Microbiology and biochemistry of the methanogenic archaeobacteria

The methane producing bacteria area diverse group of organisms that function in nature with other groups of strictly anaerobic bacteria to convert complex organic matter to methane and carbon dioxide. The methanogens belong to the archaeobacteria, a third primary kingdom distinct from all other procaryotes (eubacteria) and eucaryotes. The distinction is based on the unique structures of cell wall and membrane components present in archaeobacteria, as well as differences in the highly conserved 16s rRNA sequences among the three kingdoms. In addition, the methanogens contain several novel cofactors that function as one-carbon carriers during the reduction of carbon dioxide to methane with electrons derived from the oxidation of H₂ or formate. Methanogens also convert acetate to methane by a pathway distinct from that for carbon dioxide reduction. The pathway involves activation of acetate to acetyl-SCoA followed by decarbonylation and reduction of the methyl group to methane coupled to the oxidation of the carbonyl group to carbon dioxide.