In biochemistry, chemosynthesis is the biological conversion of one or more
carbon molecules and nutrients into organic matter using the oxidation of
inorganic 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 are available,
the energy available from the reaction between CO2 and H2 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. Process
Giant tube worms use bacteria in their trophosome to fix carbon dioxide and
produce sugars and amino acids. Some reactions produce sulfur:
hydrogen sulfide chemosynthesis:12H2S + 6CO2 → C6H12O6 + 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, yellow globules of sulfur are present and visible in the
cytoplasm. Discovery
In 1890, Sergei Nikolaevich Vinogradskii proposed a novel life process called
chemosynthesis. His discovery suggested that some microbes could live solely on
inorganic matter and emerged during his physiological research in the 1880s in
Strassburg and Zurich on sulfur, iron, and nitrogen bacteria.
= Hydrothermal vents = This was confirmed nearly 90 years
later, when hydrothermal ocean vents were predicted to exist in the 1970s.
The hot springs and strange creatures were discovered by Alvin, the world's
first deep-sea submersible, in 1977 at the Galapagos Rift. At about the same
time, Harvard graduate student Colleen Cavanaugh proposed chemosynthetic
bacteria that oxidize sulfides or elemental sulfur as a mechanism by which
tube worms could survive near hydrothermal vents. Cavanaugh later
managed to confirm that this was indeed the method by which the worms could
thrive, and is generally credited with the discovery of chemosynthesis.
A 2004 television series hosted by Bill Nye named chemosynthesis as one of the
100 greatest scientific discoveries of all time.
= Oceanic crust = In 2013, researchers reported their
discovery of bacteria living in the rock of the oceanic crust below the thick
layers of sediment, and apart from the hydrothermal vents that form along the
edges of the tectonic plates. Preliminary findings are that these
bacteria subsist on the hydrogen produced by chemical reduction of
olivine by seawater circulating in the small veins that permeate the basalt
that comprises oceanic crust. The bacteria synthesize methane by combining
hydrogen and carbon dioxide. 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
described 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
to be near certainty in the long run, and possible within a generation.
See also Primary nutritional groups
Autotroph Heterotroph
Photosynthesis Movile Cave
References External links
Chemosynthetic Communities in the Gulf of Mexico