Chemoautotrofer

Chemoautotrophs are organisms that obtain energy by chemical reactions and fix carbon dioxide to build organic matter. They function as primary producers in ecosystems that receive little or no light, such as deep-sea hydrothermal vents, cold seeps, subterranean aquifers, and certain soils and wetlands.

Most chemoautotrophs are chemolithoautotrophs. They derive energy from the oxidation of inorganic electron donors such as molecular hydrogen (H2), hydrogen sulfide (H2S), ammonia (NH3) or nitrite (NO2-), and ferrous iron (Fe2+). The electrons from these reactions are transferred to a terminal electron acceptor, typically oxygen but also nitrate, sulfate, or other inorganic compounds under anaerobic conditions. Carbon is fixed from CO2 into organic compounds using pathways such as the Calvin cycle, the reverse tricarboxylic acid cycle, the reductive acetyl-CoA pathway, or the 3-hydroxypropionate cycle. These pathways enable inorganic energy sources to support growth without sunlight.

Chemoautotrophs are included in both Bacteria and Archaea. Notable bacterial groups include ammonia-oxidizing bacteria such as Nitrosomonas, sulfur-oxidizing genera such as Thiobacillus and Thiomicrospira, iron-oxidizing Acidithiobacillus, and hydrogen-oxidizing species. Archaea include thermophilic and acidophilic chemolithoautotrophs such as Sulfolobus and related groups. These organisms often live in communities anchored to mineral substrates and contribute to biogeochemical cycles of nitrogen, sulfur, and iron.

Ecological and practical significance: they underpin chemosynthetic ecosystems and serve as primary producers in darkness. They participate in wastewater treatment nitrification, bioleaching, and environmental metal cycling, and they have informed research into metabolism and adaptations to extreme conditions.

History: Concept of chemoautotrophy emerged from the work of Sergei Winogradsky in the late 19th and early 20th centuries, who demonstrated that some microbes could gain energy from inorganic compounds and fix CO2, laying the foundation for chemolithotrophy and chemolithoautotrophy.