Haloarchaea

"Halobacteria" redirects here. For the genus, see Halobacterium.
Haloarchaea
Halobacterium sp. strain NRC-1, each cell about 5 µm in length.
Scientific classification
Domain: Archaea
Kingdom: Archaea
Phylum: Euryarchaeota
Class: Halobacteria
Grant et al. 2002
Order
Synonyms
  • Halomebacteria Cavalier-Smith 2002
  • Haloarchaea

In taxonomy, the Halobacteria (also Halobacteriacea) 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. 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 which it uses to transform light energy into chemical energy by a process unrelated to chlorophyll-based photosynthesis.

Taxonomy

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 May 2016, the family Halobacteriaceae comprises 50 genera 213 species.

Domain : Archaea

Euryarchaeota

non-valid

Classification of Gupta et al.[11][12]

Halobacteriales

　　

Haladaptatus, Halalkalicoccus, Haloarchaeobius, Halarchaeum, Halobacterium, Halocalculus, Halorubellus, Halorussus, "Halosiccatus", Halovenus, Natronoarchaeum, Natronomonas, Salarchaeum.

　　

Halapricum, Haloarcula, Halomicroarcula, Halomicrobium, Halorientalis, Halorhabdus, Halosimplex.

　　

Halococcus.

Haloferacales

　　

Halabellus, Haloferax, Halogeometricum, (Halogranum), Halopelagius, Haloplanus, Haloquadratum, Halosarcina.

　　

Halobaculum, (Halogranum), Halohasta, Halolamina, Halonotius, Halopenitus, Halorubrum, Salinigranum.

Natrialbales

　　

Halobiforma, Halopiger, Halostagnicola, Haloterrigena, Halovarius, Halovivax, Natrialba, Natribaculum, Natronobacterium, Natronococcus, Natronolimnobius, Natronorubrum, Salinarchaeum.

Living environment

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).[13]

Phototrophy in haloarchaea

Bacteriorhodopsin is used to absorb light, which provides energy to transport protons (H+) across the cellular membrane. The concentration gradient generated from this process can then be used to synthesize ATP. Many haloarchaea also possess related pigments, including 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.[14]

Cellular shapes

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

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.[15]

See also

References

  1. ↑ See the NCBI webpage on Halobacteria. Data extracted from the "NCBI taxonomy resources". National Center for Biotechnology Information. Retrieved 2007-03-19.
  2. ↑ Minegishi, H., Echigo, A., Shimane, Y., Kamekura, M., Tanasupawat, S., Visessanguan, W., Usami, R. (2012) "Halobacterium piscisalsi Yachai et al. 2008 is later heterotypic synonym of Halobacterium salinarum Elazari-Volcani 1957." Int J Syst Evol Microbiol. 62: 2160-2162
  3. ↑ Ugalde JA, Narasingarao P, Kuo S, Podell S, Allen EE. (2013) Draft Genome Sequence of "Candidatus Halobonum tyrrellensis" Strain G22, Isolated from the Hypersaline Waters of Lake Tyrrell, Australia. Genome Announc. 12;1(6).
  4. ↑ Filker S, Kaiser M, Rosselló-Móra R, Dunthorn M, Lax G, Stoeck T. (2014) "Candidatu Haloectosymbiotes riaformosensis" (Halobacteriaceae), an archaeal ectosymbiont of the hypersaline ciliate Platynematum salinarum. Syst Appl Microbiol. 37(4):244-251.
  5. ↑ Hassani II, Robert C, Michelle C, Raoult D, Hacène H, Desnues C. (2013) Non-contiguous finished genome sequence and description of Halopiger djelfamassiliensis sp. nov.Stand Genomic Sci. 9(1):160-174.
  6. ↑ Ikram HI, Catherine R, Caroline M, Didier R, Hocine H, Christelle D. (2014) Non-contiguous finished genome sequence and description of Halopiger goleamassiliensis sp. nov.Stand Genomic Sci. 9(3):956-959.
  7. ↑ McDuff S, King GM, Neupane S, Myers MR. (2016) Isolation and characterization of extremely halophilic CO-oxidizing Euryarchaeota from hypersaline cinders, sediments and soils, and description of a novel CO oxidizer, Haloferax namakaokahaiae Mke2.3T, sp. nov.FEMS Microbiol Ecol. 92(4).
  8. ↑ Sánchez-Nieves R, Facciotti MT, Saavedra-Collado S, Dávila-Santiago L, Rodríguez-Carrero R, Montalvo-Rodríguez R. (2016) Draft genome sequence of Halorubrum tropicale strain V5, a novel halophilic archaeon isolated from the solar salterns of Cabo Rojo, Puerto Rico. Genom Data. 6;7:284-286.
  9. ↑ Sánchez-Nieves R, Facciotti MT, Saavedra-Collado S, Dávila-Santiago L, Rodríguez-Carrero R, Montalvo-Rodríguez R. (2016) Draft genome of Haloarcula rubripromontorii strain SL3, a novel halophilic archaeon isolated from the solar salterns of Cabo Rojo, Puerto Rico. Genom Data. 6;7:287-289.
  10. ↑ Jaakkola ST, Pfeiffer F, Ravantti JJ, Guo Q, Liu Y, Chen X, Ma H, Yang C, Oksanen HM, Bamford DH.(2016) The complete genome of a viable archaeum isolated from 123-million-year-old rock salt. Environ Microbiol. 18(2):565-579.
  11. ↑ Gupta, R.S., Naushad, S., Baker, S. (2015) CPhylogenomic analyses and molecular signatures for the class Halobacteria and its two major clades: a proposal for division of the class Halobacteria into an emended order Halobacteriales and two new orders, Haloferacales ord. nov. and Natrialbales ord. nov., containing the novel families Haloferacaceae fam. nov. and Natrialbaceae fam. nov.." Int J Syst Evol Microbiol. 65: 1050-1069
  12. ↑ Gupta RS, Naushad S, Fabros R, Adeolu M. (2016) "A phylogenomic reappraisal of family-level divisions within the class Halobacteria: proposal to divide the order Halobacteriales into the families Halobacteriaceae, Haloarculaceae fam. nov., and Halococcaceae fam. nov., and the order Haloferacales into the families, Haloferacaceae and Halorubraceae fam nov." Antonie Van Leeuwenhoek. 2016 Feb 2. [Epub ahead of print]
  13. ↑ DasSarma, Shiladitya (2007). "Extreme Microbes". American Scientist. 95 (3): 224–231. doi:10.1511/2007.65.1024. ISSN 0003-0996.
  14. ↑ This paragraph taken directly from the Academic Dictionaries and Encyclopedias page on Halobacterium
  15. ↑ DasSarma, Shiladitya. "Extreme Halophiles Are Models for Astrobiology" (PDF). Archived from the original (PDF) on 2007-02-02. Retrieved 2007-03-17.

Further reading

Scientific journals

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External links

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