Microbes That Thrive In The Saline Dead Sea
The Transjordanian plateaus to the east and the Judaean highlands to the west border the Dead Sea. The Dead Sea is the body of water on Earth's surface with the deepest point. The Dead Sea's waters are incredibly salty, and typically, the salt content rises as you get closer to the lake's bottom. All life is prohibited by the lake's severe salinity, with the exception of microorganisms. When there is flooding, fish brought in by the Jordan or by smaller streams perish swiftly. With the exception of the flora along the rivers, the plant life around the shoreline is sporadic and primarily composed of halophytes.
Obligate halophilic bacteria, such as the pink, pleomorphic Halobacterium sp., a Sarcina-like coccus, and the facultatively halophilic green alga Dunaliella, make up the majority of the local flora. It is possible to separate sulfate reducers from bottom sediments.
The recent discovery by Camille Thomas and his team-
Molecular fossils have recently been discovered in Dead Sea sediments by Camille Thomas, a geomicrobiologist at the University of Geneva, and his colleagues, suggesting that bacteria may have been there as latest as 12,000 years ago. It is the first time that researchers have found a life form in this ecosystem other than archaea, which raises the possibility that comparable life exists (or has lived in the past) in other similar environments on Earth and other parts of the solar system, including Mars.
Thomas and his coworkers took part in an international effort that sank 430 meters into the lake bottom in 2010 to gain a previously unattainable insight into the past of our climate. After examining the samples for a number of years, Thomas' team discovered archaea hidden beneath the silt. It demonstrated that these creatures were capable of surviving both in the lake and in the silt below, where the environment is considerably more hostile.
Thomas and his coworkers examined gypsum layers that were laid down 12,000, 85,000, and 120,000 years ago. Gypsum is a mineral that is left behind after seawater evaporates. They discovered wax esters, energy-rich compounds that tiny creatures produce and store when food becomes limited, ensnared within them. The research team comes to the conclusion that ancient bacteria must have generated the substances because archaea cannot manufacture them and multicellular creatures are extremely unlikely to survive such harsh environments.
The Dead Sea environment may still support bacterial life, but Thomas and his colleagues discovered interesting clues. They smelled rotten eggs when they first opened a large vial of current sediments, for instance—a recognizable indicator of hydrogen sulfide gas, which is frequently generated by bacteria. The researchers are not convinced that bacteria still exist beneath the salty lake because the gas might have a nonbiological origin, such as geothermal activity (for which Yellowstone National Park is famous).
Weber contends that even if they do not, microorganisms most likely coexist in a comparable environment across the vast subsurface ecosystem of Earth. According to him, scientists will gain a better understanding of how and where life emerges on Earth and other worlds as they keep track of the harsh settings in which it may thrive.
How can we connect the discovery to life on Mars?
Consider Mars: in 2011, the Opportunity rover operated by NASA discovered gypsum, the same material that Thomas had discovered in the Dead Sea deposits. Its existence shows that the Red Planet's seas and lakes drained as it warmed. But before they did, Tomaso Bontognali, a scientist at the Space Exploration Institute in Switzerland who was not involved in the Dead Sea study, believes that these lakes of water would have resembled the Dead Sea quite a bit—possibly even down to the biological processes.
Working on the ExoMars rover for the European Space Agency, which will touch down on Mars's old ocean floor in 2021, is Bontognali. It will employ a condensed version of Thomas' team's approach to evaluate sediment cores. According to Bontognali, the Dead Sea evidence "makes the concept that life may have lived on Mars more feasible."
Stay tuned to learn more about such extremophiles.