Syntrophaceticus was notably the second most dominant genus in the biofilm samples of R1 and R3, with average relative abundances of approximately 9% and 12%, respectively, and the third most dominant in R2, with an average relative abundance of about 7%. While the specific roles of the Syntrophaceticus species detected in our experiments remain unclear, its dominance suggests probable syntrophic cooperation with hydrogenotrophic methanogenic archaea . This observation also corresponds with the higher acetate concentrations observed in R3, which may support the greater abundance of this genus in that reactor.