High-pressure Methanogenesis Reveals Metabolic Adaptation to Dissolved CO<sub>2</sub> Limitation

This study investigated the effects of elevated hydrostatic pressure on methane production and gene expression in a hydrogenotrophic methanogen isolated from subseafloor sediments at biogenic gas hydrate sites, with a focus on the implications of CO₂ availability. Using high-pressure cultivation, the methane production rate decreased by 15% at 25 MPa, while a transcriptomic anal-ysis revealed the marked up-regulation of methyl-coenzyme M reductase and ATP synthase. These results suggest that methanogens compensate for pressure-driven constraints on CO₂ utilization by increasing the expression of key methanogenic enzymes, underscoring the overlooked role of CO₂ in deep biosphere microbial processes.