Methanogenesis and methanogenic pathways in a peat from subarctic permafrost

• Published in: Environmental Microbiology
• Main Authors: Metje, Martina, Frenzel, Peter
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2007
• Subjects: Arctic; permafrost; Subarctic; Siberia
• Online Access: http://dx.doi.org/10.1111/j.1462-2920.2006.01217.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1462-2920.2006.01217.x; http://onlinelibrary.wiley.com/wol1/doi/10.1111/j.1462-2920.2006.01217.x/fullpdf

Summary Few studies have dealt so far with methanogenic pathways and populations in subarctic and arctic soils. We studied the effects of temperature on rates and pathways of CH 4 production and on the relative abundance and structure of the archaeal community in a mildly acidic peat from a permafrost region in Siberia (67°N). We monitored the production of CH 4 and CO 2 over time and measured the consumption of Fe(II), ethanol and volatile fatty acids. All experiments were performed with and without specific inhibitors [2‐bromoethanesulfonate (BES) for methanogenesis and CH 3 F for acetoclastic methanogenesis]. The optimum temperature for methanogenesis was between 26°C and 28°C [4.3 μmol CH 4 (g dry weight) −1 day −1 ], but the activity was high even at 4°C [0.75 μmol CH 4 (g dry weight) −1 day −1 ], constituting 17% of that at 27°C. The population structure of archaea was studied by terminal restriction fragment length polymorphism analysis and remained constant over a wide temperature range. Acetoclastic methanogenesis accounted for about 70% of the total methanogenesis. Most 16S rRNA gene sequences clustered with Methanosarcinales , correlating with the prevalence of acetoclastic methanogenesis. In addition, sequences clustering with Methanobacteriales were recovered. Fe reduction occurred in parallel to methanogenesis. At lower and higher temperatures Fe reduction was not affected by BES. Because butyrate was consumed during methanogenesis and accumulated when methanogenesis was inhibited (BES and CH 3 F), it is proposed to serve as methanogenic precursor, providing acetate and H 2 by syntrophic oxidation. In addition, ethanol and caproate occurred as intermediates. Because of thermodynamic constraints, homoacetogenesis could not compete with hydrogenotrophic methanogenesis.