Desulfobulbaceae
The Desulfobulbaceae form a family within the delta Proteobacteria. Are facultative anaerobic, gram -negative bacteria. All representatives are up to Desulforhopalus movable ( motile ) and have a single, polar flagellate.
The names in the preceding syllable desulfo - represents the pathway of Desulfurikation, the reduction of sulfate ( SO42 - ) to hydrogen sulfide (H2S). It also speaks of the 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).
The dissimilatorsche sulfate reduction is an indicator for the order Desulfobacterales, Desulfovibrionales and some species of the order Syntrophobacterales within the Deltaproteobacteria. Almost all types of Desulfobulbaceae use fermentation as an additional pathway. Also, the reduction of nitrate has been demonstrated in several species, for example in propionicus Desulfobulbus, Desulforhopalus singaporensis.
Characteristics and ecology
The most rod-shaped cells occur singly, in pairs or in chains. They do not form spores. The cells of the genus Desulforhopalus contain gas vacuoles. All species occur in seawater and brackish water, the genera Desulfobulbus and Desulfocapsa in digested sludge ( sapropel ) of fresh water. Desulfobulbus also rumen and animal feces was in the sewage sludge, have been found. Also psychrophilic ( cold-loving ) species are present, the genus Desulfotalea in cold marine sediments was discovered at temperatures around -1 ° C on the coast of Spitsbergen and the species named accordingly (D. psychrophila and D. arctica). Another psychrophilic species is Desulforhopalus vacuolatus.
By the sulfate reduction gives the toxic to organisms as well as for the sulfate- hydrogen sulfide. However, hydrogen sulfide reacts with iron, by the following precipitation of the resulting sparingly soluble sulfides (eg FeS, iron (II ) sulfide ) is detoxified the environment.
All sulfate-reducers play an important role in the sulfur cycle. The majority of the naturally occurring hydrogen sulfide produced by this bacteria.
Metabolism
Sulfate respiration
The Desulfurikation is dissimilativ in bacteria known as Sulfatatmer. In contrast to the assimilative sulfate reduction ( sulfate assimilation ) into which almost all bacteria and many eukaryotes (most plants, fungi, animals, however, do not ) are capable of emerging through the reduction of hydrogen sulfide will be immediately rejected and not used for the development of amino acids. The reduction of sulfur compounds is thus used in the sulfate-reducers ( Sulfatatmern ) intended exclusively for energy production.
In the sulfate form of the breathing as energy metabolism, oxygen is not as aerobic respiration, but the electron sulfate. Simple organic compounds serve as donors, they are oxidized. The corresponding sulfur compounds are reduced here to sulfides and hydrogen sulfide. Types of Desulfobulbaceae use not only sulfate but also sulfite, thiosulfate and elemental sulfur. The gain in energy occurs at an electron transport chain ( respiratory chain, oxidative phosphorylation), including, inter alia, in the Desulfobulbaceae cytochromes ( C and B ) as components.
Typical organic molecules that are used in Desulfobulbaceae as electron donors and as carbon sources (not all species) include: fatty acids, malate, primary alcohols, lactate, acetate, propionate and pyruvate. All kinds of Desulfobulbus, Desulfotalea, and the nature Desulforhopalus vacuolatus and use Desulfofustis glycolicus, but only in the presence of acetate, and H2 as the electron donor in sulfate respiration. The organic molecules are usually not completely oxidized acetate is often the final product. Desulfofustis glycolicus oxidized glycolate and glyoxylate completely to CO2.
When used for sulfate respiration enzymes are dissimilatory sulfite reductases ( dSiRs ). The Desulfobulbaceae only the enzyme Desulforubidin was found. Other dSirRs are Desulfoviridin, P582 (eg nigrificans Desulfotomaculum, a Gram-positive bacterium of the Clostridiales ) and Desulfofuscidin.
Desulfurizierer appear in many bacteria, phylogenetically widely separated lines of the domain. This pathway has therefore probably more times independently in evolution. Except for the delta proteobacteria sulfate respiration still occurs in the Phylum Thermodesulfobacteria and in the order Clostridiales the Department Firmicutes on ( genus Desulfotomaculum ). Also in the Archaea domain Desulfurizierer can be found, for example, the genus Archaeglobus. In the counting also to the Delta group orders Desulfurellaceae and Desulfurellales you find sulfur-reducing species. They can not reduce sulfate, only elemental sulfur and thiosulfate are used as a power source of these types. Therefore, here the prefix desulfur, it refers to the elemental sulfur (sulfur ). In English this is called the " Sulfur -Reducing Prokaryotes ".
Fermentation
If there is insufficient sulfur compounds ( sulfate, sulfide, thiosulfate ) are present, switch to the fermentative metabolism of many Desulfurizierer ( fermentation). Are all representatives of Desulfobulbaceae for fermentation able Except for the chemolithoautotrophic genus Desulfocapsa. For example, can grow in the presence of lactate or pyruvate some types of Desulfobulbus in this case and produce by fermentation of acetate. Desulfobulbus rhabdoformis grows by fermentation of malate and fumarate.
Disproportionation
Another pathway for energy for different Sulfatatmer is the disproportionation of inorganic sulfur compounds. These sulfur compounds such as thiosulfate, sulfite are converted to sulfate and sulfide ( hydrogen sulphide). The resulting proton gradient is used for the production of ATP. Among the Desulfobulbaceae was at Desulfobulbus, Desulforhopalus singaporensis and observed in the types of Desulfocapsa this pathway.
Some species, such as Desulfobulbus propionicus and Desulfocapsa also took advantage of elemental sulfur in the disproportionation. Desulfobulbus propionicus is one of the first species where the disproportionation of elemental sulfur was detected in cultures.
Sulfate and oxygen
Until the 80s, sulfate-reducing bacteria were anaerobically as strict ( obligate ), so only under complete exclusion of oxygen viable considered. Recent research results have shown, however that SRBs tolerate oxygen and continue to use even under the influence of oxygen sulfate as an energy source
Among the Desulfobulbaceae (eg Desulfovibrio, Desulfobacterium autotrophicum ) a certain tolerance to oxygen at low concentrations ( microaerobically ) was, for example, in cultures of Desulfolobus propionicus, and other sulfate observed. Furthermore, it was shown that other sulfate- and Desulfobulbus use (for example, Desulfovibrio, desulfuricans ) under these conditions, and oxygen as an electron acceptor.
Even in the oxic zones of mats of cyanobacteria, where at times there is a produced by the photosynthesis high concentration of oxygen, these bacteria have been discovered and demonstrated a high sulfate reduction rate.
Power Line
A particular type of bacteria belonging to the family of Desulfobulbaceae may form in the region of the seabed so-called live cables, by the flow electrons. Here, thousands of bacteria together close to up to two inches long filaments. That way you can use the oxygen that is present only in the upper soil layer and reach the nutrients that are located below in the bottom layer.
System
This family consists of the following genera and species ( selection):
- Desulfobulbus Widdel 1981 Desulfobulbus elongatus Samain et al. 1985
- Desulfobulbus japonicus Suzuki et al. 2007
- Desulfobulbus propionicus Widdel 1981
- Desulfobulbus rhabdoformis Lien et al. 1998
- Desulfocapsa Janssen et al. 1997 Desulfocapsa sulfexigens Corrig. Finster et al. 2000
- Desulfocapsa thiozymogenes Janssen et al. 1997
- Desulfofustis Friedrich et al. 1996 Desulfofustis glycolicus Friedrich et al. 1996
- Desulfopila Suzuki et al. 2007 Desulfopila aestuarii Suzuki et al. 2007
- Desulforhopalus Isaksen & Teske 1999 Desulforhopalus singaporensis Lie et al. 2000
- Desulforhopalus vacuolatus Isaksen & Teske 1999
- Desulfotalea garlic et al. 1999 Desulfotalea arctica garlic et al. 1999
- Desulfotalea psychrophila garlic et al. 1999
- Desulfurivibrio Sorokin et al. 2008 Desulfurivibrio alkaliphilus Sorokin et al. 2008