Wolfe cycle

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Wolfe cycle

The Wolfe Cycle is a methanogenic pathway used by archaea; the archaeon takes H2 and CO2 and cycles them through a various intermediates to create methane. [1] The Wolfe Cycle is modified in different orders and classes of archaea as per the resource availability and requirements for each species, but it retains the same basic pathway. [1] The pathway begins with the reducing carbon dioxide to formylmethanofuran. [1] The last step uses heterodisulfide reductase (Hdr) to reduce heterodisulfide into Coenzyme B and Coenzyme M using Fe4S4 clusters. [1] [2] Evidence suggests this last step goes hand-in-hand with the first step, and feeds back into it, creating a cycle. [1] At various points in the Wolfe Cycle, intermediates that are formed are taken out of the cycle to be used in other metabolic processes. [1] [3] Since intermediates are being taken out at various points in the cycle, there is also a replenishing (anaplerotic) reaction that feeds into the Wolfe cycle, this is to regenerate necessary intermediates for the cycle to continue. [1] Overall, including the replenishing reaction, the Wolfe Cycle has a total of nine steps. [1] While Obligate reducing methanogens perform additional steps to reduce CO2 to .

Contents

Discovery

In 1971, in a review published by Robert Stoner Wolfe, information regarding methanogenesis in M. bryantii was published. At the time, the only thing known about this process was that Coenzyme M was involved. [4] In addition, methanogenesis was thought to follow a linear pathway. It was not until 1986 that the reduction of to was proposed to occur in a cycle when it was shown that Steps 8 and 1 are coupled. [4]

Steps

The Wolfe Cycle follows multiple pathways, depending on the microbe. Below are generalized steps in the Wolfe Cycle.

stepsreactantsEnzymes [4] Products used in cycle
1Formyl-methanofuran dehydrogenase
2Formyltransferase
3methenyl-H4MPT cyclohydrolase
4methylene-H4MPT dehydrogenase
5methylene-H4MPT reductase
6methyl-H4MPT/HSCoM methyl transferase
7methyl-S-CoM reductase
8electron bifurcating hydrogenase-heterodisulfide reductase complex
9F420-reducing hydrogenase

Related Research Articles

Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They belong to the domain Archaea and are members of the phylum Euryarchaeota. Methanogens are common in wetlands, where they are responsible for marsh gas, and can occur in the digestive tracts of animals including ruminants and humans, where they are responsible for the methane content of belching and flatulence. In marine sediments, the biological production of methane, termed methanogenesis, is generally confined to where sulfates are depleted below the top layers. Methanogens play an indispensable role in anaerobic wastewater treatments. Other methanogens are extremophiles, found in environments such as hot springs and submarine hydrothermal vents as well as in the "solid" rock of Earth's crust, kilometers below the surface in the deep biosphere.

Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with anaerobic bacteria. The production of methane is an important and widespread form of microbial metabolism. In anoxic environments, it is the final step in the decomposition of biomass. Methanogenesis is responsible for significant amounts of natural gas accumulations, the remainder being thermogenic.

<span class="mw-page-title-main">Biological carbon fixation</span> Series of interconnected biochemical reactions

Biological carbon fixation, or сarbon assimilation, is the process by which living organisms convert inorganic carbon to organic compounds. These organic compounds are then used to store energy and as structures for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use chemosynthesis in the absence of sunlight. Chemosynthesis is carbon fixation driven by chemical energy rather than from sunlight. 

Methylotrophs are a diverse group of microorganisms that can use reduced one-carbon compounds, such as methanol or methane, as the carbon source for their growth; and multi-carbon compounds that contain no carbon-carbon bonds, such as dimethyl ether and dimethylamine. This group of microorganisms also includes those capable of assimilating reduced one-carbon compounds by way of carbon dioxide using the ribulose bisphosphate pathway. These organisms should not be confused with methanogens which on the contrary produce methane as a by-product from various one-carbon compounds such as carbon dioxide. Some methylotrophs can degrade the greenhouse gas methane, and in this case they are called methanotrophs. The abundance, purity, and low price of methanol compared to commonly used sugars make methylotrophs competent organisms for production of amino acids, vitamins, recombinant proteins, single-cell proteins, co-enzymes and cytochromes.

Methanosarcina acetivorans is a versatile methane producing microbe which is found in such diverse environments as oil wells, trash dumps, deep-sea hydrothermal vents, and oxygen-depleted sediments beneath kelp beds. Only M. acetivorans and microbes in the genus Methanosarcina use all three known metabolic pathways for methanogenesis. Methanosarcinides, including M. acetivorans, are also the only archaea capable of forming multicellular colonies, and even show cellular differentiation. The genome of M. acetivorans is one of the largest archaeal genomes ever sequenced. Furthermore, one strain of M. acetivorans, M. a. C2A, has been identified to possess an F-type ATPase along with an A-type ATPase.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.

<span class="mw-page-title-main">Coenzyme M</span> Chemical compound

Coenzyme M is a coenzyme required for methyl-transfer reactions in the metabolism of archaeal methanogens, and in the metabolism of other substrates in bacteria. It is also a necessary cofactor in the metabolic pathway of alkene-oxidizing bacteria. CoM helps eliminate the toxic epoxides formed from the oxidation of alkenes such as propylene. The structure of this coenzyme was discovered by CD Taylor and RS Wolfe in 1974 while they were studying methanogenesis, the process by which carbon dioxide is transformed into methane in some anaerobic bacteria. The coenzyme is an anion with the formula HSCH
2
CH
2
SO
3
. It is named 2-mercaptoethanesulfonate and abbreviated HS–CoM. The cation is unimportant, but the sodium salt is most available. Mercaptoethanesulfonate contains both a thiol, which is the main site of reactivity, and a sulfonate group, which confers solubility in aqueous media.

Coenzyme B is a coenzyme required for redox reactions in methanogens. The full chemical name of coenzyme B is 7-mercaptoheptanoylthreoninephosphate. The molecule contains a thiol, which is its principal site of reaction.

<span class="mw-page-title-main">Wood–Ljungdahl pathway</span> A set of biochemical reactions used by some bacteria

The Wood–Ljungdahl pathway is a set of biochemical reactions used by some bacteria. It is also known as the reductive acetyl-coenzyme A (acetyl-CoA) pathway. This pathway enables these organisms to use hydrogen as an electron donor, and carbon dioxide as an electron acceptor and as a building block for biosynthesis.

<i>Methanobacterium</i> Genus of archaea

Methanobacterium is a genus of the Methanobacteria class in the Archaea kingdom, which produce methane as a metabolic byproduct. Despite the name, this genus belongs not to the bacterial domain but the archaeal domain. Methanobacterium are nonmotile and live without oxygen, which is toxic to them, and they only inhabit anoxic environments.

<span class="mw-page-title-main">Coenzyme-B sulfoethylthiotransferase</span> Class of enzymes

In enzymology, coenzyme-B sulfoethylthiotransferase, also known as methyl-coenzyme M reductase (MCR) or most systematically as 2-(methylthio)ethanesulfonate:N-(7-thioheptanoyl)-3-O-phosphothreonine S-(2-sulfoethyl)thiotransferase is an enzyme that catalyzes the final step in the formation of methane. It does so by combining the hydrogen donor coenzyme B and the methyl donor coenzyme M. Via this enzyme, most of the natural gas on earth was produced. Ruminants produce methane because their rumens contain methanogenic prokaryotes (Archaea) that encode and express the set of genes of this enzymatic complex.

Methanobrevibacter smithii is the predominant archaeon in the microbiota of the human gut. M. smithii has a coccobacillus shape. It plays an important role in the efficient digestion of polysaccharides by consuming the end products of bacterial fermentation. Methanobrevibacter smithii is a single-celled microorganism from the Archaea domain. M. smithii is a methanogen, and a hydrogenotroph that recycles the hydrogen by combining it with carbon dioxide to methane. The removal of hydrogen by M. smithii is thought to allow an increase in the extraction of energy from nutrients by shifting bacterial fermentation to more oxidized end products.

<span class="mw-page-title-main">Cofactor F430</span> Chemical compound

F430 is the cofactor (sometimes called the coenzyme) of the enzyme methyl coenzyme M reductase (MCR). MCR catalyzes the reaction EC 2.8.4.1 that releases methane in the final step of methanogenesis:

In the taxonomy of microorganisms, the Methanothrix is a genus of methanogenic archaea within the Euryarchaeota. Methanothrix cells were first isolated from a mesophilic sewage digester but have since been found in many anaerobic and aerobic environments. Methanothrix were originally understood to be obligate anaerobes that can survive exposure to high concentrations of oxygen, but recent studies have shown at least one Candidatus operational taxonomic unit proposed to be in the Methanothrix genus not only survives but remains active in oxic soils. This proposed species, Ca. Methanothrix paradoxum, is frequently found in methane-releasing ecosystems and is the dominant methanogen in oxic soils.

<i>Methanococcus maripaludis</i> Species of archaeon

Methanococcus maripaludis is a species of methanogenic archaea found in marine environments, predominantly salt marshes. M. maripaludis is a non-pathogenic, gram-negative, weakly motile, non-spore-forming, and strictly anaerobic mesophile. It is classified as a chemolithoautotroph. This archaeon has a pleomorphic coccoid-rod shape of 1.2 by 1.6 μm, in average size, and has many unique metabolic processes that aid in survival. M. maripaludis also has a sequenced genome consisting of around 1.7 Mbp with over 1,700 identified protein-coding genes. In ideal conditions, M. maripaludis grows quickly and can double every two hours.

Hydrogenotrophs are organisms that are able to metabolize molecular hydrogen as a source of energy.

<span class="mw-page-title-main">CO-methylating acetyl-CoA synthase</span> Enzyme

Acetyl-CoA synthase (ACS), not to be confused with acetyl-CoA synthetase or acetate-CoA ligase, is a nickel-containing enzyme involved in the metabolic processes of cells. Together with carbon monoxide dehydrogenase (CODH), it forms the bifunctional enzyme Acetyl-CoA Synthase/Carbon Monoxide Dehydrogenase (ACS/CODH) found in anaerobic microorganisms such as archaea and bacteria. The ACS/CODH enzyme works primarily through the Wood–Ljungdahl pathway which converts carbon dioxide to Acetyl-CoA. The recommended name for this enzyme is CO-methylating acetyl-CoA synthase.

The sulfate-methane transition zone (SMTZ) is a zone in oceans, lakes, and rivers typically found below the sediment surface in which sulfate and methane coexist. The formation of a SMTZ is driven by the diffusion of sulfate down the sediment column and the diffusion of methane up the sediments. At the SMTZ, their diffusion profiles meet and sulfate and methane react with one another, which allows the SMTZ to harbor a unique microbial community whose main form of metabolism is anaerobic oxidation of methane (AOM). The presence of AOM marks the transition from dissimilatory sulfate reduction to methanogenesis as the main metabolism utilized by organisms.

In enzymology, a formylmethanofuran dehydrogenase (EC 1.2.99.5) is an enzyme that catalyzes the chemical reaction:

Ralph Stoner Wolfe was an American microbiologist, who contributed to the discovery of the single-celled archaea as the third domain of life. He was a pioneer in the biochemistry of methanogenesis.

References

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  2. Wu, Jue; Chen, Shi-Lu (2022-02-18). "Key Piece in the Wolfe Cycle of Methanogenesis: The S–S Bond Dissociation Conducted by Noncubane [Fe 4 S 4 ] Cluster-Dependent Heterodisulfide Reductase". ACS Catalysis. 12 (4): 2606–2622. doi:10.1021/acscatal.1c06036. ISSN   2155-5435.
  3. Vo, Chi Hung; Goyal, Nishu; Karimi, Iftekhar A; Kraft, Markus (January 2020). "First Observation of an Acetate Switch in a Methanogenic Autotroph ( Methanococcus maripaludis S2)". Microbiology Insights. 13: 117863612094530. doi:10.1177/1178636120945300. ISSN   1178-6361. PMC   7416134 . PMID   32843840.
  4. 1 2 3 Balch, William E.; Ferry, James G. (2021-01-01), Poole, Robert K.; Kelly, David J. (eds.), "Chapter One - The Wolfe cycle of carbon dioxide reduction to methane revisited and the Ralph Stoner Wolfe legacy at 100 years", Advances in Microbial Physiology, 79, Academic Press: 1–23, doi:10.1016/bs.ampbs.2021.07.003, PMID   34836609, S2CID   244550528 , retrieved 2023-11-27