Hydrogenotrophic Methanogenesis by Moderately Acid-Tolerant Methanogens of a Methane-Emitting Acidic Peat

Abstract

The emission of methane (1.3 mmol of CH 4 m ؊2 day ؊1 ), precursors of methanogenesis, and the methanogenic microorganisms of acidic bog peat (pH 4.4) from a moderately reduced forest site were investigated by in situ measurements, microcosm incubations, and cultivation methods, respectively. Bog peat produced CH 4 (0.4 to 1.7 mol g [dry wt] of soil ؊1 day ؊1 ) under anoxic conditions. At in situ pH, supplemental H 2 -CO 2 , ethanol, and 1-propanol all increased CH 4 production rates while formate, acetate, propionate, and butyrate inhibited the production of CH 4 ; methanol had no effect. H 2 -dependent acetogenesis occurred in H 2 -CO 2 -supplemented bog peat only after extended incubation periods. Nonsupplemented bog peat initially produced small amounts of H 2 that were subsequently consumed. The accumulation of H 2 was stimulated by ethanol and 1-propanol or by inhibiting methanogenesis with bromoethanesulfonate, and the consumption of ethanol was inhibited by large amounts of H 2 ; these results collectively indicated that ethanol-or 1-propanol-utilizing bacteria were trophically associated with H 2 -utilizing methanogens. A total of 10 9 anaerobes and 10 7 hydrogenotrophic methanogens per g (dry weight) of bog peat were enumerated by cultivation techniques. A stable methanogenic enrichment was obtained with an acidic, H 2 -CO 2 -supplemented, fatty acid-enriched defined medium. CH 4 production rates by the enrichment were similar at pH 4.5 and 6.5, and acetate inhibited methanogenesis at pH 4.5 but not at pH 6.5. A total of 27 different archaeal 16S rRNA gene sequences indicative of Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae were retrieved from the highest CH 4 -positive serial dilutions of bog peat and methanogenic enrichments. A total of 10 bacterial 16S rRNA gene sequences were also retrieved from the same dilutions and enrichments and were indicative of bacteria that might be responsible for the production of H 2 that could be used by hydrogenotrophic methanogens. These results indicated that in this acidic bog peat, (i) H 2 is an important substrate for acid-tolerant methanogens, (ii) interspecies hydrogen transfer is involved in the degradation of organic carbon, (iii) the accumulation of protonated volatile fatty acids inhibits methanogenesis, and (iv) methanogenesis might be due to the activities of methanogens that are phylogenetic members of the Methanobacteriaceae, Methanomicrobiales, and Methanosarcinaceae.

Nitrogen and methanogen community composition within and among three Sphagnum dominated peatlands in Scandinavia

“…The family belongs to the order Methanomicrobiales, which produces methane by the reduction of carbon dioxide and oxidation of hydrogen (Deppenmeier, 2002;Liu and Whitman, 2008). The hydrogenotrophy has been shown to be the main pathway of methane production in acidic bogs (Horn et al, 2003;Galand et al, 2005). This fits with the pH-driven regulation of the two methanogenic pathways observed by Kotsyurbenko et al (2007), i.e.…”

Psychrophilic methanogenic community development during long-term cultivation of anaerobic granular biofilms

“…Such a shift is likely as a result of enhanced homoacetogenic activity (Schulz and Conrad, 1996). Conversely, methanogenesis has been shown to predominantly proceed through the hydrogenotrophic route in low-temperature natural (Horn et al, 2003;Kotsyurbenko et al, 2007) and engineered anaerobic bioreactors Connaughton et al, 2006;Syutsubo et al, 2008). Under low-temperature conditions, improved thermodynamics of methane formation from H 2 / CO 2 , coupled with the enhanced solubility and therefore accessibility of H 2 /CO 2 in the reactor liquor, are thought to account for this phenomenon (Lettinga et al, 2001).…”

“…Psychrotrophic and psychrophilic Archaea contribute significantly to the biomass in the predominantly cold biosphere (for example, c. 10 28 cells in the world's oceans) and typically, these habitats are characterized by hypoxic/anoxic conditions and are low in inorganic terminal electron acceptors (Horn et al, 2003). Under such conditions, organic matter is principally biotransformed through methanogenesis (Conrad et al, 1989).…”

“…Increased acetate production through enhanced homoacetogenic activity may account for this phenomenon in low-temperature environments (Schulz and Conrad, 1996). However, hydrogenotrophic methanogenesis has also been shown to play an important role in cold terrestrial habitats (Horn et al, 2003;Kotsyurbenko et al, 2007). It is proposed that the predicted increase in global temperatures will result in substantially increased methane emissions from cold biomes (Galand et al, 2003).…”

Carbon flow from volcanic CO2 into soil microbial communities of a wetland mofette

“…We expected the reduction of CO 2 by methanogens and/or acetogens to become the thermodynamically dominant electron accepting process in the wetlands after depletion of the usually small pools of alternative electron acceptors. Because hydrogenotrophic methanogens and metabolically versatile acetogens can tolerate slightly acidic conditions (Kü sel et al, 2000;Horn et al, 2003), these anaerobes might be favored by the low pH, anoxic conditions, as well as the high availability of CO 2 in mofette soil (Drake et al, 2009(Drake et al, , 2013, thus providing an important link in the carbon flow from volcanic CO 2 to soil carbon.…”