Lithotroph

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 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 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 kingdom Bacteria or the kingdom Archaea. The term "lithotroph" was created from the Greek terms 'lithos' (rock) and 'troph' (consumer), meaning "eaters of rock". Many lithoautotrophs are extremophiles, but this is not universally so.

Different from a lithotroph is an organotroph, an organism which obtains its reducing agents from the catabolism of organic compounds.

The term was suggested in 1946 by Lwoff and collaborators.

Lithotrophs consume reduced inorganic compounds (rich in electrons).

A chemolithotroph (named after the process of chemolithotropy) 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. For some substrates, 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. This group of organisms includes sulfur oxidizers, nitrifying bacteria, iron oxidizers, and hydrogen oxidizers.

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