Microbiology, IWWR, Faculty of Science, Radboud University, Nijmegen, the Netherlands.
Microbial Physiology Group, MPI for Marine Microbiology, Bremen, Germany.
Appl Environ Microbiol. 2018 Jan 17;84(3). doi: 10.1128/AEM.02186-17. Print 2018 Feb 1.
Methane is a very potent greenhouse gas and can be oxidized aerobically or anaerobically through microbe-mediated processes, thus decreasing methane emissions in the atmosphere. Using a complementary array of methods, including phylogenetic analysis, physiological experiments, and light and electron microscopy techniques (including electron tomography), we investigated the community composition and ultrastructure of a continuous bioreactor enrichment culture, in which anaerobic oxidation of methane (AOM) was coupled to nitrate reduction. A membrane bioreactor was seeded with AOM biomass and continuously fed with excess methane. After 150 days, the bioreactor reached a daily consumption of 10 mmol nitrate · liter · day The biomass consisted of aggregates that were dominated by nitrate-dependent anaerobic methane-oxidizing " Methanoperedens"-like archaea (40%) and nitrite-dependent anaerobic methane-oxidizing " Methylomirabilis"-like bacteria (50%). The " Methanoperedens" spp. were identified by fluorescence hybridization and immunogold localization of the methyl-coenzyme M reductase (Mcr) enzyme, which was located in the cytoplasm. The " Methanoperedens" sp. aggregates consisted of slightly irregular coccoid cells (∼1.5-μm diameter) which produced extruding tubular structures and putative cell-to-cell contacts among each other. " Methylomirabilis" sp. bacteria exhibited the polygonal cell shape typical of this genus. In AOM archaea and bacteria, cytochrome proteins were localized in the cytoplasm and periplasm, respectively, by cytochrome staining. Our results indicate that AOM bacteria and archaea might work closely together in the process of anaerobic methane oxidation, as the bacteria depend on the archaea for nitrite. Future studies will be aimed at elucidating the function of the cell-to-cell interactions in nitrate-dependent AOM. Microorganisms performing nitrate- and nitrite-dependent anaerobic methane oxidation are important in both natural and man-made ecosystems, such as wastewater treatment plants. In both systems, complex microbial interactions take place that are largely unknown. Revealing these microbial interactions would enable us to understand how the oxidation of the important greenhouse gas methane occurs in nature and pave the way for the application of these microbes in wastewater treatment plants. Here, we elucidated the microbial composition, ultrastructure, and physiology of a nitrate-dependent AOM community of archaea and bacteria and describe the cell plan of " Methanoperedens"-like methanotrophic archaea.
甲烷是一种非常强效的温室气体，可以通过微生物介导的过程好氧或厌氧氧化，从而减少大气中的甲烷排放。我们使用包括系统发育分析、生理实验以及光和电子显微镜技术（包括电子断层扫描）在内的互补方法，研究了连续生物反应器富营养化培养物的群落组成和超微结构，其中甲烷的厌氧氧化（AOM）与硝酸盐还原相偶联。 膜生物反应器接种了 AOM 生物质，并连续过量供应甲烷。 150 天后，生物反应器达到每天消耗 10mmol 硝酸盐·升·天的水平。 生物量由聚集体组成，聚集体主要由硝酸盐依赖的厌氧甲烷氧化“Methanoperedens”-样古菌（40%）和亚硝酸盐依赖的厌氧甲烷氧化“Methylomirabilis”-样细菌（50%）组成。“Methanoperedens”spp. 通过荧光杂交和甲基辅酶 M 还原酶（Mcr）酶的免疫金定位来鉴定，Mcr 酶位于细胞质中。“Methanoperedens”sp. 聚集体由稍不规则的球形细胞（约 1.5-μm 直径）组成，这些细胞产生伸出的管状结构和彼此之间的推测细胞间接触。“Methylomirabilis”sp. 细菌表现出该属特有的多边形细胞形状。在 AOM 古菌和细菌中，细胞色素蛋白分别通过细胞色素染色定位于细胞质和周质中。我们的结果表明，AOM 细菌和古菌在厌氧甲烷氧化过程中可能密切合作，因为细菌依赖古菌获取亚硝酸盐。未来的研究将旨在阐明硝酸盐依赖 AOM 中细胞间相互作用的功能。在自然和人为生态系统（如废水处理厂）中，进行硝酸盐和亚硝酸盐依赖的厌氧甲烷氧化的微生物非常重要。在这两个系统中，发生了大量未知的复杂微生物相互作用。揭示这些微生物相互作用将使我们能够了解重要温室气体甲烷在自然界中是如何氧化的，并为这些微生物在废水处理厂中的应用铺平道路。在这里，我们阐明了硝酸盐依赖的 AOM 古菌和细菌群落的微生物组成、超微结构和生理学，并描述了“Methanoperedens”-样甲烷营养古菌的细胞计划。
