chemosynthetic

Chemosynthesis is a biological process by which some organisms convert inorganic carbon into organic matter using chemical energy rather than sunlight. In chemosynthetic ecosystems, chemoautotrophs fix carbon dioxide into biomass, forming the base of the food web in environments where light is absent or scarce.

Chemosynthetic metabolism relies on oxidation–reduction reactions in which inorganic compounds act as electron donors. Common donors include hydrogen sulfide (H2S), hydrogen gas (H2), ammonia (NH3), nitrite (NO2-), and ferrous iron (Fe2+). Electron acceptors can be oxygen or other compounds such as nitrate (NO3-) or sulfate (SO4^2-). Through these redox reactions, cells generate ATP and reducing power required for carbon fixation.

Most chemosynthetic organisms are chemolithoautotrophs, meaning they obtain energy from inorganic substrates and fix carbon dioxide into organic matter. They employ carbon fixation pathways such as the Calvin cycle or the reverse tricarboxylic acid cycle. Some organisms may be chemoorganoheterotrophs that rely on organic substrates for carbon while still deriving energy from inorganic oxidation.

Chemosynthesis plays a crucial ecological role in habitats lacking sunlight, notably deep-sea hydrothermal vents. In these systems, microbial chemosynthesis supports communities of vent animals, including tubeworms, clams, and various crustaceans, often through symbiotic relationships with microbial partners. Similar processes occur in cold seeps, sulfur springs, and certain terrestrial or subsurface environments, where inorganic chemical energy sustains diverse life without photosynthesis.

Historically, the discovery of chemosynthesis demonstrated that life can acquire energy and build biomass from inorganic chemistry, expanding the understanding of possible biospheres on Earth.