Thiotrichales
Thiomargarita namibiensis (Image: NASA)
Thiotrichales are an order of Proteobacteria. It is a in cell shape, ecology and metabolism very diverse group of gram- negative bacteria. An important feature of many types is to be used as an energy source by the oxidation for the metabolism ability inorganic sulfur compounds as a carbon source for the construction of the cell material serves carbon dioxide. They are referred to as chemolithotroph, and are provided to the group of sulfur bacteria. With Thiomargarita namibiensis this order contains the largest known bacterium.
Features
It is mostly aerobic, in need of oxygen bacteria, some also tolerate low oxygen contents of the environment are so microaerobically. Many species form stapled together by single-cell filaments with filament -like structures. A well-known example is the question asked to the Thiotrichaceae kind Beggiatoa alba. By twisting and wrapping the filaments, the bacterium forms a braid, it can be coated lake bottoms, white carpets arise. Other species, such as from Thiotrix, form rosettes. And coccoid and rod-shaped cells are found, for example, in different types of Piscirickettsiaceae. Some species are movable by scourges, others can move easily without flagella. The extremely large bacteria of this order include except Thiomargarita namibiensis eg Beggiatoa and Thiothrix yet.
Ecology and metabolism
Many representatives of the Thiotrichales gain energy by oxidation of inorganic sulfur compounds such as sulfide ( S2 - ), elemental sulfur and hydrogen sulfide. They are among the colorless sulfur bacteria called. " Colorless " refers to the lack of photopigments, these bacteria are not capable of photosynthesis. This distinguishes them from the photoautotrophic sulfur bacteria, which include, for example, the Schwefelpupurbakterien include with species such as Chromatium and Thiocapsa. Wherein the colorless sulfur bacteria is referred in relation to the cell morphology of the filamentous sulfur bacteria, such cell structures can be found for example in Thiothrix and Beggiatoa. Since sulfur bacteria use inorganic compounds, such as sulfide in metabolism as electron donors, they belong to the group of lithotrophic or chemolithotrophic bacteria ( ancient Greek λίθος lithos "stone" and ancient Greek τροφή trophe " diet ").
Some types of sulfur-oxidizing Thiotrichales here are obligately chemolithoautotrophic, that is, they can only use inorganic substances for energy and structure of the cell substance (carbon dioxide ), organic compounds, they may not apply. Members of the genus Thiomicrospira include, for example, to obligate chemolithotrophic bacteria, they were isolated from hydrothermal vents. Also, some strains of Beggiatoa are obligate chemolithoautotrophically. Other species are facultative chemolithoautotrophic, they can also use organic matter as a carbon source other than the inorganic substances ( carbon dioxide). Many strains of Beggiatoa are optional chemolithoautotrophically. Other strains of Beggiatoa rely absolutely on organic sources of carbon, they are not able to use inorganic sources of carbon.
By analysis of the metabolism of Beggiatoa alba Sergei Nikolayevich Winogradski able to prove that some bacteria are able to oxidize hydrogen sulfide to sulfate. This observation led to the development of the concept of chemolithotrophy: Certain organisms are capable of photosynthesis without exclusively inorganic materials for the construction of cell Substanze and energy development to use.
The sulfur-oxidizing bacteria of the Thiotrichales play an important role in the sulfur cycle of the earth. The majority of the sulfur-oxidizing Thiotrichales is bound to aquatic sites with neutral pH values. This distinguishes them from other ecologically important group of colorless sulfur bacteria, which produce sulfuric acid ( H2SO4) and are thus adapted to environments with low pH values . These acidophilic microorganisms include, for example, species of Thiobacillus and Acidithiobacillus. Also, some archaea, such as Sulfolobus, are acidophilic sulfur bacteria. The sulfur-oxidizing Thiotrichales colonize aquatic habitats that are rich in hydrogen sulfide or thiosulfate as mud layers in lakes and ponds, sewage, sulfur springs or sea beds.
With species of the genus Methylophaga (Family Piscirickettsiaceae ) are also represented methylotrophic bacteria in the order Thiotrichales. Methylotrophic bacteria use so-called C1 compounds for energy gain and as a carbon source for cell substance. With C1 compounds are molecules that do not contain direct carbon -carbon bonds, such as methanol, methylamine, and dimethylamine. Also, some pathogenic species are present in the order. Francisella tularensis is the causative agent of tularemia. This occurs in rodents disease can be transmitted to humans. Piscirickettsia salmonis is ( Oncorhynchus kisutch ) pathogenic for different fish species such as Atlantic salmon (Salmo salar) and coho salmon.
System
The families and genera:
- Francisellaceae Sjöstedt 2005 Francisella Dorofe'ev 1947
- Cycloclasticus Dyksterhouse et al. 1995
- Hydrogenovibrio Nishihara et al. 1991
- Methylophaga Janvier et al. 1985
- Piscirickettsia Fryer et al. 1992
- Sulfurivirga Takai et al. 2006
- Thioalkalimicrobium Sorokin et al. 2001
- Thiomicrospira Kuenen and Veldkamp 1972
- Thiotrichaceae Garrity et al. 2005 Achromatium Schewiakoff 1893
- Beggiatoa Trevisan 1842
- Leucothrix Oersted in 1844
- Thiobacterium (ex Janke 1924) La Riviere and Kuenen 1989
- Thiomargarita Schulz et al. 1999
- Thioploca Lauterborn 1907
- Thiospira Visloukh 1914
- Thiothrix Winogradsky 1888