Chemosynthesis

In biochemistry, chemosynthesis is the biological conversion of one or more carbon-containing molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic compounds (e.g. hydrogen gas, hydrogen sulfide) or methane as a source of energy, rather than sunlight, as in photosynthesis. Chemoautotrophs, organisms that obtain carbon through chemosynthesis, are phylogenetically diverse, but groups that include conspicuous or biogeochemically-important taxa include the sulfur-oxidizing gamma and epsilon proteobacteria, the aquificaeles, the methanogenic archaea and the neutrophilic iron-oxidizing bacteria.

Many microorganisms in dark regions of the oceans also use chemosynthesis to produce biomass from single carbon molecules. Two categories can be distinguished. In the rare sites at which hydrogen molecules (H₂) are available, the energy available from the reaction between CO₂ and H₂ (leading to production of methane, CH₄) can be large enough to drive the production of biomass. Alternatively, in most oceanic environments, energy for chemosynthesis derives from reactions in which substances such as hydrogen sulfide or ammonia are oxidized. This may occur with or without the presence of oxygen.

Many chemosynthetic microorganisms are consumed by other organisms in the ocean, and symbiotic associations between chemosynthesizers and respiring heterotrophs are quite common. Large populations of animals can be supported by chemosynthetic secondary production at hydrothermal vents, methane clathrates, cold seeps, whale falls, and isolated cave water.

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