Methanogen

Methanogens are obligate anaerobic archaea that either consume or produce CO₂, producing CH₄. Methanotrophs consume CH₄.

Requirements for growth:

• Anoxic sediments

• Animal digestive systems (rumen of cattle, sheep, elk, camels)

• Geothermal sources of H₂ + CO₂

• Artificial biodegradation facilities

• Endozymbiots of anaerobic protozoa

As herbivores, they live off the complex carbohydrate cellulose. Methane produced in rumen creates pressure, thereby causing risk of explosion. H₂ is methanogenic e^- donor. Hydrogen consumption of methanogens coupled to hydrogren production of something else. Why syntrophy? Mutual beenfit. Complementation of two or more organisms metabolic capabilities to catabolize a substance not cpaable of being catabolized by either one alone.

Methanogenic substrates include CO₂-type substrates (including formate, CO₂+H₂ combined; CO): 4H₂ + CO₂ → reduction → CH₄ + 2H₂O ΔG = -131 kJ.

Methyl substrates (methanol):

CH₃OH + H₂ → CH₄ + H₂O ΔG = -113 kJ
4CH₃OH → 3CH₄ + CO₂ + 2H₂O ΔG = -319 kJ

Acetotrophic substrates:

CH₃COO- + H₂O → CH₄ + HCO₃ ΔG = -31