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Lithotroph

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A lithotroph is an organism whose energy source is inorganic-chemical reactions; compare organotrophs, which use organic molecules, usually biomolecules, as their energy source. Most lithotrophs' energy-source chemical reactions can be interpreted as electron-transfer (redox) reactions; such reactions require an electron donor (reducer) and an electron acceptor (oxidizer).

Reducers:

H2 -> 2H+ + 2e
H2S -> 2H+ + S + 2e
Fe++ -> Fe+++ + e

Oxidizers:

O2 + 4H+ + 4e -> 2H2O
NO3- + 6H+ + 5e -> (1/2)N2 + 3H2O
SO4-- + 8H+ + 6e -> S + 4H2O

Organotrophs fit into this scheme because they use organic molecules as reducers -- and sometimes also as oxidizers (fermentation).

Methanogens use this reaction, in which carbon dioxide can be interpreted as the oxidizer:

CO2 + 4H2 -> CH4 + 2H2O

Lithotrophs are usually autotrophic, and in some ecologies, like hydrothermal vents, lithotrophs are the primary producers.

See also: autotroph, chemotroph, heterotroph, organotroph, phototroph

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