Temperatures in nearly 4,000 feet below the seafloor may set the limit for the existence of life, but certain microorganisms thrive in this extremely hot subseafloor.
The conditions within this "deep biosphere" had been studied by scientists since the mid-1990s, particularly on how life thrived in an environment that is food-deprived and extremely isolated.
In 2016, a science expedition joined by international scientists set out to sea on board the Japanese scientific drillship, Chikyu, to study the temperature limit of the deep subseafloor biosphere. They collected sediment samples from a drill hole that cut through the geological subduction zone of the Nankai Trough off Japan.
Their findings revealed a subsurface habitat in which microbes were found living at temperatures approaching 250 degrees Fahrenheit, according to Gizmodo. Technically, this level of heat could fry humans. More surprisingly, the scientists found a very small, but very active microbial community that "manages to beat the heat" under these deep and hot conditions.
The scientists also determined from the number of cells in the sediment an extraordinarily high metabolic rates per cell for the deep biosphere. The published article in Nature Communications shed light to survival strategies of microbes living in such harsh conditions.
How microorganisms survive the extreme conditions
The team theorized that high metabolic rates are essential for microorganisms to thrive and live in extreme temperatures as it allows microbes to repair cells damaged by heat.
"We propose that the organisms are forced to maintain a high metabolic turnover, which approaches the activity of microbes living in surface sediments and in laboratory cultures, to provide the energy required to repair thermal cell damage," said lead author Felix Beulig from the University of Bayreuth in Science X Network.
Study leader, Tina Treude, UCLA professor of marine geomicrobiology, claimed that the energy required to repair thermal damage to cells increases with temperature. Because of this, more energy is needed to counteract the changes in the amino acids, as well as the loss of protein function.
Bo Barker Jørgensen from Aarhus University, who is one of the pioneers of deep biosphere research featured in SFam Journals, also found the discovery fascinating
"To find life thriving with high metabolic rates at these high temperatures in the deep seabed nourishes our imagination of how life could evolve or survive in similar environments on planetary bodies beyond Earth."
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A very interesting reason for the very high activity
New observations also propose that microbes have ample access to nutrients supplied by the heating of organic materials, specifically hydrogen and acetate.
Although the findings might seem "counterintuitive to many," geologist Virginia Edgcomb explains that the high activity of the cells are there for a significant reason.
Jennifer Biddle, an associate professor at the University of Delaware who's not affiliated with the research, complimented the pre-existing work demonstrating the activities of these microbial communities.
"Once cells find their 'happy place' in the subsurface, they have plenty of power to grow," she commented. Although she noted on limitation which is the microbes in question were not identified.
Furthermore, the scientists think microbes can survive in even hotter environments, further down the deeper subseafloor.
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