<P> Halophiles are organisms that thrive in high salt concentrations . They are a type of extremophile organisms . The name comes from the Greek word for "salt - loving". While most halophiles are classified into the Archaea domain, there are also bacterial halophiles and some eukaryota, such as the alga Dunaliella salina or fungus Wallemia ichthyophaga . Some well - known species give off a red color from carotenoid compounds, notably bacteriorhodopsin . Halophiles can be found anywhere with a concentration of salt five times greater than the salt concentration of the ocean, such as the Great Salt Lake in Utah, Owens Lake in California, the Dead Sea, and in evaporation ponds . </P> <P> Halophiles are categorized as slight, moderate, or extreme, by the extent of their halotolerance . Slight halophiles prefer 0.3 to 0.8 M (1.7 to 4.8%--seawater is 0.6 M or 3.5%), moderate halophiles 0.8 to 3.4 M (4.7 to 20%), and extreme halophiles 3.4 to 5.1 M (20 to 30%) salt content . Halophiles require sodium chloride (salt) for growth, in contrast to halotolerant organisms, which do not require salt but can grow under saline conditions . </P>

Halophiles require what in high concentrations for growth