Methanogenesis or biomethanation, is biochemical process influencing the Earth's carbon cycle. Specialized microorganisms, methanogens convert organic material into methane (CH4), an important energy source.
About Methanogenesis
Methanogenesis the production of methane from organic matter in anaerobic settings. It occurs in wetlands, landfills and digestive systems of ruminants like cows and sheep.
In anaerobic digestion, complex organic materials are broken down by various microbial communities. This culminates in methane production.
Methanogens of the domain Archaea are able to produce methane in major amounts. Methanogens thrive in extreme conditions, like hot springs or salt lakes.
They're exceptionally versatile, able to use substrates such as carbon dioxide, hydrogen, acetate, and methanol to drive methane production.
Operating primarily in anaerobic, or oxygen-free, environments, methanogens perform the final act of breaking down organic matter during anaerobic digestion.
Some bacteria are also able to produce methane. Major genera include Methanobacterium, Methanosarcina, Methanococcus and Methanospirillum.
Methanogens also have a strong effect on ecosystems. In wetlands, important to the carbon cycle, methanogenesis helps control greenhouse gas emissions.
These environments create anaerobic conditions to support a diverse microbial community. They include both methanogens and methane eating bacteria.
Wetlands emit less than 30% of carbon content as methane. This creates a balance between carbon storage and emissions. Some methanogens can survive temperatures exceeding 100°C (212°F).
In digestive systems of ruminants, methanogens help decompose tough plant materials. The process enables animals to extract energy from fibrous diets.
Methane produced during ruminant digestion promotes emissions in agriculture. Overproduction of methane from farm animals is due to the immense scale of livestock raised for meat production through the world.
In humans, according to a PubMed study, 30 - 62% of healthy subjects produce methane. Methane is made through anaerobic fermentation of endogenous and exogenous carbohydrates by microbes in humans.
While some methane may have beneficial functions, people with high methane levels often have problems like constipation, flatulence, bloating and diarrhea. Antibiotics reduce internal production of methane by humans.
Lactose intolerant people may be especially vulnerable. Without enough lactase, the enzyme making milk sugar digestion possible, the unabsorbed lactose moves through the digestive system to the large intestine.
Bacteria in the colon ferment or break down the lactose, producing fatty acids and other products. Gases excreted include carbon dioxide (CO2), hydrogen gas or dihydrogen (H2) and methane.
Microorganisms known as methanotrophs, primarily bacteria, consume methane. These include Gammaproteobacteria, Alphaproteobacteria and Methylacidiphilum infernorum. Methanotrophic bacteria break down 30 million metric tons of methane per year
Various archaea species of phylum Euryarchaeot produce methane, and many also consume it. In the natural world this ensures energy for the consumers and control of methane emissions.
The Methanogenic Process
Methanogenesis comes after hydrolysis, acidogenesis, and acetogenesis as the fourth and final stage of anaerobic digestion. Microbes decompose organic materials like plant matter and animal waste. Methanogens convert byproducts of these into methane.
Hydrolysis: Microorganisms break down complex organic materials into simpler substances like sugars, amino acids, and fatty acids.
Acidogenesis: Next, fermentative bacteria convert these simpler compounds into volatile fatty acids, along with hydrogen and carbon dioxide.
Acetogenesis: Acetogenic bacteria then convert volatile fatty acids into acetate, adding more hydrogen and carbon dioxide to the mix.
Methanogenesis: Finally, methanogenic archaea produce methane and carbon dioxide by using acetate and hydrogen created in earlier phases.
Methanogens use various substrates to produce methane. These include carbon dioxide (CO2), acetic acid (CH3COOH) and hydrogen (H2).
Some methanogens produce methane from carbon dioxide and hydrogen through CO2 reduction. Others use acetate as a substrate.
Methanogens often exist in symbiotic relationships with other anaerobic bacteria. Bacteria reduce complex organic matter, creating compounds like hydrogen and acetate, used by methanogens for methane production.
Environments vary widely. The archaea genera Methanococcus, some in extreme marine habitats, and Methanosarcina, often found in anaerobic digesters, use waste products exuded by other microbes.
Natural Methane Accumulation: Earth’s Natural Gas Reservoirs
Methanogenesis is also a foundational process behind some of the Earth’s natural gas reserves. An estimated 70-90% of methane in natural gas originates from biological processes, especially methanogenesis.
Methanogens function in biogas production, which captures methane from organic waste. Natural biogas is composed mainly of methane and carbon dioxide.
Methanogenesis and Climate Change
In nature, methane production is used as biofuel for microbe and essential processes. Methanogenesis is associated with climate change due to overactivity of organisms like humans.
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