Enhanced Rock Weathering as a Source of Metals to Promote Methanogenesis and Counteract CO 2 Sequestration.

Enhanced weathering of (ultra)mafic rocks has been proposed as a promising approach to sequester atmospheric CO ₂ and mitigate climate change. However, these silicate rocks contain varying amounts of trace metals, which are essential cofactors of metallaenzymes in methanogens. We found that weathering of crushed peridotite and basalt significantly promoted the growth and methanogenesis of a model methanogen─ Methanosarcina acetivorans C2A under the condition of excess substrate. The released trace metals from peridotite and basalt, especially Fe, Ni, and Co, accounted for the promotion effect. Observation at different spatial scales showed a close association between the rocks and cells. Proteomic analysis revealed that rock amendment significantly enhanced the expression of core metalloenzymes in the methylotrophic methanogenesis pathway. Our study uncovers a previously unrecognized but important negative effect of enhanced rock weathering on methane production, which may counteract the carbon sequestration effort.