Methanogenesis and methanogenic partnerships

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Abstract
The microbial formation of methane from organic compounds greater than C 2 in chain length demands a mixture of methanogenic and chemoheterotrophic non-methanogenic bacteria. The chemoheterotrophic, non-methanogens initiate the reactions by well established pathways, hydrolysing complex polymers and fermenting the unit constituents to smaller end-product molecules, which are further metabolized by other chemoheterotrophs to acetic acid, H 2 and CO 2 . The methanogens are essential physiological partners in the overall conversion of the initial substrates to this level because they oxidize H 2 and reduce CO 2 to form methane. The ultimate sformation of acetate as the chief intermediate in this fermentation depends on the removal of H 2 by the methanogens. Otherwise, these acetogenic reactions are not thermodynamically feasible. Acetate, the major precursor of CH 4 in fermentation systems, is converted to CH 4 and CO 2 via a unique aceticlastic reaction. Examples of microbial partnerships producing methane from the fermentation of organic com­ pounds are described