Desulfuromonadales

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Desulfuromonadales
Geobacter sulfurreducens

Geobacter sulfurreducens

Systematics
Classification : Creature
Domain : Bacteria (bacteria)
Department : Proteobacteria
Class : Deltaproteobacteria
Order : Desulfuromonadales
Scientific name
Desulfuromonadales
corrig. Kuever et al. 2006

The Desulfuromonadales form an order within the Deltaproteobacteria . Like all proteobacteria, they are gram negative . Through anaerobic respiration, they use elemental sulfur, manganese or iron to generate energy in the metabolism. One speaks of the Fe (III), sulfur or Mn (IV) reduction. Also nitrate and trichloroacetic, as well as other metals such as technetium or cobalt can be reduced by some of these bacteria and thus in energy metabolism are used.

The species of this order are mostly rod-shaped. Usually they are motile by a scourge, Pelobacter and Malonomonas, however, only in the early growth stages of the colonies, others are immobile.

properties

The members of this order are mostly obligately anaerobic , that is, they can only live in the complete absence of oxygen, but there are some microaerobic species. For example, Malonomonas tolerates low levels of oxygen. Desulfuromusa kysingii also tolerates a small amount of oxygen (2%), but does not grow. Most Desulfuromonadales are mesophilic, so their optimum growth is at medium temperatures. Geopsychrobacter is psychrophilic (likes the cold), it grows at temperatures between 4 and 30 ° C, the optimum is 22 ° C. Geothermobacter ehrlichii is thermophilic and was found in a hydrothermal spring on the Juan de Fuca ridge . It grows at temperatures between 35 and 65 ° C.

Desulfuromonadales have been isolated from anoxic habitats in fresh water , sea ​​water and brackish water . Malonomonas occurs in anoxic marine sediments; this genus has not yet been found in freshwater. Geobacter seems to play the predominant role within the Fe (III) -reducing bacteria in soils.

ecology

Some species of Desulfuromonas can live in the presence of acetate in a mutualistic association with species of phototrophic, sulfur-forming bacteria, the green sulfur bacteria (Chlorobiaceae). With this syntrophism, the energy metabolism and thus the growth of both partners is mutually promoted through the exchange of certain metabolic products. For example, the green sulfur bacterium Prosthecochloris aestuarii forms elemental sulfur (S 0 ) from hydrogen sulfide, from which Desulfuromonas in turn, as long as acetate is present, forms hydrogen sulfide (H 2 S) through sulfur reduction . This creates a shortened sulfur cycle.

By reducing trivalent iron ions (Fe 3+ ) to bivalent (Fe 2+ ) or from elemental sulfur to hydrogen sulfide, Desulfuromonadales play an important role in the sulfur and iron cycle of the earth. Furthermore, iron-reducing bacteria are interesting in terms of evolution. It is assumed that Fe (III) reduction is one of the first forms of anaerobic respiration in bacteria, alongside sulfur reduction. This form of metabolism is found mainly in the early development lines of bacteria and archaea .

Due to their ability to break down aromatic compounds such as toluene , some Geobacter strains are important for cleaning polluted soils and groundwater.

Geobacter metallireducens can also use uranium as an electron acceptor : The hexavalent uranium U (VI), which is water-soluble in the form of uranyl ions (UO 2 2+ ), is reduced to tetravalent uranium U (IV) through the bacterial transfer of 2 electrons, which in turn is the water-insoluble uranium dioxide (UO 2 , the mineral uraninite ) precipitates. As a result, this bacterium can be used to clean up water contaminated with uranium.

metabolism

Energy sources of this bacterial order are anaerobic respiration and fermentation . In anaerobic respiration, Desulfuromonadales uses elemental sulfur (S 0 ), polysulfides or trivalent iron (Fe 3+ ) instead of oxygen (as in aerobic respiration) as electron acceptors in the respiratory chain and thus reduces them. The electron donors are simple organic compounds such as. B. acetate. The released energy is used to form ATP . The organic electron donors are mostly completely oxidized to CO 2 via the citric acid cycle. With sulfur reduction ( sulfur breathing ), sulfur is reduced to hydrogen sulfide (H 2 S), with iron reduction (iron breathing) trivalent iron ions (Fe 3+ ) are reduced to bivalent ones (Fe 2+ ). Other substances can also be reduced, e.g. B. Manganese (IV), cobalt , technetium , nitrate and trichloroacetic acid .

The family history of the iron (III) and manganese (IV) -reducing bacteria is diverse. Many of these bacteria, which completely oxidize acetate in the process, are found in the Geobacteraceae . Others with this property are e.g. B. Species of Shewanella ( Gammaproteobacteria ), Acidithiobacillus ferrooxidans ( Betaproteobacteria ) and Deferribacter themophilus ( Deferribacteres ).

Manganese (IV) -, iron (III) - and sulfur reduction are used exclusively for energy generation, not for building metabolism, e.g. B. for the construction of amino acids, are therefore not assimilatory, the end products, Mn (II), Fe (II) or hydrogen sulfide are excreted immediately.

Sulfur reduction

All kinds of Desulfuromonadaceae as well as Geobacter sulfurreducens , Geobacter humireducens and Pelobacter carbinolicus are sulfur breathers. In Pelobacter carbinolicus , the sulfur as well as the iron reduction was demonstrated. Simple organic compounds such as acetate serve as electron donors in energy metabolism and as sources of building materials. Other materials that can be used for various types include: a .: glutamate , fumarate , alanine , oxaloacetate and pyruvate . Desulfuromonas palmitatis oxidizes a. a. also long-chain fatty acids . It can also use elementary, molecular hydrogen H 2 as an electron donor in the energy metabolism.

Desulfuromonas acetoxidans reduces elemental sulfur to hydrogen sulfide and uses acetate as an electron donor, which is completely oxidized to carbon dioxide (CO 2 ) via the citric acid cycle :

CH 3 COOH + 2 H 2 O + 4 S 0  → 2 CO 2 + 4 H 2 S

In English one speaks of the "sulfur reducing bacteria". The prefix desulfur- in the system stands for sulfur reduction. When these bacteria breathe sulfur, sulfate, thiosulfate and sulfite are not used as electron acceptors. This is what distinguishes them from sulfate bacteria ( sulfate-reducing bacteria). However, some sulfate reducers (sulfate mer) are also able to use elemental sulfur as an electron acceptor.

Some other known bacteria that reduce elemental sulfur are: Desulfovibrio gigas , species of Desulfomicrobium , Desulfurella acetivorans, and Wolinella succinogenes . Sulfur-reducing archaea are: Sulfolobus ambivalens , Pyrobaculum islandicum , Stygiolobus azoricus and Thermodiscus maritimus .

Iron Reduction and Other Electron Acceptors

Iron is widespread in nature and is an important metabolic element that was used for energy metabolism early in evolution. Many species of the Desulfuromonadales order reduce Fe 3+ to Fe 2+ . The iron (III) ions can be split off from various iron compounds, some examples are: iron (III) chloride , iron (III) oxide and iron (III) citrate . Geobacter metallireducens reduces Fe (III) to Fe (II), for example with acetate as the electron donor:

CH 3 COO - + 8 Fe 3+ + 4 H 2 O → 2HCO 3 - + 8 Fe 2+ + 9 H +

All types of Geobacter , Geothermobacter and Geopsychrobacter as well as Pelobacter carbinolicus , P. acetylenicus and P. venetianus use trivalent iron (Fe 3+ ) as an electron acceptor. In addition to sulfur, many types of Desulfuromonadaceae also use iron as an electron acceptor.

In Desulfuromusa kysingii and in some species of Geobacter (e.g. Geobacter metallireducens and Geobacter humireducens ) nitrate can also serve as an electron acceptor. Nitrate is reduced to ammonia and not to elemental, molecular nitrogen N 2 , as is the case with denitrification .

Manganese is also used by some species, e.g. B: Desulfuromonas palmitatise , Geobacter metallireducens and Desulfuromonas acetexigens , reduced and used as an electron acceptor. Mn (IV) is reduced to Mn (II). Trichlorobacter (Geobacteraceae) uses trichloroacetic acid as an electron acceptor and reduces it to dichloroacetic acid and hydrogen chloride (HCl). There is a relatively wide variety of metals that are reduced in energy metabolism by some species, for example Cobalt Co (III) and Technetium Tc (VII) from Geobacter sulfurreducens . Tc (VII) is also used by Geobacter metallireducens as an electron acceptor. However, it is unclear whether the Tc (VII) reduction also enables these species to grow. Uranium U (VI) can also be used by Geobacter metallireducens as the only electron acceptor and is reduced to U (IV). This bacterium grows when U (VI) is the only electron acceptor. Also Shewanella putrefaciens , a bacterial species of Gammaproteobacteria shows that ability. Other Fe (III) and manganese (IV) breathers as well as many sulfate-reducing bacteria (e.g. Desulfovibrio ) have also been shown to have the ability to reduce U (VI), but no growth was observed.

fermentation

Some members of the Desulfuromonadales are also capable of fermentation (for a differentiation from the term fermentation, see there). Usually acetate is the end product. All types of Desulfuromusa can use this energy metabolism in addition to anaerobic breathing. All members of the Pelobacteraceae are also capable of fermentation. In addition to acetate, ethanol can also be produced here ( Pelobacter acetylenicus , P. carbinolicus and P. venetianus ), with P. propionicus also propionate . P. acidigallici forms acetate and CO 2 . Malonomonas can be cultivated on an agar medium with malonate as the only energy and carbon source, from malonate acetate is produced as the end product, malate and fumarate can also be used of this type, end products are then succinate and CO 2 .

history

Sulfur reduction, in which acetate acts as an electron donor, was only discovered in 1976 in the bacterium Desulfuromonas acetoxidans . Geobacter metallireducens was isolated from sediments of the Potomac River by Lovley and co-workers in 1987 and named the GS-15 bacterial strain. In 1988 its energy metabolism with complete oxidation of acetate (and other carbon compounds) combined with Fe (III) reduction was demonstrated and in 1993 the bacterium was named Geobacter metallireducens .

Geobacter metallireducens is an intensely studied iron reducer and is among other things. a. of particular interest in geomicrobiology and especially in the study of the metabolic pathway of iron reduction.

Systematics

The order Desulfuromonadales consists of the following families and genera:

Another, older, but still used system consists of only two families:

  • Desulfuromonadaceae
    • Desulfuromonas
    • Desulfuromusa
    • Malonomonas
    • Pelobacter
  • Geobacteraceae
    • Geoalkalibacter Zavarzina et al. 2007
    • Geobacter
    • Geopsychrobacter
    • Geothermobacter
    • Trichlorobacter

swell

  1. ↑ Holmes DE, Nicoll JS, Bond DR, Lovley DR .: Potential role of a novel psychrotolerant member of the family Geobacteraceae, Geopsychrobacter electrodiphilus gen. Nov., Sp. nov., in electricity production by a marine sediment fuel cell . In: Applied and Environmental Microbiology . Vol. 70, No. 10, 2004, pp. 6023-6030 online
  2. ↑ [Kashefi K, Holmes DE, Baross JA, Lovley DR .: Thermophily in the Geobacteraceae: Geothermobacter Ehrlichii gen. Nov., Sp. nov., a novel thermophilic member of the Geobacteraceae from the "Bag City" hydrothermal vent . In: Applied and Environmental Microbiology . Vol. 69, No. 5, 2003 pp. 2985-2993, PMID 12732575 ]
  3. ↑ Bo B. Jørgensen, Niels P. Revsbech, T. Henry Blackburn, and Yehuda Cohen: Enrichment of Geobacter Species in Response to Stimulation of Fe (III) Reduction in Sandy Aquifer Sediments . In: Applied and Environmental Microbiology Vol. 38, No. 1, 1979, pp. 46-58, PMID 10833228
  4. ↑ Biebl, H. and N. Pfennig: Growth yields of green sulfur bacteria in mixed cultures with sulfur and sulfate reducing bacteria . In: Archives of Microbiology . Vol. 117, 1978, pp. 9-16. doi: 10.1007 / BF00689344
  5. ↑ Vargas, M., K. Kashefi, EL Blunt-Harris, and DR Lovley .: Microbiological evidence for Fe (III) reduction on early Earth . In: Nature , Vol. 395, 1998, pp. 65-67. PMID 9738498
  6. ↑ Lovley, DR, EJP Phillips, DJ Lonergan and PK Widman: Fe (III) and S 0 reduction by Pelobacter carbinolicus . In: Applied and Environmental Microbiology Vol. 61, 1995, pp. 2132-2138 PMID 7793935
  7. ↑ Lovley, DR, EJP Phillips, YA Gorby, and ER Landa: Microbial reduction of uranium . In: Nature . Vol. 350, 1991, pp. 413-416 Nature Online .
  8. ↑ Lovley, DR, EE Roden, EJP Phillips, and JC Woodward: Enzymatic iron and uranium reduction by sulfate-reducing bacteria . In: Marine Geology . Vol. 113, 1993, pp. 41-53.
  9. ↑ Pfennig, N. and Biebl, H .: Desulfuromonas acetoxidans gen. Nov. and sp. nov., a new anaerobic, sulfur-reducing, acetate oxidizing bacterium. In: Archives of Microbiology . Vol. 110, 1976. pp. 3-12. doi: 10.1007 / BF00303588
  10. ↑ Lovley DR, Stolz JF, Nord GL, Phillips EJP: Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism . In: Nature . Vol. 330, 1987, pp. 252-254. Nature Online
  11. ↑ Lovley, DR and EJP Phillips: Novel mode of microbial energy metabolism: organic carbon oxidation coupled to dissimilatory reduction of iron or manganese . In: Applied and Environmental Microbiology . Vol. 54, 1988, pp. 1472-1480. On-line
  12. ↑ Systematics according to National Center for Biotechnology Information (NCBI) (status: December 23, 2012)
  13. ↑ JP Euzéby: List of Prokaryotic Names with Standing in Nomenclature - Desulfuromonadales ( Memento of the original of August 8, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.bacterio.cict.fr

literature

  • Oliver Klimmek, Achim Kröger: Oxidative phosphorylation with sulfur instead of oxygen . In Biospektrum (journal), Vol. 8, 2002, No. 2 ISSN  0947-0867 pp. 153-157 online
  • Michael T. Madigan, John M. Martinko, Jack Parker: Brock - Microbiology . 11th edition. Pearson Studium, Munich 2006, ISBN 3-8274-0566-1
  • George M. Garrity: Bergey's manual of systematic bacteriology . 2nd Edition. Springer, New York 2005, Vol. 2: The Proteobacteria Part C: The Alpha-, Beta-, Delta-, and Epsilonproteabacteria ISBN 0-387-24145-0
  • Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer , Erko Stackebrandt (Eds.) The Prokaryotes, A Handbook of the Biology of Bacteria . 7 volumes, 3rd edition, Springer, New York et al. O., 2006, ISBN 0-387-30740-0 . Vol. 2: Ecophysiology and Biochemistry ISBN 0-387-2549-27

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