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Lithotroph

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Lithotroph

Lithotrophs are a diverse group of organisms using 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 catabolism of organic compounds.

Contents

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

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 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 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

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

External links

  1. ^ Zwolinski, Michele D. "Lithotroph." Weber State University. p. 1-2.
  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.  
  3. ^ 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
  4. ^ http://www.springerreference.com/docs/html/chapterdbid/324421.html
  5. ^ 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.  
  6. ^ http://www.uta.edu/biology/chrzanowski/classnotes/microbial_diversity/Chemolithotrophs2.pdf
  7. ^ Ogunseitan, Oladele (2008). Microbial Diversity: Form and Function in Prokaryotes. John Wiley & Sons. p. 169. 
  8. ^ 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
  9. ^ http://www.bio.umass.edu/biology/conn.river/calvin.html
  10. ^ Jorge G. Ibanez; Margarita Hernandez-Esparza; Carmen Doria-Serrano; Mono Mohan Singh (2007). Environmental Chemistry: Fundamentals. Springer. p. 156.  
  11. ^ 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.  
  12. ^ Lengeler, Joseph W.; Drews, Gerhart; Schlegel, Hans Günter (1999). Biology of the Prokaryotes. Georg Thieme Verlag. p. 249.  
  13. ^ Reddy, K. Ramesh; DeLaune, Ronald D. (2008). Biogeochemistry of Wetlands: Science and Applications. CRC Press. p. 466.  
  14. ^ Canfield, Donald E.; Kristensen, Erik; Thamdrup, Bo (2005). Aquatic Geomicrobiology. Elsevier. p. 285.  
  15. ^ a b Meruane G, Vargas T (2003). "Bacterial oxidation of ferrous iron by Acidithiobacillus ferrooxidans in the pH range 2.5–7.0" (PDF). Hydrometallurgy 71 (1): 149–58.  
  16. ^ a b Zwolinski, Michele D. "Lithotroph." Weber State University. p. 7.
  17. ^ a b "Nitrifying bacteria." PowerShow. p. 12.
  18. ^ 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" (PDF). Physics and Chemistry of the Earth. 
  19. ^ 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.  
  20. ^ a b Zwolinski, Michele D. "Lithotroph." Weber State University. p. 3.
  21. ^ Steele, Andrew; Beaty, David, eds. (September 26, 2006). "Final report of the MEPAG Astrobiology Field Laboratory Science Steering Group (AFL-SSG)". The Astrobiology Field Laboratory (.doc). U.S.A.:  
  22. ^ a b Grotzinger, John P. (January 24, 2014). "Introduction to Special Issue - Habitability, Taphonomy, and the Search for Organic Carbon on Mars".  
  23. ^ a b Various (January 24, 2014). "Special Issue - Table of Contents - Exploring Martian Habitability".  
  24. ^ Various (January 24, 2014). "Special Collection - Curiosity - Exploring Martian Habitability".  
  25. ^ Grotzinger, J.P. et al. (January 24, 2014). "A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars".  

References

See also

On January 24, 2014, NASA reported that current studies by the Mars is now a primary NASA objective.[22][23]

It has been suggested that biosignatures) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and biotic reactions.[21]

Astrobiology

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.

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.

Geological significance

  • 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.

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

Chemolithotrophs versus photolithotrophs

  • 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.

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 versus lithoautotrophs

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

Photolithotrophs

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
2
O (water)[15]
Nitrosifying bacteria Nitrosomonas NH3 (ammonia) → NO
2
(nitrite) + e[16]
O
2
(oxygen) → H
2
O (water)[16]
Nitrifying bacteria Nitrobacter NO
2
(nitrite) → NO
3
(nitrate) + e[17]
O
2
(oxygen) → H
2
O (water)[17]
Chemotrophic purple sulfur bacteria Halothiobacillaceae S2−
(sulfide) → S0
(sulfur) + e
O
2
(oxygen) → H
2
O (water)
Sulfur-oxidizing bacteria Chemotrophic Rhodobacteraceae
and Thiotrichaceae
S0
(sulfur) → SO2−
4
(sulfate) + e
O
2
(oxygen) → H
2
O (water)
Aerobic hydrogen bacteria Cupriavidus metallidurans H2 (hydrogen) → H2O (water) + e[18] O
2
(oxygen) → H
2
O (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 Desulfovibrio paquesii 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
2
O (water) → H
2
(hydrogen)

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

[14][13][12][11][10] In chemolithotrophs, the compounds - the

[9] There is a fairly large variation in the types of inorganic substrates that these

Overview of the Metabolic Process

[8]

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