Halobacteriales
Halobacterium sp.
- Halobacterium
- Haloarcula
- Halococcus
- Haloferax
- Halorubrum
The halobacteria are a group of unicellular microorganisms from the group of archaea. The special characteristic of this group is their penchant for extremely salty environments (extreme Halophilie ). Halobacteria not only tolerated salt concentrations up to saturation, they need to grow, a minimum salt concentration of 1.5 mol / l NaCl (equivalent to about 9 %). Halo bacteria occur in natural salt lakes or in salt mines for the extraction of sea salt for example. They become the dominant population when the NaCl concentration reached a molar concentration of at least 2.5 mol / l.
Properties
Halo bacteria reproduce by cell division and do not form spores. Most halobacteria have no proper motion, but some strains move by means of flagella located at the cell ends.
The cytoplasmic membrane of halobacteria contains red to orange-colored carotenoids, called Bacterioruberine ( C50- carotenoids ). Because of these dyes dye Halobacteria the brine in which they live, pink to deep red.
Some species of halobacteria operate a simplified way of prototrophy. If the oxygen in short supply, they interrupt their normally aerobic lifestyle with oxidative energy metabolism. They produce the purple dye -protein complex bacteriorhodopsin, which is other than the Bacterioruberinen incorporated into the cytoplasmic membrane, consists of a protein member and a dye portion and having a light absorption maximum at about 570 nm. This complex acts by absorption of light as a proton pump protons are transported from the cytoplasm to the outside. The resulting proton concentration difference between the cytoplasm and the external medium is used for energy production (ATP synthesis).
In addition to the light-driven proton pump, it has been found in halobacteria, a light-driven chloride ion pump transports the chloride ions from the external medium into the cell interior. It is formed by a similarly structured the bacteriorhodopsin protein called halorhodopsin. , They have both membrane-spanning α -helix chains which anchor the protein in the cell membrane. The reason why the bacteriorhodopsin transports the small protons, while the much larger pump halorhodopsin can chloride ions is represented by the three-dimensional structure of the protein size of the ion channels. According to current knowledge, the chloride ion pump to increase the osmotic pressure, which results in the additional intake of water by itself and promotes cell division of halobacteria serves.
In animals in the photoreceptor cells of the eye retina very similar to bacteriorhodopsin structured protein called rhodopsin is included. This protein is used here, however, the conversion of light energy into the electro-chemical potentials of the excitation optic nerve cells. As the name suggests, it is similar to bacteriorhodopsin and halorhodopsin built. Inspired by the endosymbiont theory, is also speculated that there has been in evolution once a takeover of part of the halobacterial genome into the genetic material of higher animals.
Taxonomy
The Halo bacteria belong to the phylum ( strain) Euryarchaeota and are summarized in the class Halobacteria with the single order Halobacteriales that contains only one family, namely the Halobacteriaceae.
The Halobacteriaceae family contains the following genera:
- Halobacterium
- Haloalkalicoccus
- Haloarcula
- Halobaculum
- Halobiforma
- Halococcus
- Haloferax
- Halogeometricum
- Halomicrobium
- Halostagnicola
- Halorhabdus
- Halorubrum
- Halo simplex
- Haloterrigena
- Halovivax
- Natrialba
- Natrinema
- Natronobacterium
- Natronococcus
- Natronolimnobius
- Natronomonas
- Natronorubrum