Ectothiorhodospiraceae
Ectothiorhodospiraceae form a family of bacteria within the gamma group of Proteobacteria. Many species live in anaerobic phototrophic anoxygen and at the same time. They are with the family Chromatiaceae the physiological group of phototrophic purple sulfur bacteria. You are movable by flagella. The cells are rod - or spirillenförmig.
Representatives of Ectothiorhodospiraceae oxidize sulfides by photosynthesis, and hydrogen sulfide to elemental sulfur and storing the sulfur in the form of beads outside the cell ( extracellularly ) from. The sulfur can then be oxidized to sulphate extracellularly. Since no oxygen is released there will be a anoxygenic photosynthesis.
Ecology
The most representative of Ectothiorhodospiraceae are alkaliphilic and halophilic. They therefore prefer habitats with high salt contents and pH values. These bacteria are anaerobic to microaerobically. Thus you need habitats in which no or very little oxygen is present. Example, they are found on mud layers in the sea or fresh water. The halophilic often found in large amounts in soda lakes, salt lakes or in salt mines.
Extremely halophilic is the genus Halorhodospira. It prefers habitats with salinities 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 color of these lakes. Halorhodospira halophila is, for example, one of the bacteria which are responsible for the strong red color of the Wadi Natrun, a soda lake in Egypt, responsible. This type is also among the most halophilic eubacteria at all.
The photosynthesis by the hydrogen sulfide oxidizing bacteria play an important role in the sulfur cycle. They convert the toxic to higher organisms hydrogen sulfide into harmless compounds such as sulfate or elemental sulfur. Sulfate can be used by other bacteria, such as the so-called Sulfatatmern ( Sulfate ) in turn. There is usually a close-knit community ( association Consortium) between these two groups, a Sulfuretum (also spelled with ph: Sulphuretum ), a shortened form of the sulfur cycle.
Also nitrifiers are present in this family. The genus Nitrospira belongs to this group and oxidized for energy nitrite to nitrate.
The condensed sulfur cycle
The Ectothiorhodospiraceae as well as the Chromatiaceae often form a close-knit community ( a Consortium) with other sulfur-and sulfate-reducing bacteria, this often forms as a Sulfuretum (plural: Sulfureta ) designated ecosystem .. These are microbial mats ( biofilms ) in which different reduce and oxidize sulfur bacteria, it is a self-contained, condensed sulfur cycle instead.
Sulfureta form at locations where standing in a oxic - anoxic transition zone light and sulfur compounds available. These ecosystems consist of several layers of bacteria. The top, oxygen-containing and exposed layer usually consists of phototrophic bacteria such as cyanobacteria. The following relatively oxygen-free layer where even light and a large mass of sulfur compounds is present, the purple sulfur bacteria dominate. It follows the formed sulphate -and sulfur reducing bacteria layer, where there is no light, and no oxygen is present.
The sulfate formed by the sulfur purple bacteria is collected in the underlying layers of the sulfur-reducing bacteria and reduced back to hydrogen sulphide. This sulfur compound is diffused again upward and can be re-oxidized. This creates a closed, condensed sulfur cycle. The dominating form in the top layer cyanobacteria organic material which is absorbed by the sulfur purple bacteria and reducing bacteria. Because of photosynthesis, these ecosystems are subject to a day-night rhythm
Sulfureta form frequently on muddy bottoms of lakes and sea bays where the water is stagnant, more or less, or in the salt lakes and soda lakes where the Ectothiorhodospiraceae occur strengthened.
The anoxygenic photosynthesis
Together with the family Chromatiaceae The Ectothiorhodospiraceae belong to the order Chromatiales and form the group of purple sulfur bacteria. Together with the non-sulfur purple bacteria, the so-called green sulfur bacteria, green non- sulfur bacteria ( Chloroflexi ) and the cyanobacteria, they are among the phototrophic bacteria. The cyanobacteria are characterized by the formation of oxygen: Since water is used as an electron donor oxygen is released. They are thus oxygen phototroph.
Ectothiorhodospiraceae use hydrogen sulfide for reduction and fixation of CO2. When the bacteria grow autotrophically and is present as the sole carbon source CO2, the synthesis of cell material ( assimilation ) is performed using the Calvin cycle. Representatives of Ectothiorhodospiraceae oxidize sulfides and hydrogen sulfide to elemental sulfur and storing the sulfur in the form of beads outside the cell ( extracellularly ) from. The sulfur can then be oxidized to sulphate extracellularly.
Other sulfur compounds, which are used by various species of this family as Donotoren are: Thiosulfate, sulfide and sulfite; and elemental sulfur can be used. Chlorophyll is usually the bacteriochlorophyll a, carotenoids are different Spirilloxanthine. Bacteriochlorophyll b also occurs in this family, such as Halorhodospira halochloris and Halorhodospira abdelmaleki.
Characteristics distinguishing the Chromatiaceae
By the extracellular deposition and further oxidation of the elemental sulfur to species of this family leave any good from the Chromatiaceae: Types of the latter store the sulfur granules within the cell. Among Ectothiorhodospiraceae Thiorhodospira superimposed sibirica sulfur but not only extracellularly but also in the periplasmic space of the cell. Furthermore, the most representative of the Chromatiaceae form gas vesicles, only the type Ectothiorhodospira vacuolata is at the Ectothiorhodospiraceae able to do so.
Genera
Genera of this family are:
- Ectothiorhodospiraceae Imhoff 1984 Acidiferrobacter Hallberg et al. 2011
- Alkalilimnicola Yakimov et al. 2001
- Alkalispirillum Rijkenberg et al. 2002
- Aquisalimonas Márquez et al. 2007
- Arhodomonas Adkins et al. 1993
- Ectothiorhodosinus Gorlenko et al. 2004
- Ectothiorhodospira Pelsh 1936
- Halorhodospira Imhoff and Suling 1997
- Natronocella Sorokin et al. 2007
- Nitrococcus Watson and Waterbury 1971
- Thioalbus Park et al. 2011
- Thioalkalivibrio Sorokin et al. 2001
- Thiohalospira Sorokin et al. 2008
- Thiorhodospira Bryantseva et al. 1999