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Tetramethylammonium hydroxide (TMAH)-degrading methanogenic consortia from a laboratory-scale completing-mixing suspended sludge (CMSS) and full-scale upflow anaerobic sludge blanket (UASB) reactors under ambient conditions were studied using an 16S rRNA-based molecular approach. As revealed by quantitative PCR, archaeal populations were more abundant than bacterial populations in both reactors by 2–3 orders of magnitude, suggesting that the methanogenic archaea played a critical role in sustaining the conversion of TMAH to methane. Barcoded high-throughput sequencing of bacterial and archaeal 16S rRNA gene amplicons revealed that the sludge from the two reactors differed markedly according to community structure. Methylotrophic Methanomethylovorans and Methanolobus, accounting for 93.9% of the total archaeal 16S rRNA sequences, were highly predominant in the CMSS reactor, which corresponds to direct methanogenesis with low TMAH. In the sludge samples taken from various heights in the UASB reactor, the methanogenic populations exhibited distinct stratification, with high abundance of methylotrophic Methanosarcina (74.0–89.5%) in bottom and top spaces of the reactor, and hydrogenotrophic Methanobacterium (70.2–76.5%) in the middle, respectively. Compared with the direct route, the results of this study indicate that the indirect pathway through interspecies hydrogen transfer-dependent conversion of TMAH is equally critical in the UASB reactor. |