Details of the methanogenic processes in deep subsurface environments, i.e., reaction pathways and responsible microorganisms are unclear. This issue can be effectively addressed by incubation experiments using subsurface water/sediment samples with high methanogenic potential, followed by subjecting the obtained enrichment culture to the analyses of metagenome, metatranscriptome, and metabolome as well as stable isotope tracer experiments. Elucidation of the methanogenic processes provides basic information required to develop innovate resource technologies such as bio-conversion of residual crude oil in a depleted oil field to natural gas for enhanced energy recovery.

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