Anaerobic respiration

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Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. [1]

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In aerobic organisms undergoing respiration, electrons are shuttled to an electron transport chain, and the final electron acceptor is oxygen. Molecular oxygen is an excellent electron acceptor. Anaerobes instead use less-oxidizing substances such as nitrate (NO−
3), fumarate (C
4H
2O2−
4), sulfate (SO2−
4), or elemental sulfur (S). These terminal electron acceptors have smaller reduction potentials than O2. Less energy per oxidized molecule is released. Therefore, anaerobic respiration is less efficient than aerobic.

As compared with fermentation

Anaerobic cellular respiration and fermentation generate ATP in very different ways, and the terms should not be treated as synonyms. Cellular respiration (both aerobic and anaerobic) uses highly reduced chemical compounds such as NADH and FADH2 (for example produced during glycolysis and the citric acid cycle) to establish an electrochemical gradient (often a proton gradient) across a membrane. This results in an electrical potential or ion concentration difference across the membrane. The reduced chemical compounds are oxidized by a series of respiratory integral membrane proteins with sequentially increasing reduction potentials, with the final electron acceptor being oxygen (in aerobic respiration) or another chemical substance (in anaerobic respiration). A proton motive force drives protons down the gradient (across the membrane) through the proton channel of ATP synthase. The resulting current drives ATP synthesis from ADP and inorganic phosphate.[ citation needed ]

Fermentation, in contrast, does not use an electrochemical gradient but instead uses only substrate-level phosphorylation to produce ATP. The electron acceptor NAD+ is regenerated from NADH formed in oxidative steps of the fermentation pathway by the reduction of oxidized compounds. These oxidized compounds are often formed during the fermentation pathway itself, but may also be external. For example, in homofermentative lactic acid bacteria, NADH formed during the oxidation of glyceraldehyde-3-phosphate is oxidized back to NAD+ by the reduction of pyruvate to lactic acid at a later stage in the pathway. In yeast, acetaldehyde is reduced to ethanol to regenerate NAD+.[ citation needed ]

There are two important anaerobic microbial methane formation pathways, through carbon dioxide / bicarbonate (HCO−
3) reduction (respiration) or acetate fermentation. [2]

Ecological importance

Anaerobic respiration is a critical component of the global nitrogen, iron, sulfur, and carbon cycles through the reduction of the oxyanions of nitrogen, sulfur, and carbon to more-reduced compounds. The biogeochemical cycling of these compounds, which depends upon anaerobic respiration, significantly impacts the carbon cycle and global warming. Anaerobic respiration occurs in many environments, including freshwater and marine sediments, soil, subsurface aquifers, deep subsurface environments, and biofilms. Even environments that contain oxygen, such as soil, have micro-environments that lack oxygen due to the slow diffusion characteristics of oxygen gas.[ citation needed ]

An example of the ecological importance of anaerobic respiration is the use of nitrate as a terminal electron acceptor, or dissimilatory denitrification, which is the main route by which fixed nitrogen is returned to the atmosphere as molecular nitrogen gas. [3] The denitrification process is also very important in host-microbe interactions. Like mitochondria in oxygen-respiring microorganisms, some single-cellular anaerobic ciliates use denitrifying endosymbionts to gain energy. [4] Another example is methanogenesis, a form of carbon-dioxide respiration, that is used to produce methane gas by anaerobic digestion. Biogenic methane is used as a sustainable alternative to fossil fuels, however, uncontrolled methanogenesis in landfill sites releases large volumes of methane into the atmosphere, where it acts as a powerful greenhouse gas. [5] Sulfate respiration produces hydrogen sulfide, which is responsible for the characteristic 'rotten egg' smell of coastal wetlands and has the capacity to precipitate heavy metal ions from solution, leading to the deposition of sulfidic metal ores. [6]

Economic relevance

Anaerobic Denitrification (ETC System) The model above shows the process of anaerobic respiration through denitrification, which uses nitrogen (in the form of nitrate, NO 3) as the electron acceptor. NO 3 goes through respiratory dehydrogenase and reduces through each step from the ubiquinose through the bc1 complex through the ATP synthase protein as well. Each reductase removes oxygen step by step so that the final product of anaerobic respiration is N2. 1. Cytoplasm 2. Periplasm Compare to the aerobic electron transport chain. Anaerobic Denitrification (ETC System).svg
Anaerobic Denitrification (ETC System)

The model above shows the process of anaerobic respiration through denitrification , which uses nitrogen (in the form of nitrate, NO
3) as the electron acceptor. NO
3 goes through respiratory dehydrogenase and reduces through each step from the ubiquinose through the bc1 complex through the ATP synthase protein as well. Each reductase removes oxygen step by step so that the final product of anaerobic respiration is N2.

1. Cytoplasm
2. Periplasm Compare to the aerobic electron transport chain.

Dissimilatory denitrification is widely used in the removal of nitrate and nitrite from municipal wastewater. An excess of nitrate can lead to eutrophication of waterways into which treated water is released. Elevated nitrite levels in drinking water can lead to problems due to its toxicity. Denitrification converts both compounds into harmless nitrogen gas. [7]

Specific types of anaerobic respiration are also critical in bioremediation, which uses microorganisms to convert toxic chemicals into less-harmful molecules to clean up contaminated beaches, aquifers, lakes, and oceans. For example, toxic arsenate or selenate can be reduced to less toxic compounds by various anaerobic bacteria via anaerobic respiration. The reduction of chlorinated chemical pollutants, such as vinyl chloride and carbon tetrachloride, also occurs through anaerobic respiration.[ citation needed ] [8]

Anaerobic respiration is useful in generating electricity in microbial fuel cells, which employ bacteria that respire solid electron acceptors (such as oxidized iron) to transfer electrons from reduced compounds to an electrode. This process can simultaneously degrade organic carbon waste and generate electricity. [9]

Examples of electron acceptors in respiration

TypeLifestyleElectron acceptorProducts Eo′ (V)Example organisms
Aerobic respiration Obligate aerobes and facultative anaerobes O2H2O, CO2+0.82 Aerobic prokaryotes
Perchlorate respiration Facultative anaerobes ClO−
4, ClO−
3		H2O, O2, Cl−+0.797 Azospira suillum , Sedimenticola selenatireducens , Sedimenticola thiotaurini , and other gram negative prokaryotes [10]
Iodate respiration Facultative anaerobes IO−
3		H2O, H2O2, I−+0.72 Denitromonas , [11] Azoarcus , Pseudomonas , and other prokaryotes [12]
Iron reduction Facultative anaerobes and obligate anaerobes Fe(III)Fe(II)+0.75Organisms within the order Desulfuromonadales (such as Geobacter , Geothermobacter , Geopsychrobacter , Pelobacter ) and Shewanella species [13]
Manganese Facultative anaerobes and obligate anaerobes Mn(IV)Mn(II) Desulfuromonadales and Shewanella species [13]
Cobalt reduction Facultative anaerobes and obligate anaerobes Co(III)Co(II) Geobacter sulfurreducens
Uranium reduction Facultative anaerobes and obligate anaerobes U(VI)U(IV) Geobacter metallireducens , Shewanella oneidensis [14]
Nitrate reduction (denitrification) Facultative anaerobes Nitrate NO−
3		(Ultimately) N2+0.40 Paracoccus denitrificans , Escherichia coli
Fumarate respiration Facultative anaerobes Fumarate Succinate +0.03 Escherichia coli
Sulfate respiration Obligate anaerobes Sulfate SO2−
4		 Sulfide HS−−0.22Many Deltaproteobacteria species in the orders Desulfobacterales, Desulfovibrionales, and Syntrophobacterales
Methanogenesis (carbon dioxide reduction) Methanogens Carbon dioxide CO2Methane CH4−0.25 Methanosarcina barkeri
Sulfur respiration (sulfur reduction) Facultative anaerobes and obligate anaerobes Sulfur S0Sulfide HS−−0.27 Desulfuromonadales
Acetogenesis (carbon dioxide reduction) Obligate anaerobes Carbon dioxide CO2 Acetate −0.30 Acetobacterium woodii
Dehalorespiration Facultative anaerobes and obligate anaerobes Halogenated organic compounds R–XHalide ions and dehalogenated compound X− + R–H+0.25 – +0.60 [15] Dehalococcoides and Dehalobacter species

See also

Further reading

Related Research Articles

Primary nutritional groups are groups of organisms, divided in relation to the nutrition mode according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light or chemical compounds; the sources of carbon can be of organic or inorganic origin.

<span class="mw-page-title-main">Cellular respiration</span> Process to convert glucose to ATP in cells

Cellular respiration is the process by which biological fuels are oxidized in the presence of an inorganic electron acceptor, such as oxygen, to drive the bulk production of adenosine triphosphate (ATP), which contains energy. Cellular respiration may be described as a set of metabolic reactions and processes that take place in the cells of organisms to convert chemical energy from nutrients into ATP, and then release waste products.

<span class="mw-page-title-main">Denitrification</span> Microbially facilitated process

Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitrification as a type of respiration that reduces oxidized forms of nitrogen in response to the oxidation of an electron donor such as organic matter. The preferred nitrogen electron acceptors in order of most to least thermodynamically favorable include nitrate (NO3−), nitrite (NO2−), nitric oxide (NO), nitrous oxide (N2O) finally resulting in the production of dinitrogen (N2) completing the nitrogen cycle. Denitrifying microbes require a very low oxygen concentration of less than 10%, as well as organic C for energy. Since denitrification can remove NO3−, reducing its leaching to groundwater, it can be strategically used to treat sewage or animal residues of high nitrogen content. Denitrification can leak N2O, which is an ozone-depleting substance and a greenhouse gas that can have a considerable influence on global warming.

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">Obligate anaerobe</span> Microorganism killed by normal atmospheric levels of oxygen

Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environments with an oxygen concentration greater than 0.5%.

Methanotrophs are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to survive.

<span class="mw-page-title-main">Sulfate-reducing microorganism</span> Microorganisms that "breathe" sulfates

Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate (SO2−
4) as terminal electron acceptor, reducing it to hydrogen sulfide (H2S). Therefore, these sulfidogenic microorganisms "breathe" sulfate rather than molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in aerobic respiration.

<span class="mw-page-title-main">Sulfur-reducing bacteria</span> Microorganisms able to reduce elemental sulfur to hydrogen sulfide

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.

Denitrifying bacteria are a diverse group of bacteria that encompass many different phyla. This group of bacteria, together with denitrifying fungi and archaea, is capable of performing denitrification as part of the nitrogen cycle. Denitrification is performed by a variety of denitrifying bacteria that are widely distributed in soils and sediments and that use oxidized nitrogen compounds such as nitrate and nitrite in the absence of oxygen as a terminal electron acceptor. They metabolize nitrogenous compounds using various enzymes, including nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (NOS), turning nitrogen oxides back to nitrogen gas or nitrous oxide.

Lithotrophs are a diverse group of organisms using an inorganic substrate to obtain reducing equivalents for use in biosynthesis or energy conservation via aerobic or anaerobic respiration. While lithotrophs in the broader sense include photolithotrophs like plants, chemolithotrophs are exclusively microorganisms; no known macrofauna possesses the ability to use inorganic compounds as electron sources. Macrofauna and lithotrophs can form symbiotic relationships, in which case the lithotrophs are called "prokaryotic symbionts". An example of this is chemolithotrophic bacteria in giant tube worms or plastids, which are organelles within plant cells that may have evolved from photolithotrophic cyanobacteria-like organisms. Chemolithotrophs belong to the domains Bacteria and Archaea. The term "lithotroph" was created from the Greek terms 'lithos' (rock) and 'troph' (consumer), meaning "eaters of rock". Many but not all lithoautotrophs are extremophiles.

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.

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.

Aerobic denitrification or co-respiration the simultaneous use of both oxygen (O2) and nitrate (NO3−) as oxidizing agents, performed by various genera of microorganisms. This process differs from anaerobic denitrification not only in its insensitivity to the presence of oxygen, but also in that it has a higher potential to create the harmful byproduct nitrous oxide.

Geopsychrobacter electrodiphilus is a species of bacteria, the type species of its genus. It is a psychrotolerant member of its family, capable of attaching to the anodes of sediment fuel cells and harvesting electricity by oxidation of organic compounds to carbon dioxide and transferring the electrons to the anode.

Dissimilatory metal-reducing microorganisms are a group of microorganisms (both bacteria and archaea) that can perform anaerobic respiration utilizing a metal as terminal electron acceptor rather than molecular oxygen (O2), which is the terminal electron acceptor reduced to water (H2O) in aerobic respiration. The most common metals used for this end are iron [Fe(III)] and manganese [Mn(IV)], which are reduced to Fe(II) and Mn(II) respectively, and most microorganisms that reduce Fe(III) can reduce Mn(IV) as well. But other metals and metalloids are also used as terminal electron acceptors, such as vanadium [V(V)], chromium [Cr(VI)], molybdenum [Mo(VI)], cobalt [Co(III)], palladium [Pd(II)], gold [Au(III)], and mercury [Hg(II)].

Dissimilatory nitrate reduction to ammonium (DNRA), also known as nitrate/nitrite ammonification, is the result of anaerobic respiration by chemoorganoheterotrophic microbes using nitrate (NO3−) as an electron acceptor for respiration. In anaerobic conditions microbes which undertake DNRA oxidise organic matter and use nitrate (rather than oxygen) as an electron acceptor, reducing it to nitrite, then ammonium (NO3−→NO2−→NH4+).

<span class="mw-page-title-main">Microbial oxidation of sulfur</span>

Microbial oxidation of sulfur is the oxidation of sulfur by microorganisms to build their structural components. The oxidation of inorganic compounds is the strategy primarily used by chemolithotrophic microorganisms to obtain energy to survive, grow and reproduce. Some inorganic forms of reduced sulfur, mainly sulfide (H2S/HS−) and elemental sulfur (S0), can be oxidized by chemolithotrophic sulfur-oxidizing prokaryotes, usually coupled to the reduction of oxygen (O2) or nitrate (NO3−). Anaerobic sulfur oxidizers include photolithoautotrophs that obtain their energy from sunlight, hydrogen from sulfide, and carbon from carbon dioxide (CO2).

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.

An oxygen minimum zone (OMZ) is characterized as an oxygen-deficient layer in the world's oceans. Typically found between 200m to 1500m deep below regions of high productivity, such as the western coasts of continents. OMZs can be seasonal following the spring-summer upwelling season. Upwelling of nutrient-rich water leads to high productivity and labile organic matter, that is respired by heterotrophs as it sinks down the water column. High respiration rates deplete the oxygen in the water column to concentrations of 2 mg/L or less forming the OMZ. OMZs are expanding, with increasing ocean deoxygenation. Under these oxygen-starved conditions, energy is diverted from higher trophic levels to microbial communities that have evolved to use other biogeochemical species instead of oxygen, these species include Nitrate, Nitrite, Sulphate etc. Several Bacteria and Archea have adapted to live in these environments by using these alternate chemical species and thrive. The most abundant phyla in OMZs are Pseudomonadota, Bacteroidota, Actinomycetota, and Planctomycetota.

<span class="mw-page-title-main">Hydrothermal vent microbial communities</span> Undersea unicellular organisms

The hydrothermal vent microbial community includes all unicellular organisms that live and reproduce in a chemically distinct area around hydrothermal vents. These include organisms in the microbial mat, free floating cells, or bacteria in an endosymbiotic relationship with animals. Chemolithoautotrophic bacteria derive nutrients and energy from the geological activity at Hydrothermal vents to fix carbon into organic forms. Viruses are also a part of the hydrothermal vent microbial community and their influence on the microbial ecology in these ecosystems is a burgeoning field of research.

References

  1. ↑ Slonczewski, Joan L.; Foster, John W. (2011). Microbiology: An Evolving Science (2nd ed.). New York: W.W. Norton. p. 166. ISBN   9780393934472.
  2. ↑ Sapart; et al. (2017). "The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis". Biogeosciences. 14 (9): 2283–2292. Bibcode:2017BGeo...14.2283S. doi: 10.5194/bg-14-2283-2017 .
  3. ↑ Simon, Jörg; Klotz, Martin G. (2013-02-01). "Diversity and evolution of bioenergetic systems involved in microbial nitrogen compound transformations". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1827 (2): 114–135. doi: 10.1016/j.bbabio.2012.07.005 . PMID   22842521.
  4. ↑ Graf, Jon S.; Schorn, Sina; Kitzinger, Katharina; Ahmerkamp, Soeren; Woehle, Christian; Huettel, Bruno; Schubert, Carsten J.; Kuypers, Marcel M. M.; Milucka, Jana (3 March 2021). "Anaerobic endosymbiont generates energy for ciliate host by denitrification". Nature. 591 (7850): 445–450. Bibcode:2021Natur.591..445G. doi: 10.1038/s41586-021-03297-6 . PMC   7969357 . PMID   33658719.
  5. ↑ Bogner, Jean; Pipatti, Riitta; Hashimoto, Seiji; Diaz, Cristobal; Mareckova, Katarina; Diaz, Luis; Kjeldsen, Peter; Monni, Suvi; Faaij, Andre (2008-02-01). "Mitigation of global greenhouse gas emissions from waste: conclusions and strategies from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. Working Group III (Mitigation)". Waste Management & Research. 26 (1): 11–32. Bibcode:2008WMR....26...11B. doi:10.1177/0734242x07088433. ISSN   0734-242X. PMID   18338699. S2CID   29740189.
  6. ↑ Pester, Michael; Knorr, Klaus-Holger; Friedrich, Michael W.; Wagner, Michael; Loy, Alexander (2012-01-01). "Sulfate-reducing microorganisms in wetlands – fameless actors in carbon cycling and climate change". Frontiers in Microbiology. 3: 72. doi: 10.3389/fmicb.2012.00072 . ISSN   1664-302X. PMC   3289269 . PMID   22403575.
  7. ↑ Nancharaiah, Y. V.; Venkata Mohan, S.; Lens, P. N. L. (2016-09-01). "Recent advances in nutrient removal and recovery in biological and bioelectrochemical systems". Bioresource Technology. 215: 173–185. Bibcode:2016BiTec.215..173N. doi:10.1016/j.biortech.2016.03.129. ISSN   1873-2976. PMID   27053446.
  8. ↑ Polasko, Alexandra Lapat; Miao, Yu; Kwok, Ivy; Park, Keunseok; Park, Junyoung O.; Mahendra, Shaily (2021). "Vinyl chloride and 1,4-dioxane metabolism by Pseudonocardia dioxanivorans CB1190". Journal of Hazardous Materials Letters. 2. doi:10.1016/j.hazl.2021.100039. S2CID   239140980.
  9. ↑ Xu, Bojun; Ge, Zheng; He, Zhen (2015-05-15). "Sediment microbial fuel cells for wastewater treatment: challenges and opportunities". Environmental Science: Water Research & Technology. 1 (3): 279–284. doi: 10.1039/c5ew00020c . hdl: 10919/64969 . ISSN   2053-1419.
  10. ↑ Melnyk, Ryan A.; Engelbrektson, Anna; Clark, Iain C.; Carlson, Hans K.; Byrne-Bailey, Kathy; Coates, John D. (2011). "Identification of a Perchlorate Reduction Genomic Island with Novel Regulatory and Metabolic Genes". Applied and Environmental Microbiology. 77 (20): 7401–7404. Bibcode:2011ApEnM..77.7401M. doi:10.1128/AEM.05758-11. PMC   3194888 . PMID   21856823.
  11. ↑ Reyes-Umana, Victor; Henning, Zachary; Lee, Kristina; Barnum, Tyler P.; Coates, John D. (2021-07-02). "Genetic and phylogenetic analysis of dissimilatory iodate-reducing bacteria identifies potential niches across the world's oceans". The ISME Journal. 16 (1): 38–49. doi:10.1038/s41396-021-01034-5. ISSN   1751-7370. PMC   8692401 . PMID   34215855. S2CID   235722250.
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  14. ↑ Wall, Judy D.; Krumholz, Lee R. (13 October 2006). "Uranium Reduction". Annual Review of Microbiology. 60: 149–166. doi:10.1146/annurev.micro.59.030804.121357. PMID   16704344.
  15. ↑ Holliger, C.; Wohlfarth, G.; Diekert, G. (1998). "Reductive dechlorination in the energy metabolism of anaerobic bacteria" (PDF). FEMS Microbiology Reviews. 22 (5): 383. doi:10.1111/j.1574-6976.1998.tb00377.x. S2CID   85965965.
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