Halophiles are extremophiles that thrive in environments with very high concentrations of salt (at least 2 M, approximately ten times the salt level of ocean water). The name comes from Greek for "salt-loving". Some halophiles are classified into the Archaea kingdom, but there are Bacterial halophiles as well. Some well-known species give off a red color due to the carotenoid compounds in the cell. These species contain the pigment bacteriorhodopsin. Organisms are categorized (slight, moderate, extreme) by the extent of their halophilism. An extremophile is an organism, usually unicellular, which thrives in or requires extreme conditions that would exceed optimal conditions for growth and reproduction in the majority of mesophilic terrestrial organisms. ... A magnified crystal of a salt (halite/sodium chloride) Salt covering the floor of Bad Water in Death Valley, CA, the lowest point in the US. A salt, in chemistry, is any ionic compound composed of cations (positively charged ions) and anions (negative ions) so that the product is neutral... In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. ...

Where Halophiles can be found (in short)

-Anywhere with a concentration of salt 5 times greater than the salt concentration of the ocean
-The Great Salt Lake, Utah
-Owens Lake, California
-The Dead Sea
-May be found on Mars in the Meridiani Plains (a hypthesized dried up salt lake)

What Halophiles do and how they work

Halophiles are found in brine salt which is used to cure animal hides, to dry them out. When the hides are left too long with the brine salt and the Halophiles, the hide will break down and decompose completely.

High salinity represents an extreme environment that relatively few organisms have been able to adapt to and occupy. Most halophilic and all halotolerant organisms expend energy to exclude salt from their cytoplasm to avoid protein aggregation (‘salting out’). In order to survive the high salinities, halophiles employ two differing strategies to prevent desiccation through osmotic movement of water out of their cytoplasm. Both strategies work by increasing the internal osmolarity of the cell. In the first, (that employed by the majority of Bacteria, some Archaea, yeasts, algae and fungi) organic compounds are accumulated in the cytoplasm – these are known as compatible solutes. These can be synthesised again or accumulated from the environment^[1]. The most common compatible solutes are neutral or zwitterionic and include amino acids, sugars, polyols, betaines and ectoines, as well as derivatives of some of these compounds. Halotolerance is the adaptation of living organisms to conditions of high salinity. ... Organelles. ... Salting out is a method of separating proteins based on the principle that proteins are less soluble at high salt concentrations. ... Desiccation is the state of extreme dryness, or the process of extreme drying. ... Osmosis is the net movement of water molecules across a semipermeable membrane from a region of low solute potential to an area of high solute potential (or equivalently, from a region of high solvent potential to a region of low solvent potential). ... Osmolality, in biology and chemistry, is a measure of moles of solute per kg of water. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota Archaea (; from Greek αρχαία, ancient ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), is a major division of living organisms. ... Saccharomyces cerevisiae is a yeast used in both baking and brewing. ... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... An organic compound is any of a large class of chemical compounds whose molecules contain carbon, with exception of carbides, carbonates and carbon oxides. ... The correct title of this article is . ... An amino acid, in its (1) normal (unionized) and (2) zwitterionic forms. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ... This article deals with sugar as food and as an important, widely traded commodity; the word also has other uses; see Sugar (disambiguation) A sugar is a form of carbohydrate; the most commonly used sugar is a white crystalline solid, sucrose; used to alter the flavor and properties (mouthfeel, perservation... Polyols are a catch-all for chemical compounds containing multiple hydroxyl groups. ... A betaine in chemistry is any neutral chemical compound with a positively charged cationic functional group such as an ammonium ion or phosphonium ion (generally: onium ions) and with a negatively charged functional group such as a carboxyl group. ... There are very few or no other articles that link to this one. ...

The second, more radical, adaptation involves the selective influx of K+ ions into the cytoplasm. This adaptation is restricted to the moderately halophilic bacterial Order Halanerobiales, the extremely halophilic archaeal Family Halobacteriaceae and the extremely halophilic bacterium Salinibacter ruber. The presence of this adaptation in three distinct evolutionary lineages suggests convergent evolution of this strategy, it being unlikely to be an ancient characteristic retained in only scattered groups or through massive lateral gene transfer ^[1] . The primary reason for this is that the entire intracellular machinery (enzymes, structural proteins etc) must be adapted to high salt levels, whereas in the compatible solute adaptation little or no adjustment is required to intracellular macromolecules – in fact, the compatible solutes often act as more general stress protectants as well as just osmoprotectants^[1]. General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... Genera Haloalkalicoccus Haloarcula Halobacterium Halobaculum Halobiforma Halococcus Haloferax Halogeometricum Halorhabdus Halorubrum Halosimplex Haloterrigena Natrialba Natrinema Natronobacterium Natronococcus Natronomonas Natronorubrum Note: The word halobacteria is also the plural form of the word halobacterium. The halobacteria (also halomebacteria) are a class of archaea, found in water saturated or nearly saturated with salt. ...

Of particular note are the extreme halophiles or haloarchaea (often known as halobacteria), a group of archaea, which require at least a 2 M salt concentration and are usually found in saturated solutions (about 36% w/v salts). These are the primary inhabitants of salt lakes, inland seas, and evaporating ponds of seawater, such as the Dead Sea and solar salterns, where they tint the water column and sediments bright colors. In other words, they will most definitely perish if they are exposed to anything besides a very high, intense salt-conditioned environment. These prokaryotes require salt for growth. The high concentration of NaCl in their environment limits the availility of oxygen for respiration. Their cellular machinery is adapted to high salt concentrations by having charged amino acids on their surfaces, allowing the retention of water molecules around these components. They are heterotrophs that normally respire by aerobic means. Most halophiles are unable to survive outside their high-salt native environment. Indeed, many cells are so fragile that when placed in distilled water they immediately lyse from the change in osmotic conditions. Haloarchaea are a member of the halophile community, in that they require high salt concentrations to grow. ... Genera Haloarcula Halobacterium Halobaculum Halococcus Haloferax Halogeometricum Halorubrum Haloterrigena Natrialba Natrinema Natronobacterium Natronococcus Natronomonas Natronorubrum The halobacteria are a family of archaea, found in water saturated or nearly saturated with salt. ... Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota Archaea (; from Greek αρχαία, ancient ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), is a major division of living organisms. ... The Dead Sea (Hebrew: ‎; Arabic: ‎) is the Earths lowest point not covered by ice, at 418 m (1371 feet) below sea level and falling[2], and the deepest hypersaline lake in the world, at 330 m (1083 feet) deep. ... Cytolysis is the lysis, or death, of cells due to the rupture of the cell membrane. ...

Haloarchaea, and particularly, the family Halobacteriaceae are members of the domain Archaea, and comprise the majority of the prokaryotic population in hypersaline environments^[2]. There are currently 15 recognised genera in the family^[3]. The domain Bacteria (mainly Salinibacter ruber) can comprise up to 25% of the prokaryotic community, but is more commonly a much lower percentage of the overall population^[4]. At times, the alga Dunaliella salina can also proliferate in this environment^[5]. Phyla / Classes Phylum Crenarchaeota Phylum Euryarchaeota     Halobacteria     Methanobacteria     Methanococci     Methanopyri     Archaeoglobi     Thermoplasmata     Thermococci Phylum Korarchaeota Phylum Nanoarchaeota Archaea (; from Greek αρχαία, ancient ones; singular Archaeum, Archaean, or Archaeon), also called Archaebacteria (), is a major division of living organisms. ...

A comparatively wide range of taxa have been isolated from saltern crystalliser ponds, including members of the following genera: Haloferax, Halogeometricum, Halococcus, Haloterrigena, Halorubrum, Haloarcula and Halobacterium families (Oren 2002). However, the viable counts in these cultivation studies have been small when compared to total counts, and the numerical significance of these isolates has been unclear. Only recently has it become possible to determine the identities and relative abundances of organisms in natural populations, typically using PCR-based strategies that target 16S small subunit ribosomal ribonucleic acid (16S rRNA) genes. While comparatively few studies of this type have been performed, results from these suggest that some of the most readily isolated and studied genera may not in fact be significant in the in-situ community. This is seen in cases such as the genus Haloarcula, which is estimated to make up less than 0.1% of the in situ community^[6] but commonly appears in isolation studies. Wikipedia does not yet have an article with this exact name. ... A Svedberg (symbol S, sometimes Sv) is a non-SI physical unit used in ultracentrifugation. ...

References

1. ^ ^{a b c} Santos, H., and da Costa, M.S. (2002) Compatible solutes of organisms that live in hot saline environments. Environmental Microbiology 4: 501-509.
2. ^ Oren, A. (2002) Molecular ecology of extremely halophilic Archaea and Bacteria. FEMS Microbiology Ecology: 1-7.
3. ^ Gutierrez, M.C., Kamekura, M., Holmes, M.L., Dyall-Smith, M.L., and Ventosa, A. (2002) Taxonomic characterisation of Haloferax sp. ("H. alicantei") strain Aa 2.2: description of Haloferax lucentensis sp. nov. Extremophiles. 2002 Dec;6(6):479-83
4. ^ Anton, J., Rossello-Mora, R., Rodriguez-Valera, F., and Amann, R. (2000) Extremely halophilic bacteria in crystallizer ponds from solar salterns. Applied and Environmental Microbiology 66: 3052-3057.
5. ^ Casamayor, E.O., Massana, R., Benlloch, S., Ovreas, L., Diez, B., Goddard, V.J., Gasol, J.M., Joint, I., Rodriguez-Valera, F., and Pedros-Alio, C. (2002) Changes in archaeal, bacterial and eukaryal assemblages along a salinity gradient by comparison of genetic fingerprinting methods in a multipond solar saltern. Environmental Microbiology 4: 338-348.
6. ^ Anton, J., Llobet-Brossa, E., Rodriguez-Valera, F., and Amann, R. (1999) Fluorescence in situ hybridization analysis of the prokaryotic community inhabiting crystallizer ponds. Environmental Microbiology 1: 517-523.

General References

• DasSarma, S. and P. DasSarma 2006. Halophiles. Encyclopedia of Life Sciences, Wiley, London.
• Madigan, Michael T., and Barry L. Narrs. "Extremeophiles." Scientific American. April 1997: 82-88
  

 www.library.thinkquest.org/CR021089/halo.htm 

See also

• biosalinity
• halotolerance

Biosalinity is the study and practice of using saline (salty) water for irrigating agricultural crops. ... Halotolerance is the adaptation of living organisms to conditions of high salinity. ...

External links

• HaloArchaea.com
• Important Groups of Prokaryotes - Kenneth Todar