Haloarchaea

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Halobacteria (plural form of the word "halobacterium") redirects here. For the genus, see halobacterium.
Haloarchaea
Halobacteria.jpg
Halobacterium sp. strain NRC-1, each cell about 5 µm in length.
Scientific classification
Domain: Archaea
Kingdom: Archaea
Phylum: Euryarchaeota
Class: Halobacteria
Order
Synonyms
  • Halobacteria Grant et al. 2002

In taxonomy, the Halobacteria (also Halomebacteria) are a class of the Euryarchaeota,[1] found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea, rather than bacteria. The name 'halobacteria' was assigned to this group of organisms before the existence of the domain Archaea was realized, and remains valid according to taxonomic rules[citation needed]. In a non-taxonomic context, halophilic archaea are referred to as haloarchaea to distinguish them from halophilic bacteria.

These microorganisms are members of the halophile community, in that they require high salt concentrations to grow. They are a distinct evolutionary branch of the Archaea, and are generally considered extremophiles, although not all members of this group can be considered as such.

Haloarchaea can grow aerobically or anaerobically. Parts of the membranes of haloarchaea are purplish in color, and large blooms of haloarchaea appear reddish, from the pigment bacteriorhodopsin, related to the retinal pigment rhodopsin. Bacteriorhodopsin is used to absorb light, which provides energy to create ATP. Haloarchaea also possess a second pigment, halorhodopsin, which pumps chloride ions in the cell in response to photons, creating a voltage gradient and assisting in the production of energy from light. The process is unrelated to other forms of photosynthesis involving electron transport however, and haloarchaea are incapable of fixing carbon from carbon dioxide.[2]

Taxonomy[edit]

The extremely halophilic, aerobic members of Archaea are classified within the family Halobacteriaceae, order Halobacteriales in Class III. Halobacteria of the phylum Euryarchaeota (International Committee on Systematics of Prokaryotes, Subcommittee on the taxonomy of Halobacteriaceae). As of June 2012, the family Halobacteriaceae comprises 39 genera.

Domain : Archaea

Phylum: Euryarchaeota

  • Class: Halobacteria
    • Order: Halobacteriales
      • Family: Halobacteriaceae
        • Haladaptatus [Hap.]
          • Haladaptatus cibarius
          • Haladaptatus litoreus
          • Haladaptatus paucihalophilus (Type species)
        • Halalkalicoccus [Hac.]
          • Halalkalicoccus jeotgali
          • Halalkalicoccus tibetensis (Type species)
        • Halarchaeum [Hla.]
          • Halarchaeum acidiphilum (Type species)
        • Haloarchaeobius [Hab.]
          • Haloarchaeobius iranensis (Type species)
        • Haloarcula [Har.]
          • Haloarcula amylolytica
          • Haloarcula argentinensis
          • Haloarcula hispanica
          • Haloarcula japonica
          • Haloarcula marismortui
          • Haloarcula quadrata
          • Haloarcula salaria
          • Haloarcula tradensis
          • Haloarcula vallismortis (Type species)
        • Halobacterium [Hbt.] (Type genus)
          • Halobacterium jilantaiense
          • Halobacterium noricense
          • Halobacterium piscisalsi (subjective junior synonym of Halobacterium salinarum)[3]
          • Halobacterium salinarum (Type species)
        • Halobaculum [Hbl.]
          • Halobaculum gomorrense (Type species)
          • Halobaculum magnesiiphilum (IJSEM in press)
        • Halobellus [Hbs.]
          • Halobellus clavatus (Type species)
          • Halobellus limi
          • Halobellus salinus
        • Halobiforma [Hbf.]
          • Halobiforma haloterrestris (Type species)
          • Halobiforma lacisalsi
          • Halobiforma nitratireducens
        • Halococcus [Hcc.]
          • Halococcus dombrowskii
          • Halococcus hamelinensis
          • Halococcus morrhuae (Type species)
          • Halococcus qingdaonensis
          • Halococcus saccharolyticus
          • Halococcus salifodinae
          • Halococcus thailandensis
        • Haloferax [Hfx.]
          • Haloferax alexandrinus
          • Haloferax denitrificans
          • Haloferax elongans
          • Haloferax gibbonsii
          • Haloferax larsenii
          • Haloferax lucentense
          • Haloferax mediterranei
          • Haloferax mucosum
          • Haloferax prahovense
          • Haloferax sulfurifontis
          • Haloferax volcanii (Type species)
        • Halogeometricum [Hgm.]
          • Halogeometricum borinquense (Type species)
          • Halogeometricum rufum
        • Halogranum [Hgn.]
          • Halogranum amylolyticum
          • Halogranum gelatinilyticum
          • Halogranum rubrum (Type species)
          • Halogranum salarium (Type species) (SAM in press)
        • Halolamina [Hlm.]
          • Halolamina pelagica (Type species)
        • Halomarina [Hmr.]
          • Halomarina oriensis (Type species)
        • Halomicrobium [Hmc.]
          • Halomicrobium katesii
          • Halomicrobium mukohataei (Type species)
          • Halomicrobium zhouii
        • Halonotius [Hns.]
          • Halonotius pteroides (Type species)
        • Halopelagius [Hpl.]
          • Halopelagius inordinatus (Type species)
        • Halopenitus [Hpt.]
          • Halopenitus persicus (Type species) (IJSEM in press)
        • Halopiger [Hpg.]
          • Halopiger aswanensis
          • Halopiger xanaduensis (Type species)
        • Haloplanus [Hpn.]
          • Haloplanus aerogenes
          • Haloplanus natans (Type species)
          • Haloplanus vescus
        • Haloquadratum [Hqr.]
          • Haloquadratum walsbyi (Type species)
        • Halorhabdus [Hrd.]
          • Halorhabdus tiamatea
          • Halorhabdus utahensis (Type species)
        • Halorientalis [Hos.]
          • Halorientalis regularis (Type species)
        • Halorubellus ["Hrb".]
          • Halorubellus litoreus (SAM in press)
          • Halorubellus salinus (Type species) (SAM in press)
        • Halorubrum [Hrr.]
          • Halorubrum aquaticum
          • Halorubrum aidingense
          • Halorubrum alkaliphilum
          • Halorubrum arcis
          • Halorubrum californiense
          • Halorubrum chaoviator
          • Halorubrum cibi
          • Halorubrum coriense
          • Halorubrum distributum
          • Halorubrum ejinorense
          • Halorubrum ezzemoulense
          • Halorubrum kocurii
          • Halorubrum lacusprofundi
          • Halorubrum lipolyticum
          • Halorubrum litoreum
          • Halorubrum luteum
          • Halorubrum orientale
          • Halorubrum saccharovorum (Type species)
          • Halorubrum sodomense
          • Halorubrum tebenquichense
          • Halorubrum terrestre
          • Halorubrum tibetense
          • Halorubrum trapanicum
          • Halorubrum vacuolatum
          • Halorubrum xinjiangense
        • Halorussus ["Hrs".]
          • Halorussus rarus (Type species) (Extremophiles [Epub ahead of print])
        • Halosarcina [Hsn.]
          • Halosarcina limi
          • Halosarcina pallida (Type species)
        • Halosimplex [Hsx.]
          • Halosimplex carlsbadense (Type species)
        • Halostagnicola [Hst.]
          • Halostagnicola alkaliphila
          • Halostagnicola kamekurae
          • Halostagnicola larsenii (Type species)
        • Haloterrigena [Htg.]
          • Haloterrigena daqingensis
          • Haloterrigena hispanica
          • Haloterrigena jeotgali
          • Haloterrigena limicola
          • Haloterrigena longa
          • Haloterrigena saccharevitans
          • Haloterrigena salina
          • Haloterrigena thermotolerans
          • Haloterrigena turkmenica (Type species)
        • Halovenus [Hvn.]
          • Halovenus aranensis (Type species) (IJSEM in press)
        • Halovivax [Hvx.]
          • Halovivax asiaticus (Type species)
          • Halovivax ruber
        • Natrialba [Nab.]
          • Natrialba aegyptia
          • Natrialba asiatica (Type species)
          • Natrialba chahannaoensis
          • Natrialba hulunbeirensis
          • Natrialba magadii
          • Natrialba taiwanensis
        • Natrinema [Nnm.]
          • Natrinema altunense
          • Natrinema ejinorense
          • Natrinema gari
          • Natrinema pallidum
          • Natrinema pellirubrum (Type species)
          • Natrinema versiforme
        • Natronoarchaeum [Nac.]
          • Natronoarchaeum mannanilyticum (Type species)
          • Natronoarchaeum philippinense (IJSEM in press)
        • Natronobacterium [Nbt.]
          • Natronobacterium gregoryi (Type species)
        • Natronococcus [Ncc.]
          • Natronococcus amylolyticus
          • Natronococcus jeotgali
          • Natronococcus occultus (Type species)
          • Natronococcus roseus (IJSEM in press)
        • Natronolimnobius [Nln.]
          • Natronolimnobius baerhuensis (Type species)
          • Natronolimnobius innermongolicus
        • Natronomonas [Nmn.]
          • Natronomonas moolapensis
          • Natronomonas pharaonis (Type species)
        • Natronorubrum [Nrr.]
          • Natronorubrum aibiense
          • Natronorubrum bangense (Type species)
          • Natronorubrum sediminis
          • Natronorubrum sulfidifaciens
          • Natronorubrum tibetense
        • Salarchaeum [Sar.]
          • Salarchaeum japonicum (Type species)
        • Salinarchaeum [Saa.]
          • Salinarchaeum laminariae

Living environment[edit]

Salt ponds with pink colored Haloarchaea

Haloarchaea require salt concentrations in excess of 2 M (or about 10%) to grow, and optimal growth usually occurs at much higher concentrations, typically 20–25%. However, Haloarchaea can grow up to saturation (about 37% salts).

Haloarchaea are found mainly in hypersaline lakes and solar salterns. Their high densities in the water often lead to pink or red colourations of the water (the cells possessing high levels of carotenoid pigments, presumably for UV protection).[4]

Cellular shapes[edit]

Haloarchaea are often considered pleomorphic, or able to take on a range of shapes—even within the one species. This makes identification by microscopic means difficult, and it is now more common to use gene sequencing techniques for identification instead.

One of the more unusually shaped Haloarchaea is the "Square Haloarchaeon of Walsby." It was classified in 2004 using a very low nutrition solution to allow growth along with a high salt concentration, square in shape and extremely thin (like a postage stamp). This shape is probably only permitted by the high osmolarity of the water, permitting cell shapes that would be difficult, if not impossible, under other conditions.

Haloarchaea as Exophiles[edit]

Haloarchaea have been proposed as a kind of life that could live on Mars; since the Martian atmosphere has a pressure below the triple point of water, freshwater species would have no habitat on the Martian surface.[5]

See also[edit]

References[edit]

  1. ^ See the NCBI webpage on Halobacteria. Data extracted from the "NCBI taxonomy resources". National Center for Biotechnology Information. Retrieved 2007-03-19. 
  2. ^ This paragraph taken directly from the Academic Dictionaries and Encyclopedias page on Halobacterium
  3. ^ Minegishi, H., Echigo, A., Shimane, Y., Kamekura, M., Tanasupawat, S., Visessanguan, W., Usami, R. "Halobacterium piscisalsi Yachai et al. 2008 is a subjective junior synonym of Halobacterium salinarum Elazari-Volcani 1957." Int J Syst Evol Microbiol. 2011 Nov 4. [Epub ahead of print]
  4. ^ DasSarma, Shiladitya (2007). "Extreme Microbes". American Scientist 95 (3): 224–231. doi:10.1511/2007.65.1024. ISSN 0003-0996. 
  5. ^ DasSarma, Shiladitya. "Extreme Halophiles Are Models for Astrobiology". Archived from the original on 2007-02-02. Retrieved 2007-03-17. 

Further reading[edit]

Scientific journals[edit]

Scientific books[edit]

  • Grant WD, Kamekura M, McGenity TJ, Ventosa A (2001). "Class III. Halobacteria class. nov.". In DR Boone and RW Castenholz, eds. Bergey's Manual of Systematic Bacteriology Volume 1: The Archaea and the deeply branching and phototrophic Bacteria (2nd ed.). New York: Springer Verlag. p. 169. ISBN 978-0-387-98771-2. 
  • Garrity GM, Holt JG (2001). "Phylum AII. Euryarchaeota phy. nov.". In DR Boone and RW Castenholz, eds. Bergey's Manual of Systematic Bacteriology Volume 1: The Archaea and the deeply branching and phototrophic Bacteria (2nd ed.). New York: Springer Verlag. p. 169. ISBN 978-0-387-98771-2. 

Scientific databases[edit]

External links[edit]