Methanogens in the Digestive Tract of Termites
Methanogenesis in the enlarged hindgut compartments of termites is a product of symbiotic digestion, fueled by hydrogen and reduced one-carbon compounds formed during the fermentative breakdown of plant fiber and humus. Methanogens are not always the pred
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Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 2 Methane as a Product of Symbiotic Digestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 3 Diversity of Methanogens in Termite Guts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 4 Differences in Methanogenic Activities and Populations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5 Coexistence with Homoacetogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 6 Association with Gut Flagellates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 7 Intercompartmental Transfer of Hydrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 8 Relationship to Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 9 Termites as a Source of Atmospheric Methane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Abstract Methanogenesis in the enlarged hindgut compartments of termites is a product of symbiotic digestion, fueled by hydrogen and reduced one-carbon compounds formed during the fermentative breakdown of plant fiber and humus. Methanogens are not always the predominant hydrogenotrophic microorganisms, especially in wood-feeding termites, but are restricted to particular microhabitats within the gut. The methanogens in lower termites belong to different lineages of Methanobacteriales that either are endosymbionts of flagellate protists or colonize the periphery of the hindgut, a habitat that is not fully anoxic. The oxygen-reducing capacities of the few isolates so far available indicate that they are well adapted to the continuous influx of oxygen across the gut wall. Higher termites, which lack gut flagellates, often have highly compartmented guts with highly dynamic physicochemical conditions, including redox and pH. The differences between the microenvironments are most pronounced in the soil-feeding species, where each A. Brune Department of Biogeochemistry, Max Planck Institute for Terrestrial Microbiology, Karl-vonFrisch-Strasse 10, 35043 Marburg, Germany e-mail: [email protected]
J.H.P. Hackstein (ed.), (Endo)symbiotic Methanogenic Archaea, Microbiology Monographs 19, DOI 10.1007/978-3-642-13615-3_6, # Springer-Verlag Berlin Heidelberg 2010
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