Halophilic Bacteria

In late summer you see scattered (and sometimes extensive) pinkish-brown to deep red muddy salt flats on Owens Lake under the hot desert sun. Near the abandoned Pittsburgh Plate Glass soda ash plant (the northwestern end of the lake) and else where on the fringes of the playa, solar evaporation ponds may be colored almost blood red.
Pink salt lakes and playas, and the bright red evaporation ponds of salt recovery plants along their shores, occur in arid regions throughout the world. The red coloration is caused by countless salt loving micro-organisms thriving in the briny water and damp salt crust.
Near the end of the last ice age (Pleistocene Epoch, circa 11,000 years ago) Owens Lake was hundreds of feet deep and covered hundreds of square miles. During thousands of years of evaporation these desert lakes mostly dried up, leaving enormous quantities of alkali salts lying in vast salt flats.
Some of these dry lake basins have become a rich scorce of chemicals. At Searles Lake, southeast of Owens Valley, mineral-rich brine is pumped to the large Kerr-McGee Chemical Plant, where where potash, borax and other minerals are recovered.
Before the Owens River was diverted by the Los Angeles Aqueduct in 1913, Owens Lake was a deep salty lake (over 100 square miles) with steamships shuttling between two busy ports.
Owens Lake has for the most part become a playa, an intermittently dry lake bed, which may hold considerable amounts of shallow water during wet years. Even when the lake appears bone dry, a layer of brine may be just beneath the thin hard crust.
Brine fly pupæ (ephydra), common insects of saline ponds and lakes, were an important part of the diet of the local Paiute Indians. (These pupæ, resembling grains of rice, occur in enormous numbers and can still be found around the shoreline where they feed upon the lake bacteria and are fed upon by migratory water fowl.)
But what makes the water turn red, like Moses and the Red Sea?
It is not just because of the chemicals in the water.
The deep red color is caused by tiny salt-loving bacteria, halobacteria. One drop of this brine contains millions of the rod-shaped cells. The bacteria produce a red carotenoid pigment, similar to that found in tomatoes. (Flamingo birds get the carotenoid pigment in their plummage from their diet of shrimp and other crustaceans.)
(In some parts of the world B-carotene is extracted commercially from salt ponds containing red salt tolorant bacteria and algæ.)
There are two main kinds of extreme salt-loving bacteria, the rod-shaped halobacteria and the spherical halococci. These are uni-cellular organisms, visible only under high magnification. These little critters are found in salt lakes around the world, including the Great Salt Lake and the Dead Sea.
These bacteria require a salinity at least three or four times that of sea water. The cells themselves contain a internal salt concentration (primarily potassium and sodium), equal to or higher than their environment. Otherwise, they would be rapidly dehydrated (plasmolyzed) in the brine. It has also been shown that the highly saline environment is essential for normal enzyme function within the cells, and to maintain the fragile protein coating around the cell membrane. (If the salt concentration drops too low, the outer protein wall dissolves and the inner cell membrane disintegrates, thus destroying the cell.
Halobacteria can thrive in concentrated brine nine times the salinity of sea water, and can even remain alive in dry salt crystals for years. Their extreme tolerance for ordinary table salt (sodium chloride) makes them a health hazard for companies using solar evaporation ponds for the production of sea salt. Sea salt is sometimes contaminated with these organisms, and they occasionally cause spoilage of fish, meats, vegetables and hides when salt has been used in the preservation process. They may also cause an unsightly discoloration of pickled foods known as "pinkeye" in salted fish.
Halobacteria are part of the arcæbacteria group, unusual bacteria that survive some of the most extreme conditions on earth. Some biologists claim these bacteria should be placed in their own Kingdom, Archæbacteria (separate from the Kingdom Monera, which includes most of the true bacteria.) Heat-loving thermophilic archæbacteria have been found at the bottom of the ocean near sulfur vents where the water temperature is hotter than boiling and there is no free oxygen. Though little muthers!
The salt crust and brine of Owens Lake is also sometimes greenish, due to the abundance of another organism, dunaliella salina. This is a uni-cellular green alga, much larger than the bacteria, though also visible only under high magnification. Dunaliella is clearly a green alga, having a distinctly green, cup-shaped chloroplast that occuping most of the cell and it is what brine shrimp feed on.
In nearby Searles Lake (see the town of Trona, to the southeast) dunaliella and the closely related species stephanoptera may be so abundant that they color the salt crust and brine a bright green. In Searles Lake they thrive in water with 33 percent dissolved salts. In solar evaporation ponds at Trona, dunaliella sometimes forms a thick green "pea soup." One drop of this thick water may contain several thousand individuals of dunaliella. In contrast to the halobacteria, a high osmotic concentration within the cells of dunaliella is produced by a very high concentration of glycerol molecules instead of by salt ions. Under less than favorable conditions, dunaliella produces a red carotenoid pigment similar to that found inside the halophilic bacteria. The red pigment may completely mask the green of its chloroplast, and salt lakes throughout the world may be colored reddish by dense populations of this organism.
Another smaller, unicellular green alga, dangeardinella saltitrix, also thrives in the brine of Owens Lake. Like the halobacteria it can survive in solid salt crust.
The distribution of halobacteria and halophilic algae, such as dangeardinella and dunaliella, in highly saline habitats throughout the world is evidence that their dormant cells may be dispersed by the wind in the form of dust clouds. (Huge alkali dust clouds are a common sight over the Owens Lake playa.)
Another alga related to dunaliella lives in snow banks. It is called "snow algæ" and is known technically as chlamydomonas nivalis. The individual cells are bright red, and from a distance the snow appears pink, remarkably like cotton candy. This WM contributor has seen such pink colored late-summer snow banks at the Barcroft research station (in the nearby White Mountains) at an elevation of 12,500 feet.
The pigment (bacteriorhodopsin) in salt-loving bacteria enables them to utilize sunlight for energy, even as green colored chlorophyl in photosynthetic plants are able to capture the sun's energy.
For more technical details, see
science.nasa.gov/headlines/y2004/10sep_radmicrobe.htm