Halophiles are organisms that inhabit environments with high concentrations of salt. Depending on the salt concentrations in their environment, halophiles can be grouped as extreme halophiles which can survive in areas with salinity as high as 35% and moderate halophiles. Moreover, there are some halophiles that survive in habitats that are slightly saline hence are halotolerant. They are found in a variety of extreme salt concentrations including salt marshes, subterranean salt deposits, dry soil, and hypersaline seas and oceans. Some halophiles also inhabit salted meats and evaporation pools. Water is the most important fluid in all biological systems thus its levels in such systems must be maintained (DasSarma & Arora, 1999). The greatest challenge these organisms face is maintaining an internal osmotic potential that balances out with that of the environment. Failure to achieve this, water will move osmotically from the cell(s) of the halophiles into their habitat. The resulting loss of water would lead to plasmolysis as the cell protoplasm would shrink and move away from the cell wall. However, halophiles have devised physiological strategies which allow them to survive the osmotic stress and also enable them to function maximally in hypersaline habitats. These organisms have membrane mechanisms and special glands which enable them to survive in hypersaline conditions.
Halophiles have a proton pump in their membranes which helps in the movement of protons across their cell membranes. This pump works when the membrane proteins undergo conformational changes and protons are actively transported across the membrane leading to high concentrations of protons in the cell and low concentrations of protons in the cell. The concentration gradient established creates an electrochemical potential that enables these organisms to pump substances in and of their cells to maintain their osmotic potential. The Na/H antiporter is a protein on the cell membrane of the halophiles which enables them to transport sodium ions in and out of the cells. High concentrations of sodium ions inside cell would trigger the active pumping of the sodium ions through the cell membrane via the antiporter protein which undergoes conformational changes to release the ions to the environment. Moreover, halophiles have a Na/K pump located in their plasma membrane which pumps in two potassium ions for every three sodium ions pumped out of their cells. The resulting charge creates a resting membrane potential within the cells leading to low concentrations of sodium ions in the cell thereby enabling them organisms to survive in the hypersaline environments. This also enables the organisms to take in such solutes as sugars, glycerol, amino acids, and their derivatives required for their biological functions (Santos, & Costa, 2002).
Some halophiles such as some species of Halococcus have chlorine pumps that actively pumps chlorine into the organisms. The potential created prevents the movement of sodium ions into the cell due to the presence of negatively charged ions in the cell. The chloride ions are retained within the cells thereby maintaining an osmotic balance with the hypersaline environment. In addition, some eukaryotic halophiles such as mangroves and marine birds have salt secreting glands that produce sodium chloride in solution in response to an osmotic imbalance resulting from feeding, mineral, or water intake (Stan-Lotter et al 2002). For these pumps and protein channels to work, signal transduction is required. The proton, Na/K, chlorine pumps, and Na/H antiporter will only work when either of the ions or protons activates the cell surface receptors such as integral transmembrane proteins. It is the reception of these signals and their transduction to the cell nucleus that enables the Na/H antiporter protein to undergo conformational changes within the cell membrane layers of fatter acid, integral proteins, and fatty acid among others to deliver the molecules being transported to the other side of the cell (Reece & Campbell 2002).
In conclusion, extremophiles including halophiles are unique due to their choice of habitats with extreme conditions. They are well adapted to these extreme conditions as they modified their physiology and behaviors to suit the conditions. Halophiles have various physiological adaptations including ion pumps and glands to enable them to survive in their habitats.
References
DasSarma, Shiladitya, & Arora, Paul. (1999). Halophiles. Nature Encyclopedia of Life Sciences. London: Nature Publishing Group.
Reece, Jane, & Campbell, Neil. (2002). Biology. San Francisco: Benjamin Cummings.
Santos, Henry, & Costa, M.S. (2002). Compatible solutes of organisms that live in hot saline environments. Environmental Microbiology 4: 501-509.
Stan-Lotter, Helga. et al. (2002). Halococcus dombrowkii sp. nov., an archaeal isolate from a Permian alpine salt deposit. International Journal of Systematic and Evolutionary Microbiology 52: 1807-1814.