Halophiles

Abstract Halophiles, salt‐loving organisms that flourish in saline environments, are classified as slight, moderate or extreme, depending on their requirement for sodium chloride. While most marine organisms are slight halophiles, moderate and extreme halophiles are generally more specialised microbes inhabiting hypersaline environments found all over the world in arid, coastal and deep‐sea locations, underground salt mines and artificial salterns. Halophilic microorganisms include heterotrophic, phototrophic and methanogenic archaea, photosynthetic, lithotrophic and heterotrophic bacteria and photosynthetic and heterotrophic eukaryotes. Examples of extremely halophilic microorganisms include Halobacterium sp. NRC‐1, an archaeon; Aphanothece halophytica , a cyanobacterium; and Dunaliella salina , a green alga. Common multicellular halophilic eukaryotes include brine shrimp and brine fly larvae that serve as an important food source for birds. In order to balance the osmotic stress of hypersaline environments, halophilic microorganisms either accumulate organic compatible solutes internally, produce acidic proteins to increase solvation and improve function in high salinity, or use a combination of strategies. Key Concepts Halophiles are salt‐loving organisms that inhabit saline and hypersaline environments and include prokaryotic (archaeal and bacterial) and eukaryotic organisms. Halophiles may be classified as slight, moderate or extreme, and as obligate halophiles or halotolerant. Many halophiles accumulate compatible solutes in cells to balance the osmotic stress in their environment. Some halophiles produce acidic proteins that function in high salinity by increasing solvation and prevent protein aggregation, precipitation and denaturation. Halophiles and their biomolecules are useful for applications in biotechnology, medicine and industry.