Lithotrophy

from Wikipedia, the free encyclopedia
Lithotrophic cyanobacteria ("blue-green algae") in a dredging pond.
Nitrosomonas eutropha , an ammonia oxidizing lithotrophic bacterium

Lithotrophy describes a special way of life ( metabolic type ) in living beings : Lithotrophic organisms are able to use inorganic reducing agents for their building metabolism . For reductions in biosynthesis , all living things use reducing coenzymes as electron carriers, which have to be regenerated. For example, plants convert NADPH into NADP + when they form sugar from CO 2 in the Calvin cycle ( carbon dioxide assimilation ). Various autotrophic organisms use other metabolic pathways with other coenzymes for biosynthesis. Lithotrophic organisms can regenerate the coenzymes necessary for assimilation through inorganic electron donors . All other organisms are organotrophic and their biosynthesis is restricted to organic electron donors. You regenerate z. B. NADPH with NADH , which supplies reduction equivalents from the breakdown of organic compounds.

In addition to inorganic reducing agents, a number of lithotrophic organisms can also use organic, mostly low-molecular organic compounds for NADPH regeneration. They are optional lithotrophic.

Origin and use of the designation

The word lithotrophy comes from ancient Greek and literally means "nourishing on stones" ( ancient Greek λίθος lithos "stone"; ancient Greek τροφή trophe "nutrition"), whereby "stone" stands for inorganic substances. The adjective for lithotrophy is lithotroph (lithotrophic living beings, lithotrophic metabolism ).

Diversity and occurrence of lithotrophic organisms

In prokaryotes lithotroph is widespread. Lithotrophic organisms occur in archaea and bacteria in different families , often together with closely related organotrophic organisms. In eukaryotes , lithotrophy takes place within organelles , most likely derived from prokaryotic endosymbionts .

Table 1. Redox potentials E 0 ' of strong (above) and weak (below) reducing agents. Colored: coenzymes
Redox reaction E ' 0 (V)
CO + H 2 O → CO 2 + 2H + + 2 e - −0.54
H 2 → 2H + + 2 e - −0.41
Ferredoxin reduced → Ferredoxin oxidized + e - −0.4
NADPH + H + → NADP + + 2 e - + 2 H + −0.32
H 2 S → S + 2H + + 2 e - −0.25
S + 4 H 2 O → SO 4 2− + 8 H + + 8 e - −0.23
NO 2 - + H 2 O → NO 3 - + 2 H + + 2 e - +0.42
NH 4 + + 2 H 2 O → NO 2 - + 8 H + + 6 e - +0.44
Fe 2+ → Fe 3+ + e - +0.78
2 H 2 O → O 2 + 4 H + + 4 e - +0.86

Lithotrophic organisms use very different inorganic electron donors (Table 1). These include very powerful reducing agents such as carbon monoxide (CO) and hydrogen (H 2 ) , from which electrons can be transferred to NADP + with energy gain . The electron donors listed under NADPH in the table, on the other hand, require energy to reduce NADP + . This applies above all to H 2 O, which can only reduce extremely strong oxidizing agents without adding energy.

In lithotrophic organisms there are not only very different enzymes and electron carriers for the use of the different electron donors, but also very different metabolic pathways for the use of inorganic reducing agents.

Photolithotrophy

If lithotrophic organisms cover their energy needs photosynthetically from light , they are called photo lithotrophic.

  • Anaerobic photolithotrophic bacteria that use H 2 S as an electron donor in anoxygenic photosynthesis and form elemental sulfur as a waste product. These include purple sulfur bacteria (Chormatiaceae) and green sulfur bacteria (Chlorobiaceae).
  • Plants and cyanobacteria differ from photolithotrophic organisms in that they use water as a reducing agent, which is known as photohydrotrophy.

A detailed description of photolithotrophic metabolic types can be found under phototrophy and photosynthesis .

Chemolithotrophy

Energy metabolism

Figure 1 : Simplified model of ATP formation through oxidation of H 2 in the periplasm at Aquifex aeolicus . On the left in the picture there is a transmembrane complex with an electron transport chain . On its outside (top), the oxidation of H 2 producesfour protons and 4 electrons. The complex transfers these to a cytochrome oxidase on the inside, where they reduce O 2 to water. Thisconsumes4 H + . Without H + being transported to the outside, a membrane potential is created that is used by the ATP synthase (right) to form ATP.

Chemo lithotrophe organisms meet their energy needs not by light but by inorganic chemical reactions, namely exergonic redox reactions .

The extent to which organisms can obtain energy from redox reactions depends not only on the redox potential of the electron donor, but also on that of the electron acceptor : the greater the difference, the more energy can be obtained from it.

  • Many chemolithotrophic organisms use the powerful oxidizing agent O 2 as an electron acceptor . You are aerobic .
  • There are also a number of anaerobic chemolithotrophic archaea and bacteria. For example, they use the relatively weak oxidizing agents sulfate and CO 2 as electron acceptors.

Almost all organisms require energy in the form of a chemiosmotic membrane potential . Your cytoplasmic membranes are positively charged on the outside and negatively charged on the inside. Inside, the concentration of negatively charged ions ( anions ) is higher than outside, positive cations such as. B. H + ions are more concentrated on the outside. In addition to the concentration gradient of the ions, there is also an electrical gradient, i.e. an electrical voltage.

All chemolithotrophic organisms use this voltage to form ATP , which is essential as an energy supplier for a wide variety of metabolic processes. It is created by the endothermic reaction

ADP + phosphate → ATP + ΔH , ΔH approx. 35 kJ / mol

This reaction is catalyzed by the enzyme ATP synthase . Its function is explained schematically in Fig. 1 on the right in the picture. The red area above is positively charged. It is located outside the cell, in the picture above the cell membrane . From there, a current of H + ions flows through the ATP synthase into the cell plasma (reddish in the picture) and supplies the energy for ATP formation.

Lithotrophic organisms maintain their membrane potential through redox reactions. H + -producing reactions are mostly localized on the outside of the cell membrane, while reactions that consume H + are more localized on the inside . At the top left of the picture, H + is created from the oxidation of hydrogen. In the lower left corner of the picture, H + is consumed. Together with the four electrons that cross the membrane through a transmembrane complex, after

4 H + + O 2 + 4 e ↔ 2 H 2 O

Water. Because of this reaction, which is to a certain extent an oxyhydrogen reaction , organisms that oxidize hydrogen to water are also called oxyhydrogen bacteria . To maintain their membrane potential, lithotrophic metabolic pathways use very different electron transport chains, coenzymes , cytochromes, etc. The important role of cell membranes is shown by the fact that they are often heavily folded, similar to thylakoids , and often have membrane stacks. To understand how organisms maintain their membrane potential, it is crucial whether redox reactions take place on the inside or outside of the cell membrane.

Reduction of NADP +

Figure 2 . Principle of the aerobic metabolism of nitrite oxidizing bacteria. NxR is an enzyme complex that catalyzes the oxidation of nitrite to nitrate. The electrons released during the oxidation are transferred to cytochrome c (cyt c ). The cytochrome c is mainly transferred to a transmembrane enzyme (I), on the inside of which O O is reduced to water. A small part of the cytochrome c gets into the transmembrane complex II. It contains an electron transport chain, the components ofwhich are reducedby the inflowing H + to such an extent that NADH can be reduced in the cytoplasm.

It is noticeable that many chemolithotropic organisms are able to regenerate the more powerful reducing agent NADPH with the use of energy, even with weaker reducing agents. The energy for the regeneration of NADPH by weaker reducing agents is provided by ATP in some of these organisms. For this purpose, an electron transport chain is used , in which the weakly reducing electrons are brought to a level with the consumption of ATP, with which NADP + can be reduced to NADPH.

In most cases, however, the direct energy supplier for such electron transport chains is the membrane potential. They work like reverse respiratory chains or reverse proton pumps . NADPH is regenerated by inflowing protons without consuming ATP.

The principle is explained in Fig. 2 using a nitrite oxidizing bacterium (Fig. 2). In the picture on the right, the membrane potential is built up by the oxidation of nitrite taking place on the outside and the reduction of O 2 taking place on the inside of the membrane . As in Fig. 1, H + is formed on the outside and consumed on the inside.
The electron carrier is a cytochrome pool. A relatively small part of the reduced cytochromes feeds their electrons into an enzyme complex II (left in the picture). In this enzyme complex, the electrons are transferred step by step to increasingly weaker oxidizing agents. Each of these steps costs energy, which is supplied by H + ions transported from the outside to the inside . In the end, such a powerful reducing agent is created that it can be used to regenerate NADH.

Lithoautotrophy

Many lithotrophic organisms cannot use organic compounds as a source of carbon for their building material requirements and are therefore dependent on inorganic carbon sources, consistently on CO 2 . They reduce these with the help of the lithotrophic NADPH. They are obligately autotrophic , more precisely lithoautotrophic . They have to produce their cell material by reducing CO 2 with NADH or NADPH.

Other, mostly facultatively lithotrophic organisms can use organic compounds as carbon sources and are facultatively heterotrophic .

  • Photolithotrophic autotrophic organisms are the primary producers of biomass in most ecosystems , e.g. B. Plants and Cyanobacteria. They do photosynthesis .
  • Chemolithotrophic autotrophic organisms are the primary producers in some lightless biotopes . In the deep sea, for example, they form the basis of a food chain for “ black smokers ”. There they produce biomass, which they gain from the oxidation of volcanic H 2 S. This is sometimes called chemosynthesis . Chemolithotrophic organisms are not limited to lightless biotopes.

Lithoheterotrophy

Various marine bacteria belonging to the Alphaproteobacteria , the so-called Roseobacter group (the best known species is Silicibacter pomeroyi ), use carbon monoxide as an exclusive source of carbon instead of carbon dioxide. In contrast to optional carbon monoxide- utilizing (carboxyotrophic) bacteria such as Oligotropha carboxidovorans and Hydrogenophaga pseudoflava , which use the enzyme carbon monoxide dehydrogenase (CODH) to first form carbon dioxide, which they then fix conventionally using RuBisCO (see energy and carbon source carbon monoxide- utilizing bacteria ), they get by with the low concentrations in seawater, which are mainly caused by abiotic degradation of organic matter. The bacteria of the Roseobacter group only gain energy from the oxidation of carbon monoxide; they have to cover the carbon needed to build up biomass through heterotrophic nutrition, i.e. the absorption of biomass. This previously unknown group of bacteria, which can be found in seawater with a large number of individuals, is important for modeling the global carbon cycle, for example.

Examples of chemolithotrophic creatures

e - -
Donor 		e - -
Acceptor 		End
product (s) 		Type example
CO O 2 CO 2 Aerobic carboxydotrophic bacteria Bradyrhizobium japonicum , Oligotropha carboxidovorans, Bacillus schlegelii
CO H 2 O H 2 + CO 2 Hydrogenogenic bacteria Carboxydothermus hydrogenoformans
Fe 2+ O 2 + H + Fe 3+ + H 2 O Iron oxidizing microorganisms Gallionella ferruginea , Sulfolobus acidocaldarius , Acidithiobacillus ferrooxidans
H 2 O 2 H 2 O Oxyhydrogen bacteria Cupriavidus metallidurans , Cupriavidus necator , Aquifex aeolicus
H 2 CO 2 CH 4 + H 2 O Methane-forming archaea Methanobacterium, Methanococcus, Methanosaeta, Methanospirillum
H 2 SO 4 2− H 2 S + H 2 O H 2 -oxidizing desulfurizing agents Desulfobacteraceae , Desulfovibrio desulfuricans
HPO 3 2− SO 4 2− HPO 4 2− + H 2 S Desulfotignum phosphitoxidans
NH 3 O 2 NO 2 - + H 2 O Ammonia oxidizing bacteria Nitrosomonas
NH 3 NO 2 - N 2 + H 2 O Anammox bacteria Planctomycetes
NO 2 - O 2 NO 3 - Nitrite oxidizing bacteria Nitrobacter
S 0 O 2 SO 4 2− Sulfur oxidizing bacteria Chemotrophic Rhodobacteraceae
Thiotrichales and Acidithiobacillus thiooxidans
S 0 NO 3 - SO 4 2− + N 2 Sulfur oxidizing, denitrifying bacteria Thiobacillus denitrificans
S 2− O 2 + H + S 0 + H 2 O halophilic sulfur oxidizing bacteria Halothiobacillaceae

Individual evidence

  1. ↑ G. Gottschalk: Bacterial Metabolism. 2nd Edition. Springer, New York 1986.
  2. ↑ Hans G. Schlegel: General microbiology. Thieme, Stuttgart / New York 1981, p. 177.
  3. ^ Georg Fuchs, Hans Günter Schlegel, Thomas Eitinger: General microbiology . 9th, completely revised and expanded edition. Georg Thieme Verlag, Stuttgart 2014, ISBN 978-3-13-444609-8 , 12. Oxidation of inorganic compounds: the chemolithotrophic way of life.
  4. ↑ Sebastiaan K Spaans, Ruud A Weusthuis, John van der Oost, Servé WM Kengen: NADPH-generating systems in bacteria and archaea . In: Frontiers in Microbiology . 6, 2015, p. 742. doi : 10.3389 / fmicb.2015.00742 .
  5. ↑ G. Gottschalk: Bacterial Metabolism. 2nd Edition. Springer, New York 1986, p. 288.
  6. ↑ Shuning Wang, Haiyan Huang, Jörg Kahnt, Rudolf K. Thauer: A Reversible Electron-Bifurcating Ferredoxin- and NAD-Dependent [FeFe] -Hydrogenase (HydABC) in Moorella . In: Journal of Bacteriology . 195, No. 6, 2013, pp. 1267-1275. doi : 10.1128 / JB.02158-12 .
  7. ↑ Anne De Poulpiquet, Alexandre Ciaccafava, Saida Benomar, Marie-Thérèse Giudici-Orticoni, Elisabeth Lojou: Carbon Nanotube enzymes Biohybrids in a Green Hydrogen Economy. In: Satoru Suzuki (Ed.): Syntheses and Applications of Carbon Nanotubes and Their Composites. 2013, ISBN 978-953-511-125-2 .
  8. ↑ bip.cnrs-mrs.fr
  9. ↑ Peter Karlson: Short textbook of biochemistry for physicians and natural scientists. Thieme, 1984.
  10. ↑ Membrane stack photo
  11. ↑ Heribert Cypionka: Fundamentals of microbiology. Springer, 2010, ISBN 978-3-642-05095-4 .
  12. ^ Alan B. Hooper, Alan A. Dispirito: In Bacteria Which Grow on Simple Reductants, Generation of a Proton Gradient Involves Extracytoplasmic Oxidation of Substrate. In: Microbiological Reviews. June 1985, pp. 140-157.
  13. ↑ S. Lücker, M. Wagner, F. Maixner, E. Pelletier, H. Koch, E. Spieck et al: Nitrospira metagenome illuminates the physiology and evolution of globally important nitrite-oxidizing bacteria. In: PNAS. 107, 2010, pp. 13479-13484. doi: 10.1073 / pnas.1003860107
  14. ↑ Genome Sequence of the Chemolithoautotrophic Nitrite-Oxidizing Bacterium Nitrobacter winogradskyi Nb-255. In: Appl. Environ. Microbiol. March 2006 vol. 72 no. 3, pp. 2050-2063.
  15. ^ Mary Ann Moran and William L. Miller (2007): Resourceful heterotrophs make the most of light in the coastal ocean. Nature Reviews Microbiology 5: 792-800. doi: 10.1038 / nrmicro1746
  16. ^ Gary M King, Carolyn F Weber: Distribution, diversity and ecology of aerobic CO-oxidizing bacteria . In: Nature Reviews Microbiology . 5, 2007, pp. 107-118. doi : 10.1038 / nrmicro1595 .
  17. ↑ Naresh Kumar Ponnuru: Carboxydothermus hydrogenoformans . In: J Phylogen Evolution Biol . 2, No. 135, 2014, p. 2. doi : 10.4172 / 2329-9002.1000135 .
  18. ↑ Meruane G, Vargas T: Bacterial oxidation of ferrous iron by Acidithiobacillus ferrooxidans in the pH range 2.5-7.0 . In: Hydrometallurgy . 71, No. 1, 2003, pp. 149-158. doi : 10.1016 / S0304-386X (03) 00151-8 .
  19. ↑ a b Libert M, Esnault L, Jullien M, Bildstein O: Molecular hydrogen: an energy source for bacterial activity in nuclear waste disposal Archived from the original on July 27, 2014. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Physics and Chemistry of the Earth . 2010. Accessed August 12, 2015. @1@ 2Template: Webachiv / IABot / www.nantes2010.com
  20. ↑ M. Guiral, C. Aubert, M.-T. Giudici-Orticoni: Hydrogen metabolism in the hyperthermophilic bacterium Aquifex aeolicus . In: Biochemical Society Transactions . 33, No. 1, 2005, pp. 22-24.
  21. ↑ Schink, Bernhard, et al. Desulfotignum phosphitoxidans sp. nov., a new marine sulfate reducer that oxidizes phosphite to phosphate. Archives of microbiology 177.5 (2002): 381-391.
  22. ↑ Metcalf, William W., Ralph S. Wolfe: Molecular genetic analysis of phosphite and hypophosphite oxidation by Pseudomonas stutzeriWM88. Journal of bacteriology 180.21 (1998): 5547-5558. [1]
  23. ↑ Kartal B, Kuypers MM, Lavik G, Schalk J, Op den Camp HJ, Jetten MS, Strous M: Anammox bacteria disguised as denitrifiers: nitrate reduction to dinitrogen gas via nitrite and ammonium . In: Environmental Microbiology . 9, No. 3, 2007, pp. 635-642. doi : 10.1111 / j.1462-2920.2006.01183.x . PMID 17298364 .

See also