Acetogenesis from CO2 in the Human Colonic Ecosystem
Figure 13.1 shows the general features of the colonic fermentation. The human diet contains high concentrations of plant polysaccharides (cellulose, hemicellulose, pectin, and starch). Except for starch, they are not digested by host enzymes and pass to the colon where they are fermented by the cooperative metabolism of a large number of different bacterial species (Cummings, 1985; Wolin and Miller, 1983). Significant amounts of starch escape host digestion and are fermented in the colon (Stephen et al., 1983; Thornton et al., 1987). The fermentation of plant polysaccharides produces acetate, propionate, and butyrate and the gases H2 and CO2 (Cummings, 1985; McNeil, 1984). CH4 is a major product of the colonie fermentation of some humans (Bond et al., 1971; Levitt, 1980). They harbor large concentrations of methane-forming Archae that use H2 to reduce CO2 to CH4 (Miller and Wolin, 1982; Weaver et al., 1986).
KeywordsHuman Feces Carbohydrate Fermentation Fecal Suspension Ecological Potential Acetogenic Bacterium
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