Methanotroph
Encyclopedia
Methanotrophs are bacteria that are able to metabolize methane
as their only source of carbon
and energy
. They can grow aerobically or anaerobically
and require single-carbon compound
s to survive. Under aerobic conditions, they combine oxygen
and methane to form formaldehyde
, which is then incorporated into organic compounds via the serine pathway or the RuMP pathway. Type I methanotrophs are part of the Gammaproteobacteria
and they use the ribulose monophosphate (RuMP) pathway to assimilate carbon. On the other hand, type II methanotrophs are part of the Alphaproteobacteria
and utilize the Serine pathway of carbon assimilation. They also characteristically have a system of internal membranes within which methane oxidation
occurs. Methanotrophs occur mostly in soils, and are especially common near environments where methane is produced. Their habitats include oceans, mud, marshes, underground environments, soils, rice paddies and landfills. They are of special interest to researchers studying global warming
, as they are significant in the global methane budget.
Gratuitous detoxification of some environmental contaminants such as chlorinated hydrocarbon
s by methanotrophs have made them attractive models for such bioremediation
processes. Equally methane is a potential greenhouse gas
far more potent that carbon dioxide
. Therefore methanotrophs play a major role in the reduction of the release of methane into the atmosphere from environments such as rice paddies, landfills, bogs and swamps where methane production is relatively high.
Differences in the method of formaldehyde fixation and membrane structure divide the methanotrophs into several groups. These include the Methylococcaceae
and Methylocystaceae
. Although both are included among the Proteobacteria
, they are members of different subclasses. Other methanotroph species are found in the Verrucomicrobiae.
Methanotrophy is a special case of methylotrophy, using single-carbon compounds that are more reduced than carbon dioxide. Some methylotrophs, however, can also make use of multi-carbon compounds which differentiates them from methanotrophs that are usually fastidious
methane and methanol oxidizers. The only facultative methanotroph isolated to date are members of the genus Methylocella.
Investigations in marine environments revealed that methane can be oxidized anaerobically by consortia of methane oxidizing archaea
and sulfate
-reducing bacteria. Anaerobic oxidation of methane
(AOM) mainly occurs in anoxic marine sediments. The exact mechanism of methane oxidation under anaerobic conditions is still a topic of debate but the most widely accepted theory is that the archaea use the reversed methanogenesis
pathway to produce carbon dioxide and another, unknown substance. This unknown intermediate is then used by the sulfate-reducing bacteria to be able to gain energy from the reduction of sulfate to hydrogen sulfide
. The anaerobic methanothrophs are not related to the known aerobic methanotrophs; the closest cultured relative to the anaerobic methanotrophs are the methanogen
s in the order of Methanosarcinales
.
Recently, a new bacterium Candidatus Methylomirabilis oxifera was identified that can couple the anaerobic oxidation of methane
to nitrite reduction without the need for a syntrophic partner. Based on the studies of Ettwig et al., it is believed that M. oxyfera oxidizes methane anaerobically by utilizing the oxygen produced internally from the dismutation of nitric oxide
into nitrogen and oxygen gas.
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
as their only source of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
and energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
. They can grow aerobically or anaerobically
Anaerobic respiration
Anaerobic respiration is a form of respiration using electron acceptors other than oxygen. Although oxygen is not used as the final electron acceptor, the process still uses a respiratory electron transport chain; it is respiration without oxygen...
and require single-carbon compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s to survive. Under aerobic conditions, they combine oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and methane to form formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
, which is then incorporated into organic compounds via the serine pathway or the RuMP pathway. Type I methanotrophs are part of the Gammaproteobacteria
Gammaproteobacteria
Gammaproteobacteria is a class of several medically, ecologically and scientifically important groups of bacteria, such as the Enterobacteriaceae , Vibrionaceae and Pseudomonadaceae. An exceeding number of important pathogens belongs to this class, e.g...
and they use the ribulose monophosphate (RuMP) pathway to assimilate carbon. On the other hand, type II methanotrophs are part of the Alphaproteobacteria
Alphaproteobacteria
Alphaproteobacteria is a class of Proteobacteria. Like all Proteobacteria, they are Gram-negative.-Characteristics:The Alphaproteobacteria comprise most phototrophic genera, but also several genera metabolising C1-compounds , symbionts of plants and animals, and a group of pathogens, the...
and utilize the Serine pathway of carbon assimilation. They also characteristically have a system of internal membranes within which methane oxidation
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
occurs. Methanotrophs occur mostly in soils, and are especially common near environments where methane is produced. Their habitats include oceans, mud, marshes, underground environments, soils, rice paddies and landfills. They are of special interest to researchers studying global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
, as they are significant in the global methane budget.
Gratuitous detoxification of some environmental contaminants such as chlorinated hydrocarbon
Organochloride
An organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...
s by methanotrophs have made them attractive models for such bioremediation
Bioremediation
Bioremediation is the use of microorganism metabolism to remove pollutants. Technologies can be generally classified as in situ or ex situ. In situ bioremediation involves treating the contaminated material at the site, while ex situ involves the removal of the contaminated material to be treated...
processes. Equally methane is a potential greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...
far more potent that carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
. Therefore methanotrophs play a major role in the reduction of the release of methane into the atmosphere from environments such as rice paddies, landfills, bogs and swamps where methane production is relatively high.
Differences in the method of formaldehyde fixation and membrane structure divide the methanotrophs into several groups. These include the Methylococcaceae
Methylococcaceae
The Methylococcaceae are a family of bacteria that obtain their carbon and energy from methane, called methanotrophs. They comprise the type I methanotrophs, in contrast to the Methylocystaceae or type II methanotrophs...
and Methylocystaceae
Methylocystaceae
The Methylocystaceae are a family of bacteria that are capable of obtaining carbon and energy from methane. Such bacteria are called methanotrophs, and in particular the Methylocystaceae comprise the type II methanotrophs, which are structurally and biochemically distinct from the Methylococcaceae...
. Although both are included among the Proteobacteria
Proteobacteria
The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....
, they are members of different subclasses. Other methanotroph species are found in the Verrucomicrobiae.
Methanotrophy is a special case of methylotrophy, using single-carbon compounds that are more reduced than carbon dioxide. Some methylotrophs, however, can also make use of multi-carbon compounds which differentiates them from methanotrophs that are usually fastidious
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
methane and methanol oxidizers. The only facultative methanotroph isolated to date are members of the genus Methylocella.
Investigations in marine environments revealed that methane can be oxidized anaerobically by consortia of methane oxidizing archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
and sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
-reducing bacteria. Anaerobic oxidation of methane
Anaerobic oxidation of methane
Anaerobic oxidation of methane is a microbial process occurring mainly in anoxic marine sediments. During AOM methane is oxidized with sulfate as the terminal electron acceptor: CH4 + SO42- → HCO3- + HS- + H2O...
(AOM) mainly occurs in anoxic marine sediments. The exact mechanism of methane oxidation under anaerobic conditions is still a topic of debate but the most widely accepted theory is that the archaea use the reversed methanogenesis
Methanogenesis
Methanogenesis or biomethanation is the formation of methane by microbes known as methanogens. Organisms capable of producing methane have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with...
pathway to produce carbon dioxide and another, unknown substance. This unknown intermediate is then used by the sulfate-reducing bacteria to be able to gain energy from the reduction of sulfate to hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
. The anaerobic methanothrophs are not related to the known aerobic methanotrophs; the closest cultured relative to the anaerobic methanotrophs are the methanogen
Methanogen
Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic conditions. They are classified as archaea, a group quite distinct from bacteria...
s in the order of Methanosarcinales
Methanosarcinales
In taxonomy, the Methanosarcinales are an order of the Methanomicrobia.-External links:...
.
Recently, a new bacterium Candidatus Methylomirabilis oxifera was identified that can couple the anaerobic oxidation of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
to nitrite reduction without the need for a syntrophic partner. Based on the studies of Ettwig et al., it is believed that M. oxyfera oxidizes methane anaerobically by utilizing the oxygen produced internally from the dismutation of nitric oxide
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
into nitrogen and oxygen gas.
External links
- Anaerobic methane oxidation
- METHANE-EATING BUG HOLDS PROMISE FOR CUTTING GREENHOUSE GAS. Media Release, GNS Science, New Zealand