Effect of Temperature on Anaerobic Ethanol Oxidation and Methanogenesis in Acidic Peat from a Northern Wetland

Abstract

The effects of temperature on rates and pathways of CH 4 production and on the abundance and structure of the archaeal community were investigated in acidic peat from a mire in northern Scandinavia (68°N). We monitored the production of CH 4 ؊1 · day ؊1 ). The theoretical lower limit for methanogenesis was calculated to be at ؊5°C. The optimum temperature for growth as revealed by real-time PCR was 25°C for both archaea and bacteria. The population structure of archaea was studied by terminal restriction fragment length polymorphism analysis and remained constant over a wide temperature range. Hydrogenotrophic methanogenesis accounted for about 80% of the total methanogenesis. Most 16S rRNA gene sequences that were affiliated with methanogens and all McrA sequences clustered with the exclusively hydrogenotrophic order Methanobacteriales, correlating with the prevalence of hydrogenotrophic methanogenesis. Fe reduction occurred parallel to methanogenesis and was inhibited by BES, suggesting that methanogens were involved in Fe reduction. Based upon the observed balance of substrates and thermodynamic calculations, we concluded that the ethanol pool was oxidized to acetate by the following two processes: syntrophic oxidation with methanogenesis (i) as an H 2 sink and (ii) as a reductant for Fe(III). Acetate accumulated, but a considerable fraction was converted to butyrate, making volatile fatty acids important end products of anaerobic metabolism.

Stable carbon isotope fractionation during methanogenesis in three boreal peatland ecosystems

“…In Alaskan peatland acetate was found to accumulate instead of being further converted to CH 4 (Duddleston et al, 2002). In a Finnish peat bog part of the acetate was found to be further converted to butyrate (Metje and Frenzel, 2005). Later studies indicated that a decreasing pH resulted in decreasing acetate turnover and in the relative dominance of hydrogenotrophic methanogenesis (Kotsyurbenko et al, 2007), and that the type of vegetation, i.e., dominance of Sphagnum P. E. Galand et al: Carbon isotope fractionation in methanogenic peatlands over vascular plants, coincides with the occurrence of acetate accumulation .…”

“…In fact, this path of CH 4 production has been demonstrated in various peat bogs ranging from Michigan (Avery et al, 1999), western Siberia (Kotsyurbenko et al, 2004) to the permafrost region of northwestern Siberia (Metje and Frenzel, 2007). In some peat ecosystems, however, acetoclastic methanogenesis is apparently impeded and CH 4 is mainly produced from H 2 /CO 2 (Lansdown et al, 1992;Horn et al, 2003;Metje and Frenzel, 2005;Prater et al, 2007). In Alaskan peatland acetate was found to accumulate instead of being further converted to CH 4 (Duddleston et al, 2002).…”

Wetland restoration and methanogenesis: the activity of microbial populations and competition for substrates at different temperatures

“…Organic acids and alcohols were measured by HPLC and GC, respectively, as described previously (Metje and Frenzel, 2005). Nitrate and sulphate were extracted from 0.15 g of wet soil or slurry by mixing with 600 µl of distilled water for 1 h. The extract was obtained as described above, and nitrate, nitrite and sulphate were determined by ion chromatography (Bak et al, 1991).…”

“…The effect of temperature on methanogenesis and methanogenic pathways has been studied in different sediments and soils showing a wide variety of reactions: methanogenesis may dominate at low temperatures, while electrons are diverted to iron reduction at the respective temperature optimum of mineralization (Metje and Frenzel, 2005). H 2 /CO 2 may be used preferably by acetogens at low temperature, but by methanogens at higher temperature (Schulz and Conrad, 1996).…”

Trophic status impacts both the magnitude and stable carbon isotope composition of methane flux from peatlands

“…In the same Finnish mire complex, Galand et al [2005] reported H 2 /CO 2 methanogenesis to be most prevalent in the order mesotrophic fen < ombrotrophic bog < oligotrophic fen and that methanogens in the mesotrophic fen were dominated by obligate acetate-utilizers of the genus Methanosaeta. Metje and Frenzel [2005] reported that $80% of methanogenesis in a northern Finnish acid mire (pH 4.1) occurred via the CO 2 /H 2 pathway and that the majority of mcrA sequences clustered with the obligate hydrogenotrophic order Methanobacteriales. The majority of methanogens within two anaerobic consortia isolated from an acid West Siberia peatland also utilized the H 2 / CO 2 pathway [Sizova et al, 2003].…”