Department of Geosciences, the Pennsylvania State University, University Park, PA, USA.
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
Geobiology. 2019 Nov;17(6):611-627. doi: 10.1111/gbi.12354. Epub 2019 Jul 31.
Archaeal ANaerobic MEthanotrophs (ANME) facilitate the anaerobic oxidation of methane (AOM), a process that is believed to proceed via the reversal of the methanogenesis pathway. Carbon isotopic composition studies indicate that ANME are metabolically diverse and able to assimilate metabolites including methane, methanol, acetate, and dissolved inorganic carbon (DIC). Our data support the interpretation that ANME in marine sediments at methane seeps assimilate both methane and DIC, and the carbon isotopic compositions of the tetrapyrrole coenzyme F430 and the membrane lipids archaeol and hydroxy-archaeol reflect their relative proportions of carbon from these substrates. Methane is assimilated via the methyl group of CH -tetrahydromethanopterin (H MPT) and DIC from carboxylation reactions that incorporate free intracellular DIC. F430 was enriched in C (mean δ C = -27‰ for Hydrate Ridge and -80‰ for the Santa Monica Basin) compared to the archaeal lipids (mean δ C = -97‰ for Hydrate Ridge and -122‰ for the Santa Monica Basin). We propose that depending on the side of the tricarboxylic acid (TCA) cycle used to synthesize F430, its carbon was derived from 76% DIC and 24% methane via the reductive side or 57% DIC and 43% methane via the oxidative side. ANME lipids are predicted to contain 42% DIC and 58% methane, reflecting the amount of each assimilated into acetyl-CoA. With isotope models that include variable fractionation during biosynthesis for different carbon substrates, we show the estimated amounts of DIC and methane can result in carbon isotopic compositions of - 73‰ to - 77‰ for F430 and - 105‰ for archaeal lipids, values close to those for Santa Monica Basin. The F430 δ C value for Hydrate Ridge was C-enriched compared with the modeled value, suggesting there is divergence from the predicted two carbon source models.
古菌厌氧甲烷营养菌（ANME）促进了甲烷（AOM）的厌氧氧化，这一过程被认为是通过逆转产甲烷途径进行的。碳同位素组成研究表明，ANME 代谢方式多样，能够同化包括甲烷、甲醇、乙酸和溶解无机碳（DIC）在内的代谢物。我们的数据支持以下解释，即在甲烷渗漏的海洋沉积物中，ANME 同时同化甲烷和 DIC，四吡咯辅酶 F430 和膜脂 archaeol 和 hydroxy-archaeol 的碳同位素组成反映了它们相对来自这些底物的碳比例。甲烷通过 CH -四氢甲烷蝶呤（H MPT）的甲基和羧化反应同化 DIC，这些羧化反应将细胞内游离的 DIC 掺入其中。与古菌脂质相比，F430 富集了 C（Hydrate Ridge 的平均 δ C 为-27‰，Santa Monica Basin 的平均 δ C 为-80‰）（Hydrate Ridge 的平均 δ C 为-97‰，Santa Monica Basin 的平均 δ C 为-122‰）。我们提出，根据用于合成 F430 的三羧酸（TCA）循环的哪一侧，其碳源来自 76%的 DIC 和 24%的甲烷（通过还原侧）或 57%的 DIC 和 43%的甲烷（通过氧化侧）。预测 ANME 脂质含有 42%的 DIC 和 58%的甲烷，反映了每种物质被同化到乙酰辅酶 A 中的量。利用包括不同碳底物在生物合成过程中可变分馏的同位素模型，我们表明估计的 DIC 和甲烷量可导致 F430 的碳同位素组成在-73‰至-77‰之间，古菌脂质的碳同位素组成在-105‰左右，与 Santa Monica Basin 相近。与模型值相比，Hydrate Ridge 的 F430 δ C 值更为丰富，表明与预测的两种碳源模型存在分歧。
