Influence of temperature and high acetate concentrations on methanogenensis in lake sediment slurries

Abstract

Methanogenesis from main methane precursors H2/CO2 and acetate was investigated in a temperature range of 2-70°C using sediments from Lake Baldegg, Switzerland. Psychrophilic, psychrotrophic, mesophilic, and thermophilic methanogenic microbial communities were enriched by incubations for 1-3 months of nonamended sediment slurries at 5, 15, 30, and 50°C. Isotope experiments with slurries amended with 14C-labeled bicarbonate and 14C-2-acetate showed that in the psychrophilic community (enriched at 5°C), about 95% of methane originated from acetate, in contrast to the thermophilic community (50°C) where up to 98% of methane was formed from bicarbonate. In the mesophilic community (30°C), acetate was the precursor of about 80% of the methane produced. When the hydrogen-carbon dioxide mixture (H2/CO2) was used as a substrate, it was directly converted to methane under thermophilic conditions (70 and 50°C). Under mesophilic conditions (30°C), both pathways, hydrogenotrophic and acetoclastic, were observed. At low temperatures (5 and 15°C), H 2/CO2 was converted into methane by a two-step process; first acetate was formed, followed by methane production from acetate. When slurries were incubated at high partial pressures of H2/CO 2, the high concentrations of acetate produced of more than 20 mM inhibited acetoclastic methanogenesis at a temperature below 15°C. However, slow adaptation of the psychrophilic microbial community to high acetate concentrations was observed. © 2007 Federation of European Microbiological Societies.