초록
<P>A combination of acetate oxidation and acetoclastic methanogenesis has been previously identified to enable high-rate methanogenesis at high temperatures (55 to 65°C), but this capability had not been linked to any key organisms. This study combined RNA–stable isotope probing on <SUP>13</SUP>C-labelled acetate and 16S amplicon sequencing to identify the active micro-organisms involved in high-rate methanogenesis. Active biomass was harvested from three bench-scale thermophilic bioreactors treating waste activated sludge at 55, 60 and 65°C, and fed with <SUP>13</SUP>-C labelled and <SUP>12</SUP>C-unlabelled acetate. Acetate uptake and cumulative methane production were determined and kinetic parameters were estimated using model-based analysis. Pyrosequencing performed on <SUP>13</SUP>C- enriched samples indicated that organisms accumulating labelled carbon were <I>Coprothermobacter</I> (all temperatures between 55 and 65°C), acetoclastic <I>Methanosarcina</I> (55 to 60°C) and hydrogenotrophic <I>Methanothermobacter</I> (60 to 65°C). The increased relative abundance of <I>Coprothermobacter</I> with increased temperature corresponding with a shift to syntrophic acetate oxidation identified this as a potentially key oxidiser. <I>Methanosarcina</I> likely acts as both a hydrogen utilising and acetoclastic methanogen at 55°C, and is replaced by <I>Methanothermobacter</I> as a hydrogen utiliser at higher temperatures.</P>