydrite and methane. Continuous iron reduction was observed during the entire incubation period. Intriguingly, ferrihydrite addition shifted the archaeal community from the dominance of hydrogenotrophic methanogens (Methanogenium) to methylotrophic methanogens (Methanococcoides). The enriched samples were then amended with C-labeled methane and different iron (oxyhydr)oxides in batch slurries to test the mechanism of iron reduction. Intensive iron reduction was observed, the highest rates with ferrihydrite, followed by hematite and then magnetite, however, no anaerobic oxidation of methane (AOM) was observed in any treatment. Further tests on the enriched slurry showed that the addition of molybdate decreased iron reduction, suggesting a link between iron reduction with sulfur cycling. This was accompanied by the enrichment of microbes capable of dissimilatory sulfate reduction and sulfur/thiosulfate oxidation, which indicates the presence of a cryptic sulfur cycle in the incubation system with the addition of iron (oxyhydr)oxides. Our work suggests that under low sulfate conditions, the presence of iron (oxyhydr)oxides would trigger a cascade of microbial reactions, and iron reduction could link with the microbial sulfur cycle, changing the kinetics of the methanogenesis process in methanic sediment.
深海甲烷沉积物中观测到溶解亚铁浓度间歇性增加，这与传统的成岩电子受体级联不同，在传统的成岩电子受体级联中，铁还原先于甲烷生成。在这里，我们通过设置长期高压培养实验，并补充水铁矿和甲烷，旨在深入了解深海甲烷沉积物中铁还原的机制及相关微生物过程。在整个培养期间，连续观察到铁还原。有趣的是，水铁矿的添加将古菌群落从产氢甲烷菌（Methanogenium）的优势转变为甲基甲烷菌（Methanococcoides）的优势。然后，将富集的样品用 C 标记的甲烷和不同的铁（氧）氢氧化物分批加入悬浮液中，以测试铁还原的机制。观察到强烈的铁还原，以水铁矿最高，其次是赤铁矿，然后是磁铁矿，但在任何处理中均未观察到甲烷的厌氧氧化（AOM）。对富集悬浮液的进一步测试表明，钼酸盐的添加降低了铁还原，表明铁还原与硫循环之间存在联系。这伴随着能够进行异化硫酸盐还原和硫/硫代硫酸盐氧化的微生物的富集，这表明在添加铁（氧）氢氧化物的培养系统中存在一个隐蔽的硫循环。我们的工作表明，在低硫酸盐条件下，铁（氧）氢氧化物的存在会引发一系列微生物反应，铁还原可能与微生物硫循环相关联，从而改变甲烷沉积物中甲烷生成过程的动力学。
