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.
Geobacter is a genus of bacteria. Geobacter species are anaerobic respiration bacterial species which have capabilities that make them useful in bioremediation. Geobacter was found to be the first organism with the ability to oxidize organic compounds and metals, including iron, radioactive metals, and petroleum compounds into environmentally benign carbon dioxide while using iron oxide or other available metals as electron acceptors. Geobacter species are also found to be able to respire upon a graphite electrode. They have been found in anaerobic conditions in soils and aquatic sediment.
In biology, syntrophy, syntrophism, or cross-feeding is the cooperative interaction between at least two microbial species to degrade a single substrate. This type of biological interaction typically involves the transfer of one or more metabolic intermediates between two or more metabolically diverse microbial species living in close proximity to each other. Thus, syntrophy can be considered an obligatory interdependency and a mutualistic metabolism between different microbial species, wherein the growth of one partner depends on the nutrients, growth factors, or substrates provided by the other(s).
Bacterial nanowires are electrically conductive appendages produced by a number of bacteria most notably from the Geobacter and Shewanella genera. Conductive nanowires have also been confirmed in the oxygenic cyanobacterium Synechocystis PCC6803 and a thermophilic, methanogenic coculture consisting of Pelotomaculum thermopropionicum and Methanothermobacter thermoautotrophicus. From physiological and functional perspectives, bacterial nanowires are diverse. The precise role microbial nanowires play in their biological systems has not been fully realized, but several proposed functions exist. Outside of a naturally occurring environment, bacterial nanowires have shown potential to be useful in several fields, notably the bioenergy and bioremediation industries.
An exoelectrogen normally refers to a microorganism that has the ability to transfer electrons extracellularly. While exoelectrogen is the predominant name, other terms have been used: electrochemically active bacteria, anode respiring bacteria, and electricigens. Electrons exocytosed in this fashion are produced following ATP production using an electron transport chain (ETC) during oxidative phosphorylation. Conventional cellular respiration requires a final electron acceptor to receive these electrons. Cells that use molecular oxygen (O2) as their final electron acceptor are described as using aerobic respiration, while cells that use other soluble compounds as their final electron acceptor are described as using anaerobic respiration. However, the final electron acceptor of an exoelectrogen is found extracellularly and can be a strong oxidizing agent in aqueous solution or a solid conductor/electron acceptor. Two commonly observed acceptors are iron compounds (specifically Fe(III) oxides) and manganese compounds (specifically Mn(III/IV) oxides). As oxygen is a strong oxidizer, cells are able to do this strictly in the absence of oxygen.
A Bioelectrochemical reactor is a type of bioreactor where bioelectrochemical processes are used to degrade/produce organic materials using microorganisms. This bioreactor has two compartments: The anode, where the oxidation reaction takes place; And the cathode, where the reduction occurs. At these sites, electrons are passed to and from microbes to power reduction of protons, breakdown of organic waste, or other desired processes. They are used in microbial electrosynthesis, environmental remediation, and electrochemical energy conversion. Examples of bioelectrochemical reactors include microbial electrolysis cells, microbial fuel cells, enzymatic biofuel cells, electrolysis cells, microbial electrosynthesis cells, and biobatteries.
Geothrix fermentans is a rod-shaped, anaerobic bacterium. It is about 0.1 µm in diameter and ranges from 2-3 µm in length. Cell arrangement occurs singly and in chains. Geothrix fermentans can normally be found in aquatic sediments such as in aquifers. As an anaerobic chemoorganotroph, this organism is best known for its ability to use electron acceptors Fe(III), as well as other high potential metals. It also uses a wide range of substrates as electron donors. Research on metal reduction by G. fermentans has contributed to understanding more about the geochemical cycling of metals in the environment.
Geobacter metallireducens is a gram-negative metal-reducing proteobacterium. It is a strict anaerobe that oxidizes several short-chain fatty acids, alcohols, and monoaromatic compounds with Fe(III) as the sole electron acceptor. It can also use uranium for its growth and convert U(VI) to U(IV).
Desulfobulbus propionicus is a Gram-negative, anaerobic chemoorganotroph. Three separate strains have been identified: 1pr3T, 2pr4, and 3pr10. It is also the first pure culture example of successful disproportionation of elemental sulfur to sulfate and sulfide. Desulfobulbus propionicus has the potential to produce free energy and chemical products.
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.
Pelobacter carbinolicus is a species of bacteria that ferments 2,3-butanediol and acetoin. It is Gram-negative, strictly anaerobic and non-spore-forming. Gra Bd 1 is the type strain. Its genome has been sequenced.
Geobacter psychrophilus is a Fe(III)-reducing bacterium. It is Gram-negative, slightly curved, rod-shaped and motile via means of monotrichous flagella. Its type strain is P35T.
Methanosarcina barkeri is the most fundamental species of the genus Methanosarcina, and their properties apply generally to the genus Methanosarcina. Methanosarcina barkeri can produce methane anaerobically through different metabolic pathways. M. barkeri can subsume a variety of molecules for ATP production, including methanol, acetate, methylamines, and different forms of hydrogen and carbon dioxide. Although it is a slow developer and is sensitive to change in environmental conditions, M. barkeri is able to grow in a variety of different substrates, adding to its appeal for genetic analysis. Additionally, M. barkeri is the first organism in which the amino acid pyrrolysine was found. Furthermore, two strains of M. barkeri, M. b. Fusaro and M. b. MS have been identified to possess an F-type ATPase along with an A-type ATPase.
OmcS nanowires are conductive filaments found in some species of bacteria, including Geobacter sulfurreducens, where they catalyze the transfer of electrons. They are multiheme c-Type cytochromes localized outside of the cell of some exoelectrogenic bacterial species, serving as mediator of extracellular electron transfer from cells to Fe(III) oxides and other extracellular electron acceptors.
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)].
Geobacter daltonii is a Gram-negative, Fe(III)- and Uranium(IV)-reducing and non-spore-forming bacterium from the genus of Geobacter. It was isolated from sediments from the Oak Ridge Field Research Center in Oak Ridge, Tennessee in the United States. The specific epithet "daltonii" was refers to Dava Dalton, who performed the initial isolation of the strain, but died shortly thereafter.
Geobacter uraniireducens is a gram-negative, rod-shaped, anaerobic, chemolithotrophic, mesophilic, and motile bacterium from the genus of Geobacter. G. uraniireducens has been found to reduce iron and uranium in sediment and soil. It is being studied for use in bioremediation projects due to its ability to reduce uranium and arsenic.
Electric bacteria are forms of bacteria that directly consume and excrete electrons at different energy potentials without requiring the metabolization of any sugars or other nutrients. This form of life appears to be especially adapted to low-oxygen environments. Most life forms require an oxygen environment in which to release the excess of electrons which are produced in metabolizing sugars. In a low oxygen environment, this pathway for releasing electrons is not available. Instead, electric bacteria "breathe" metals instead of oxygen, which effectively results in both an intake of and excretion of electrical charges.
Jonathan Richard Lloyd is a professor of geomicrobiology and director of the Williamson Research Centre for Molecular Environmental Science, and is based in the Department of Earth and Environmental Sciences at the University of Manchester. His research is based at the interface between microbiology, geology and chemistry. His research focuses on the mechanisms of microbial metal-reduction, with emphasis on the environmental impact and biotechnological applications of metal-reducing bacteria. Some of the contaminants he studies include As, Tc, Sr, U, Np and Pu. Current activities are supported by funds from NERC, BBSRC, EPSRC, the EU and industry. Lloyd is also a senior visiting fellow at the National Nuclear Laboratory, which helps support the development of a nuclear geomicrobiology programme.
Gemma Reguera is a Spanish-American microbiologist and professor at Michigan State University. She is the editor-in-chief of the journal Applied and Environmental Microbiology and was elected fellow of the American Academy of Microbiology in 2019. She is the recipient of the 2022 Alice C. Evans Award for Advancement of Women from the American Society for Microbiology. Her lab's research is focused on electrical properties of metal-reducing microorganisms.
