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
microbes; 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 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 lithoautotrophs are
extremophiles, but this is not universally so.