Overall, the AS inoculum proved most effective for rapid CO conversion, outperforming both AD and CM. While CM eventually adapted to CO conditions, its prolonged adaptation period and initial high VFA levels may have slowed methanogen enrichment, rather than microbial diversity itself being a limiting factor. These findings suggest that successful CO conversion in TBRs is driven by the enrichment and activity of functional microbial groups rather than overall microbial diversity. . These findings invalidated our hypothesis that fresh inoculum sources like CM could adapt more readily to CO conversion by a shift in microbial community composition. We initially expected that a diverse microbial community in CM would enable better adaptation compared to AS and AD, which have already adapted to anaerobic digestion conditions. Instead, our results align with previous studies , indicating that the microbial community in cow manure is less suited for CO conversion than anaerobic sludge or digestate.