化学合成無機栄養生物

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/12/17 17:58:02」(JST)

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Lithotrophs are a diverse group of organisms using inorganic substrate (usually of mineral origin) to obtain reducing equivalents for use in biosynthesis (e.g., carbon dioxide fixation) or energy conservation (i.e., ATP production) via aerobic or anaerobic respiration.^[1] Known chemolithotrophs are exclusively microbes; no known macrofauna possesses the ability to utilize inorganic compounds as energy sources. Macrofauna and lithotrophs can form symbiotic relationships, in which case the lithotrophs are called "prokaryotic symbionts". An example of this is chemolithotrophic bacteria in giant tube worms or plastids, which are organelles within plant cells that may have evolved from photolithotrophic cyanobacteria-like organisms. Lithotrophs belong to either the domain Bacteria or the domain Archaea. The term "lithotroph" was created from the Greek terms 'lithos' (rock) and 'troph' (consumer), meaning "eaters of rock". Many lithoautotrophs are extremophiles, but this is not universally so.

Different from a lithotroph is an organotroph, an organism which obtains its reducing agents from the catabolism of organic compounds.

1 Biochemistry
- 1.1 Chemolithotrophs
  - 1.1.1 Habitat of Chemolithotrophs
  - 1.1.2 Overview of the Metabolic Process
- 1.2 Photolithotrophs
- 1.3 Lithoheterotrophs versus lithoautotrophs
- 1.4 Chemolithotrophs versus photolithotrophs
2 Geological significance
3 Astrobiology
4 See also
5 References
6 External links

Biochemistry

Lithotrophs consume reduced compounds (rich in electrons).

Chemolithotrophs

A chemolithotroph (named after the process of chemolithotropy) is able to use inorganic reduced compounds as a source of energy. This process is accomplished through oxidation and ATP synthesis. The majority of chemolithotrophs are able to fix carbon dioxide (CO2) through the Calvin cycle, a metabolic pathway in which carbon enters as CO2 and leaves as glucose.^[2] For some substrates, the cells must cull through large amounts of inorganic substrate to secure just a small amount of energy. This makes their metabolic process inefficient in many places and hinders them from thriving.^[3] This group of organisms includes sulfur oxidizers, nitrifying bacteria, iron oxidizers, and hydrogen oxidizers.

The term "chemolithotropy" refers to a cell’s acquisition of energy from the oxidation of inorganic compounds, also known as electron donors. This form of metabolism is believed to occur only in prokaryotes and was first characterized by Russian microbiologist Sergei Winogradsky.^[4]

Habitat of Chemolithotrophs

The survival of these prokaryotic bacteria is dependent on the physiochemical conditions of their environment. Although they are sensitive to certain factors such as quality of inorganic substrate, they are able to thrive under some of the most inhospitable conditions in the world, such as temperatures above 110 degrees Celsius and below 2 pH.^[5] The most important requirement for chemolithotropic life is an abundant source of rich inorganic compounds.^[6] These compounds are crucial for chemolithotrophs because they provide a suitable energy source/electron donor from which the microorganisms can fix CO2 and produce the energy they need to survive. Since chemosynthesis can take place in the absence of sunlight, these organisms are found mostly around hydrothermal vents and other locations rich in inorganic substrate.

The energy obtained from inorganic oxidation varies depending on the substrate and the reaction. For example, the oxidation of hydrogen sulfide to elemental sulfur produces far less energy (50.1 kcal/mol or 210.4 kJ/mol) than the oxidation of elemental sulfur to sulfate (149.8 kcal/mol or 629.2 kJ/mol).^[7] The majority of lithotrophs fix carbon dioxide through the Calvin cycle, an energetically expensive process.^[2] For some substrates, such as ferrous iron, the cells must cull through large amounts of inorganic substrate to secure just a small amount of energy. This makes their metabolic process inefficient in many places and hinders them from thriving.^[8]

Overview of the Metabolic Process

There is a fairly large variation in the types of inorganic substrates that these microorganisms can use to produce energy. The chemolithotrophs that are best documented are aerobic respirers, meaning that they use oxygen in their metabolic process. The list of these microorganisms that employ anaerobic respiration though is growing. At the heart of this metabolic process is an electron transport system that is similar to that of chemoorganotrophs. The major difference between these two microorganisms is that chemolithotrophs directly provide electrons to the electron transport chain, while chemoorganotrophs must generate their own cellular reducing power by oxidizing reduced organic compounds. Chemolithotrophs bypass this by obtaining their reducing power directly from the inorganic substrate or by the reverse electron transport reaction.^[9]

In chemolithotrophs, the compounds - the electron donors - are oxidized in the cell, and the electrons are channeled into respiratory chains, ultimately producing ATP. The electron acceptor can be oxygen (in aerobic bacteria), but a variety of other electron acceptors, organic and inorganic, are also used by various species. Some lithotrophs produce organic compounds from carbon dioxide in a process called chemosynthesis, much as plants do in photosynthesis. Plants use energy from sunlight to drive carbon dioxide fixation, since both water and carbon dioxide are low in energy. By contrast, the hydrogen compounds used in chemosynthesis are high in energy, so chemosynthesis can take place in the absence of sunlight (e.g., around a hydrothermal vent). Other lithotrophs are able to directly utilize inorganic substances, e.g., iron, hydrogen sulfide, elemental sulfur, or thiosulfate, for some or all of their energy needs.^[10]^[11]^[12]^[13]^[14]

Here are a few examples of chemolithotrophic pathways, any of which may use oxygen, sulfur or other molecules as electron acceptors:

Name	Examples	Source of energy and electrons	Respiration electron acceptor
Iron bacteria	Acidithiobacillus ferrooxidans	Fe²⁺ (ferrous iron) → Fe³⁺ (ferric iron) + e^-^[15]	O 2 (oxygen) → H 2O (water)^[15]
Nitrosifying bacteria	Nitrosomonas	NH₃ (ammonia) → NO− 2 (nitrite) + e^-^[16]	O 2 (oxygen) → H 2O (water)^[16]
Nitrifying bacteria	Nitrobacter	NO− 2 (nitrite) → NO− 3 (nitrate) + e^-^[17]	O 2 (oxygen) → H 2O (water)^[17]
Chemotrophic purple sulfur bacteria	Halothiobacillaceae	S2− (sulfide) → S0 (sulfur) + e^-	O 2 (oxygen) → H 2O (water)
Sulfur-oxidizing bacteria	Chemotrophic Rhodobacteraceae and Thiotrichaceae	S0 (sulfur) → SO2− 4 (sulfate) + e^-	O 2 (oxygen) → H 2O (water)
Aerobic hydrogen bacteria	Cupriavidus metallidurans	H₂ (hydrogen) → H₂O (water) + e^-^[18]	O 2 (oxygen) → H 2O (water)^[18]
Anammox bacteria	Planctomycetes	NH₃ (ammonia) → N 2 (nitrogen) + e^-^[19]	NO− 2 (nitrite)^[19]
Thiobacillus denitrificans	Thiobacillus denitrificans	S0 (sulfur) → SO2− 4 (sulfate) + e^-^[20]	NO− 3 (nitrate)^[20]
Sulfate-reducing bacteria: Hydrogen bacteria		H₂ (hydrogen) → H₂O (water) + e^-^[18]	Sulfate (SO2− 4)^[18]
Sulfate-reducing bacteria: Phosphite bacteria	Desulfotignum phosphitoxidans	PO3− 3 (phosphite) → PO3− 4 (phosphate) + e^-	Sulfate (SO2− 4)
Methanogens	Archaea	H₂ (hydrogen) → H₂O (water) + e^-	CO₂ (carbon dioxide)
Carboxydotrophic bacteria	Carboxydothermus hydrogenoformans	carbon monoxide (CO) → carbon dioxide (CO₂) + e^-	H 2O (water) → H 2 (hydrogen)

Photolithotrophs

Photolithotrophs obtain energy from light and therefore use inorganic electron donors only to fuel biosynthetic reactions (e. g., carbon dioxide fixation in lithoautotrophs).

Lithoheterotrophs versus lithoautotrophs

Lithotrophic bacteria cannot use, of course, their inorganic energy source as a carbon source for the synthesis of their cells. They choose one of three options:

Lithoheterotrophs do not have the possibility to fix carbon dioxide and must consume additional organic compounds in order to break them apart and use their carbon. Only a few bacteria are fully heterolithotrophic.
Lithoautotrophs are able to use carbon dioxide from the air as carbon source, the same way plants do.
Mixotrophs will take up and utilise organic material to complement their carbon dioxide fixation source (mix between autotrophy and heterotrophy). Many lithotrophs are recognised as mixotrophic in regard of their C-metabolism.

Chemolithotrophs versus photolithotrophs

In addition to this division, lithotrophs differ in the initial energy source which initiates ATP production:

Chemolithotrophs use the above-mentioned inorganic compounds for aerobic or anaerobic respiration. The energy produced by the oxidation of these compounds is enough for ATP production. Some of the electrons derived from the inorganic donors also need to be channeled into biosynthesis. Mostly, additional energy has to be invested to transform these reducing equivalents to the forms and redox potentials needed (mostly NADH or NADPH), which occurs by reverse electron transfer reactions.
Photolithotrophs use light as energy source. These bacteria are photosynthetic; photolithotrophic bacteria are found in the purple bacteria (e. g., Chromatiaceae), green bacteria (Chlorobiaceae and Chloroflexi) and Cyanobacteria. Purple and green bacteria oxidize sulfide, sulfur, sulfite, iron or hydrogen. Cyanobacteria extract reducing equivalents from water, i.e., they oxidise water to oxygen. The electrons obtained from the electron donors are not used for ATP production (as long as there is light); they are used in biosynthetic reactions. Some photolithotrophs shift over to chemolithotrophic metabolism in the dark.

Geological significance

Lithotrophs participate in many geological processes, such as the weathering of parent material (bedrock) to form soil, as well as biogeochemical cycling of sulfur, nitrogen, and other elements. They may be present in the deep terrestrial subsurface (they have been found well over 3 km below the surface of the planet), in soils, and in endolith communities. As they are responsible for the liberation of many crucial nutrients, and participate in the formation of soil, lithotrophs play a critical role in the maintenance of life on Earth.

Lithotrophic microbial consortia are responsible for the phenomenon known as acid mine drainage, whereby energy-rich pyrites and other reduced sulfur compounds present in mine tailing heaps and in exposed rock faces is metabolized to form sulfates, thereby forming potentially toxic sulfuric acid. Acid mine drainage drastically alters the acidity and chemistry of groundwater and streams, and may endanger plant and animal populations. Activities similar to acid mine drainage, but on a much lower scale, are also found in natural conditions such as the rocky beds of glaciers, in soil and talus, on stone monuments and buildings and in the deep subsurface.

Astrobiology

It has been suggested that biominerals could be important indicators of extraterrestrial life and thus could play an important role in the search for past or present life on the planet Mars. Furthermore, organic components (biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions.^[21]

On January 24, 2014, NASA reported that current studies by the Curiosity and Opportunity rovers on Mars will now be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic and/or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable.^[22]^[23]^[24]^[25] The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on the planet Mars is now a primary NASA objective.^[22]^[23]

References

^ Zwolinski, Michele D. "Lithotroph." Weber State University. p. 1-2.
^ ^a ^b Kuenen, G. (2009). "Oxidation of Inorganic Compounds by Chemolithotrophs". In Lengeler, J.; Drews, G.; Schlegel, H. Biology of the Prokaryotes. John Wiley & Sons. p. 242. ISBN 9781444313307.
^ http://books.google.com/books?id=vXbJa4X5oHsC&pg=PA243&lpg=PA243&dq=types+of+chemolithotrophs&source=bl&ots=6JeFZSiRKM&sig=CmXWyhmNwuBoR6iX5mXG19wZ5u0&hl=en&sa=X&ei=fM6RUe6jFurhiALIvoCICg&ved=0CGkQ6AEwCA#v=onepage&q=types%20of%20chemolithotrophs&f=false
^ http://www.springerreference.com/docs/html/chapterdbid/324421.html
^ Kuenen, G. (2009). "Oxidation of Inorganic Compounds by Chemolithotrophs". In Lengeler, J.; Drews, G.; Schlegel, H. Biology of the Prokaryotes. John Wiley & Sons. p. 243. ISBN 9781444313307.
^ http://www.uta.edu/biology/chrzanowski/classnotes/microbial_diversity/Chemolithotrophs2.pdf
^ Ogunseitan, Oladele (2008). Microbial Diversity: Form and Function in Prokaryotes. John Wiley & Sons. p. 169.
^ http://books.google.com/books?id=vXbJa4X5oHsC&pg=PA243&lpg=PA243&dq=types+of+chemolithotrophs&source=bl&ots=6JeFZSiRKM&sig=CmXWyhmNwuBoR6iX5mXG19wZ5u0&hl=en&sa=X&ei=fM6RUe6jFurhiALIvoCICg&ved=0CGkQ6AEwCA#v=onepage&q=types%20of%20chemolithotrophs&f=false
^ http://www.bio.umass.edu/biology/conn.river/calvin.html
^ Jorge G. Ibanez; Margarita Hernandez-Esparza; Carmen Doria-Serrano; Mono Mohan Singh (2007). Environmental Chemistry: Fundamentals. Springer. p. 156. ISBN 978-0-387-26061-7.
^ Kuenen, G. (2009). "Oxidation of Inorganic Compounds by Chemolithotrophs". In Lengeler, J.; Drews, G.; Schlegel, H. Biology of the Prokaryotes. John Wiley & Sons. p. 249. ISBN 9781444313307.
^ Lengeler, Joseph W.; Drews, Gerhart; Schlegel, Hans Günter (1999). Biology of the Prokaryotes. Georg Thieme Verlag. p. 249. ISBN 978-3-13-108411-8.
^ Reddy, K. Ramesh; DeLaune, Ronald D. (2008). Biogeochemistry of Wetlands: Science and Applications. CRC Press. p. 466. ISBN 978-1-56670-678-0.
^ Canfield, Donald E.; Kristensen, Erik; Thamdrup, Bo (2005). Aquatic Geomicrobiology. Elsevier. p. 285. ISBN 978-0-12-026147-5.
^ ^a ^b Meruane G, Vargas T (2003). "Bacterial oxidation of ferrous iron by Acidithiobacillus ferrooxidans in the pH range 2.5–7.0". Hydrometallurgy 71 (1): 149–58. doi:10.1016/S0304-386X(03)00151-8.
^ ^a ^b Zwolinski, Michele D. "Lithotroph." Weber State University. p. 7.
^ ^a ^b "Nitrifying bacteria." PowerShow. p. 12.
^ ^a ^b ^c ^d Libert M, Esnault L, Jullien M, Bildstein O (2010). "Molecular hydrogen: an energy source for bacterial activity in nuclear waste disposal". Physics and Chemistry of the Earth.
^ ^a ^b Kartal B, Kuypers MM, Lavik G, Schalk J, Op den Camp HJ, Jetten MS, Strous M (2007). "Anammox bacteria disguised as denitrifiers: nitrate reduction to dinitrogen gas via nitrite and ammonium". Environmental Microbiology 9 (3): 635–42. doi:10.1111/j.1462-2920.2006.01183.x. PMID 17298364.
^ ^a ^b Zwolinski, Michele D. "Lithotroph." Weber State University. p. 3.
^ et al (September 26, 2006). "Final report of the MEPAG Astrobiology Field Laboratory Science Steering Group (AFL-SSG)". In Steele, Andrew; Beaty, David. The Astrobiology Field Laboratory (.doc)|format= requires |url= (help). U.S.A.: Mars Exploration Program Analysis Group (MEPAG) - NASA. p. 72. Retrieved 2009-07-22.
^ ^a ^b Grotzinger, John P. (January 24, 2014). "Introduction to Special Issue - Habitability, Taphonomy, and the Search for Organic Carbon on Mars". Science 343 (6169): 386–387. doi:10.1126/science.1249944. Retrieved January 24, 2014.
^ ^a ^b Various (January 24, 2014). "Special Issue - Table of Contents - Exploring Martian Habitability". Science 343 (6169): 345–452. Retrieved January 24, 2014.
^ Various (January 24, 2014). "Special Collection - Curiosity - Exploring Martian Habitability". Science. Retrieved January 24, 2014.
^ Grotzinger, J.P. et al. (January 24, 2014). "A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars". Science 343 (6169). doi:10.1126/science.1242777. Retrieved January 24, 2014.

External links

Minerals and the Origins of Life (Robert Hazen, NASA) (video, 60m, April 2014).

English Journal

Microbial Heterotrophic Production in an Oligotrophic Acidic Geothermal Lake: Responses to Organic Amendments and Terrestrial Plant Litter.

Wolfe GV1, Fitzhugh C, Almasary A, Green A, Bennett P, Wilson M, Siering P.
FEMS microbiology ecology.FEMS Microbiol Ecol.2014 May 28. doi: 10.1111/1574-6941.12360. [Epub ahead of print]
Boiling Springs Lake (BSL) is an oligotrophic, acidic geothermal feature where even very low levels of microbial heterotrophic production still exceed autotrophy. To test whether allochthonous leaf litter inputs fuel this excess, we quantified leaf litterfall, leaching and decomposition kinetics, an
PMID 24890617

Anaerobic sulfur metabolism coupled to dissimilatory iron reduction in the extremophile Acidithiobacillus ferrooxidans.

Osorio H1, Mangold S, Denis Y, Ñancucheo I, Esparza M, Johnson DB, Bonnefoy V, Dopson M, Holmes DS.
Applied and environmental microbiology.Appl Environ Microbiol.2013 Apr;79(7):2172-81. doi: 10.1128/AEM.03057-12. Epub 2013 Jan 25.
Gene transcription (microarrays) and protein levels (proteomics) were compared in cultures of the acidophilic chemolithotroph Acidithiobacillus ferrooxidans grown on elemental sulfur as the electron donor under aerobic and anaerobic conditions, using either molecular oxygen or ferric iron as the ele
PMID 23354702

In situ Spectroscopy on Intact Leptospirillum ferrooxidans Reveals that Reduced Cytochrome 579 is an Obligatory Intermediate in the Aerobic Iron Respiratory Chain.

Blake RC 2nd1, Griff MN.
Frontiers in microbiology.Front Microbiol.2012 Apr 12;3:136. doi: 10.3389/fmicb.2012.00136. eCollection 2012.
Electron transfer reactions among colored cytochromes in intact bacterial cells were monitored using an integrating cavity absorption meter that permitted the acquisition of accurate absorbance data in suspensions of cells that scatter light. The aerobic iron respiratory chain of Leptospirillum ferr
PMID 22518111

Japanese Journal

SC-3 菌類の硫黄酸化と無機環境における生育(微生物生態学の拡大のために, シンポジウム)

片山葉子
日本微生物生態学会講演要旨集 (25), 49, 2009-11-21
NAID 110007520383

Chemolithotrohic Bacteria : Distributions, Functions and Significance in Volcanic Environments

King Gary M.
Microbes and environments 22(4), 309-319, 2007-12
… These systems, which also are typically characterized by temperature and pH extremes, have yielded a rich variety of chemolithotrophic bacteria, and contributed much to our understanding of chemolithotroph ecology and physiology. …
NAID 110006473357

Hydrogenimonas thermophila gen. nov., sp. nov., a novel thermophilic, hydrogen-oxidizing chemolithotroph within the ε-Proteobacteria, isolated from a black smoker in a Central Indian Ridge hydrothermal field