Mesophilic syntrophic acetate oxidation during methane formation in biogasreactors

The reaction pathway for the formation of methane from acetate was investig ated in sludge from 13 different biogas reactors. By following the conversi on of [2-C-14]acetate and [C-14]bicarbonate it was shown that methane forma tion by syntrophic acetate oxidation was the dominating mechanism for aceto trophic methanogenesis in sludge containing high levels of salts, mainly am monium, and volatile fatty acids. In one biogas reactor the degree of syntr ophic acetate oxidation increased as the concentrations of salts and volati le fatty acids increased. Statistical evaluation with principal component a nalysis showed a close correlation between the degree of syntrophic acetate oxidation and the concentrations of ammonium and potassium. The acetate de gradation rate was lower (10-800 times) in biogas reactors in which methane was formed through syntrophic acetate oxidation than in biogas reactors wh ere acetate was directly cleaved to methane and carbon dioxide. Microscopic observations revealed a predominance of one type of methanogen in the reac tors with syntrophic acetate oxidation. Isolation and characterization, inc luding substrate spectrum, mol% G+C, polyamine and 16S rRNA analysis, showe d that the strains were hydrogenotrophic methanogens belonging to the genus Methanoculleus. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.