The process in which organic matter is degraded
anaerobically by cooperation of several organisms in which some produce
H2 and some use H
2.
An interesting phenomenon in the bacterial
methanogenesis (the consumption of material and release of
methane gas) is the coupling of two bacterial classes. The breakdown of complex biological
polymers such as
cellulose or
protein into methane goes through many stages, each of which has specialized
microbes that carry it out. H
2 producing
fatty acid oxidizing bacteria (also known as
syntrophs) take fatty acids or
alcohols generated by other microbes and use them as growth substrates. These bacteria release H
2 during breakdown of the fatty acid which is then used as an energy source for
methanogens or
sulfate-reducing bacteria. When syntrophs are oxidizing the fatty acids into carbon dioxide and H
2, the production of
ATP is coupled to this reaction. Thus, buildup of H
2 would make this process less efficient. The methanogens and sulfate-reducing bacteria are therefore helpful to the syntrophs, as they consume the excess hydrogen and convert it to methane. A great example of
symbiosis.