Ectothiorhodospiraceae

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Ectothiorhodospiraceae
Systematics
Domain : Bacteria (bacteria)
Department : Proteobacteria
Class : Gammaproteobacteria
Order : Chromatiales
Family : Ectothiorhodospiraceae
Scientific name
Ectothiorhodospiraceae
Imhoff 1984

Ectothiorhodospiraceae are a family of bacteria within the gamma group of Proteobacteria . Many representatives live anoxygenically phototrophic and at the same time anaerobic . Together with the Chromatiaceae family, they form the physiological group of phototrophic sulfur- purple bacteria . They are agile by scourges. The cells are rod-shaped or spiral-shaped.

Representatives of the Ectothiorhodospiraceae oxidize sulphides or hydrogen sulphide to elemental sulfur through photosynthesis and deposit the sulfur in the form of globules outside the cell (extracellular). The sulfur can then be further oxidized to sulfate extracellularly. Since no oxygen is released, anoxygenic photosynthesis takes place.

ecology

Most of the representatives of the Ectothiorhodospiraceae are alkaliphilic and halophilic . They therefore prefer habitats with high salinity and pH values. These bacteria are anaerobic to microaerobic. You therefore need habitats in which there is no or very little oxygen. You are e.g. B. to be found on layers of mud in the sea or fresh water. The halophiles are often found in large quantities in soda lakes , salt lakes or even in salt pans .

The genus Halorhodospira is extremely halophilic . It prefers habitats with a salt content of 15–25%. Halorhodospira and other species occur in very large quantities in highly saline and alkaline soda lakes and cause the characteristic red or green coloration of these lakes. Halorhodospira halophila is e.g. B. one of the bacteria that are responsible for the strong red color of Wadi Natrun , a soda lake in Egypt. This species is also one of the most strongly halophilic eubacteria ever.

The bacteria oxidizing hydrogen sulfide through photosynthesis play an important role in the sulfur cycle . They convert hydrogen sulfide, which is poisonous for higher organisms, into harmless compounds such as sulfate or elemental sulfur. Sulphate can in turn be used by other bacteria, such as the so-called sulphate mers ( desulphuricants ). Usually there is a close association (association) between these two groups, a sulfuretum (also written with ph : Sulphuretum), a shortened form of the sulfur cycle.

There are also nitrifiers in this family. The genus Nitrococcus belongs to this group and oxidizes nitrite to nitrate for energy production .

The shortened sulfur cycle

The Ectothiorhodospiraceae as well as the Chromatiaceae often form a close community with other sulfur- and sulfate-reducing bacteria, often forming an ecosystem called Sulfuretum (plural: Sulfureta). It is a matter of microbe mats ( biofilms ) in which various bacteria reduce and oxidize sulfur, a closed, shortened sulfur cycle takes place.

Sulfureta form at locations where light and sulfur compounds are available in an oxic-anoxic transition zone. These ecosystems are made up of multiple layers of bacteria. The uppermost, oxygen-containing and exposed layer usually consists of phototrophic bacteria such as cyanobacteria . In the next relatively oxygen-free layer where there is still light and a large amount of sulfur compounds, the purple sulfur bacteria dominate. This is followed by the layer formed by sulfate- and sulfur-reducing bacteria, there is no light and no oxygen.

The sulphate formed by the purple sulfur bacteria is caught in the layers below by the sulfur-reducing bacteria and reduced again to hydrogen sulphide. This sulfur compound diffuses upwards again and can be oxidized again. A closed, shortened sulfur cycle is created. The dominant cyanobacteria in the top layer form organic material which is absorbed by the purple sulfur bacteria and the reducing bacteria. Due to photosynthesis, these ecosystems are subject to a day-night rhythm .

Sulfureta often form on the muddy bottoms of lakes and bays, where the water more or less stagnates, or in the salt lakes and soda lakes, where the Ectothiorhodospiraceae are more common.

Anoxygenic photosynthesis

The Ectothiorhodospiraceae belong together with the family Chromatiaceae of the order Chromatiales and form the group of sulfur purple bacteria. Together with the sulfur-free purple bacteria (Rhodospirillaceae), the green sulfur bacteria (Chlorobiaceae), the green non-sulfur bacteria (Chloroflexi) and the cyanobacteria , they belong to the phototrophic bacteria. The cyanobacteria are characterized by the formation of oxygen: Since water serves as an electron donor, oxygen is released. They are therefore oxygen phototrophic.

Ectothiorhodospiraceae use hydrogen sulfide to reduce and fix CO 2 . If the bacteria grow autotrophically and CO 2 is the only source of carbon , the build-up of cell material ( assimilation ) takes place with the help of the Calvin cycle . Representatives of the Ectothiorhodospiraceae oxidize sulfides or hydrogen sulfide to elemental sulfur and deposit the sulfur in the form of globules outside the cell (extracellular). The sulfur can then be further oxidized to sulfate extracellularly.

Other sulfur compounds that are used as donors by various species in this family are: thiosulfates , sulfides, and sulfites ; elemental sulfur can also be used. Chlorophyll is mostly bacteriochlorophyll a, carotenoids are various spirilloxanthines. Bacteriochlorophyll b also occurs in this family, e.g. B. Halorhodospira halochloris and Halorhodospira abdelmaleki .

Distinguishing features to the Chromatiaceae

Due to the extracellular deposition and further oxidation of the elemental sulfur, species of this family can be easily distinguished from the Chromatiaceae: Species of the latter store the sulfur grains within the cell. Among the Ectothiorhodospiraceae, Thiorhodospira sibirica not only deposits the sulfur extracellularly, but also in the periplasmic space of the cell. Furthermore, most representatives of the Chromatiaceae form gas vesicles, with the Ectothiorhodospiraceae only the species Ectothiorhodospira vacuolata is able to do this .

Genera

The genus Acidiferrobacter , which used to belong to the Ectothiorhodospiraceae family , was transferred to the newly established order Acidiferrobacterales in 2015 .

The following is a list of some genera of the Ectothiorhodospiraceae:

swell

  1. ↑ Norbert Pfennig: The phototrophic bacteria and their role in the sulfur cycle In: Plant and Soil (August 1975) Volume 43, Numbers 1-3 ISSN  0032-079X
  2. ↑ Joseph W. Lengeler, Gerhart Drews , Hans G. Schlegel (Eds.) Biology of the Prokaryotes . Georg Thieme Verlag, Stuttgart, 1999, ISBN 3-13-108411-1 , Chapter 31: Habitats of Prokaryotes
  3. ↑ Irina Bryantseva, Vladimir M. Gorlenko, Elena I. Kompantseva, Johannes F. Imhoff, Jörg Suling and Lubov 'Mityushina: Thiorhodospira sibirica gen. Nov., Sp. nov., a new alkaliphilic purple sulfur bacterium from a Siberian soda lake. In: International Journal of Systematic Bacteriology (1999), 49, pp. 697-703
  4. ↑ JP Euzéby: List of Prokaryotic names with Standing in Nomenclature - Ectothiorhodospiraceae (as of April 28, 2019)

literature

  • Michael T. Madigan, John M. Martinko, Jack Parker: Brock - Microbiology . 11th edition. Pearson Studium, Munich 2006, ISBN 3-8274-0566-1
  • Johannes Imhoff: The Family Ectothiorhodospiraceae In: 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. 6: Proteobacteria: Gamma Subclass ISBN 0-387-30746-X .
  • Jörg Overmann and Ferrau Garcia-Pichel: The Phototrophic Way of Life In: 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
  • George M. Garrity: Bergey's manual of systematic bacteriology . 2nd Edition. Springer, New York, 2005, Volume 2: The Proteobacteria, Part B: The Gammaproteobacteria