Chemosynthesis

Venenivibrio stagnispumantis gains energy by oxidizing hydrogen gas.

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 also 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 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.

It has been hypothesized that chemosynthesis may support life below the surface of Mars, Jupiter's moon Europa, and other planets. [1] Chemosynthesis may have also been the first type of metabolism that evolved on Earth, leading the way for cellular respiration and photosynthesis to develop later.


Process

Giant tube worms use bacteria in their trophosome to fix carbon dioxide (using hydrogen sulfide as an energy source) and produce sugars and amino acids. [2] Some reactions produce sulfur:

hydrogen sulfide chemosynthesis: [3]
12H2S + 6CO2 → C6H12O6 (= carbohydrate) + 6H2O + 12S

instead of releasing oxygen gas as in photosynthesis, the process produces solid globules of sulfur. In bacteria capable of chemosynthesis, such as purple sulfur bacteria[ citation needed], yellow globules of sulfur are present and visible in the cytoplasm.

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