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( Lithotroph)
A lithotroph is an organism which uses an inorganic substrate (usually of mineral origin) to obtain reducing equivalents for use in biosynthesis (e.g. carbon dioxide fixation) or energy conservation via aerobic or anaerobic respiration.[1] Lithotrophs are exclusively microbes or plants; macrofauna do not possess the capability to utilize 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 deep sea worms or plastids, which are organelles within plant cells that may have evolved from photolithotrophic cyanobacteria-like organisms. Lithotrophs belong either to the domain Bacteria or Archaea. The term "Lithotroph" is created from the terms 'lithos' (rock) and 'troph' (consumer). It literally is the "eaters of rock." Many lithoautotrophs are extremophiles, but this is not universally so. Lithotrophs consume reduced compounds (rich in electrons). 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. Photolithotrophs obtain energy from light and therefore use inorganic electron donors only to fuel biosynthetic reactions (e. g. carbon dioxide fixation in lithoautotrophs). Lithotrophs participate in many geological processes, such as the weathering of parent material (bedrock) to form soil, as well as biogeochemical cycling of sulfur, nitrogen, and other elements. They may be present in the deep terrestrial subsurface (they have been found well over a 3 km below the surface of the planet), in soils, and in endolith communities. As they are responsible for the liberation of many crucial nutrients, and participate in the formation of soil, lithotrophs play a crucial role in the maintenance of life on Earth. Lithotrophic microbial consortia are responsible for the phenomenon known as acid mine drainage, whereby energy-rich pyrites and other reduced sulfur compounds present in mine tailing heaps and in exposed rock faces is metabolized to form sulfates, thereby forming potentially toxic sulfuric acid. Acid mine drainage drastically alters the acidity and chemistry of groundwater and streams, and may endanger plant and animal populations. 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.
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