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 also groups that include conspicuous or biogeochemically-important taxa include the sulfur-oxidizing gamma and epsilon proteobacteria, the Aquificae, 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.

Venenivibrio
Venenivibrio stagnispumantis gains energy by oxidizing hydrogen gas.

Hydrogen sulfide chemosynthesis 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 while fixing carbon dioxide as in photosynthesis, hydrogen sulfide chemosynthesis produces solid globules of sulfur in the process. In bacteria capable of chemoautotrophy (a form a chemosynthesis), such as purple sulfur bacteria[4], yellow globules of sulfur are present and visible in the cytoplasm.

Discovery

Gollner Riftia pachyptila
Giant tube worms (Riftia pachyptila) have an organ containing chemosynthetic bacteria instead of a gut.

In 1890, Sergei Nikolaevich Vinogradskii (or Winogradsky) proposed a novel type of life process called "anorgoxydant". 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.

In 1897, Wilhelm Pfeffer coined the term "chemosynthesis" for the energy production by oxidation of inorganic substances, in association with autotrophic carbon dioxide assimilation - what would be named today as chemolithoautotrophy. Later, the term would be expanded to include also chemoorganoautotrophs, which are organisms that use organic energy substrates in order to assimilate carbon dioxide.[5] Thus, chemosynthesis can be seen as a synonym of chemoautotrophy.

The term "chemotrophy", less restrictive, would be introduced in the 1940s by André Lwoff for the production of energy by the oxidation of electron donors, organic or not, associated with auto- or heterotrophy.[6][7]

Hydrothermal vents

The suggestion of Vinogradskii 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.[8]

A 2004 television series hosted by Bill Nye named chemosynthesis as one of the 100 greatest scientific discoveries of all time.[9][10]

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.[11]

See also

References

  1. ^ Julian Chela-Flores (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 0-7923-6020-6
  2. ^ Biotechnology for Environmental Management and Resource Recovery. Springer. 2013. p. 179. ISBN 9788132208761.
  3. ^ Campbell N.A. e.a. (2008) Biology 8. ed. Pearson International Edition, San Francisco. ISBN 978-0-321-53616-7
  4. ^ The purple phototrophic bacteria. Hunter, C. Neil, 1954-. Dordrecht: Springer. 2009. ISBN 9781402088148. OCLC 304494953.CS1 maint: others (link)
  5. ^ Kellerman, M.Y., G. Wegener, M. Elvert, M.Y. Yoshinaga, Y-S. Lin, T. Holler, X.P. Millar, K. Knittel, and K-U. Hinrichs (2012). Autotrophy as a predominant mode of carbon fixation in anaerobic methane-oxidizing microbial communities. Proc. Natl. Acad. Sci. USA 109(47):19321-19326
  6. ^ Kelly, D. P., & Wood, A. P. (2006). The chemolithotrophic prokaryotes. In: The prokaryotes (pp. 441-456). Springer New York, [1].
  7. ^ Schlegel, H.G. (1975). Mechanisms of chemo-autotrophy. In: Marine ecology, Vol. 2, Part I (O. Kinne, ed.), pp. 9-60, [2].
  8. ^ Cavenaugh, Colleen M., et al, "Prokaryotic Cells in the Hydrothermal Vent Tube Worms Rifttia Jones:Possible Chemoautotrophic Symbionts," Science, Vol 213, Issue 4505, 17 July 1981, pp. 340-342.
  9. ^ "100 Greatest Discoveries (2004-2005)" IMDb.
  10. ^ "Greatest Discoveries." Archived March 19, 2013, at the Wayback Machine Science. Watch the "Greatest Discoveries in Evolution" online.
  11. ^ "Life deep within oceanic crust sustained by energy from interior of Earth", ScienceDaily, retrieved March 16, 2013.

External links

Autotroph

An autotroph or primary producer, is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) from simple substances present in its surroundings, generally using energy from light (photosynthesis) or inorganic chemical reactions (chemosynthesis). They are the producers in a food chain, such as plants on land or algae in water (in contrast to heterotrophs as consumers of autotrophs). They do not need a living source of energy or organic carbon. Autotrophs can reduce carbon dioxide to make organic compounds for biosynthesis and also create a store of chemical energy. Most autotrophs use water as the reducing agent, but some can use other hydrogen compounds such as hydrogen sulfide. Some autotrophs, such as green plants and algae, are phototrophs, meaning that they convert electromagnetic energy from sunlight into chemical energy in the form of reduced carbon.

Autotrophs can be photoautotrophs or chemoautotrophs. Phototrophs use light as an energy source, while chemotrophs use electron donors as a source of energy, whether from organic or inorganic sources; however in the case of autotrophs, these electron donors come from inorganic chemical sources. Such chemotrophs are lithotrophs. Lithotrophs use inorganic compounds, such as hydrogen sulfide, elemental sulfur, ammonium and ferrous iron, as reducing agents for biosynthesis and chemical energy storage. Photoautotrophs and lithoautotrophs use a portion of the ATP produced during photosynthesis or the oxidation of inorganic compounds to reduce NADP+ to NADPH to form organic compounds.

Bathyacmaea

Bathyacmaea is a genus of deep-sea limpet, marine gastropod mollusk in the family Pectinodontidae. Species in this genus inhabit the dark, chemosynthesis-based marine communities of ocean vents and cold seeps near Japan.

Bathyacmaea secunda

Bathyacmaea secunda is a species of very small (adults are typically about 6 mm in length), deep-sea limpet, a marine gastropod mollusk in the family Pectinodontidae. This species inhabits the dark, chemosynthesis-based marine communities of ocean vents and cold seeps near Japan (e.g. the Okinawa Trough).

It is distinct from other true limpets in the following ways, among others: its intestine runs through its ventricle, it has a pair of radular "teeth" with long shafts, and its statocysts are isolated from the pleural ganglia and pedal ganglia. It also has a ctenidium rather than the usual set of circumpallial gills, lacks osphradia, and does not have even rudimentary eyes.

For these reasons, along with a comparison of the development of the shell at the microscopic level, it has been argued that B. secunda is not closely related to the Patelloidea or the Neolepetopsidae as one might expect based on simple morphological characteristics and similarity of appearance. This species has a surprising number of traits in common with the Acmaeidae, however, suggesting a possible close connection with that family rather than the other true limpet families.

Carbon fixation

Carbon fixation or сarbon assimilation is the conversion process of inorganic carbon (carbon dioxide) to organic compounds by living organisms. The most prominent example is photosynthesis, although chemosynthesis is another form of carbon fixation that can take place in the absence of sunlight. Organisms that grow by fixing carbon are called autotrophs. Autotrophs include photoautotrophs, which synthesize organic compounds using the energy of sunlight, and lithoautotrophs, which synthesize organic compounds using the energy of inorganic oxidation. Heterotrophs are organisms that grow using the carbon fixed by autotrophs. The organic compounds are used by heterotrophs to produce energy and to build body structures. "Fixed carbon", "reduced carbon", and "organic carbon" are equivalent terms for various organic compounds.

Chemosynthesis (nanotechnology)

In molecular nanotechnology, chemosynthesis is 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-.

Chemosynthesis can be applied in many different areas of research, including in positional assembly of molecules. This is where molecules are assembled in certain positions in order to perform specific types of chemosynthesis using molecular building blocks. In this case synthesis is most efficiently performed through the use of molecular building blocks with a small amount of linkages. Unstrained molecules are also preferred, which is when molecules undergo minimal external stress, which leads to the molecule having a low internal energy. There are two main types of synthesis: additive and subtractive. In additive synthesis the structure starts with nothing, and then gradually molecular building blocks are added until the structure that is needed is created. In subtractive synthesis they start with a large molecule and remove building blocks one by one until the structure is achieved.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.

Colleen Cavanaugh

Colleen Cavanaugh is an American academic microbiologist best known for her studies of hydrothermal vent ecosystems. As of 2016, she is the Edward C. Jeffrey Professor of Biology in the Department of Organismic and Evolutionary Biology at Harvard University and is affiliated with the Rowland Institute. Cavanaugh was the first to propose that the deep-sea giant tube worm, Riftia pachyptila, obtains its food from bacteria living within its cells, an insight which she had as a graduate student at Harvard. Significantly, she made the connection that these chemoautotrophic bacteria were able to play this role through their use of chemosynthesis, the biological oxidation of inorganic compounds (e.g., hydrogen sulfide) to synthesize organic matter from very simple carbon-containing molecules, thus allowing organisms such as the bacteria (and dependent organisms such as tube worms) to exist in deep ocean without sunlight.

Current solar income

The current solar income of the Earth, or an ecozone or ecoregion or any area, is the amount of solar energy that falls on it as sunlight. This is thought important in some branches of green economics, as the ultimate measure of renewable energy.

Buckminster Fuller first described the concept in his 1970 paper Cosmic Costing, contrasting the photosynthesis on which natural capital and sustainable infrastructural capital depend, with the chemosynthesis of extracting and using fossil fuels.

Paul Hawken is a more recent advocate of the concept, and views it as central to his notion of a restorative economy. It remains a popular notion among those who believe that toxic waste and maintenance problems of direct solar energy devices can ultimately be overcome, or that yields of passive or biological means of gathering and using this energy as biofuels can be made to approximate those of fossil fuels.

Deep sea

The deep sea or deep layer is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms (1800 m) or more. Little or no light penetrates this part of the ocean, and most of the organisms that live there rely for subsistence on falling organic matter produced in the photic zone. For this reason, scientists once assumed that life would be sparse in the deep ocean, but virtually every probe has revealed that, on the contrary, life is abundant in the deep ocean.

From the time of Pliny until the late nineteenth century...humans believed there was no life in the deep. It took a historic expedition in the ship Challenger between 1872 and 1876 to prove Pliny wrong; its deep-sea dredges and trawls brought up living things from all depths that could be reached. Yet even in the twentieth century scientists continued to imagine that life at great depth was insubstantial, or somehow inconsequential. The eternal dark, the almost inconceivable pressure, and the extreme cold that exist below one thousand meters were, they thought, so forbidding as to have all but extinguished life. The reverse is in fact true....(Below 200 meters) lies the largest habitat on earth.

In 1960, the Bathyscaphe Trieste descended to the bottom of the Mariana Trench near Guam, at 10,911 m (35,797 ft; 6.780 mi), the deepest known spot in any ocean. If Mount Everest (8,848 metres) were submerged there, its peak would be more than a mile beneath the surface. The Trieste was retired, and for a while the Japanese remote-operated vehicle (ROV) Kaikō was the only vessel capable of reaching this depth. It was lost at sea in 2003. In May and June 2009, the hybrid-ROV (HROV) Nereus returned to the Challenger Deep for a series of three dives to depths exceeding 10,900 meters.

It has been suggested that more is known about the Moon than the deepest parts of the ocean. Little was known about the extent of life on the deep ocean floor until the discovery of thriving colonies of shrimps and other organisms around hydrothermal vents in the late 1970s. Before the discovery of the undersea vents, it had been accepted that almost all life on earth obtained its energy (one way or another) from the sun. The new discoveries revealed groups of creatures that obtained nutrients and energy directly from thermal sources and chemical reactions associated with changes to mineral deposits. These organisms thrive in completely lightless and anaerobic environments in highly saline water that may reach 300 °F (150 °C), drawing their sustenance from hydrogen sulfide, which is highly toxic to almost all terrestrial life. The revolutionary discovery that life can exist under these extreme conditions changed opinions about the chances of there being life elsewhere in the universe. Scientists now speculate that Europa, one of Jupiter's moons, may be able to support life beneath its icy surface, where there is evidence of a global ocean of liquid water.

Deep sea community

A deep sea community is any community of organisms associated by a shared habitat in the deep sea. Deep sea communities remain largely unexplored, due to the technological and logistical challenges and expense involved in visiting this remote biome. Because of the unique challenges (particularly the high barometric pressure, extremes of temperature and absence of light), it was long believed that little life existed in this hostile environment. Since the 19th century however, research has demonstrated that significant biodiversity exists in the deep sea.

The three main sources of energy and nutrients for deep sea communities are marine snow, whale falls, and chemosynthesis at hydrothermal vents and cold seeps.

Deep sea creature

The term deep sea creature refers to organisms that live below the photic zone of the ocean. These creatures must survive in extremely harsh conditions, such as hundreds of bars of pressure, small amounts of oxygen, very little food, no sunlight, and constant, extreme cold. Most creatures have to depend on food floating down from above.

These creatures live in very demanding environments, such as the abyssal or hadal zones, which, being thousands of meters below the surface, are almost completely devoid of light. The water is between 3 and 10 degrees Celsius and has low oxygen levels. Due to the depth, the pressure is between 20 and 1,000 bars. Creatures that live hundreds or even thousands of meters deep in the ocean have adapted to the high pressure, lack of light, and other factors.

Electrolithoautotroph

An electrolithoautotroph is an organism which feeds on electricity. These organisms use electricity to convert carbon dioxide to organic matters by using electrons directly taken from solid-inorganic electron donors. Electrolithoautotrophs are microorganisms which are found in the deep crevices of the ocean. The warm, mineral-rich environment provides a rich source of nutrients. The electron source for carbon assimilation from diffusible Fe2+ ions to an electrode under the condition that electrical current is the only source of energy and electrons. Electrolithoautotrophs form a third metabolic pathway compared to photosynthesis (plants converting light into sugar) and chemosynthesis (animals consuming food).

Holozoic nutrition

Holozoic nutrition (Greek: holo-whole ; zoikos-of animals) is a type of heterotrophic nutrition that is characterized by the internalization (ingestion) and internal processing of gaseous, liquids or solid food particles. Protozoa, such as amoebas, and most of the free living animals, such as humans, exhibit this type of nutrition.

In Holozoic nutrition the energy and organic building blocks are obtained by ingesting and then digesting other organisms or pieces of other organisms, including blood and decaying organic matter. This contrasts with holophytic nutrition, in which energy and organic building blocks are obtained through photosynthesis or chemosynthesis, and with saprozoic nutrition, in which digestive enzymes are released externally and the resulting monomers (small organic molecules) are absorbed directly from the environment.

There are several stages of holozoic nutrition, which often occur in separate compartments within an organism (such as the stomach and intestines):

Ingestion: In animals, this is merely taking food in through the mouth. In protozoa, this most commonly occurs through phagocytosis.

Digestion: The physical breakdown of complex large and organic food particles and the enzymatic breakdown of complex organic compounds into small, simple molecules.

Absorption: The active and passive transport of the chemical products of digestion out of the food-containing compartment and into the body or cytoplasm.

Assimilation: Utilization of the absorbed molecules for various metabolic processes.

Egestion: The expulsion of undigested material, commonly called defecating

Movile Cave

Movile Cave (Romanian: Peștera Movile) is a cave near Mangalia, Constanța County, Romania discovered by Cristian Lascu in 1986 a few kilometers from the Black Sea coast. It is notable for its unique groundwater ecosystem rich in hydrogen sulfide and carbon dioxide but low in oxygen. Life in the cave has been separated from the outside for the past 5.5 million years and it is based completely on chemosynthesis rather than photosynthesis.

Primary nutritional groups

Primary nutritional groups are groups of organisms, divided in relation to the nutrition mode according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light and organic or inorganic compounds; the sources of carbon can be of organic or inorganic origin.

The terms aerobic respiration, anaerobic respiration and fermentation do not refer to primary nutritional groups, but simply reflect the different use of possible electron acceptors in particular organisms, such as O2 in aerobic respiration, or nitrate (NO3−), sulfate (SO42−) or fumarate in anaerobic respiration, or various metabolic intermediates in fermentation. Because all ATP-generating steps in fermentation involve modifications of metabolic intermediates instead of the use of an electron transport chain fermentation is often referred to as substrate-level phosphorylation.

Primary production

In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae predominate in this role. Ecologists distinguish primary production as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not.

Radiotrophic fungus

Radiotrophic fungi are fungi which appear to perform radiosynthesis, that is, to use the pigment melanin to convert gamma radiation into chemical energy for growth. This proposed mechanism may be similar to anabolic pathways for the synthesis of reduced organic carbon (e.g., carbohydrates) in phototrophic organisms, which convert photons from visible light with pigments such as chlorophyll whose energy is then used in photolysis of water to generate usable chemical energy (as ATP) in photophosphorylation or photosynthesis. However, whether melanin-containing fungi employ a similar multi-step pathway as photosynthesis, or some chemosynthesis pathways, is unknown.

Sergei Winogradsky

Sergei Nikolaievich Winogradsky (or Vinogradskiy; Ukrainian: Сергій Миколайович Виноградський; 1 September 1856 – 25 February 1953) was a Russian microbiologist, ecologist and soil scientist who pioneered the cycle-of-life concept.Winogradsky discovered the first known form of lithotrophy during his research with Beggiatoa in 1887. He reported that Beggiatoa oxidized hydrogen sulfide (H2S) as an energy source and formed intracellular sulfur droplets. This research provided the first example of lithotrophy, but not autotrophy.

His research on nitrifying bacteria would report the first known form of chemoautotrophy, showing how a lithotroph fixes carbon dioxide (CO2) to make organic compounds.

Snottite

Snottite, also snoticle, is a microbial mat of single-celled extremophilic bacteria which hang from the walls and ceilings of caves and are similar to small stalactites, but have the consistency of nasal mucus. In the Frasassi Caves in Italy, over 70% of cells in Snottite have been identified as Acidithiobacillus thiooxidans, with smaller populations including an archaeon in the uncultivated 'G-plasma' clade of Thermoplasmatales (>15%) and a bacterium in the Acidimicrobiaceae family (>5%).The bacteria derive their energy from chemosynthesis of volcanic sulfur compounds including H2S and warm-water solution dripping down from above, producing sulfuric acid. Because of this, their waste products are highly acidic (approaching pH=0), with similar properties to battery acid. Researchers at the University of Texas have suggested that this sulfuric acid may be a more significant cause of cave formation than the usual explanation offered of the carbonic acid formed from carbon dioxide dissolved in water.Snottites were brought to attention by researchers Diana Northup and Penny Boston studying them (and other organisms) in a toxic sulfur cave called Cueva de Villa Luz (Cave of the Lighted House), in Tabasco, Mexico. The term "snottite" was given to these cave features by Jim Pisarowicz in 1986.

Brian Cox's BBC series Wonders of the Solar System saw a scientist examining snottites in the caves and positing that if there is life on Mars, it may be similarly primitive and hidden beneath the surface of the Red Planet.

Trophosome

A trophosome is an organ found in some animals that houses symbiotic bacteria that provide food for their host. Trophosomes are located in the coelomic cavity in the vestimentiferan tube worms (Sibloglinidae, e.g. the giant tube worm Riftia pachyptila) and in symbiotic flatworms of the genus Paracatenula. In both these animals, the symbiotic bacteria that live in the trophosome oxidize sulfur or sulfide found in the worm's environment and produce organic molecules by carbon dioxide fixation that the hosts can use for nutrition and as an energy source. This process is known as chemosynthesis or chemolithoautotrophy.

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