Lithotrophs are a diverse group of organisms using inorganic substrate (usually of mineral origin) to obtain reducing equivalents for use in biosynthesis (e.g., carbon dioxide fixation) or energy conservation (i.e., ATP production) via aerobic or anaerobic respiration. Known chemolithotrophs are exclusively microorganisms; no known macrofauna possesses the ability to use inorganic compounds as energy 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. Lithotrophs belong to either the domain Bacteria or the domain 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.
A chemolithotroph (named after the process of chemolithotrophy) is able to use inorganic reduced compounds as a source of energy. This process is accomplished through oxidation and ATP synthesis. The majority of chemolithotrophs are able to fix carbon dioxide (CO2) through the Calvin cycle, a metabolic pathway in which carbon enters as CO2 and leaves as glucose. This group of organisms includes sulfur oxidizers, nitrifying bacteria, iron oxidizers, and hydrogen oxidizers.
The term "chemolithotrophy" refers to a cell’s acquisition of energy from the oxidation of inorganic compounds, also known as electron donors. This form of metabolism is believed to occur only in prokaryotes and was first characterized by microbiologist Sergei Winogradsky.
The survival of these bacteria is dependent on the physiochemical conditions of their environment. Although they are sensitive to certain factors such as quality of inorganic substrate, they are able to thrive under some of the most inhospitable conditions in the world, such as temperatures above 110 degrees Celsius and below 2 pH. The most important requirement for chemolithotropic life is an abundant source of rich inorganic compounds. These compounds are crucial for chemolithotrophs because they provide a suitable energy source/electron donor from which the microorganisms can fix CO2 and produce the energy they need to survive. Since chemosynthesis can take place in the absence of sunlight, these organisms are found mostly around hydrothermal vents and other locations rich in inorganic substrate.
The energy obtained from inorganic oxidation varies depending on the substrate and the reaction. For example, the oxidation of hydrogen sulfide to elemental sulfur produces far less energy (50.1 kcal/mol or 210.4 kJ/mol) than the oxidation of elemental sulfur to sulfate (149.8 kcal/mol or 629.2 kJ/mol). The majority of lithotrophs fix carbon dioxide through the Calvin cycle, an energetically expensive process. For some substrates, such as ferrous iron, the cells must cull through large amounts of inorganic substrate to secure just a small amount of energy. This makes their metabolic process inefficient in many places and hinders them from thriving.
There is a fairly large variation in the types of inorganic substrates that these microorganisms can use to produce energy. Sulfur is one of many inorganic substrates that can be utilized in different reduced forms depending on the specific biochemical process that a lithotroph uses. The chemolithotrophs that are best documented are aerobic respirers, meaning that they use oxygen in their metabolic process. The high electronegativity of oxygen and resulting large energy gains makes it ideal for use as a Terminal Electron Acceptor (TEA). The list of these microorganisms that employ anaerobic respiration though is growing. At the heart of this metabolic process is an electron transport system that is similar to that of chemoorganotrophs. The major difference between these two microorganisms is that chemolithotrophs directly provide electrons to the electron transport chain, while chemoorganotrophs must generate their own cellular reducing power by oxidizing reduced organic compounds. Chemolithotrophs bypass this by obtaining their reducing power directly from the inorganic substrate or by the reverse electron transport reaction. Certain specialized chemolithotrophic bacteria utilize different derivatives of the Sox system; a central pathway specific to sulfur oxidation. This ancient and unique pathway illustrates the power that chemolithotrophs have evolved to utilize from inorganic substrates, such as sulfur.
In chemolithotrophs, the compounds - the electron donors - are oxidized in the cell, and the electrons are channeled into respiratory chains, ultimately producing ATP. The electron acceptor can be oxygen (in aerobic bacteria), but a variety of other electron acceptors, organic and inorganic, are also used by various species. Aerobic bacteria such as the nitrifying bacteria, Nitrobacter, utilize oxygen to oxidize nitrite to nitrate. Some lithotrophs produce organic compounds from carbon dioxide in a process called chemosynthesis, much as plants do in photosynthesis. Plants use energy from sunlight to drive carbon dioxide fixation, since both water and carbon dioxide are low in energy. By contrast, the hydrogen compounds used in chemosynthesis are high in energy, so chemosynthesis can take place in the absence of sunlight (e.g., around a hydrothermal vent). Ecosystems establish in and around hydrothermal vents as the abundance of inorganic substances, namely hydrogen, are constantly being supplied via magma in pockets below the sea floor. Other lithotrophs are able to directly utilize inorganic substances, e.g., iron, hydrogen sulfide, elemental sulfur, or thiosulfate, for some or all of their energy needs.
Here are a few examples of chemolithotrophic pathways, any of which may use oxygen, sulfur or other molecules as electron acceptors:
|Name||Examples||Source of energy and electrons||Respiration electron acceptor|
|Iron bacteria||Acidithiobacillus ferrooxidans||Fe2+ (ferrous iron) → Fe3+ (ferric iron) + e−||O|
2 (oxygen) → H
|Nitrosifying bacteria||Nitrosomonas||NH3 (ammonia) → NO−
2 (nitrite) + e−
2 (oxygen) → H
2 (nitrite) → NO−
3 (nitrate) + e−
2 (oxygen) → H
|Chemotrophic purple sulfur bacteria||Halothiobacillaceae||S2−
(sulfide) → S0
(sulfur) + e−
2 (oxygen) → H
|Sulfur-oxidizing bacteria||Chemotrophic Rhodobacteraceae
(sulfur) → SO2−
4 (sulfate) + e−
2 (oxygen) → H
|Aerobic hydrogen bacteria||Cupriavidus metallidurans||H2 (hydrogen) → H2O (water) + e−||O|
2 (oxygen) → H
4 (ammonium) → NO−
2 (nitrogen) + H
2O (water) 
|Thiobacillus denitrificans||Thiobacillus denitrificans||S0
(sulfur) → SO2−
4 (sulfate) + e−
|Sulfate-reducing bacteria: Hydrogen bacteria||Desulfovibrio paquesii||H2 (hydrogen) → H2O (water) + e−||Sulfate (SO2−|
|Sulfate-reducing bacteria: Phosphite bacteria||Desulfotignum phosphitoxidans||PO3−
3 (phosphite) → PO3−
4 (phosphate) + e−
|Methanogens||Archaea||H2 (hydrogen) → H2O (water) + e−||CO2 (carbon dioxide)|
|Carboxydotrophic bacteria||Carboxydothermus hydrogenoformans||carbon monoxide (CO) → carbon dioxide (CO2) + e−||H|
2O (water) → H
Photolithotrophs obtain energy from light and therefore use inorganic electron donors only to fuel biosynthetic reactions (e. g., carbon dioxide fixation in lithoautotrophs).
Lithotrophic bacteria cannot use, of course, their inorganic energy source as a carbon source for the synthesis of their cells. They choose one of three options:
In addition to this division, lithotrophs differ in the initial energy source which initiates ATP production:
Lithotrophs participate in many geological processes, such as the formation of soil and the biogeochemical cycling of carbon, nitrogen, and other elements. Lithotrophs also associate with the modern-day issue of acid mine drainage. Lithotrophs may be present in a variety of environments, including deep terrestrial subsurfaces, soils, mines, and in endolith communities.
A primary example of lithotrophs that contribute to soil formation is Cyanobacteria. This group of bacteria are nitrogen-fixing photolithotrophs that are capable of using energy from sunlight and inorganic nutrients from rocks as reductants. This capability allows for their growth and development on native, oligotrophic rocks and aids in the subsequent deposition of their organic matter (nutrients) for other organisms to colonize. Colonization can initiate the process of organic compound decomposition: a primary factor for soil genesis. Such a mechanism has been attributed as part of the early evolutionary processes that helped shape the biological Earth.
Biogeochemical cycling of elements is an essential component of lithotrophs within microbial environments. For example, in the carbon cycle, there are certain bacteria classified as photolithoautotrophs that generate organic carbon from atmospheric carbon dioxide. Certain chemolithoautotrophic bacteria can also produce organic carbon, some even in the absence of light. Similar to plants, these microbes provide a usable form of energy for organisms to consume. On the contrary, there are lithotrophs that have the ability to ferment, implying their ability to convert organic carbon into another usable form. Another example is the cycling of nitrogen. Many lithotrophic bacteria play a role in reducing inorganic nitrogen (nitrogen gas) to organic nitrogen (ammonium) in a process called nitrogen fixation. Likewise, there are many lithotrophic bacteria that also convert ammonium into nitrogen gas in a process called denitrification. Carbon and nitrogen are important nutrients, essential for metabolic processes, and can sometimes be the limiting factor that affects organismal growth and development. Thus, lithotrophs are key players in both providing and removing these important resource.
Lithotrophic microbes are responsible for the phenomenon known as acid mine drainage. Typically occurring in mining areas, this process concerns the active metabolism of energy-rich pyrites and other reduced sulfur components to sulfate. One example is the acidophilic bacterial genus, A. ferrooxidans, that utilize iron(II) sulfide (FeS2) and oxygen (O2) to generate sulfuric acid. The acidic product of these specific lithotrophs has the potential to drain from the mining area via water run-off and enter the environment.
Acid mine drainage drastically alters the acidity (pH values of 2 - 3) and chemistry of groundwater and streams, and may endanger plant and animal populations downstream of mining areas. Activities similar to acid mine drainage, but on a much lower scale, are also found in natural conditions such as the rocky beds of glaciers, in soil and talus, on stone monuments and buildings and in the deep subsurface.
It has been suggested that biominerals could be important indicators of extraterrestrial life and thus could play an important role in the search for past or present life on the planet Mars. Furthermore, organic components (biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions.
On January 24, 2014, NASA reported that current studies by the Curiosity and Opportunity rovers on Mars will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective.
Anammox, an abbreviation for anaerobic ammonium oxidation, is a globally important microbial process of the nitrogen cycle that takes place in many natural environments. The bacteria mediating this process were identified in 1999, and were a great surprise for the scientific community. "Anammox" is also the trademarked name for an anammox-based ammonium removal technology developed by the Delft University of Technology.Chemotroph
Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic (chemoorganotrophs) or inorganic (chemolithotrophs). The chemotroph designation is in contrast to phototrophs, which use solar energy. Chemotrophs can be either autotrophic or heterotrophic. Chemotrophs are found in ocean floors where sunlight cannot reach them because they are not dependent on solar energy. Ocean floors often contain underwater volcanos that can provide heat as a substitute for sunlight's warmth.Electron transport chain
An electron transport chain (ETC) is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. This creates an electrochemical proton gradient that drives the synthesis of adenosine triphosphate (ATP), a molecule that stores energy chemically in the form of highly strained bonds. The molecules of the chain include peptides, enzymes (which are proteins or protein complexes), and others. The final acceptor of electrons in the electron transport chain during aerobic respiration is molecular oxygen although a variety of acceptors other than oxygen such as sulfate exist in anaerobic respiration.
Electron transport chains are used for extracting energy via redox reactions from sunlight in photosynthesis or, such as in the case of the oxidation of sugars, cellular respiration. In eukaryotes, an important electron transport chain is found in the inner mitochondrial membrane where it serves as the site of oxidative phosphorylation through the action of ATP synthase. It is also found in the thylakoid membrane of the chloroplast in photosynthetic eukaryotes. In bacteria, the electron transport chain is located in their cell membrane.
In chloroplasts, light drives the conversion of water to oxygen and NADP+ to NADPH with transfer of H+ ions across chloroplast membranes. In mitochondria, it is the conversion of oxygen to water, NADH to NAD+ and succinate to fumarate that are required to generate the proton gradient.
Electron transport chains are major sites of premature electron leakage to oxygen, generating superoxide and potentially resulting in increased oxidative stress.
The electron transport chain consists of a spatially separated series of redox reactions in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force driving these reactions is the Gibbs free energy of the reactants and products. The Gibbs free energy is the energy available ("free") to do work. Any reaction that decreases the overall Gibbs free energy of a system is thermodynamically spontaneous.
The function of the electron transport chain is to produce a transmembrane proton electrochemical gradient as a result of the redox reactions. If protons flow back through the membrane, they enable mechanical work, such as rotating bacterial flagella. ATP synthase, an enzyme highly conserved among all domains of life, converts this mechanical work into chemical energy by producing ATP, which powers most cellular reactions.
A small amount of ATP is available from substrate-level phosphorylation, for example, in glycolysis. In most organisms the majority of ATP is generated in electron transport chains.Endolith
An endolith is an organism (archaeon, bacterium, fungus, lichen, algae or amoeba) that lives inside rock, coral, animal shells, or in the pores between mineral grains of a rock. Many are extremophiles, living in places long imagined inhospitable to life. They are of particular interest to astrobiologists, who theorize that endolithic environments on Mars and other planets constitute potential refugia for extraterrestrial microbial communities.Food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or trees which use radiation from the Sun to make their food) and ending at apex predator species (like grizzly bears or killer whales), detritivores (like earthworms or woodlice), or decomposer species (such as fungi or bacteria). A food chain also shows how the organisms are related with each other by the food they eat. Each level of a food chain represents a different trophic level. A food chain differs from a food web, because the complex network of different animals' feeding relations are aggregated and the chain only follows a direct, linear pathway of one animal at a time. Natural interconnections between food chains make it a food web.
A common metric used to the quantify food web trophic structure is food chain length. In its simplest form, the length of a chain is the number of links between a trophic consumer and the base of the web and the mean chain length of an entire web is the arithmetic average of the lengths of all chains in a food web.Many food webs have a keystone species (Such as Sharks) . A keystone species is a species that has a large impact on the surrounding environment and can directly affect the food chain. If this keystone species dies off it can set the entire food chain off balance. Keystone species keep herbivores from depleting all of the foliage in their environment and preventing a mass extinction.Food chains were first introduced by the Arab scientist and philosopher Al-Jahiz in the 10th century and later popularized in a book published in 1927 by Charles Elton, which also introduced the food web concept.List of Greek and Latin roots in English/P–Z
The following is an alphabetical list of Greek and Latin roots, stems, and prefixes commonly used in the English language from P to Z. See also the lists from A to G and from H to O.
Some of those used in medicine and medical technology are not listed here but instead in the entry for List of medical roots, suffixes and prefixes.Lithoautotroph
A lithoautotroph or chemolithoautotroph is a microbe which derives energy from reduced compounds of mineral origin. Lithoautotrophs are a type of lithotrophs with autotrophic metabolic pathways. Lithoautotrophs are exclusively microbes; macrofauna do not possess the capability to use mineral sources of energy. Most lithoautotrophs belong to the domain Bacteria, while some belong to the domain Archaea. For lithoautotrophic bacteria, only inorganic molecules can be used as energy sources. The term "Lithotroph" is from Greek lithos (λίθος) meaning "rock" and trōphos (τροφοσ) meaning "consumer"; literally, it may be read "eaters of rock". Many lithoautotrophs are extremophiles, but this is not universally so.
Lithoautotrophs are extremely specific in using their energy source. Thus, despite the diversity in using inorganic molecules in order to obtain energy that lithoautotrophs exhibit as a group, one particular lithoautotroph would use only one type of inorganic molecule to get its energy.Lysobacter
The genus Lysobacter belongs to the family Xanthomonadaceae within the Gammaproteobacteria and includes 13 named species: Lysobacter enzymogenes, L. antibioticus, L. gummosus, L. brunescens, L. defluvii, L. niabensis, L. niastensis, L. daejeonensis, L. yangpyeongensis, L. koreensis, L. concretionis, L. spongiicola, and L. capsici. Lysobacter spp. were originally grouped with myxobacteria because they shared the distinctive trait of gliding motility, but they uniquely display a number of traits that distinguish them from other taxonomically and ecologically related microbes including high genomic G+C content (typically ranging between 65 and 72%) and the lack of flagella. The feature of gliding motility alone has piqued the interest of many, since the role of gliding bacteria in soil ecology is poorly understood. In addition, while a number of different mechanisms have been proposed for gliding motility among a wide range of bacterial species, the genetic mechanism in Lysobacter remains unknown. Members of the Lysobacter group have gained broad interest for production of extracellular enzymes. The group is also regarded as a rich source for production of novel antibiotics, such as β-lactams containing substituted side chains, macrocyclic lactams and macrocyclic peptide or depsipeptide antibiotics like the katanosins.Methanocaldococcus sp. FS406-22
Methanocaldococcus sp. FS406-22 is an archaea in the genus Methanocaldococcus. It is an anaerobic, piezophilic, diazotrophic, hyperthermophilic marine archaeon. This strain is notable for fixing nitrogen at the highest known temperature of nitrogen fixers recorded to date. The 16S rRNA gene of Methanocaldococcus sp. FS406-22, is almost 100% similar to that of Methanocaldococcus jannaschii, a non-nitrogen fixer.Microbial metabolism
Microbial metabolism is the means by which a microbe obtains the energy and nutrients (e.g. carbon) 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.Organotroph
An organotroph is an organism that obtains hydrogen or electrons from organic substrates. This term is used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes. Some organotrophs such as animals and many bacteria, are also heterotrophs. Organotrophs can be either anaerobic or aerobic.
Antonym: Lithotroph, Adjective: Organotrophic.Scalindua
"Candidatus Scalindua" is a bacterial genus, and a proposed member of the order Planctomycetes. These bacteria lack peptidoglycan in their cell wall and have a compartmentalized cytoplasm. They are ammonium oxidizing bacteria found in marine environments.Sergei Winogradsky
Sergei Nikolaievich Winogradsky (or Vinogradskiy; Ukrainian: Сергій Миколайович Виноградський; 1 September 1856 – 25 February 1953) was a Russian microbiologist, ecologist and soil scientist who pioneered the cycle-of-life concept.Winogradsky discovered the first known form of lithotrophy during his research with Beggiatoa in 1887. He reported that Beggiatoa oxidized hydrogen sulfide (H2S) as an energy source and formed intracellular sulfur droplets. This research provided the first example of lithotrophy, but not autotrophy.
His research on nitrifying bacteria would report the first known form of chemoautotrophy, showing how a lithotroph fixes carbon dioxide (CO2) to make organic compounds.
(Bacteriochlorophylls a and b)
(Bacteriochlorophylls c and d)