Dominant and Active Methanogens in the Production Waters From a High-Temperature Petroleum Reservoir by DNA- and RNA-Based Analysis

Methane metabolism in deep subsurface petroleum reservoirs is of paramount interest in the global biogeochemical cycle of carbon. Methanogenesis in such habitats is driven mostly by methanogens in syntrophic association with bacteria. In the present study, methanogenic communities in production water samples from six wells of a high-temperature petroleum reservoir were analyzed based on both genomic 16S rDNA and metabolically active 16S rRNA. The PCR-amplified <i>mcrA</i> gene analysis showed that <i>Methanosaeta</i> (26%) and <i>Methanomassiliicoccus</i> (56%) were separately the dominant members in sample W2_71 and W9_18 at the DNA level. In comparison, the RNA-based analysis showed that <i>Methanosaeta</i> (63 ∼ 83%) followed by <i>Methanolinea</i> (16 ∼ 23%) were the most active methanogens, which were different from the communities of genomic DNA. While several lines of studies indicated that CO₂-reducing methanogens of the genus <i>Methanothermobacter</i> was the most frequently detected phylotype in deep-subsurface petroleum reservoirs. Redundancy analysis (RDA) showed the possible correlation between active methanogens (<i>Methanosaeta</i>) and environmental factors (CO₃^2-). The datasets indicated the importance of investigating methanogenic community by integrating DNA- and RNA-based approaches. These results provide new insight into active methanogens in high-temperature petroleum reservoirs, and promote a comprehensive understanding of methanogens as well as their potential methanogenic pathways in such environments.

深部地下石油储层中的甲烷代谢，在全球碳生物地球化学循环中具有极高的研究价值。此类生境中的产甲烷过程，主要由与细菌形成互营共生关系的产甲烷古菌所驱动。本研究针对某高温石油储层6口井的产出水样品，分别基于基因组16S rDNA和具有代谢活性的16S rRNA，对其中的产甲烷古菌群落进行了分析。经PCR扩增的mcrA基因分析显示，在DNA层面，W2_71和W9_18样品中的优势类群分别为鬃毛甲烷菌属（Methanosaeta，26%）和产甲烷嗜球菌属（Methanomassiliicoccus，56%）。与之相比，基于RNA的分析结果显示，鬃毛甲烷菌属（63%~83%）紧随纤发甲烷菌属（Methanolinea，16%~23%）为活性最强的产甲烷古菌，这与基因组DNA层面的群落结构存在显著差异。过往多项研究显示，热自养甲烷杆菌属（Methanothermobacter）的CO₂还原型产甲烷古菌，是深部地下石油储层中检出频次最高的系统发育型（phylotype）。冗余分析（Redundancy Analysis，RDA）显示，活性产甲烷古菌（鬃毛甲烷菌属）与环境因子（碳酸根离子CO₃²⁻）之间存在潜在关联。本数据集证实了结合DNA与RNA层面分析方法开展产甲烷古菌群落研究的重要性。本研究结果为高温石油储层中的活性产甲烷古菌提供了新的认知视角，同时有助于全面理解此类生境中产甲烷古菌及其潜在的产甲烷代谢途径。