Chemosynthesis
Encyclopedia
In biochemistry, 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
. Chemoautotrophs
, organism
s 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 Aquificae
les, the Methanogen
ic 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 vent
s, methane clathrate
s, cold seep
s, and whale fall
s.
It has been hypothesized that chemosynthesis may support life below the surface of Mars
, Jupiter's
moon Europa
, and other planets.
Giant tube worm
s use bacteria to react hydrogen sulfide
with oxygen as a source of energy.
Some reactions produce sulfur, such as:
Hydrogen sulfide chemosynthesis: CO2 + O2 + 4H2S → CH2O + 4S + 3H2O
(CH2O is used to mean carbohydrate
, not formaldehyde
.)
Instead of releasing oxygen
gas as in photosynthesis
, solid globules of sulfur
are produced. In bacteria that can do this, such as purple sulfur bacteria
, yellow globules of sulfur are present and visible in the cytoplasm.
(or Winogradsky) 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.
This was confirmed nearly 90 years later, when hydrothermal ocean
vents were predicted to exist in 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 worm
s 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.
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 molecule
s 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 protein
s. For instance, sheet diamond or carbon nanotube
s 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 protein
s 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.
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
or methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
) and nutrients into organic matter using the oxidation of inorganic molecules (e.g. hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
gas, hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
) or methane as a source of energy, rather than sunlight, as in photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
. Chemoautotrophs
Chemotroph
Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic or inorganic . The chemotroph designation is in contrast to phototrophs, which utilize solar energy...
, organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s 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 Aquificae
Aquificae
The Aquificae phylum is a diverse collection of bacteria that live in harsh environmental settings. They have been found in hot springs, sulfur pools, and thermal ocean vents. Members of the genus Aquifex, for example, are productive in water between 85 to 95 °C. They are the dominant members of...
les, the Methanogen
Methanogen
Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic conditions. They are classified as archaea, a group quite distinct from bacteria...
ic 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
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
or ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
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
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
associations between chemosynthesizers and respiring heterotrophs are quite common. Large populations of animals can be supported by chemosynthetic secondary production at hydrothermal vent
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...
s, methane clathrate
Methane clathrate
Methane clathrate, also called methane hydrate, hydromethane, methane ice, "fire ice", natural gas hydrate or just gas hydrate, is a solid clathrate compound in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice...
s, cold seep
Cold seep
A cold seep is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool...
s, and whale fall
Whale fall
Whale fall is the term used for a whale carcass that has fallen to the ocean floor. Whale falls were first observed in the 1980s, with the advent of deep-sea robotic exploration....
s.
It has been hypothesized that chemosynthesis may support life below the surface of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, Jupiter's
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
moon Europa
Europa (moon)
Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
, and other planets.
Giant tube worm
Giant tube worm
Giant tube worms, Riftia pachyptila, are marine invertebrates in the phylum Annelida related to tube worms commonly found in the intertidal and pelagic zones...
s use bacteria to react hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
with oxygen as a source of energy.
Some reactions produce sulfur, such as:
Hydrogen sulfide chemosynthesis: CO2 + O2 + 4H2S → CH2O + 4S + 3H2O
(CH2O is used to mean carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
, not formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
.)
Instead of releasing oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
gas as in photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
, solid globules of sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
are produced. In bacteria that can do this, such as purple sulfur bacteria
Purple sulfur bacteria
The purple sulfur bacteria are a group of Proteobacteria capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in hot springs or stagnant water. Unlike plants, algae, and cyanobacteria, they do not use water as their...
, yellow globules of sulfur are present and visible in the cytoplasm.
Discovery
In 1890, Sergei Nikolaevich VinogradskiiSergei Winogradsky
Sergei Nikolaievich Winogradsky was a Ukrainian-Russian microbiologist, ecologist and soil scientist who pioneered the cycle of life concept. He discovered the first known form of lithotrophy during his research with Beggiatoa in 1887...
(or Winogradsky) 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.
This was confirmed nearly 90 years later, when hydrothermal ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
vents were predicted to exist in 1970s. The hot springs and strange creatures were discovered by Alvin
DSV Alvin
Alvin is a manned deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts. The vehicle was built by General Mills' Electronics Group in the same factory used to manufacture breakfast cereal-producing...
, the world's first deep-sea submersible, in 1977 at the Galapagos Rift. At about the same time, Harvard graduate student Colleen Cavanaugh
Colleen Cavanaugh
Colleen Cavanaugh, Ph.D., is a microbiologist and Edward C. Jeffrey Professor of Biology at Harvard University who has studied hydrothermal vent ecosystems for over 20 years. As a graduate student, Cavanaugh was the first to propose that the giant tube worm, Riftia pachyptila, obtains its food...
proposed chemosynthetic bacteria that oxidize sulfides or elemental sulfur as a mechanism by which tube worm
Tube worm
A tube worm is a worm-like sessile invertebrate that anchors its tail to an underwater surface and secretes around its body a mineral tube, into which it can withdraw its entire body.Tube worms are found among the following taxa:...
s 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
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
series hosted by Bill Nye
Bill Nye
William Sanford "Bill" Nye , popularly known as Bill Nye the Science Guy, is an American science educator, comedian, television host, actor, mechanical engineer, and scientist...
named chemosynthesis as one of the 100 greatest scientific discoveries of all time.
Use of term in molecular nanotechnology
The term chemosynthesis is also used in molecular nanotechnologyMolecular nanotechnology
Molecular nanotechnology is a technology based on the ability to build structures to complex, atomic specifications by means of mechanosynthesis. This is distinct from nanoscale materials...
broadly to refer to any chemical synthesis
Chemical synthesis
In chemistry, chemical synthesis is purposeful execution of chemical reactions to get a product, or several products. This happens by physical and chemical manipulations usually involving one or more reactions...
where reactions
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
occur due to random thermal motion, a class which encompasses almost all of modern synthetic chemistry. The human-authored processes of chemical engineering
Chemical engineering
Chemical engineering is the branch of engineering that deals with physical science , and life sciences with mathematics and economics, to the process of converting raw materials or chemicals into more useful or valuable forms...
are accordingly represented as biomimicry
Biomimicry
Biomimicry or biomimetics is the examination of nature, its models, systems, processes, and elements to emulate or take inspiration from in order to solve human problems. The term biomimicry and biomimetics come from the Greek words bios, meaning life, and mimesis, meaning to imitate...
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
Mechanosynthesis
Mechanosynthesis is any chemical synthesis in which reaction outcomes are determined by the use of mechanical constraints to direct reactive molecules to specific molecular sites.-Introduction:...
, a hypothetical process where individual molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s are mechanically manipulated to control reactions to human specification. Since photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
and other natural processes create extremely complex molecules to the specifications contained in RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
and stored long-term in DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
form, advocates of molecular engineering
Molecular engineering
Molecular engineering is any means of manufacturing molecules. It may be used to create, on an extremely small scale, most typically one at a time, new molecules which may not exist in nature, or be stable beyond a very narrow range of conditions....
claim that an artificial process can likewise exploit a chain of long-term storage, short-term storage, enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
-like copying mechanisms similar to those in the cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, and ultimately produce complex molecules which need not be protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s. For instance, sheet diamond or carbon nanotube
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
s 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
Food chain
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
from the sun via chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
. Since more than one such pathway exists to creating complex molecules, even extremely specific ones such as protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s edible to fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, 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.