What Lives in Water Four Times Saltier Than the Sea? Quite a Lot
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Organisms that require high salt to grow fill salt lakes and salt pans, turn them pink, and solve a problem that would kill almost anything else within minutes.
The problem salt creates
Water moves across a membrane from where dissolved material is dilute towards where it is concentrated, so a cell in very salty water loses water outward, shrinks and stops working, which is why salting preserves food and why drinking seawater is fatal. Any organism living in brine must therefore balance the concentration inside its cells against the outside, and there are only two ways to do that. It can accumulate salt inside to match, which requires every protein in the cell to work in concentrated salt. Or it can accumulate some other soluble substance instead, which is less disruptive and costs energy to make.
The two solutions
Both strategies exist and they suit different lifestyles:
- •Accumulating potassium salt inside to match the outside
- •That requires proteins rebuilt to function in high salt
- •Those organisms cannot survive in fresh water at all
- •Accumulating compatible solutes such as glycerol instead
- •Those proteins work normally and the cell tolerates a range
- •The second is more flexible and more expensive to run
Why salt lakes turn pink
The colour of a hypersaline lake or a commercial salt pan comes directly from the organisms in it. Certain salt-loving microbes produce large quantities of red and orange pigments that protect them from intense sunlight and, in one group, also act as a light-driven pump that moves ions across the membrane and supplies energy without any need for chlorophyll. A brine shrimp species grazing on them concentrates the same pigments and turns pink itself, and flamingos eating the shrimp become pink by the same route, which is why the colour propagates all the way up a very short food chain.
Where they actually live
The habitats are more varied than salt lakes and several of them are made by people. Natural sites include the Dead Sea, Great Salt Lake, the salt lakes of the Andes and Antarctica, and deep brine pools on the sea floor where salt deposits have dissolved into dense layers that do not mix with the water above. Solar salt works, where seawater is evaporated in shallow ponds, are effectively cultivated habitats and are where most commercial study happens. Salted fish, hides and other preserved foods are colonised by the same organisms, which is a spoilage problem rather than a curiosity. And salt deposits deep underground hold them in fluid trapped inside crystals.
Why they are studied
Interest in these organisms runs well beyond the lakes they live in. Their enzymes function in conditions that destroy ordinary ones, which makes them useful in industrial processes involving high salt or low water. The light-driven ion pump has become a standard tool in neuroscience, inserted into nerve cells so that they can be switched on or off with light, which is the basis of a widely used experimental technique. They are studied as models for life in conditions found elsewhere in the solar system, since brines are among the likelier places liquid water persists. And some have been recovered, contentiously, from salt deposits hundreds of millions of years old.
The takeaway
A cell in brine loses water outward unless it balances the concentration inside, and it does that either by filling with potassium salt, which requires every protein rebuilt to work in salt, or by making a compatible substance instead, which is flexible and costly. Pigments protecting them from sunlight turn salt lakes pink, and that colour passes to brine shrimp and then to flamingos.