Chemosynthesis

Chemosynthesis is a biochemical process by which organisms synthesize organic matter using energy obtained from the oxidation of inorganic molecules, rather than from sunlight. It is carried out by chemoautotrophs, microorganisms that fix carbon dioxide into organic compounds to form biomass, thereby serving as primary producers in ecosystems where photosynthesis is not possible.

In chemosynthetic metabolism, energy is released when reduced inorganic compounds are oxidized. Common electron donors include hydrogen sulfide (H2S), ammonia (NH3), ferrous iron (Fe2+), hydrogen (H2), and other reduced sulfur or nitrogen compounds. The acquired energy powers the fixation of CO2 by pathways such as the Calvin cycle or the reverse tricarboxylic acid (reverse TCA) cycle, producing sugars and other organic molecules.

Chemosynthetic bacteria and archaea inhabit diverse environments, notably deep-sea hydrothermal vents, cold seeps, and subsurface habitats where sunlight does not reach. At vents and seeps, symbiotic relationships between chemosynthetic microbes and macroorganisms (such as tubeworms, clams, and mussels) support entire ecosystems. Some chemoautotrophs are free-living, forming microbial mats or plumes.

Electron acceptors vary: many chemotrophs use oxygen, but some operate anaerobically with nitrate, sulfate, or carbon dioxide as alternative electron acceptors. Chemosynthesis provides an alternative basis for life on Earth and is a subject of study for understanding potential life on other worlds, as well as for biotechnological applications in bioremediation and bioenergy.