lithotroph

Lithotrophs are microorganisms that obtain electrons from inorganic substrates, using those inorganic redox reactions to drive energy metabolism. They often fix carbon dioxide or other inorganic carbon sources to build cellular material, and most are chemolithoautotrophs, though some can use organic carbon alongside inorganic electron donors in mixotrophic lifestyles.

Common inorganic electron donors include molecular hydrogen (H2), hydrogen sulfide (H2S), elemental sulfur (S0) and other reduced sulfur compounds such as thiosulfate, ammonia (NH3), nitrite (NO2-), ferrous iron (Fe2+), and manganous (Mn2+). The carbon source is typically CO2 or bicarbonate, enabling autotrophic growth, but there are lithotrophs that assimilate organic carbon as part of their metabolism.

Electron acceptors vary: many lithotrophs respire aerobically using oxygen, while others use alternative electron acceptors such as nitrate, sulfate, ferric iron, or, in some anaerobic cases like hydrogenotrophic methanogens, CO2 as an electron acceptor. The precise energy yield depends on the pair of donor and acceptor and on the organism’s physiology.

Ecology and significance: lithotrophs are found in diverse environments, including soils, freshwater and marine systems, deep subsurface habitats, and extreme environments such as hydrothermal vents and acidic mine drainages. They play key roles in biogeochemical cycles, notably nitrogen, sulfur, iron, and carbon, and are leveraged in applied contexts such as bioleaching and bioremediation. Notable examples include ammonia-oxidizing bacteria (e.g., Nitrosomonas), nitrite-oxidizing bacteria (e.g., Nitrobacter), iron- and sulfur-oxidizing bacteria (e.g., Acidithiobacillus, Thiobacillus, Leptospirillum), and various sulfur-oxidizing archaea.