halophily

Halophily, or halophilism, is the tendency of organisms to live in or require high salt concentrations. Organisms with halophily are called halophiles. They are found across domains—bacteria, archaea, and some eukaryotes—in hypersaline environments such as salt lakes, salterns, and saline soils, as well as in salted foods and industrial brines. Halophiles range from moderate halophiles that grow best at roughly 3–15% NaCl to extreme halophiles that require more than 15% NaCl for growth.

Two primary osmoregulatory strategies distinguish halophiles. Some adopt a salt-in strategy, accumulating inorganic ions such as K+ and maintaining cellular machinery that functions at high ionic strength. Others use compatible solutes—organic osmolytes like glycine betaine or ectoine—to balance external salinity while keeping intracellular salt concentrations lower. Halophilic archaea, such as many Halobacteriales, often rely on the salt-in mechanism, whereas many halophilic bacteria and some halophilic eukaryotes use compatible solutes. Adaptations include proteins with surfaces adapted to high salt and membranes that withstand high ionic conditions.

Prominent halophiles include the archaeal genera Halobacterium and Haloferax; bacteria such as Salinibacter ruber and Halomonas species; and the alga Dunaliella salina. Due to their salt stability, halophiles have biotechnological potential for salt-tolerant enzymes, bioremediation of saline waste streams, and the production of compatible solutes, as well as for informing studies of life in extreme environments and the limits of habitability.