Microbes brave briny basins
Life proves it can thrive in the severest conditions.
A community of microorganisms has been discovered in one of the saltiest environments on Earth, ultra-saturated salt basins deep in the Mediterranean Sea. The salt solution there is so concentrated, microbiologists are mystified as to how the organisms are able to survive.
About 6 million years ago, the Mediterranean had dried up, having been separated from the Atlantic Ocean. Over time, sediment covered the salty deposits in the desolate basin. Eventually the area was reconnected with the Atlantic and filled with water again.
Now, places where these underwater salty deposits are exposed are exceptionally briny, containing up to 476 grams of magnesium chloride per litre. It was assumed that life could not exist in such conditions. The dense, viscous brine, which is twice as salty as soy sauce, would inexorably suck water molecules out of any cell.
But Paul van der Wielen, a microbiologist now at the Kiwa Water Research institute in Nieuwegein in the Netherlands, wanted to make sure. He and his colleagues focused on four such locations in the Mediterranean: l'Atalante, Bannock, Discovery and Urania salt basins, which are up to 500 metres beneath the surface. The work was carried out as part of the BioDeep project, a collaboration of research groups across Europe.
The researchers sent a robotic submarine down to retrieve water samples from the basins. When they analysed the samples, they were excited to find DNA, proving that microorganisms do exist there.
"So long as water is present in an environment, there appear to be few real limits to microbial life," comments Kevin Purdy, a microbiologist at the University of Reading, UK, who studies salt-loving organisms. He says that calcium chloride brines, such as Don Juan Pond in Antarctica, are now the only hypersaline environment in which life has yet to be found.
The team sequenced the DNA fragments they retrieved, and discovered around 50 previously unknown species of bacteria, as well as 20 new species of primitive microbes called archaea.
Archaea were recognized several decades ago as being separate from bacteria. They can exist in some of the planet's most hostile environments, such as thermal vents, and are thought to resemble the most ancient forms of life. The species the team found are very different from known archaeal species, and may belong to a separate evolutionary branch within the group, van der Wielen says.
The researchers now hope to isolate live samples of the microorganisms from the basins and grow them in the lab, to get a better idea of how they function.
Further investigation of the proteins and enzymes used by the microbes could prove useful for industry and biotech companies, who are always seeking ways to carry out reactions under extreme conditions.
But van der Wielen and his colleagues also point to a more far-reaching implication of their findings. They suggest that the existence of these hardy microbes lends support to the idea that life might exist in similar briny spots known to exist on other planets.
- Van der Wielen P. W. J. J., et al. Science, 307. 121 - 123 (2005).