Desulfovibrionales

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Desulfovibrionales
Desulfovibrio vulgaris

Desulfovibrio vulgaris

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

The Desulfovibrionales form an order within the Deltaproteobacteria . With the exception of Lawsonia and Bilophila , all species of this order can reduce sulfate through anaerobic respiration . Bacteria with this property are called desulfurizers . They play an important role in the sulfur cycle through the formation of hydrogen sulfide from sulfate . The cell shape is rod-shaped or curved, usually they have flagella. Like all proteobacteria, they are gram negative .

Ecology and occurrence

Many species of this order are mesophilic , which means they need temperatures between 30 and 40 degrees to grow. Also thermophilic members at temperatures between 50 and 60 degrees are present but some species were in geothermal found environments in the sea. This order is represented in almost all aquatic habitats (sea, freshwater, groundwater). Typically these organisms are found in environments with neutral pH. Few of them like Desulfonatronovibrio are also alkaliphilic , they require high pH levels for growth.

Lawsonia (Desulfovibrionaceae) is not one of the desulfurizers. It is an obligatory intercellular parasite found in intestinal cells of pigs. Bilophila is also not one of the sulfate-reducing bacteria. a. found in patients with appendicitis.

The importance of the sulfate-reducing bacteria for the sulfur cycle in nature is enormous. Most of the hydrogen sulfide is formed by sulfate respiration. The large incidence of sulfur deposits in Louisiana and on the Texas Gulf Coast was likely caused by various sulfate breathers, such as Desulfovibrio desulfuricans .

Metabolism and Desulfurication

In the sulfate-reducing bacteria is also called sulfate respiration or dissimilatory sulfate reduction . Corresponding bacteria are as sulfate-reducers , Sulfatatmer or sulfate- (engl .: sulfate reducing bacteria ;, SRB and sulfate reducing prokaryotes denoted SRP). With sulfate respiration, sulfate (SO 4 2− ) is reduced to hydrogen sulfide (H 2 S).

In this form of oxidative energy metabolism , the electron acceptor is not oxygen as in aerobic respiration, but sulfate, sulfite or thiosulfate . Simple organic compounds or elementary, molecular hydrogen (H 2 ) serve as donors , they are oxidized. The corresponding sulfur compounds are reduced to sulfides or hydrogen sulfide. Organic substances are usually not completely oxidized, but acetate is the end product. Complete oxidation with CO 2 as the end product is less common (e.g. with Desulfothermus naphthaee ).

In sulphate reduction, adenosine phosphosulphate (APS) is generally initially formed from sulphate and adenosine triphosphate (ATP) with elimination of diphosphate (pyrophosphate) . In a further step, adenosine monophosphate (AMP) and sulfite are formed from this with the aid of the enzyme APS reductase with reduction . Sulphite is then reduced to H 2 S. The dissimilatory sulfite reductases (dSiRs) are used for this purpose. The desulfovibrionales are mostly the enzyme desulfoviridin . Other dSiRs are Desulforubidin (mainly in the order Desulfobulbaceae , also found in Desulfomicrobium norvegicum ), P582 (e.g. in Desulfotomaculum nigrificans , a gram-positive bacterium of the Clostridiales ) and Desulfofuscidin (e.g. in Thermodesulforhabdus the Syntrophobactereae.

The sulfate reduction is referred to as "dissimilative" in bacteria known as sulfatmer, although it is not a dissimilation (no components of organisms are broken down). In contrast to the assimilative sulphate reduction (sulphate assimilation), the reduction of sulfur compounds in the case of the desulphuricants (sulphates) serves exclusively to generate energy. On the other hand, the assimilatory sulfate reduction, which almost all bacteria and also many eukaryotes (most plants and fungi; animals, however, are not) capable of, the build-up of organism components containing sulfur, for example amino acids, in contrast to the sulfate reduction of the desulfuricants, which the reduction causes Immediately excrete the resulting hydrogen sulfide.

Bilophila (Desulfovibrionaceae) was u. a. found in the digestive tract of humans. It cannot reduce sulfate, but needs organic sulfur sources such as taurine . Sulphite can be obtained from this. Sulphite is in turn reduced to sulphide by an enzyme, a dissimilatory sulphite reductase (dSIR or DSR). The enzyme used is very similar to that of Desulfovibrio (Desulfoviridin). Since Bilophila is not able to use inorganic sulfate, she is not placed among the desulfuricants. It is believed that during evolution the ability to desulfurize was lost.

The dissimilatory sulfate reduction is a characteristic of this order but also of the Desulfobacterales and Syntrophobacterales within the Deltaproteobacteria . This metabolic pathway also exists in the Thermodesulfobacteria and in the gram-positive order Clostridiales (genus Desulfotomaculum ). There are also desulfurizers in the domain Archaea (e.g. Archaeglobus ).

Iron, manganese and other electron acceptors

Trivalent iron (Fe 3+ ) can also serve as an alternative electron acceptor in anaerobic respiration in various types of desulfovibrionales. Fe 3+ is reduced to Fe 2+ . Desulfovibrio desulfuricans takes z. B. the trivalent iron ion in the form of iron (III) chloride. Lactate serves as a donor .

Manganese reduction also occurs in various members. For example, Desulfovibrio desulfuricans and Desulfomicrobium baculatum reduce Mn (IV) to Mn (II).

Some species of this order can also use nitrate as an electron acceptor: Desulfovibrio desulfuricans , for example, reduces nitrate to ammonia . In the case of the genus Desulfovibrio , the ability to use uranium as an electron acceptor has been demonstrated: U (VI) is reduced to U (IV). Desulfovibrio vulgaris uses cytochrome c3 as a uranium reductase. However, if U (VI) is the only electron acceptor that can be used by the bacterium, no growth was observed. A bacterium that can use U (VI) as the only electron acceptor and also shows growth is z. B. Geobacter metallireducens from Geobacteraceae . Also Shewanella putrefaciens , a bacterial species of Gammaproteobacteria shows that ability.

Almost all bacteria of this order are fermenters too . Common organic compounds that are frequently fermented include: a. Fumarate , malate and pyruvate . There is a wide variety of substances that can be fermented. For example, Desulfovibrio aminophilus fermented u. a. Threonine , peptone and glycine .

Disproportionation

Some types of desulfovibrionales are disproportionate . During disproportionation, sulfur compounds such as thiosulfate or sulfite are converted to sulfate and sulfide (hydrogen sulfide). The resulting proton gradient is used to produce ATP . Some species of Desulfovibrionales use this route, for example Desulfovibrio oxyclinae and Desulfovibrio cuneatus , when acetate is present, grows through the disproportionation of sulfite and thiosulfite. Other disproportionators are Desulfovibrio aminophilus and possibly Desulfonatronovibrio .

Desulfurizer and Oxygen

Until the 1980s, all sulfate-reducing bacteria were regarded as obligately anaerobic , i.e. only viable if oxygen was excluded. This view has changed in recent years. In a few species, a low tolerance to oxygen (microaerobic) was found in cultures. The Desulfovibrio oxyclinae species is also able to grow microaerobically and even use oxygen as an electron acceptor for growth. The oxygen tolerance and use of Desulfovibrio has been particularly studied in recent years.

Also in the oxic zones of bacterial mats of the cyanobacteria , where high oxygen concentrations prevail due to photosynthesis, sulfate reducers such as. B. Desulfovibrio found. A high sulphate reduction rate was also detected there.

Systematics

The following families and genera belong to this order (selection):

swell

  1. ↑ Heike Laue, Michael Friedrich, Jürgen Ruff, Alasdair M. Cook: Dissimilatory Sulfite Reductase (Desulfoviridin) of the Taurine-Degrading, Non-Sulfate-Reducing Bacterium Bilophila wadsworthia RZATAU Contains a Fused DsrB-DsrD Subunit. In: Journal of Bacteriology . March 2001, Vol. 183, No. 5, pp. 1727-1733.
  2. ^ DR Lovley, PK Widman, JC Woodward, EJ Phillips: “Reduction of Uranium by Cytochrome c3 of Desulfovibrio vulgaris”, in: Appl. Environ. Microbiol. 1993 , 59 (11) , 3572-3576; PMID 8285665 , PMC 182500 (free full text).
  3. ^ DR Lovley, EJ Phillips: "Reduction of Uranium by Desulfovibrio desulfuricans", in: Appl. Environ. Microbiol. 1992 , 58 (3) , 850-856; PMID 1575486 ; PMC 195344 (free full text).
  4. ↑ DR Lovley, EJP Phillips, YA Gorby, ER Landa: "Microbial Reduction of Uranium", in: Nature 1991 , 350 , 413-416; doi : 10.1038 / 350413a0 .
  5. ↑ LK Baumgartner, RP Reid, C. Dupraz, AW Decho, DH Buckley, JR Spear, KM Przekop, PT Visscher: Sulfate reducing bacteria in microbial mats: Changing paradigms, new discoveries. In: Sedimentary Geology. 185 (2006): pp. 131-145. PDF ( Memento of the original from September 30, 2007 in the Internet Archive ) 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. @1@ 2Template: Webachiv / IABot / colloid.org
  6. ↑ Heribert Cypionka : Oxygen respiration by Desulfovibrio species. In: Annual review of microbiology. 2000, vol. 54, pp. 827-848 (126 ref.)
  7. ^ Waltraud Dilling, Heribert Cypionka : Aerobic respiration in sulfate-reducing bacteria. In: FEMS Microbiology Letters. 71 (1-2): 123-127 (1990). doi : 10.1111 / j.1574-6968.1990.tb03809.x .
  8. ^ National Center for Biotechnology Information (NCBI) and JP Euzéby: List of Prokaryotic Names with Standing in Nomenclature. ( System: Order Desulfovibrionales ( Memento of the original from April 5, 2011 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. Status: 23 December 2012 @1@ 2Template: Webachiv / IABot / www.bacterio.cict.fr

literature

  • 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-Verlag, New York et al. O. 2006, ISBN 0-387-30740-0 . Vol. 2: Ecophysiology and Biochemistry. ISBN 0-387-2549-27 .

Web links