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Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon is converted to organic compounds by living organisms. The compounds are then used to store energy and as structure for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use a process called chemosynthesis in the absence of sunlight.
An acetogen is a microorganism that generates acetate (CH3COO−) as an end product of anaerobic respiration or fermentation. However, this term is usually employed in a narrower sense only to those bacteria and archaea that perform anaerobic respiration and carbon fixation simultaneously through the reductive acetyl coenzyme A (acetyl-CoA) pathway (also known as the Wood-Ljungdahl pathway). These genuine acetogens are also known as "homoacetogens" and they can produce acetyl-CoA (and from that, in most cases, acetate as the end product) from two molecules of carbon dioxide (CO2) and four molecules of molecular hydrogen (H2). This process is known as acetogenesis, and is different from acetate fermentation, although both occur in the absence of molecular oxygen (O2) and produce acetate. Although previously thought that only bacteria are acetogens, some archaea can be considered to be acetogens.
Sulfur-reducing bacteria are microorganisms able to reduce elemental sulfur (S0) to hydrogen sulfide (H2S). These microbes use inorganic sulfur compounds as electron acceptors to sustain several activities such as respiration, conserving energy and growth, in absence of oxygen. The final product of these processes, sulfide, has a considerable influence on the chemistry of the environment and, in addition, is used as electron donor for a large variety of microbial metabolisms. Several types of bacteria and many non-methanogenic archaea can reduce sulfur. Microbial sulfur reduction was already shown in early studies, which highlighted the first proof of S0 reduction in a vibrioid bacterium from mud, with sulfur as electron acceptor and H
2 as electron donor. The first pure cultured species of sulfur-reducing bacteria, Desulfuromonas acetoxidans, was discovered in 1976 and described by Pfennig Norbert and Biebel Hanno as an anaerobic sulfur-reducing and acetate-oxidizing bacterium, not able to reduce sulfate. Only few taxa are true sulfur-reducing bacteria, using sulfur reduction as the only or main catabolic reaction. Normally, they couple this reaction with the oxidation of acetate, succinate or other organic compounds. In general, sulfate-reducing bacteria are able to use both sulfate and elemental sulfur as electron acceptors. Thanks to its abundancy and thermodynamic stability, sulfate is the most studied electron acceptor for anaerobic respiration that involves sulfur compounds. Elemental sulfur, however, is very abundant and important, especially in deep-sea hydrothermal vents, hot springs and other extreme environments, making its isolation more difficult. Some bacteria – such as Proteus, Campylobacter, Pseudomonas and Salmonella – have the ability to reduce sulfur, but can also use oxygen and other terminal electron acceptors.
Acetogenesis is a process through which acetate is produced either by the reduction of CO2 or by the reduction of organic acids, rather than by the oxidative breakdown of carbohydrates or ethanol, as with acetic acid bacteria.
Reticulitermes flavipes, the eastern subterranean termite, is the most common termite found in North America. These termites are the most economically important wood destroying insects in the United States and are classified as pests. They feed on cellulose material such as the structural wood in buildings, wooden fixtures, paper, books, and cotton. A mature colony can range from 20,000 workers to as high as 5 million workers and the primary queen of the colony lays 5,000 to 10,000 eggs per year to add to this total.
In biology, syntrophy, synthrophy, or cross-feeding is the phenomenon of one species feeding on the metabolic products of another species to cope up with the energy limitations by electron transfer. In this type of biological interaction, metabolite transfer happens between two or more metabolically diverse microbial species that live in close proximity to each other. The growth of one partner depends on the nutrients, growth factors, or substrates provided by the other partner. Thus, syntrophism can be considered as an obligatory interdependency and a mutualistic metabolism between two different bacterial species.
Hydrogen-oxidizing bacteria are a group of facultative autotrophs that can use hydrogen as an electron donor. They can be divided into aerobes and anaerobes. The former use hydrogen as an electron donor and oxygen as an acceptor while the latter use sulphate or nitrogen dioxide as electron acceptors. Species of both types have been isolated from a variety of environments, including fresh waters, sediments, soils, activated sludge, hot springs, hydrothermal vents and percolating water.
Desulfovirgula is a genus of sulfate reducing, anaerobic, endospore-forming, Gram-positive, thermophilic, motile, rod-shaped bacteria, isolated from an underground mining site in an area of Japan characterized by high geothermal activity.
Oxobacter is a genus of Gram-positive obligately anaerobic rod-shaped acetogenic bacteria. The sole species in the genus is Oxobacter pfennigii, formerly known as Clostridium pfennigii. This endospore-forming microorganism catabolizes pyruvate to acetate and CO2, while sugars and amino acids are not utilized as energy sources.
Ethanol from coal is the ethanol produced using coal as its carbon source. The anaerobic bacterium Clostridium ljungdahlii produces ethanol and acetic acid from CO, CO2, and H2 in synthesis gas. Early studies with C. ljungdahlii showed that relatively high concentrations of ethanol were produced. This process involves three main steps:
- Gasification: Thermal gasification at temperatures of up to 2,200°F in a reducing, very low oxygen atmosphere transforms organic materials into simple CO, CO2 and H2 gases.
- Fermentation: The acetogenic C. ljungdahlii convert the carbon monoxide into ethanol.
- Distillation: Ethanol is separated from hydrogen and water.
The Xanthobacteraceae are a family of bacteria that includes Azorhizobium, a genus of rhizobia. Xanthobacteraceae bacteria are diverse and Gram-negative, rod-shaped, and may be motile or non-motile depending on the specific bacteria. Their cells range in size from 0.4–1.0 × 0.8–6 µm, but when grown in the presence of alcohol as the sole carbon source, they can reach up to 10 µm in length. These bacteria do not form spores and have opaque, slimy colonies that appear slightly yellow due to the presence of zeaxanthin dirhamnoside.
Desulfobacter hydrogenophilus is a strictly anaerobic sulfate-reducing bacterium. It was isolated and characterized in 1987 by Friedrich Widdel of the University of Konstanz (Germany). Like most sulfate-reducing bacteria (SRB), D. hydrogenophilus is capable of completely oxidizing organic compounds (specifically acetate, pyruvate and ethanol) to CO2, and therefore plays a key role in biomineralization in anaerobic marine environments. However, unlike many SRB, D. hydrogenophilus is a facultative lithoautotroph, and can grow using H2 as an electron donor and CO2 as a carbon source. D. hydrogenophilus is also unique because it is psychrophilic (and has been shown to grow at temperatures as low as 0 °C or 32 °F). It is also diazotrophic, or capable of fixing nitrogen.
Thermoanaerobacter kivui is a thermophilic, anaerobic, nonspore-forming species of bacteria.
Sporomusa termitida is a species of bacteria. It is an acetogen first isolated from termites. Its cells are strictly anaerobic, Gram-negative, endospore-forming, straight to slightly curved rods that are motile by means of lateral flagella.
Treponema primitia is a bacterium, the first termite gut spirochete to be isolated, together with Treponema azotonutricium.
Hydrogenotrophs are organisms that are able to metabolize molecular hydrogen as a source of energy.
Acetitomaculum ruminis is a Gram-positive bacterium species from the genus of Acetitomaculum which has been isolated from the rumen of a bovine in the United States. Acetitomaculum ruminis utilize formate, glucose and CO2.
Atribacterota is a phylum of bacteria, which are common in anoxic sediments rich in methane. They are distributed worldwide and in some cases abundant in anaerobic marine sediments, geothermal springs, and oil deposits. Genetic analyzes suggest a heterotrophic metabolism that gives rise to fermentation products such as acetate, ethanol, and CO2. These products in turn can support methanogens within the sediment microbial community and explain the frequent occurrence of Atribacterota in methane-rich anoxic sediments. According to phylogenetic analysis, Atribacterota appears to be related to several thermophilic phyla within Terrabacteria or may be in the base of Gracilicutes. According to research, Atribacterota shows patterns of gene expressions which consists of fermentative, acetogenic metabolism. These expressions let Atribacterota to be able to create catabolic and anabolic functions which are necessary to generate cellular reproduction, even when the energy levels are limited due to the depletion of dissolved oxygen in the areas of sea waters, fresh waters, or ground waters.
Coprothermobacterales is a taxonomic order of thermophilic bacteria in the class Coprothermobacteria of the phylum Coprothermobacterota.
Sphingomonas aliaeris is a rod-shaped, strictly aerobic, Gram-negative, non-spore-forming, red-orange-pigmented species of bacteria, which has been isolated primarily from pork steak packed under CO2-enriched modified atmosphere. Its name derives from Latin alius (for “other”) and aer (for “air” or “atmosphere”). It was identified to be a potential food spoilage organism, which is non-pathogenic to humans.
References
- ↑ LSPN lpsn.dsmz.de
- ↑ Kane MD, Breznak JA (1991). "Acetonema longum gen. nov. sp. nov., an H2/CO2 acetogenic bacterium from the termite, Pterotermes occidentis". Arch Microbiol. 156 (2): 91–8. doi:10.1007/bf00290979. PMID 1723588. S2CID 21214522.
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