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Hostile conditions: Ectoine helps bacteria to survive in saline environments
In an environment where the air shimmers and the noontime temperature of 60 degrees Celsius drops to zero degrees at night, where the air humidity is an arid five percent and the salt eats away at everything, it is difficult for a human being to survive. Animals too avoid this little patch of the earth, the salt lakes of Wadi Natrun not far from the Egyptian capital of Cairo. Within a brief time, any unprotected creature, any plant would dry out and be buried in the salty sand blowing over this barren terrain. Bacteria are the only life forms to have found a home here, where they have lived for millions of years in the harshest conditions on earth. In the 1980s, the secret of their survival became known to researchers, who turned it to use for humanity at the start of the new millennium. Ectoin is the substance with which the bacteria known as Halorhodospira halochloris protect their cells from drying out. It is a "compatible solute" produced under stress conditions. It can therefore prevent the cells in the skin from drying out in just such a condition of stress—and thereby prevent wrinkles and other skin damage.
In search of the unknown
"A skin cell has the same problem as the bacterium in a salt lake, namely the scarcity of available water. A cell that lives in an ecosystem with a high concentration of salt is compelled to influence osmosis in its favor, because otherwise it would dry out. It must be able to retain the water," says Volker Müller, professor of Molecular Microbiology and Bioenergetics at Frankfurt University. He has made a hobby of these salt-loving bacteria that live under the most extreme conditions. "As the organ of the human body with the largest surface area, the skin is constantly losing water to evaporation. With ectoin, we can now give the skin cells something that allows them to retain the water."
And not only the unicellular organisms of Wadi Natrun produce ectoin; many halophilic (salt-loving) bacteria use this solute to help them survive in the most inhospitable regions—in salt works, salt marshes or soda lakes. Although their existence has been known for over a hundred years, researchers were for a long time ignorant of their survival strategy. The discovery of ectoin was due entirely to the keen instincts of the researchers, says Müller; it was "a real stroke of good fortune." One reason is that you can only search for something if you know what it is. But ectoin has a special structural characteristic that makes it very difficult to detect chemically. Extracting the substance initially proved just as difficult as its discovery. At first, these bacteria were cultivated—and then destroyed. Subsequently cleaning away the dead bacteria cells was always a major effort. However, the researchers then hit upon a brilliant idea: "milking" the bacteria.
"After all, milk comes from a cow, but you don't have to kill the cow to get it," says Müller. "A natural principle is used to do the milking in both cases." When, for example, it rains in the salt marshes of the North Sea, where these bacteria also live, the cells that previously lived in a saline environment are full to the brim with ectoin. Normal cells would now immediately absorb rainwater in order to bring their own concentration of minerals up to the level of the external environment—and then burst. But the halophilic bacteria protect themselves with a trick: "They get rid of the ectoin very quickly via their mechanosensitive valves, emergency valves, as it were, which react to membrane pressure." When the concentration of salt rises again, the production of new ectoin begins. Researchers apply this principle by first exposing the bacteria in the lab to a high concentration of salt for a certain length of time and then rinsing them with a cleansing solution without salt and nutrients—the ectoin is released and now only has to be filtered out.