Chemosynthesis

Chemosynthesis is the biological conversion of one or more carbon molecules (usually carbon dioxide or methane) and nutrients into organic matter using the oxidation of inorganic molecules (e.g. hydrogen gas, hydrogen sulfide) or methane as a source of energy, rather than sunlight, as in photosynthesis. Large populations of animals can be supported by chemosynthetic primary production at hydrothermal vents, methane clathrates, cold seeps, and whale falls. Chemoautotrophs, organisms that obtain carbon through chemosynthesis, and are responsible for the primary production in oxygen-deficient environments, generally fall into four groups: methanogens, halophiles, sulfur reducers, and thermoacidophiles.

Many microorganisms in dark regions of the oceans use chemosynthesis to produce biomass from 1-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 between O₂ and substances such as hydrogen sulfide or ammonia. In this second case, the chemosynthetic microorganisms are dependent on photosynthesis which occurs elsewhere and which produces the O₂ that they require. Many chemosynthetic microorganisms are consumed by other organisms in the ocean, and symbiotic associations between chemosynthesizers and respiring heterotrophs are quite common.

It has been hypothesized that chemosynthesis may support life below the surface of Mars, Jupiter's moon Europa, and other planets. [Chela-Flores, J. (2000): "Terrestrial microbes as candidates for survival on Mars and Europa", in: Seckbach, Joseph (ed.) "Journey to Diverse Microbial Worlds: Adaptation to Exotic Environments", Springer, pp. 387–398. ISBN 0792360206]

Hydrogen sulfide chemosynthesis: CO₂ + O₂ + 4{H₂S} → CH₂O + 4{S} + 3{H₂O}

Note that the CH₂O (carbohydrate) is used as the food source.

Hydrogen sulfide chemosynthesis:6{CO₂} + 6{H₂O} + 3{H₂S} → C₆H₁₂O₆ + 3{H₂SO₄}

Broader use of term in molecular nanotechnology

The term chemosynthesis is also used in molecular nanotechnology broadly to refer to any chemical synthesis where reactions occur due to random thermal motion, a class which encompasses almost all of modern synthetic chemistry. The human-authored processes of chemical engineering are accordingly represented as biomimicry of the natural phenomena above, and the entire class of non-photosynthetic chains by which complex molecules are constructed is desribed as chemo-.

This form of engineering is then contrasted with mechanosynthesis, a hypothetical process where individual molecules are mechanically manipulated to control reactions to human specification. Since photosynthesis and other natural processes create extremely complex molecules to the specifications contained in RNA and stored long-term in DNA form, advocates of molecular engineering claim that an artificial process can likewise exploit a chain of long-term storage, short-term storage, enzyme-like copying mechanisms similar to those in the cell, and ultimately produce complex molecules which need not be proteins. For instance, sheet diamond or carbon nanotubes could be produced by a chain of non-biological reactions that have been designed using the basic model of biology.

Use of the term chemosynthesis reinforces the view that this is feasible by pointing out that several alternate means of creating complex proteins, mineral shells of mollusks and crustaceans, etc., evolved naturally, not all of them dependent on photosynthesis and a food chain from the sun via chlorophyll. Since more than one such pathway exists to creating complex molecules, even extremely specific ones such as proteins edible to fish, the likelihood of humans being able to design an entirely new one is considered (by these advocates) to be near certainty in the long run, and possible within a generation.

Discovery

In 1890, Sergei Nikolaevich Vinogradskii (Winogradsky) proposed a novel life process called chemosynthesis. His discovery suggested that some microbes could live solely on inorganic matter emerged during his physiological research in 1880s in Strassburg and Zurich on sulfur, iron, and nitrogen bacteria.

This was confirmed nearly 100 years later, when hydrothermal vents were predicted to exist in 1970's. The hot springs and strange creatures were discovered by Alvin, the world's first deep-sea submersible, expedition, in 1977 to the Galapagos Rift. Chemosynthesis told scientist that there could be another source of life besides sunlight.

References

Annoted Reference

* "The Origin of Life and Evolution." 100 Greatest Discoveries. [http://www.tvo.org/TVO/WebObjects/TVO.woa/wo/45OUlJpac8YdVVjnUcb1B0/4.0.7.29.9.5.3.3.3.3.0 TVO] . CICA, Ottawa. 16 Jan. 2007, 19h00. :Note: This film discusses life, evolution and extinction. For more information see [http://www.imdb.com/title/tt0442715/ IMDB] .

See also

* Autotroph
* Heterotroph

External links

* [http://www.gomr.mms.gov/homepg/regulate/environ/chemo/chemo.html Chemosynthetic Communities in the Gulf of Mexico]