As halophiles or halo -tolerant ( derived from the Greek hals, halos = salt) are referred to organisms that live in environments with high salt concentration. Applies not only salt, but also any other mineral salt as salt.

Halophiles (ie " salt -loving " ) organisms are adapted to high salt concentrations, it can adjust or die their growth when the salinity drops below a certain threshold. Depending on the degree of adaptation to different Halophiles weak, moderate or extreme.

Halo -tolerant (ie " salt -enduring " ) organisms thrive in principle, also in a low-salt environment. However, they are often weak competitive and are displaced in saline habitats. Due to their ability to adapt to higher salt concentrations, they can occupy ecological niches here.


Characteristic of all habitats with increased salinity is a reduced water activity. Water here is bound by soluble salts and can be held only by special adaptations in the cell body. In addition, high ion concentrations have a detrimental effect on metabolic processes. Such environments form as salt lakes, saline evaporation ponds, coastal strip, but also small-scale sites such as the surface of desert plants. The salinity of these habitats varies and can reach a saturated ( 30 percent ) saline. The salt composition of the individual sites may, however, differ considerably: Is the salinity thalassohaliner locations largely determined by sodium chloride, so many athalassohaline salt lakes are rich in calcium, magnesium and carbonate. In this case, the so-called soda lakes, leads to the high pH value that living organisms here are also alkaliphilic or alkali- tolerant. In addition, the salinity may be subject to continuous or abrupt changes, such as the drying up of a lake, in the mixing of water masses in estuaries, tidal zones or during heavy rains.


If the salt concentration in the environment of an organism higher or lower than in the cell body, it always forces an adjustment, for different salt concentrations are always striving to equalize. But only water can diffuse between the cell interior and the surrounding area; Salt ions can overcome cell membranes difficult. This leads to the following situation: If the concentration in the environment of low, water diffuses into the cell. This is for example in habitat " freshwater " of the case, the environment is hypoosmotic. If the concentration is higher, the body loses water. This is for example the case in salt lakes, where the environment is hyperosmotic. In both cases there is a change in salt concentration within the organism. Life processes are, however, always to a certain availability of water - bound in the cell - and thus at certain salt concentrations. Therefore Almost all organisms actively regulate their internal salt concentration.

Multicellular organisms that live in a hyperosmotic environment, have developed for this specific organs, such as salt glands or kidneys.

Halo -tolerant and halophilic unicellular achieve adaptation by two different strategies:

  • The first possibility is the inclusion of the inorganic salts in the cytoplasm ( "salt -in" strategy).

This variant is mainly found in halophilic protozoa. Their life processes (ie especially their enzymes ) are adapted to high salt concentrations that their functionality is lost with decreasing salt concentration.

  • The second possibility is the accumulation of organic compounds inside the cell, referred to as compatible solutes or Osmoprotektanten ( " Organic osmolytes " strategy ).

This variant prefer halotolerant unicellular. Increasing the salt concentration in the environment, the cell produces osmotically active organic substances ( for example, certain carbohydrates, amino acids, polyols, betaines and ectoines ). These small molecules are similar salts readily soluble in water and produce the same osmotic effect. However, they affect cell metabolism non-negative.

Extreme halophiles

Halophilic and halotolerant organisms are found in all domains of life. However, the successful colonization of the most saline habitats remains single-celled organisms such as bacteria, archaea and some algae reserved. Some of these single-celled organisms were found unusual and unprecedented cell lines, namely, three - and four square cells.

Extremely halophilic unicellular organisms live in salt lakes, salt pans or pickled foods. Even in saturated sodium chloride solution (5 mol / l NaCl), certain archaea live, but grow slowly. These microorganisms live mostly aerobic or phototrophic chemoorganotroph - that carry out photosynthesis. Some of these phototrophic unicellular organisms use light by bacteriorhodopsin for the outward proton transport. The resulting proton gradient across the cell membrane may be used for ATP synthesis. This process represents a simple and probably original form of photosynthesis

Phototrophic halophilic unicellular organisms are the cause of the intense color that have salt and soda lakes or sea salt works. The pigments of these organisms are so highly concentrated that they virtually walk through the entire food chain: color halophilic crustaceans that feed on the microorganisms and, finally, the Flamingos, in turn, eat the crabs.

Extreme environments are often poor in species. This is also true for sites with high salt concentrations. However, an exception to the alkaline soda lakes: Although they are also species-poor, but extremely rich in individuals. So you have next to estuaries and reefs about the highest rate of biomass production and among the most productive ecosystems in the world.

Some genera of halophilic unicellular organisms:

  • Prokaryotes: Halobacterium Halococcus, Ectothiorhodospira, Halorhodospira, Haloanaerobium, Halobacteroides
  • Eukaryotes: Dunaliella

Halobacterium noricense and various Halococcus were salifodinae among others found in Bad Ischl salt mine and salt mine Altausee.

Haloquadratum walsbyi ( " salt Square" ) is a species of the genus in the family of Haloquadratum Halobacteriaceae is adapted to high salt concentrations. Green and flat square it optimizes photosynthesis by floating and dominated world in basins in which seawater thickens for salt extraction, before a rise in magnesium chloride concentration in the liquid phase dies every life.