Mesophilic syntrophic acetate oxidation during methane formation by a triculture at high ammonium concentration

Abstract

In a mesophilic (37°C) triculture at a high ammonium concentration and pH8, methanogenesis from acetate occurred via syntrophic acetate oxidation. Studies with 14C-labelled substrates showed that the amount of labelled methane formed from 1-14C-labelled acetate was equal to that formed from 2-14C-labelled acetate. Labelled methane was also formed from H14CO3-. These results clearly showed that both the methyl and carboxyl groups of acetate were oxidized to CO2 and that CO2 was reduced to CH4 through hydrogenotrophic methanogenesis. During growth of the triculture, a significant isotopic exchange between the carboxyl group of acetate and bicarbonate occurred. As a result, there was a decrease in the specific activity of 1-14C-acetate, and the production of 14CO2 was slightly higher from 1-14C- than from 2-14C-acetate. For each mole acetate degraded, 0.94 mol methane was formed; 9.2 mmol acetate was metabolized during the 294 days of incubation.