Gastro-enteric methane versus sulphate and volatile fatty acid production

The breakdown of low digestible components present in food during passage through the human and animal gastro-intestinal (GI) tract is performed by the highly diverse microbial community present in this ecosystem. Fermentation of these substances yields, besides CO₂ and volatile fatty acids, H₂, which is used as a substrate by three different H₂-consuming bacteria. Sulphate-reducing bacteria (SRB) use H₂ to reduce SO _inf4 ^sup2- to H₂S, hydrogenotrophic methane-producing bacteria (MPB) use H₂ to reduce CO₂ to CH₄ and reductive acetogens (RAC) use H₂ to reduce CO₂ to CH₃COOH. A competition between these three bacterial groups exists for the common H₂ substrate. This results generally in the dominance of one group above the other two.