Thiotrichales

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Thiotrichales
Thiomargarita namibiensis (Image: NASA)

Thiomargarita namibiensis (Image: NASA)

Systematics
Domain : Bacteria (bacteria)
Department : Proteobacteria
Class : Gammaproteobacteria
Order : Thiotrichales
Scientific name
Thiotrichales
Garrity et al. 2005

Thiotrichales are an order of the Proteobacteria . It is a very diverse group of gram-negative bacteria in terms of cell shape, ecology and metabolism . An important characteristic of many species is the ability to use inorganic sulfur compounds through oxidation as a source of energy for metabolism, while carbon dioxide serves as a source of carbon for the construction of cell matter. They are called chemolithotrophic and belong to the group of sulfur bacteria . With Thiomargarita namibiensis , this order contains the largest known bacterium.

features

These are mostly aerobic , oxygen-dependent bacteria, some also tolerate low levels of oxygen in the environment, so they are microaerobic. Many species form filaments with thread-like structures through individual cells attached to one another. A well-known example is the species Beggiatoa alba , which belongs to the Thiotrichaceae . By twisting and wrapping the filaments, the bacterium forms a network, white carpets covering the seabed can arise. Other species, such as thiotrix , form rosettes. Also coccoid and rod-shaped cells occur such. B. in different species of the Piscirickettsiaceae . Some species are motile by flagella, others can glide without flagella. The extremely large bacteria of this order include Thiomargarita namibiensis z. B. Beggiatoa and Thiothrix .

Ecology and metabolism

Many representatives of the Thiotrichales gain energy by oxidizing inorganic sulfur compounds, such as B. Sulphide (S 2− ), elemental sulfur and hydrogen sulphide . During the oxidation z. B. formed sulfate . One also speaks of the sulfur oxidizing bacteria or sulfuricants . They belong to the so-called colorless sulfur bacteria. "Colorless" refers to the missing photopigments, these bacteria are not capable of photosynthesis. This distinguishes them from the photoautotrophic sulfur bacteria to which z. B. the sulfur pupur bacteria , with species such as Chromatium and Thiocapsa count. The colorless sulfur bacteria are also referred to as filamentous sulfur bacteria with regard to the cell morphology. B. Thiothrix and Beggiatoa . Since sulfur bacteria use inorganic compounds such as sulfide as electron donors in their metabolism , they belong to the group of lithotrophic or chemolithotrophic bacteria ( ancient Greek λίθος lithos , German 'stone' and τροφή trophe , German 'nutrition' ).

Some types of sulfur-oxidizing Thiotrichales are obligate chemolithoautotrophic, i.e. In other words, they can only use inorganic substances to generate energy and build up the cell substance (carbon dioxide); they cannot utilize organic compounds. Members of the genus Thiomicrospira include z. B. to the obligate chemolithotrophic bacteria, they were isolated from hydrothermal sources. Some strains of Beggiatoa are also obligate chemolithoautotroph. Other types are optionally chemolithoautotrophic, they can use organic substances as a carbon source in addition to the inorganic substances (carbon dioxide). Many strains of Beggiatoa are facultatively chemolithoautotrophic. Other tribes of Beggiatoa are absolutely dependent on organic sources for the carbon, they are not able to use inorganic sources for the carbon.

By analyzing the metabolism of Beggiatoa alba , Sergei Nikolajewitsch Winogradski was 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 able to use only inorganic substances without photosynthesis to build up cell substance and generate energy.

The sulfur-oxidizing bacteria species of the Thiotrichales play an important role in the earth's sulfur cycle . Most of the sulfur-oxidizing Thiotrichales are bound in aquatic locations with neutral pH values. This distinguishes them from another ecologically significant group of colorless sulfur bacteria that produce sulfuric acid (H 2 SO 4 ) and are therefore adapted to environments with low pH values. These acidophilic microorganisms include, for. B. Species of Thiobacillus and Acidithiobacillus . Some archaebacteria , such as Sulfolobus , are also acidophilic sulfur oxidizers. The sulfur-oxidizing Thiotrichales colonize aquatic habitats that are rich in hydrogen sulfide or thiosulfate, such as layers of mud in lakes and ponds, waste water, sulfur springs or even the seabed.

With species of the genus Methylophaga (family Piscirickettsiaceae), methylotrophic bacteria in the order Thiotrichales are also represented. Methylotrophic bacteria use so-called C1 compounds for energy gain and as a carbon source for the cell substance. C1 compounds are molecules that do not contain any direct carbon-carbon bonds, e.g. B. methanol , methylamine and dimethylamine . Some pathogenic species are also present in the order. Francisella tularensis is the cause of tularemia . This disease, which occurs in rodents, can also be transmitted to humans. Piscirickettsia salmonis is pathogenic for various fish species, such as the Atlantic salmon ( Salmo salar ) and the silver salmon ( Oncorhynchus kisutch ).

Systematics

The families and some genera

The genera Fangia and Caedibacter are currently (November 30, 2018) not assigned to any particular family.

swell

  1. a b c d George M. Garrity: Bergey's manual of systematic bacteriology 2nd edition
  2. JP Euzéby: List of Prokaryotic names with Standing in Nomenclature - Order Thiotrichales (as of November 30, 2018)

literature

  • George M. Garrity: Bergey's manual of systematic bacteriology . 2nd Edition. Springer, New York, 2005, Volume 2: The Proteobacteria, Part B: The Gammaproteobacteria ISBN 0-387-24144-2
  • Michael T. Madigan, John M. Martinko, Jack Parker: Brock - Microbiology . 11th edition. Pearson Studium, Munich 2006, ISBN 3-8274-0566-1

Web links

Commons : Thiotrichales  - collection of images, videos and audio files