chemolithotrophs

Chemolithotrophs are microorganisms that obtain energy by oxidizing inorganic compounds and typically fix carbon dioxide as their sole carbon source. They are chemotrophs, deriving energy from chemical reactions rather than light, and lithotrophs, using inorganic electron donors rather than organic ones. In chemolithotrophy, energy is released by oxidation of inorganic reduced compounds such as molecular hydrogen (H2), hydrogen sulfide (H2S), reduced sulfur compounds, ferrous iron (Fe2+), ammonia (NH3), or nitrite (NO2-). The electrons are transferred to an electron acceptor, most commonly oxygen in aerobic chemolithotrophs or alternative electron acceptors such as nitrate, ferric iron, or sulfate in anaerobic conditions.

Most chemolithotrophs are autotrophs, fixing CO2 through pathways such as the Calvin cycle, the reverse tricarboxylic acid cycle, or other carbon fixation routes. A minority are chemolithoheterotrophs, using inorganic energy sources while assimilating organic carbon.

Ecologically, chemolithotrophs are important primary producers in many ecosystems, particularly in environments where organic nutrients are scarce. They are central to biogeochemical cycles, including the carbon, nitrogen, sulfur, and iron cycles. Habitats include deep-sea hydrothermal vents, cold seeps, sulfur-rich springs, alkaline or acidic hot springs, soils, and oxic–anoxic interfaces.

Notable examples include ammonia-oxidizing bacteria such as Nitrosomonas, nitrite-oxidizing bacteria such as Nitrobacter, sulfur-oxidizing bacteria such as Thiobacillus and Thiomicrospira, and iron-oxidizing organisms like Acidithiobacillus ferrooxidans. In archaea, groups such as Sulfolobus oxidize sulfur compounds.