Abstract

Research : Biogeosciences

Hydrogen and carbon isotope systematics in hydrogenotrophic methanogenesis under H2-limited and -enriched conditions: Implications for the origin of methane and its isotopic diagnosis

Okumura T, Kawagucci S, Saito Y, Matsui Y, Takai K, and Imachi H
Keywords:
Methane, Hydrogenotrophic methanogenesis, Hydrogen isotope ratio, Carbon isotope ratio, H2 availability, Culture experiments

Hydrogen and carbon isotope systematics of H2O–H2–CO2–CH4 in hydrogenotrophic methanogenesis and their relation to H2 availability were investigated. Two H2-syntrophic cocultures of fermentatively hydrogenogenic bacteria and hydrogenotrophic methanogens under conditions of <102 Pa-H2 and two pure cultures of hydrogenotrophic methanogens under conditions of ~105 Pa-H2 were tested. Carbon isotope fractionation between CH4 and CO2 during

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Cartoons of intra- and trans-membrane fluxes of the molecules in hydrogenotrophic methanogenesis relating to hydrogen and carbon isotope systematics. Each five panel represents methanogenic characteristics with respect to growth rate and pH2 condition for the growth. Red arrows represent significant molecular fluxes relating with CH4 isotope ratios. Light green and blue arrows represent significant molecular fluxes not relating with CH4 isotope ratios. Grey arrows represent negligible molecular fluxes. Dash-dotted circles are cell membrane, and arrows enclosed by dotted lines represent multistep methanogenic reaction (numbers of the arrows have no meaning). A term “H2O” in cartoon represents both H2O and H+. See main text for details

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