Halobacteria
| Halobacteriaceae | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Halobacterium sp. |
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| Systematics | ||||||||||
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| Scientific name of the class | ||||||||||
| Halobacteria | ||||||||||
| Grant et al. 2002 | ||||||||||
| Scientific name of the order | ||||||||||
| Halobacteriales | ||||||||||
| Grant & Larsen 1989 | ||||||||||
| Scientific name of the family | ||||||||||
| Halobacteriaceae | ||||||||||
| Gibbons 1974 |
The halobacteria (also haloarchaea ) are a group of unicellular microorganisms from the group of archaea . The special characteristic of this group is their preference for extremely salty environments ( extreme halophilia ). Halobacteria not only tolerate salt concentrations up to saturation, they need a minimum salt concentration of around 1.5 mol / l NaCl (corresponds to around 9%) in order to grow . Halobacteria occur, for example, in natural salt lakes or in salt pans for the extraction of sea salt. They become the dominant population when the NaCl concentration reaches a molar concentration of at least 2.5 mol / l.
properties
Halobacteria multiply through cell division and do not form spores . Most halobacteria have no movement of their own, but some strains move by means of flagella located at the cell ends .
Red to orange-colored carotenoids , lycopene (C 40 -) and so-called bacterioruberins (C 50 carotenoids) are embedded in the cytoplasmic membrane of the halobacteria . The brine in which they live appears pink to intensely red due to these pigments .
Some types of halobacteria operate a simplified type of phototrophy . If oxygen becomes scarce, they interrupt their normally aerobic lifestyle with oxidative energy metabolism . They then produce the purple-colored dye-protein complex bacteriorhodopsin , which, in addition to the bacterioruberins, is also embedded in the cytoplasmic membrane , consists of a protein part and a dye part and has a light absorption maximum at around 570 nm. This complex acts as a proton pump by absorbing light ; protons are transported out of the cytoplasm. The resulting difference in proton concentration between the cytoplasm and the external medium is used to generate energy ( ATP synthesis ).
In addition to the light-driven proton pump, a light-driven chloride ion pump has also been found in the halobacteria , which transports chloride ions from the external medium into the cell interior. It is formed by a protein with a similar structure to bacteriorhodopsin called halorhodopsin. They both have membrane- spanning α-helix chains that anchor the protein in the cell membrane. The reason why the bacteriorhodopsin transports the small protons while the halorhodopsin can pump the much larger chloride ions is the size of the ion channels given by the three-dimensional structure of the proteins . According to current knowledge, the chloride ion pump is used to increase the osmotic pressure , which entails the additional absorption of water and promotes cell division of the halobacteria.
In animals, the visual cells of the retina of the eye contain a protein called rhodopsin , which is very similar to bacteriorhodopsin . However, this protein is used here to convert light energy into the electrochemical excitation potentials of the optic nerve cells . As the name suggests, it has a structure similar to bacteriorhodopsin and halorhodopsin. Stimulated by the endosymbiotic theory , there is speculation here as to whether part of the halobacterial genome was taken over into the genetic makeup of higher animals in evolution .
Systematics
The halobacteria belong to the division ( Divisio ) or Phylum Euryarchaeota and are grouped in the class Halobacteria (synonym Halomebacteria, also "Haloarchaea") with the only order Halobacteriales that contains only one family , namely the Halobacteriaceae.
The Halobacteriaceae family contains the following genera (as of 2014):
- Haladaptatus Savage et al. 2007 emend. Roh et al. 2010
- Halalkalicoccus Xue et al. 2005
- Halarchaeum Minegishi et al. 2010
- Haloarchaeobius Makhdoumi-Kakhki et al. 2012
- Haloarcula Torreblanca et al. 1986
- Halobacterium Elazari-Volcani 1957 emend. Oren et al. 2009
- Halobaculum Oren et al. 1995
- Halobellus Cui, et al. 2011
- Halobiforma Hezayen et al. 2002 emend. Oren et al. 2009
- Halococcus Schoop 1935 emend. Oren et al. 2009
- Haloferax Torreblanca et al. 1986 emend. Oren et al. 2009
- Halogeometricum Montalvo-Rodríguez et al. 1998
- Halogranum Cui et al. 2010 emend. Cui et al. 2011
- Halolamina Cui et al. 2011
- Halomarina Inoue, et al. 2011
- Halomicrobium Oren et al. 2002
- Halonotius Burns et al. 2010
- Halopelagius Cui, et al. 2010 emend. Zhang et al. 2013
- Halopenitus Amoozegar et al. 2012
- Halopiger Gutiérrez et al. 2007
- Haloplanus Bardavid, et al. 2007 emend. Cui et al. 2010 emend. Qiu et al. 2014
- Haloquadratum Burns et al. 2007
- Halorhabdus Wainø et al. 2000 emend. Antunes et al. 2008
- Halorientalis Cui et al. 2011 emend. Amoozegar, et al. 2014
- Halorubrum McGenity & Grant 1996 emend. Oren et al. 2009
- Halosarcina Savage, et al. 2008 emend. Cui et al. 2010
- Halosimplex Vreeland et al. 2003 emend. Han & Cui 2014
- Halostagnicola Castillo et al. 2006
- Haloterrigena Ventosa et al. 1999 emend. Oren et al. 2009
- Halovenus Makhdoumi-Kakhki et al. 2012
- Halovivax Castillo et al. 2006
- Natrialba Kamekura & Dyall-Smith 1996 emend. Oren et al. 2009
- Natrinema McGenity et al. 1998 emend. Xin et al. 2000
- Natronoarchaeum Shimane et al. 2010
- Natronobacterium Tindall et al. 1984
- Natronococcus Tindall et al. 1984
- Natronolimnobius Itoh et al. 2005
- Natronomonas Kamekura et al. 1997 emend. Burns et al. 2010
- Natronorubrum Xu et al. 1999 emend. Oren et al. 2009
- Salarchaeum Shimane et al. 2011
literature
- Georg Fuchs (ed.): General microbiology . 9th, completely revised and exp. Edition. Thieme, Stuttgart 2014, ISBN 978-3-13-444609-8 .
Individual evidence
- ↑ a b Aidan C. Parte: LPSN — list of prokaryotic names with standing in nomenclature . In: Nucleic Acids Research . tape 42 , D1, January 2014, p. D613 – D616 , doi : 10.1093 / nar / gkt1111 .