Methanogen

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Methanogen

Methanogens are archaea

Archaea

The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . Archaea, like bacteria, are prokaryotic....
that produce methane

Methane

Methane is a chemical compound with the molecular formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees....
as a metabolic byproduct in anoxic conditions. They are common in wetlands, where they are responsible for marsh gas, and in the guts of animals such as ruminant

Ruminant

Physiologically, a ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first stomach, known as the rumen, then regurgitating the semi-digested mass, now known as cud, and chewing it again....
s and humans, where they are responsible for the methane content of flatulence

Flatulence

Flatulence is the production of a mixture of gases in the gastrointestinal tract of mammals or other animals that are byproducts of the digestion process....
. In marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology....
sediment

Sediment

Sediment is any particulate matter that can be sediment transport by fluid dynamics, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers....
s biomethanation is generally confined to where sulfate

Sulfate

In inorganic chemistry, a sulfate is a salt of sulfuric acid....
s are depleted, below the top layers. Others are extremophile

Extremophile

An extremophile is an organism that thrives in and may even require physically or geochemically extreme environment that are detrimental to the majority of life on Earth....
s, found in environments such as hot spring

Hot spring

A hot spring is a Spring that is produced by the emergence of Geothermal groundwater from the earth's crust . There are hot springs all over the earth, on every continent and even under the oceans and seas....
s and submarine hydrothermal vents as well as in the "solid" rock of the earth's crust, kilometers below the surface.

Physical description
Methanogens are usually coccoid or rod shaped.

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Physical description

Methanogens are usually coccoid or rod shaped. There are over 50 described species of methanogens, which do not form a monophyletic group, although all methanogens belong to Euryarchaeota

Euryarchaeota

In the alpha taxonomy of microorganisms, the Euryarchaeota are a phylum of the Archaea.The Euryarchaeota include the methanogens, which produce methane and are often found in intestines, the halobacteria, which survive extreme concentrations of salt, and some extremely thermophilic aerobes and anaerobes....
. Methanogens are also anaerobic

Anaerobic organism

An anaerobic organism is any organism that does not require oxygen for growth and may even die in its presence....
. Although methanogens cannot function under aerobic conditions they can sustain oxygen stresses for prolonged times.

An exception is Methanosarcina barkeri, which contains a superoxide dismutase

Superoxide dismutase

The enzyme superoxide dismutase , catalyzes the dismutation of superoxide into oxygen and hydrogen peroxide. As such, it is an important antioxidant defense in nearly all cells exposed to oxygen....
(SOD) enzyme and may survive longer. Some, called hydrogenotrophic, use carbon dioxide

Carbon dioxide

Carbon dioxide is a chemical compound composed of two oxygen atoms covalent bond to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state....
(CO₂) as a source of carbon, and hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
as a reducing agent. Some of the CO₂ is reacted with the hydrogen to produce methane, which produces an electrochemical gradient

Electrochemical gradient

An electrochemical gradient is a spatial variation of both electrical potential and chemical concentration across a membrane. Both components are often due to ion gradients, particularly proton gradients, and the result can be a type of potential energy available for work in a cell....
across a membrane, used to generate ATP

Adenosine triphosphate

This article is about the chemical used by cells as an energy carrier. For other uses, see ATP .Adenosine-5'-triphosphate is a multifunctional nucleotide, and plays an important role in cell biology as a coenzyme that is the "molecule unit of currency" of intracellular energy transfer....
through chemiosmosis

Chemiosmosis

Chemiosmosis is the diffusion of ions across a selectively-permeable membrane. More specifically, it relates to the generation of Adenosine triphosphate by the movement of hydrogen ions across a inner membrane during cellular respiration....
. In contrast, plants and algae use water as their reducing agent.

Methanogens lack a polymer that is found in the cell walls of other prokaryotes. Some methanogens have a cell wall that is composed of pseudomurein. Other methanogens that don't have a pseudomurein have at least one paracrystalline array (S-layer) which is made up of proteins that fit together like a puzzle.

Methanogens and environments

Although most marine biogenic methane is the result of CO₂ reduction, a small amount is derived from acetate

Acetate

An acetate, or ethanoate, is either a salt or ester of acetic acid.In chemistry, the abbreviation Ac refers to the acetyl group. The anion and the functional group may be written as -OAc and AcO-, or OAc respectively....
(CH₃COO^-). Archaea that catabolize this for energy are referred to as acetotrophic or aceticlastic. Methylotrophic archaea utilize methylated compounds such as methylamine

Methylamine

Methylamine is the organic compound with a chemical formula of CH3NH2. This colourless gas is a derivative of ammonia, wherein one H atom is replaced by a methyl group....
s, methanol

Methanol

Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a chemical compound with chemical formula carbonhydrogen3oxygenhydrogen ....
, and methanethiol

Methanethiol

Methanethiol is a colorless gas with a smell like rotten cabbage. It is a natural substance found in the blood, brain, and other animal as well as plant tissues....
as well.

Methanogens play the vital ecological role in anaerobic environments of removing excess hydrogen and fermentation products that have been produced by other forms of anaerobic respiration

Anaerobic respiration

Anaerobic respiration is the process of generating energy through cellular respiration , without the use of oxygen....
. Methanogens typically thrive in environments in which all other electron acceptor

Electron acceptor

An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process....
s (such as oxygen

Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, nitrate

Nitrate

In inorganic chemistry, a nitrate is a salt of nitric acid with an ion composed of one nitrogen and three oxygen atoms . In organic chemistry the esters of nitric acid and various alcohols are called nitrates....
, sulfate

Sulfate

In inorganic chemistry, a sulfate is a salt of sulfuric acid....
, and trivalent iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
) have been depleted. In the deep rock they obtain their hydrogen from the thermal and radioactive breakdown of water.

Methanogens have been found in several extreme environments on Earth - buried under kilometres of ice in Greenland and living in hot, dry desert soil. They can still reproduce from temperatures of 15 to 100 degrees Celsius.They are known to be the most common prokaryotes archaebacteria in deep subteranean habitats.

Live microbes making methane were found in a glacial ice core sample retrieved from three kilometres under Greenland by researchers from the University of California, Berkeley, US.

Another study has also discovered methanogens in a harsh environment on Earth. Researchers studied dozens of soil and vapour samples from five different desert environments in Utah, Idaho and California in the US, and in Canada and Chile. Of these, five soil samples and three vapour samples from the vicinity of the Mars Desert Research Station in Utah were found to have signs of viable methanogens.

Some scientists have proposed that the presence of methane in the Martian

MARS

In cryptography, MARS is a block cipher that was IBM's submission to the Advanced Encryption Standard process. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm....
atmosphere may be indicative of native methanogens on that planet.

Closely related to the methanogens are the anaerobic methane oxidizers, which utilize methane as a substrate in conjunction with the reduction of sulfate and nitrate. Most methanogens are autotrophic producers, but those which oxidize CH₃COO^- are classed as chemoheterotrophs instead.

Types of methanogens

Methanobacterium bryantii
Methanobacterium formicum
Methanobrevibacter arboriphilicus
Methanobrevibacter gottschalkii
Methanobrevibacter ruminantium
Methanobrevibacter smithii
Methanobrevibacter smithii

Methanobrevibacter smithii is the dominant Archaea in the human gut. It is important for the efficient digestion of polysaccharides because it consumes end products of bacterial fermentation....
Methanocalculus chunghsingensis
Methanococcoides burtonii
Methanococcus aeolicus
Methanococcus deltae
Methanococcus jannaschii
Methanococcus maripaludis
Methanococcus vannielii
Methanocorpusculum labreanum
Methanoculleus bourgensis (Methanogenium olentangyi & Methanogenium bourgense)
Methanoculleus marisnigri
Methanofollis liminatans
Methanogenium cariaci
Methanogenium frigidum
Methanogenium organophilum
Methanogenium wolfei
Methanomicrobium mobile
Methanopyrus kandleri
Methanoregula boonei
Methanosaeta concilii
Methanosaeta thermophila
Methanosarcina acetivorans
Methanosarcina acetivorans

Methanosarcina acetivorans is a versatile methanogen which is found in such diverse environments as oil wells, trash dumps, deep sea hydrothermal vents, and oxygen depleted sediments beneath kelp beds....
Methanosarcina barkeri
Methanosarcina mazei
Methanosphaera stadtmanae

Methanospirillium hungatei
Methanothermobacter defluvii (Methanobacterium defluvii)
Methanothermobacter thermautotrophicus (Methanobacterium thermoautotrophicum)
Methanothermobacter thermoflexus (Methanobacterium thermoflexum)
Methanothermobacter wolfei (Methanobacterium wolfei)
Methanothrix sochngenii