Abstract
Factors affecting propionate oxidation in a methanogenic microbial community derived from an anaerobic-digester sludge of cattle waste were investigated. The sludge was inoculated into a propionate-containing artificial wastewater medium, and cultures were incubated at mesophilic (30°C) and thermophilic (55°C) temperatures by a subculture technique. During subculture, however, the rate of propionate oxidation rapidly declined. To stabilize propionate oxidation, the use of some additives was examined. The addition of sulfate, pyruvate, fumarate, hemin, or yeast extract did not prevent the decrease in the rate of propionate oxidation. The addition sludge extract (supernatant fluid fraction of sludge autoclaved at 121°C) efficiently stabilized propionate oxidation. Although, the addition of dry powder of the sludge extract prepared at 110°C stabilized methane fermentation, that of sludge extract ash did not stabilize the process. Moreover, the addition of a low-molecular-weight fraction (below ca. 14,000) obtained by the dialysis of the sludge extract also stabilized the process. The present results indicate that effective components for stabilizing propionate oxidation in the sludge extract are low-molecular-weight organic compounds.
