Lithotrophs are a diverse group of organisms using an 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.
[1] 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.
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.
The majority of chemolithotrophs are chemolithoautotrophs, able to fix carbon dioxide (CO2) through the Calvin cycle, a metabolic pathway in which CO2 is converted to glucose.
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.
[8] The most important requirement for chemolithotropic life is an abundant source of inorganic compounds,[9] which provide a suitable electron donor in order to fix CO2 and produce the energy the microorganism needs 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.
Chemolithotrophs bypass this by obtaining their reducing power directly from the inorganic substrate or by the reverse electron transport reaction.
[13] Certain specialized chemolithotrophic bacteria use different derivatives of the Sox system; a central pathway specific to sulfur oxidation.
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.
[15] Other lithotrophs are able to directly use inorganic substances, e.g., ferrous iron, hydrogen sulfide, elemental sulfur, thiosulfate, or ammonia, for some or all of their energy needs.
[27] Carbon and nitrogen are important nutrients, essential for metabolic processes, and can sometimes be the limiting factor that affects organismal growth and development.
Typically occurring in mining areas, this process concerns the active metabolism of pyrites and other reduced sulfur components to sulfate.
[29] 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.
[32][33][34][35] The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective.