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Applied and Environmental Microbiology, January 2003, p. 74-83, Vol. 69, No. 1
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.1.74-83.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

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

Marcus A. Horn, Carola Matthies, Kirsten Küsel, Andreas Schramm, and Harold L. Drake*

Department of Ecological Microbiology, BITOEK, University of Bayreuth, D-95440 Bayreuth, Germany

Received 17 June 2002/ Accepted 2 October 2002

The emission of methane (1.3 mmol of CH4 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 CH4 (0.4 to 1.7 µmol g [dry wt] of soil-1 day-1) under anoxic conditions. At in situ pH, supplemental H2-CO2, ethanol, and 1-propanol all increased CH4 production rates while formate, acetate, propionate, and butyrate inhibited the production of CH4; methanol had no effect. H2-dependent acetogenesis occurred in H2-CO2-supplemented bog peat only after extended incubation periods. Nonsupplemented bog peat initially produced small amounts of H2 that were subsequently consumed. The accumulation of H2 was stimulated by ethanol and 1-propanol or by inhibiting methanogenesis with bromoethanesulfonate, and the consumption of ethanol was inhibited by large amounts of H2; these results collectively indicated that ethanol- or 1-propanol-utilizing bacteria were trophically associated with H2-utilizing methanogens. A total of 109 anaerobes and 107 hydrogenotrophic methanogens per g (dry weight) of bog peat were enumerated by cultivation techniques. A stable methanogenic enrichment was obtained with an acidic, H2-CO2-supplemented, fatty acid-enriched defined medium. CH4 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 CH4-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 H2 that could be used by hydrogenotrophic methanogens. These results indicated that in this acidic bog peat, (i) H2 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.

* Corresponding author. Mailing address: Department of Ecological Microbiology, BITOEK, University of Bayreuth, 95440 Bayreuth, Germany. Phone: [49] (0)921-555 640. Fax: [49] (0)921-555 793. E-mail: harold.drake{at}bitoek.uni-bayreuth.de.

Applied and Environmental Microbiology, January 2003, p. 74-83, Vol. 69, No. 1
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.1.74-83.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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