Chemoautotrophy

Chemoautotrophy is a form of metabolism in which organisms obtain energy by oxidizing inorganic or organic chemical compounds and use that energy to fix carbon dioxide into organic matter. Chemoautotrophs are autotrophs, meaning they synthesize biomass from inorganic carbon, and they rely on chemical reactions rather than light as an energy source.

Depending on electron donors, chemoautotrophs can be lithoautotrophs (energy from inorganic compounds such as H2, H2S, S0, Fe2+, NH3, NO2−) or chemoorganoautotrophs (energy from oxidation of organic compounds). Carbon is fixed primarily through pathways such as the Calvin cycle, the reverse TCA cycle, or the reductive acetyl-CoA pathway, enabling production of sugars and other biomass from CO2 or bicarbonate.

Nitrogen- and sulfur-oxidizing bacteria, iron-oxidizers, hydrogen-oxidizers, and some archaea are common chemoautotrophs. These organisms often inhabit environments lacking sunlight or rich in reduced inorganic compounds, such as deep-sea hydrothermal vents, cold seeps, sulfur-rich caves, and certain soils and aquifers. They form the base of local food webs and contribute to biogeochemical cycling of carbon, nitrogen, sulfur, and iron, sometimes driving mineral dissolution or bioleaching.

The concepts of chemotrophy and autotrophy were established by early microbiologists such as Winogradsky and Beijerinck, highlighting life’s ability to convert chemical energy directly into organic matter independent of photosynthesis.