Desulfovibrionales
Desulfovibrio vulgaris
The Desulfovibrionales form an order within the Deltaproteobacteria. With the exception of Lawsonia and Bilophila all species of this order can reduce sulfate by anaerobic respiration. Bacteria with this property are called Desulfurizierer. 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 wear flagella. Like all Proteobacteria, they are gram - negative.
Ecology and occurrence
Many species of this order are mesophilic, ie they need for growth temperatures between 30 and 40 degrees. Also thermophilic members at temperatures between 50 and 60 degrees are present, some species have been found in geothermal environments in the sea. This order is represented in almost all aquatic habitats (sea, freshwater, groundwater). Generally these organisms used in environments from neutral pH. Few such Desulfonatronovibrio are also alkaliphilic, they require high pH values for growth.
Lawsonia ( Desulfovibrionaceae ) is not among the Desulfurizierer. It is an obligate intercellular parasite, found in intestinal cells of pigs. Bilophila also is not among the sulfate -reducing bacteria, it was with appendicitis found inter alia in patients.
The importance of sulfate-reducing bacteria in the sulfur cycle in nature is enormous. The largest portion of the hydrogen sulfide formed by sulfate respiration. The large deposits of sulfur deposits in Louisiana and on the Gulf Coast of Texas was probably produced by different Sulfatatmern as Desulfovibrio desulfuricans.
Metabolism and Desulfurikation
When Desulfurikation one also speaks of sulfate respiration or dissimilatory sulfate reduction. Such bacteria are referred to as sulfate-reducers, sulfate reducers or Sulfatatmer :; referred (English sulfate reducing bacteria, SRB and sulfate reducing prokaryotes SRP). According to the sulfate respiration sulfate ( SO42 - ) to hydrogen sulfide (H2S) is reduced.
In this form the oxidative energy metabolism is not oxygen, as in the aerobic respiration, it sulfate, sulfite, thiosulfate or the electron acceptor. Simple organic compounds or elemental, molecular hydrogen (H2 ) are used as donors, they are oxidized. The corresponding sulfur compounds are reduced here to sulfides and hydrogen sulfide. Organic compounds are usually not completely oxidized, but acetate is the end product. Complete oxidation with CO2 as the end product is rare (eg Desulfothermus naphthaee ).
When sulfate reduction is generally first of sulfate and adenosine triphosphate ( ATP) with elimination of diphosphate ( pyrophosphate ) Adenosinphosphosulfat (APS ) was formed. In the further step, reduce adenosine monophosphate ( AMP) and sulfite is formed therefrom by the enzyme APS reductase. Sulfite is then reduced to H2S. For this, the dissimilatory Sulfitreduktasen ( dSiRs ) are used. The Desulfovibrionales are mostly the enzyme Desulfoviridin. Other dSiRs are Desulforubidin ( detected mainly in order Desulfobulbaceae even at Desulfomicrobium norvegicum ), P582 (eg nigrificans Desulfotomaculum, a Gram-positive bacterium of the Clostridiales ) and Desulfofuscidin (eg Thermodesulforhabdus the Syntrophobacteraceae ).
The sulfate reduction is called when the bacteria known as Sulfatatmer as " dissimilativ ," although it is not a dissimilation is ( there are no organisms constituents are removed). In contrast to the assimilative sulfate reduction ( sulfate assimilation ) the reduction of sulfur compounds in the sulfate-reducers ( Sulfatatmern ) is used exclusively for energy production. On the other hand serving the assimilatory sulfate reduction, to which almost all bacteria and many eukaryotes (most plants and fungi, animals, however, does not ) are able to build-up of sulfur-containing organisms components, such as amino acids, unlike the sulfate reducing the sulfate-reducers that the by the reduction excrete the resulting hydrogen sulfide immediately.
Bilophila ( Desulfovibrionaceae ) was found among others in the digestive tract of humans. You can not reduce sulfate, but requires organic sulfur sources such as taurine. Sulfite thereof can be obtained. Sulfite is again reduced by an enzyme, a dissimilatory sulfite reductase ( DSIR, and DSR) sulfide. The used enzyme closely resembles that of Desulfovibrio ( Desulfoviridin ). As Bilophila is not able to use inorganic sulfate, it is not provided to the sulfate-reducers. It is believed that the ability is lost to Desulfurikation during evolution.
Dissimilatory sulfate reduction is a hallmark of this order but also the Desulfobacterales and Syntrophobacterales within the Deltaproteobacteria. Furthermore, there is this metabolic pathway even when the Thermodesulfobacteria and in Gram- positive order Clostridiales ( Desulfotomaculum genus ). Also in the Archaea domain (eg Archaeglobus ) there Desulfurizierer.
Iron, manganese and other electron
Also, trivalent iron ( Fe3 ) can serve as an alternative electron acceptor in anaerobic respiration in different species of Desulfovibrionales. Fe3 is thereby reduced to Fe2 . Desulfovibrio desulfuricans takes, for example, to the trivalent iron ion in the form of iron ( III) chloride. As a donor lactate serves.
Manganese reduction also occurs in different members. For example, reducing Desulfovibrio desulfuricans and Desulfomicrobium baculatum Mn ( IV) to Mn (II).
Some species of this order can also use nitrate as an electron acceptor: Desulfovibrio desulfuricans, for example, reduced nitrate to ammonia. Of the genus Desulfovibrio, the ability to use uranium electron detected: U (VI) is reduced to U ( IV). Desulfovibrio vulgaris cytochrome c3 used as uranium reductase. When U (VI ) is present as the only usable for the electron bacterium, but no growth was observed. A bacterium which is U ( VI) can be used as a single electron, and this also shows growth, for example, Geobacter metallireducens the Geobacteraceae. Shewanella putrefaciens Also, a bacterial species of Gammaproteobacteria, shows that ability.
Almost all bacteria of this order are also fermenter. Common organic compounds are often fermented, inter alia, fumarate, malate, and pyruvate. There is a great diversity of substances which can be fermented. For example, fermented Desulfovibrio aminophilus et al threonine, peptone and glycine.
Disproportionation
Some types of Desulfovibrionales are Disproportionierer. In the disproportionation of sulfur compounds such as thiosulfate or sulfite to sulfate and sulfide ( hydrogen sulphide) are implemented. The resulting proton gradient is used for the production of ATP. Some types of Desulfovibrionales use this method, for example growing Desulfovibrio oxyclinae and Desulfovibrio cuneatus when acetate is present, by the disproportionation of sulfite and thiosulfite. More Disproportionierer are Desulfovibrio aminophilus and possibly Desulfonatronovibrio.
Desulfurizierer and oxygen
Until the 80s, all sulfate -reducing bacteria were regarded as obligate anaerobic, viable so only in the absence of oxygen. This view has changed in recent years. In a few species a low oxygen tolerance ( microaerobically ) was found in cultures. Thus, the type is Desulfovibrio oxyclinae also able to grow and to microaerobically even use oxygen as an electron acceptor for the growth. Tolerance to oxygen and use of Desulfovibrio were especially studied in recent years.
Also in the oxic zones of bacterial mats of cyanobacteria, where rule by photosynthesis high oxygen concentrations, sulfate reducers have been found, such as Desulfovibrio. There is also a high rate of sulfate reduction was detected.
System
At this order include the following families and genera (selection):
- Desulfovibrionaceae Küver et al. 2006 Desulfovibrio Kluyver and van Niel 1936
- Bilophila Baron et al. 1990
- Desulfocurvus Desulfocurvus Klouche et al. 2009
- Lawsonia McOrist et al. 1995
- Desulfohalobiaceae Küver et al. 2006 Desulfohalobium Ollivier et al. 1991
- Desulfohalophilus
- Desulfonatronospira Sorokin et al. 2008
- Desulfonatronovibrio Zhilina et al. 1997
- Desulfonauticus Audiffrin et al. 2003
- Desulfothermus Küver et al. 2006
- Desulfovermiculus Belyakova et al. 2007
- Desulfomicrobiaceae Küver et al. 2006 Desulfomicrobium Rozanova et al. 1994
- Desulfonatronospira Sorokin et al. 2008 Desulfonatronospira delicata Sorokin et al. 2008
- Desulfonatronumaceae Küver et al. 2006 Desulfonatronum Pikuta et al. 1998