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The study of organic matter in sediments helps to better understand the distant past. What was the climate? Which organisms populated the Earth?
In what conditions did they live? Researchers from the University of Geneva (UNIGE), Switzerland, and the University of Lyon, France, examined the sediments in the Dead Sea, where salinity is unparalleled, which makes it One of the most hostile environments on the planet. Geologists drilled a 400-meter hole in the heart of the Dead Sea before analyzing each layer of sediment and traces of a strategy allowing bacteria to survive by feeding on the remains of other organisms. . This discovery, to read in the newspaper Geologywill deepen our understanding of how life can develop even in the most severe conditions. It also provides vital search leads to detect life on other planets.
The study of the deep biosphere – the microbial presence in sediments – helps us to understand the various aspects of Earth's evolution and the multiple climatic changes it has undergone. "It's about studying the bacteria and archaea – the oldest life forms on Earth – living in sediments, and analyzing the processes of transformation resulting from their presence, what it's called diagenesis, "says Daniel Ariztegui, professor in the Department of Earth Sciences at UNIGE's Faculty of Science.
An international team has been working on reconstructing the Dead Sea climate over the past 200,000 years. Although the surface of the lake and its depth are roughly equivalent to those of Lake Geneva, the Dead Sea loses one meter per year, which explains its ever increasing salinity: 275 grams of salt per liter against 20 to 40 grams per liter . in the oceans. Nevertheless, microbial life remains in this extreme environment. But is it possible that a form of life has managed to adapt to the Dead Sea sediments – a particularly hostile environment isolated from the surface without light, without oxygen or frequent food intake? Scientists drilled a hole 400 meters deep and 10 centimeters in diameter in the heart of the Dead Sea to find traces of microbial presence in the sediments by analyzing sediment samples for each meter dug.
Necrophilous bacteria
"We started by freezing the collected samples to preserve any genetic material that could break down at room temperature," says Dr. Camille Thomas, a researcher at UNIGE's Department of Earth Sciences. "We then used different techniques, such as scanning electron microscopy, to identify very remnant microbe remnants that could have changed the original composition of the sediments." The goal was also to extract organic compounds entrapped in salt, such as as DNA or lipids. "This allows us to identify the organisms that live or have lived in the sediments and helps us understand how they manage to survive under these conditions," continues Professor Ariztegui.
Previous research had shown that one could find archaea in the most salty environments of the Dead Sea. "But here we have discovered molecules known as isoprenoid wax esters that can not be produced by archaea, but only by bacteria from archaeal fragments," says Dr. Thomas. This proves that another form of life that the archaea has developed and that it is potentially still present in these sediments: bacteria. "The Archaea have the ability to withstand the very high levels of salinity of the Dead Sea. Until now, they were the only ones to have been identified in the deep waters of the Dead Sea. But it turns out that another population can overcome these intense conditions by feeding on archaeal corpses: bacteria – which we thought were less well adapted. "By becoming" scavengers ", these bacteria have acclimated to one of the most severe environments on our planet and have contributed to the chemical changes found in the Dead Sea sediments.
Geomicrobiology represents the future of the search for life in space
The study, funded by the Swiss National Science Foundation (SNSF), focuses on the boundary between geology and microbiology – a field known as geomicrobiology, which seeks to understand the mechanisms that underlie the formation of the life and Earth, as hostile conditions are. "Determining how life adapts in the most hostile conditions also opens important avenues of research to discover life on other planets," enthuses Professor Ariztegui. "And that gives us an idea not only of what we should be looking for, but also helps us to develop more and more sophisticated microbial techniques."
UNIVERSITY OF GENEVA
Header Image – Dead Sea – Credit: Wilson44691
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