Desulfobulbaceae

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Desulfobulbaceae
Systematics
Domain : Bacteria (bacteria)
Department : Proteobacteria
Class : Deltaproteobacteria
Order : Desulfobacterales
Family : Desulfobulbaceae
Scientific name
Desulfobulbaceae
Kuever et al. 2006

The Desulfobulbaceae form a family within the Deltaproteobacteria . They are facultatively anaerobic , gram-negative bacteria. Except for Desulforhopalus , all representatives are motile and have a single, polar flagellate.

The syllable Desulfo- in front of the name stands for the metabolic pathway of desulfurication , the reduction of sulfate (SO 4 2− ) to hydrogen sulfide (H 2 S). One also speaks of sulfate respiration or dissimilatory sulfate reduction. Corresponding bacteria are referred to as desulfuricants, sulfate reducing bacteria or sulfate reducing bacteria (SRB; or sulfate reducing prokaryotes, SRP).

The dissimilatory sulfate reduction is a characteristic of the order Desulfobacterales , Desulfovibrionales and some species of the order Syntrophobacterales within the Deltaproteobacteria . Almost all types of Desulfobulbaceae use fermentation as an additional metabolic pathway. The reduction of nitrate has also been demonstrated in some species, e.g. B. Desulfobulbus propionicus , Desulforhopalus singaporensis .

Features and ecology

The mostly rod-shaped cells occur individually, in pairs or in chains. They do not form spores. The cells of the genus Desulforhopalus contain gas vacuoles. All species occur in sea water and brackish water, the genera Desulfobulbus and Desulfocapsa also in the sapropel of fresh water. Desulfobulbus was also found in sewage sludge, rumen and animal feces. Also psychrophilic (cold-loving) species are present, the genus was Desulfotalea discovered in cold ocean sediments at temperatures of about -1 ° C on the coast of Spitsbergen and the species named accordingly ( D. psychrophila and D. arctica ). Another psychrophilic species is Desulforhopalus vacuolatus .

The sulphate reduction produces hydrogen sulphide, which is toxic for organisms and also for sulphate reducers. However, hydrogen sulfide reacts with iron, and the surrounding area is detoxified by the subsequent precipitation of the poorly soluble sulfides (e.g. FeS, iron (II) sulfide).

All desulfurizers play a major role in the sulfur cycle . Most of the naturally occurring hydrogen sulfide is produced by these bacteria.

metabolism

Sulphate breathing

Desulfurication is dissimilative in bacteria known as sulfate bacteria. In contrast to the assimilative sulphate reduction (sulphate assimilation), which almost all bacteria and also many eukaryotes (most plants and fungi, but animals are not) capable of, the hydrogen sulphide produced by the reduction is excreted immediately and is not used to build up amino acids. The reduction of sulfur compounds is used by the desulphuricants (sulphate mothers) exclusively to generate energy.

In sulphate respiration as a form of energy metabolism, it is not oxygen as in aerobic respiration, but sulphate the electron acceptor . Simple organic compounds serve as donors , they are oxidized. The corresponding sulfur compounds are reduced to sulfides or hydrogen sulfide. Species of Desulfobulbaceae not only make use of sulfate, but also sulfite , thiosulfate, and elemental sulfur. The energy is gained on an electron transport chain ( respiratory chain , oxidative phosphorylation) which, in the Desulfobulbaceae, contains cytochromes (c and b) as components.

Typical organic molecules that are used in Desulfobulbaceae as electron donors and as carbon sources (not in all types) include: fatty acids , malate , primary alcohols, lactate , acetate , propionate and pyruvate . All species of Desulfobulbus , Desulfotalea , as well as the species Desulforhopalus vacuolatus and Desulfofustis glycolicus also use H 2 as an electron donor during sulfate respiration , but only in the presence of acetate . The organic molecules are usually not completely oxidized; acetate is often the end product. Desulfofustis glycolicus completely oxidizes glycolate and glyoxylate to CO 2 .

The enzymes used for sulfate respiration are dissimilatory sulfite reductases (dSiRs). Only the enzyme desulforubidin was found in the Desulfobulbaceae . Other dSirRs are desulfoviridin , P582 (e.g. in Desulfotomaculum nigrificans , a gram-positive bacterium of the Clostridiales ) and desulfofuscidin .

Desulfurizers appear in many phylogenetically widely separated lines of the bacteria domain . This metabolic pathway has probably developed independently of one another several times in evolution. Apart from the deltaproteobacteria, sulfate respiration occurs in the Phylum Thermodesulfobacteria and in the order Clostridiales of the Firmicutes department (genus Desulfotomaculum ). Desulfurizers can also be found in the domain Archaea , e.g. B. the genus Archaeglobus . Sulfur-reducing species can be found in the Desulfurellaceae and Desulfurellales orders, which also belong to the delta group . They cannot reduce sulfate, only elemental sulfur and also thiosulfate are used by these species as an energy source. Hence the prefix desulfur here , it refers to the elemental sulfur (sulfur). In English one speaks here of the "Sulfur-Reducing Prokaryotes".

fermentation

If there are not enough sulfur compounds (sulfate, sulfide, thiosulfate), many desulfurizers switch to fermentative metabolism (fermentation). With the exception of the chemolithoautotrophic genus Desulfocapsa , all representatives of Desulfobulbaceae are capable of fermentation. For example, some species of Desulfobulbus in this case can grow in the presence of lactate or pyruvate and produce acetate through fermentation. Desulfobulbus rhabdoformis grows through the fermentation of malate and fumarate.

Disproportionation

Another metabolic pathway to generate energy for various sulphates is the disproportionation of inorganic sulfur compounds. Sulfur compounds such as thiosulfate and sulfite are converted into sulfate and sulfide (hydrogen sulfide). The resulting proton gradient is used to produce ATP . This metabolic pathway was observed among the Desulfobulbaceae in Desulfobulbus , Desulforhopalus singaporensis and in the species of Desulfocapsa .

Some species, such Desulfobulbus propionicus and Desulfocapsa used in the disproportionation and elemental sulfur. Desulfobulbus propionicus is one of the first species in which the disproportionation of elemental sulfur could be demonstrated in culture.

Sulfate reducers and oxygen

Up until the 1980s, sulfate-reducing bacteria were regarded as strictly (obligatory) anaerobic, i.e. only viable under the complete exclusion of oxygen. However, recent research has shown that SRBs tolerate oxygen and continue to use sulfate as an energy source even under the influence of oxygen.

Among the Desulfobulbaceae, for example, cultures of Desulfolobus propionicus and other sulfate reducers (e.g. Desulfovibrio , Desulfobacterium autotrophicum ) have observed a certain tolerance to oxygen in low concentrations (microaerobic). It was also shown that Desulfobulbus and other sulfate reducers (e.g. Desulfovibrio , Desulfuricans ) also use oxygen as an electron acceptor under these conditions.

Even in the oxic zones of cyanobacterial mats , where there is a high concentration of oxygen generated by photosynthesis, these bacteria have been discovered and a high rate of sulfate reduction has been demonstrated.

power line

A certain type of bacteria that belongs to the Desulfobulbaceae family can form so-called living cables (cable bacteria ) through which electrons flow in the area of ​​the sea floor . Thousands of bacteria combine to form filaments up to two centimeters long. This allows you to use the oxygen that is only available in the upper soil layer and get nutrients that are further down in the soil layer.

Systematics

This family consists of the following genera and species (selection):

  • Candidatus electronema
    • Candidatus Electronema nielsenii
    • Candidatus Electronema palustris
  • Candidatus Electrothrix
    • Candidatus Electrothrix aarhusiensis
    • Candidate Electrothrix Japonica
    • Candidatus Electrothrix marina

swell

  1. ^ Knoblauch, C., K. Sahm and BB Jørgensen. Psychrophilic sulfatereducing bacteria isolated from permanently cold Arctic marine sediments: description of Desulfofrigus oceanense gen. Nov., Sp. nov., Desulfofrigus fragile sp. nov., Desulfofaba gelida gen. nov., sp. nov., Desulfotalea psychrophila gen. nov., sp. nov. and Desulfotalea arctica sp. nov. Int. J. Syst. Bacteriol. (1999) 49: pp. 1631-1643. PMID 10555345
  2. ↑ May Faurschou Isaksen, Andreas Teske: Desulforhopalus vacuolatus gen. Nov., Sp. nov., a new moderately psychrophilic sulfate-reducing bacterium with gas vacuoles isolated from a temperate estuary. Arch Microbiol (1996) 166: pp. 160-168 doi: 10.1007 / s002030050371
  3. ↑ George M. Garrity: Bergey's manual of systematic bacteriology , p. 989
  4. ↑ 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): p. 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
  5. ↑ 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
  6. ↑ Dror Minz, Susan Fishbain, Stefan J. Green, Gerard Muyzer, Yehuda Cohen, Bruce E. Rittmann and David A. Stahl: Unexpected Population Distribution in a Microbial Mat Community: Sulfate-Reducing Bacteria Localized to the Highly Oxic Chemocline in Contrast to a Eukaryotic Preference for Anoxia In: Applied and Environmental Microbiology , October 1999, p. 4659-4665, vol. 65, no. 10, PMC 91621 (free full text)
  7. ↑ Nina Weber: Current flow: bacteria form living cables in the sea floor. In: Spiegel Online . October 24, 2012, accessed June 10, 2018 .
  8. ↑ Systematics according to National Center for Biotechnology Information (NCBI) (status: December 23, 2012)

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 0-387-25492-7

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