halophiles

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 domain, but there are also bacterial halophiles and some eukaryota, such as the alga Dunaliella salina. Some well-known species give off a red color from carotenoid compounds. Such species contain the photosynthetic pigment bacteriorhodopsin. Halophiles are categorized slight, moderate or extreme, by the extent of their halotolerance.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