The composition and relative abundances of total sequences representing methanogenic archaea in mixed cultures enriched with acetate, H₂/CO₂, or MeOH; (A) phylogenetic placements of archaeal 16S rRNA gene amplicons detected in the enrichment cultures; the highlighted lobes indicate major clades of archaea known or suspected to produce CH₄; the circles indicate best phylogenetic placements of archaeal taxa identified across all enrichment conditions; the size of the circle is proportional to the number of actual sequence variants (ASVs) detected; large shaded areas indicate archaeal superphyla, including Diapherotrites, Parvarchaeota, Aenigmarchaeota, Nanohaloarchaeota, and Nanoarchaeota (DPANN) and Thaumarchaeota, Aigarchaeota, Crenarchaeota, and Korarchaeota (TACK); see Supplemental Information for details on tree construction and fragment placement methodology; (B) relative abundances of total sequences representing methanogenic archaea in mixed cultures; panels (C) MeOH, (D) H₂/CO₂, and (E) acetate depict qPCR data showing the proportional changes of total bacterial and total archaeal (methanogen) 16S rRNA genes in the mixed cultures without N₂O and in the presence of 10 and 30 μM N₂O; error bars represent the standard deviation of replicate samples (n = 9, three technical replicates of triplicate biological samples).