High-throughput Barcoded Sequencing Analysis Revealed Direct and Indirect Methanogenesis of Tetramethylammonium Hydroxide (TMAH) in Ambient Methanogenic Reactors

Tetramethyl ammonium hydroxide (TMAH) degrading methanogenic consortia from a bench-scale chemostat and a full-scale upflow anaerobic sludge blanket reactor at ambient conditions were studied using the 16S rRNA-based molecular approach. As revealed by quantitative PCR, the archaeal populations were more abundant than the bacterial populations in both reactors by orders of 102-103 magnitudes, suggesting that the methanogenic archaea played an important role in sustaining the conversion of TMAH to methane. The barcoded high-throughput sequencing of bacterial and archaeal 16S rRNA gene amplicons revealed that the sludges from the chemostat and UASB reactor differed markedly in the community structures. The methane was mainly produced via direct methanogenesis of TMAH in the chemostat, because the methylotrophic methanogens such as Methanomethylovorans spp. and Methanolobus spp., accounting to 93.9% of total archaeal 16S rRNA sequences, were highly predominant. In the sludge from different heights of the UASB reactor, the archaeal populations exhibited a distinctive vertical stratification, with high sequence abundance (74–89.5%) of methylotrophic Methanosarcina spp. in the bottom and top space of the reactor and hydrogenotrophic Methanobacterium spp. in the heights of 100-200 cm (70.2–76.5%). Compared to direct methanogenesis, the results of this study for the first time indicated an interspecies hydrogen transfer–dependent conversion of quaternary amine was equally important in the ambient UASB reactor.