Data_Sheet_1_Zonation of the active methane-cycling community in deep subsurface sediments of the Peru trench.PDF

The production and anaerobic oxidation of methane (AOM) by microorganisms is widespread in organic-rich deep subseafloor sediments. Yet, the organisms that carry out these processes remain largely unknown. Here we identify members of the methane-cycling microbial community in deep subsurface, hydrate-containing sediments of the Peru Trench by targeting functional genes of the alpha subunit of methyl coenzyme M reductase (mcrA). The mcrA profile reveals a distinct community zonation that partially matches the zonation of methane oxidizing and –producing activity inferred from sulfate and methane concentrations and carbon-isotopic compositions of methane and dissolved inorganic carbon (DIC). McrA appears absent from sulfate-rich sediments that are devoid of methane, but mcrA sequences belonging to putatively methane-oxidizing ANME-1a-b occur from the zone of methane oxidation to several meters into the methanogenesis zone. A sister group of ANME-1a-b, referred to as ANME-1d, and members of putatively aceticlastic Methanothrix (formerly Methanosaeta) occur throughout the remaining methanogenesis zone. Analyses of 16S rRNA and mcrA-mRNA indicate that the methane-cycling community is alive throughout (rRNA to 230 mbsf) and active in at least parts of the sediment column (mRNA at 44 mbsf). Carbon-isotopic depletions of methane relative to DIC (−80 to −86‰) suggest mostly methane production by CO2 reduction and thus seem at odds with the widespread detection of ANME-1 and Methanothrix. We explain this apparent contradiction based on recent insights into the metabolisms of both ANME-1 and Methanothricaceae, which indicate the potential for methanogenetic growth by CO2 reduction in both groups.

微生物介导的甲烷生成与甲烷厌氧氧化（anaerobic oxidation of methane, AOM）广泛存在于富含有机质的海底深部沉积物中。然而，执行这些代谢过程的微生物类群在很大程度上仍未被探明。本研究靶向甲基辅酶M还原酶α亚基功能基因（mcrA），对秘鲁海沟深部含天然气水合物沉积物中的甲烷循环微生物群落进行了系统鉴定。mcrA基因图谱揭示出独特的群落分带特征，其与基于硫酸盐、甲烷浓度以及甲烷和溶解无机碳（dissolved inorganic carbon, DIC）的碳同位素组成所推断的甲烷氧化与产甲烷活性分带部分吻合。在不含甲烷的富硫酸盐沉积物中未检测到mcrA基因，但属于推定甲烷氧化类群ANME-1a-b的mcrA序列，可从甲烷氧化带延伸至产甲烷带内数米深处。ANME-1a-b的姊妹支系ANME-1d，以及推定的乙酸营养型产甲烷菌甲烷丝状菌属（Methanothrix，原名为Methanosaeta）的成员，广泛分布于其余产甲烷带中。对16S rRNA与mcrA-mRNA的分析表明，甲烷循环群落全程保持活性（可检测至230米深海沉积物岩心深度，meters below sea floor, mbsf），且至少在沉积物柱的部分区域具有代谢活性（44 mbsf处可检测到mRNA）。相较于溶解无机碳（DIC），甲烷的碳同位素亏损（-80‰至-86‰）表明甲烷主要通过CO₂还原途径生成，这与广泛检测到ANME-1和甲烷丝状菌科（Methanothricaceae）成员的结果看似矛盾。我们结合近期关于ANME-1与甲烷丝状菌科代谢机制的研究进展解释了这一表观矛盾：两类群均具备通过CO₂还原途径进行产甲烷生长的潜力。