Lithoautotrophy

Lithoautotrophy is a metabolic strategy in which organisms obtain energy by oxidizing inorganic compounds (lithotrophy) and fix inorganic carbon (CO2 or bicarbonate) to synthesize biomass (autotrophy). In lithoautotrophs, electrons come from the oxidation of reduced inorganic substrates such as molecular hydrogen (H2), reduced sulfur species (H2S, S0, thiosulfate), ferrous iron (Fe2+), manganese(II) (Mn2+), ammonia (NH3), or carbon monoxide (CO). The energy from these redox reactions drives ATP production and reducing power, which powers carbon fixation via autotrophic pathways, most commonly the Calvin cycle but also reverse TCA or other variants depending on lineage.

Habitat and distribution: Many lithoautotrophs inhabit environments where organic carbon is scarce but inorganic reduced compounds are available, such as deep-sea hydrothermal vents, cold seeps, subterranean rocks, acidic mines, and oxic or microoxic soils and freshwater sediments. They form the base of primary production in aphotic zones and contribute to biogeochemical cycles of nitrogen, sulfur, iron, and carbon.

Ecology and metabolism: Some lithoautotrophs are aerobic, using oxygen as the terminal electron acceptor; others are anaerobic, employing nitrate, sulfate, or ferric iron as electron acceptors. Nitrifying bacteria (ammonia- or nitrite-oxidizing) are classic lithoautotrophs, as are sulfur-oxidizing and iron-oxidizing bacteria. Archaeal lineages also participate in lithoautotrophy, including ammonia-oxidizing and other chemolithoautotrophic systems.

Significance: Lithoautotrophy supports life in environments with limited organic matter, drives primary production in dark ecosystems, and mediates global cycles by fixing CO2 and coupling it to the oxidation of inorganic substrates.