Halotolerance

Halotolerance refers to the ability of an organism to survive and often grow in higher-than-normal salt concentrations. The term is most commonly used in microbiology, where organisms may be described as halotolerant or halophilic. Halotolerant organisms can tolerate elevated salinity without requiring it, while halophiles either require or prefer salt for growth. Within halophiles, ranges are often described as moderate (roughly 3–14% NaCl) and extreme (15–30% NaCl). Some classifications also distinguish stenohaline from euryhaline species: stenohaline tolerate only a narrow salinity range, whereas euryhaline tolerate a broad range.

Mechanisms: to cope with osmotic stress, halotolerant and halophilic organisms employ strategies such as accumulation of compatible solutes (glycine betaine, proline, trehalose) to balance intracellular osmolarity, or salt-in strategies in which intracellular ions are maintained at high concentrations, stabilized by specialized proteins and enzymes. Membrane transporters such as Na+/H+ antiporters and K+ channels help regulate ion homeostasis. Protein structures and DNA repair mechanisms also adapt to high-salt environments. Halophiles of the salt-in type are often found among Archaea, whereas many halotolerant eubacteria and fungi use compatible solutes.

Examples: bacteria like Staphylococcus aureus and Bacillus species display halotolerance; halophilic archaea such as Halobacterium species; algae such as Dunaliella salina; halophyte plants such as Salicornia and Spartina occupy coastal and saline habitats.

Ecology and applications: halotolerance enables life in saline environments including salt marshes, saline soils, and desalination byproducts; it is exploited in biotechnological processes and bioremediation, and informs food preservation and shelf life of salted products.