Anaerobic conversion of organic matter leads to the intermediate formation of volatile fatty acids (VFA), primarily butyrate, propionate and acetate. The present investigation examined methanogenesis from the VFA by microbial populations associated with natural and man-made cold habitats. Sites that were investigated included lake sediments, tundra wetland soil, sludge lagoons, manure store and anaerobic reactors operated at 3–9°C. Sharp increases in methanogenesis from VFA were observed as incubation temperatures were increased to 30°C. Low temperatures resulted in significant methane production, and butyrate was identified as an important VFA intermediate formed and degraded during sample incubations. The addition of butyrate and propionate to samples indicated that butyrate is degraded preferentially over propionate. Dilution of samples and, hence, microbial populations led to the accumulation of acetate and hydrogen when butyrate and propionate were degraded. Thus, at low temperatures, a highdensity of hydrogen- and acetate-utilizing methanogens is needed for methanogenesis from VFA to occur. An aggregation of proton-reducing acetogenic bacteria and methanogens accelerates this process.

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