Methanogens are anaerobic unicellular organisms, that release methane as a waste product of cellular metabolism. All of the methanogens are lithotrophs that can make their own energy only by methanogenesis, or the production of methane. They are found mostly in anaerobic freshwater environments, such as lake sediments and the digestive tracts of animals. In these habitats, methanogens play an important role in the degradation of complex organic compounds. Methanogens are also found in extreme environments such as hydrothermal vents, where they thrive at temperatures above 100ºC. Methanogens produce 109 tons of methane per year. About half is reoxidized by methanotrophic bacteria, but most of the rest escapes to the atmosphere, where it is a potent greenhouse gas.



Cell structure:
Methanogens are made primarily in two shapes, cocci and rods.
Can also be found having a plate like structure
Have unique enzymes and cofacters

The left image shows a plated methonogen, the right image shows a cluster of cocci methanogens.




These are found living in such anerobic environments as
• the muck of swamps and marshes;
• the rumen of cattle (where they live on the hydrogen and CO2 produced by other microbes living along with them);
• sewage sludge;
• the gut of termites.
They are chemoautotrophs; using hydrogen as a source of electrons for reducing carbon dioxide to food and giving off methane ("marsh gas", CH4) as a byproduct.
4H2 + CO2 -> CH4 + 2H2O

In this reaction, the electron donor is hydrogen, and carbon dioxide serves as the electron acceptor. Methane can also be generated from other methyl compounds, including methanol and acetate

What would happen if these bacertia did not occur?
Organic acids and alcohols would accummulate. The organisms would drown in their own wastes.
Many would stop growing or die.