The high relative abundance of Methanothermobacter across the reactors and the negligible H₂ levels observed suggested that CO was primarily converted to H₂ and CO₂, which then derived hydrogenotrophic methanogenesis . However, the metabolic pathways involved in CO conversion in our experiment remain unclear. The detected species, Methanothermobacter midas_s_9547 and Methanothermobacter midas_s_9533 were unclassified (species-level composition shown in Figure ). This limits our understanding of their specific metabolic processes in CO conversion. Nevertheless, the high abundance of Methanothermobacter across reactors emphasized its critical role in CO conversion within biofilms during the enrichment process.