Methane Oxidizing and Producing Bacteria (World of Microbiology and Immunology)
Methane is a chemical compound that consists of a carbon atom to which are bound four hydrogen atoms. The gas is a major constituent of oxygen-free mud and water, marshes, the rumen of cattle and other animals, and the intestinal tract of mammals. In oxygen-free (anaerobic) environments, methane can be produced by a type of bacteria known as methanogenic bacteria. Methane can also be used as an energy source by other bacteria that grow in the presence of oxygen (aerobic bacteria), which break down the compound into carbon dioxide and water. These bacteria are known as methane oxidizing bacteria.
Bacteria from a number of genera are able to oxidize methane. These include Methylosinus, Methylocystis, Methanomonas, Methylomonas, Methanobacter, and Methylococcus. A characteristic feature of methane-oxidizing bacteria is the presence of an extensive system of membranes inside the bacterial cell. The membranes house the enzymes and other biochemical machinery needed to deal with the se of methane as an energy source.
The oxidation of methane by bacteria requires oxygen. The end result is the production of carbon dioxide and water. Methane oxidation is restricted to prokaryotes. Eukaryotic microorganisms such as algae and fungi do not oxidize methane.
The production of methane is a feature of anaerobic bacteria. Examples of methane producing genera are Methanobacterium, Methanosarcina, Methanococcus, and Methanospirillum. Methanogenic bacteria are widespread in nature, and are found in mud, sewage, and sludge and in the rumen of sheep and cattle. Some methanogenic bacteria have adapted to live in extreme environments. For example, Methanococcus jannaschii has an optimum growth temperature of 85° C (185° F), which is achieved in hot springs and thermal vents in the ocean. Such anaerobic bacteria are among the oldest life forms on Earth. They evolved long before the presence of photosynthetic green plants, and so existed in an oxygen-free world.
In the rumen, the methane-producing bacteria occupy a central role in regulating the anaerobic breakdown (fermentation) of food. The bacteria remove hydrogen gas through the se of the gas in the reduction of carbon dioxide to form methane. By producing methane, the concentration of hydrogen is kept at a low level that allows other bacterial species to grow. This microbial diversity makes fermentation more efficient.
The bacterial production of methane is of economic importance. "Biogas" obtained from digesters can be a commercial and domestic energy source, although more economic sources of energy currently limit this use. In large-scale livestock operations, the use of methane producing bacteria is being increasing popular as a means of odor-control.
As on Earth, methane producing bacteria may be one of the earliest forms of life on other planets. Experiments that duplicate the atmosphere of the planet Mars have been successful in growing methane producing bacteria. Aside from its fundamental scientific importance, the discovery might be exploited in future manned missions to Mars. Methane is described as being a greenhouse gas, which means it can warm the surface atmosphere. On a small-scale, methane production might create a more hospitable atmosphere on the surface of Mars. Additionally, the combustible nature of methane, utilized on Earth as a biogas, could someday provide rocket fuel for spacecraft.
See also Biogeochemical cycles; Chemoautotrophic and chemolithitrophic bacteria; Extremophiles