Fig. 4

Schematic representation describing the main degradation pathways of the substrates and the responsible MAGs. Green and red arrows indicate pathways enriched with up- and downregulated genes, respectively. Orange arrow indicates the connection between MAGs which mostly upregulated electron transport chain mechanisms, and hydrogenotrophic archaea. Orange dashed arrow specifically highlights the proposed syntrophic association between Coprothermobacter proteolyticus UC0011 and Methanothermobacter wolfeii UC0008. Metabolic representation of R2 was based on the change in abundance of the indicated MAGs, while for R1 and R3 it was based on gene expression data. R1 single-stage reactor, R2 acidogenic reactor of the two-stage configuration, R3 methanogenic reactor of the two-stage configuration, extH₂ external hydrogen, intH₂ internal hydrogen