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

In a mesophilic (37 degree C) triculture at a high ammonium concentration and pH8, methanogenesis from acetate occurred via syntrophic acetate oxidation. Studies with super(14)C-labelled substrates showed that the amount of labelled methane formed from 1- super(14)C-labelled acetate was equal to that formed from 2- super(14)C-labelled acetate. Labelled methane was also formed from H super(14)CO sub(3) super(-). These results clearly showed that both the methyl and carboxyl groups of acetate were oxidized to CO sub(2), and that CO sub(2) was reduced to CH sub(4) 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- super(14)C-acetate, and the production of super(14)CO sub(2) was slightly higher from 1- super(14)C- than from 2- super(14)C-acetate. For each mole acetate degraded, 0.94 mol methane was formed; 9.2 mmol acetate was metabolized during the 294 days of incubation. An acetate-oxidizing syntrophic association consisting of an acetogenic bacterium and a sulphate-reducing bacterium (Desulfomicrobium aspheronum) has been described.