Haloferax volcanii

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Haloferax volcanii
Scientific classification
Domain: Archaea
Kingdom: Euryarchaeota
Phylum: Euryarchaeota
Class: Halobacteria
Order: Halobacteriales
Family: Methanobacteriaceae
Genus: Haloferax
Binomial name
Haloferax
Torreblanca et al. 1986
Species
  • H. alexandrinus
  • H. denitrificans
  • H. elongans
  • H. gibbonsii
  • H. larsenii
  • H. lucentense
  • H. mediterranei
  • H. mucosum
  • H. prahovense
  • H. sulfurifontis
  • H. volcanii

In taxonomy, Haloferax volcanii is a species of organism in the genus Haloferax in the Archaea.

Description and significance

Haloferax volcanii is a species of halophile which exists in extreme saline environments. Recently an isolate of this species was studied by researchers at University of California, Berkeley, as part of a project on the survival of haloarchaea on Mars. Like other halophiles, H. volcanii has been isolated in high-saline environments, most commonly the Dead Sea, the Great Salt Lake, and oceanic environments with high sodium chloride concentrates.

Genome structure

The genome of H. volcanii consists of a large (4 Mb), multicopy chromosome and several megaplasmids.

The genome has been completely sequenced and a paper discussing it was published in 2010.[1] The molecular biology of H. volcanii has been extensively studied for the last decade in order to discover more about DNA replication, DNA repair and RNA synthesis. The archaeal proteins used in these processes are extremely similar to Eukaryotic proteins and so are studied primarily as a model system for these organisms. H. volcanii undergoes prolific horizontal gene transfer through a mechanism of "mating"- cell fusion.

Cell structure and metabolism

Reproduction among H. volcanii occurs asexually by binary fission. This practice is similar to that of other Archaea and, indeed, that of bacteria.

H. volcanii cells have no cell wall and, like many archaea, therefore use their exterior S-layer for structure. They are typically recognisable by their 'dished crisp' shape, but are somewhat pleiomorphic so may be seen in other shapes including coccoid.
Haloferax volcanii grown in laboratory conditions and imaged using a phase contrast microscope. Cells were mounted on an agar pad.
The membranes of this organism are made of the typical ether linked membrane lipids found solely in archaea and also contain a high level of carotenoids including lycopene, which gives them their distinctive red colour.

H. volcanii use a salt in method to maintain osmostasis, rather than the typical compatible solutes method seen in bacteria. This method involves the maintenance of a high degree of potassium ions in the cell to balance the sodium ions outside. For this reason H. volcanii has a complex ion regulation system and is chemoautotrophic.

Due to the salt in method cytoplasmic proteins are structured to fold in the presence of high ionic concentrations. As such they typically have a large number of charged residues on the exterior section of the protein and very hydrophobic residues forming a core. This structure increases their stability in saline and even high temperature environments considerably, but comes at some loss of processivity compared to bacterial homologs.

H. volcanii respire as their sole source of ATP, unlike several other halobateriacae, such as Halobacterium salinarium they are incapable of photphosphorylation as they lack the necessary bacterioruberin.

Ecology

Isolates of H. volcanii are commonly found in high-salinity aquatic environments, such as the Dead Sea. Their precise role in the ecosystem is uncertain, but the carbohydrates contained within these organisms potentially serve many practical purposes. Because of their ability to maintain homeostasis in spite of the salt around them, H. volcanii could be an important player in advancements in biotechnology. As it is likely that H. volcanii and comparable species are ranked among the earliest living organisms, they also provide information related to genetics and evolution.[2]

DNA damage and repair

In prokaryotes the DNA genome is organized in a dynamic structure, the nucleoid, which is embedded in the cytoplasm. Exposure of Haloferax volcanii to stresses that damage the DNA cause compaction and reorganization of the nucleoid.[3] Compaction depends on the Mre11-Rad50 protein complex that is employed in the homologous recombinational repair of DNA double-strand breaks.[3] proposed that nucleoid compaction is part of a DNA damage response that accelerates cell recovery by helping DNA repair proteins to locate targets, and by facilitating the search for intact DNA sequences during homologous recombination.

See also

References

  1. ↑ Hartman AL, Norais C, Badger JH, Delmas S, Haldenby S, Madupu R, Robinson J, Khouri H, Ren Q, Lowe TM, Maupin-Furlow J, Pohlschroder M, Daniels C, Pfeiffer F, Allers T, Eisen JA. 2010. The complete genome sequence of Haloferax volcanii DS2, a model archaeon. PLoS ONE 5(3): e9605. PMID 20333302
  2. ↑ See the NCBI webpage on Haloferax. Data extracted from the "NCBI taxonomy resources". National Center for Biotechnology Information. Retrieved 2007-03-19. 
  3. ↑ 3.0 3.1 Delmas S, Duggin IG, Allers T. (2013). DNA damage induces nucleoid compaction via the Mre11-Rad50 complex in the archaeon Haloferax volcanii. Mol Microbiol 87(1):168-79. doi: 10.1111/mmi.12091. PMID 23145964

Further reading

Scientific journals

  • Oren A, Ventosa A (2000). "International Committee on Systematic Bacteriology Subcommittee on the taxonomy of Halobacteriaceae. Minutes of the meetings, 16 August 1999, Sydney, Australia". Int. J. Syst. Evol. Microbiol. 50: 1405–1407. PMID 10843089. 
  • Torreblanca M, Rodriquez-Valera F, Juez G, Ventosa A, Kamekura M, Kates M (1986). "Classification of non-alkaliphilic halobacteria based on numerical taxonomy and polar lipid composition, and description of Haloarcula gen. nov. and Haloferax gen.nov". Syst. Appl. Microbiol. 8: 89–99. 

Scientific books

  • Gibbons, NE (1974). "Family V. Halobacteriaceae fam. nov.". In RE Buchanan and NE Gibbons, eds. Bergey's Manual of Determinative Bacteriology (8th ed.). Baltimore: The Williams & Wilkins Co. ISBN 0-683-01117-0. 

Scientific databases

External links

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