New research discovers surprising activity among organisms thriving on the deep, superheated sea floor

Sediment samples were collected from the deep and hot undersea biosphere during IODP 370 expedition aboard the Japanese science drill ship. Credit: JAMSTEC

Since the discovery of the deep undersea biosphere in the mid-1990s, scientists have studied the conditions in which organisms thrive in this generally isolated and food-deprived environment and have wondered what conditions limit the existence of life. In 2016, a group of international scientists set out to sea aboard the Japanese science drill ship, Chikyu, to study the temperature limits of the deep undersea biosphere. Sediment samples were collected from a drill hole cutting the geological subduction zone in the Nankai Basin off Japan.

At this site, the temperature rises sharply with a depth of up to 120 ° C, a temperature close to the maximum for life, at 1200 meters below the sea floor. To their surprise, the scientists found a very small but very active microbial community that thrives under these deep and hot conditions.

The scientists determined the number of cells in the sediment and measured metabolic rates by highly sensitive radioactive measurements of methane production and sulfate reduction. They discovered that the metabolic rates of each cell were unusually high in the deep biosphere. The new findings, published January 25 in the journal Nature Communicationsabout samples collected in 2016 sheds light on the survival strategies of organisms that live in this harsh environment.

“We suggest that organisms be forced to maintain a high metabolic turnover, which approximates that of microbes living in surface sediments and in laboratory cultures, to provide the energy needed to repair thermal cell damage,” said Felix Polig of the University of Bayreuth. , who is the lead author of the study. “The energy required to repair thermal damage to cellular components increases sharply with temperature, and it is likely that most of this energy is needed to counteract the constant change of amino acids and loss of protein function,” said study leader Tina Triod, UCLA professor. Marine Aquatic Biology.

The detection of microbial metabolic activity in sediments with less than 500 cells per cubic centimeter of sediment is far from trivial, and is seven times lower than the average for surface sediments. “We worked under sterile, highly controlled conditions and performed a large number of simultaneous control experiments with sample incubations,” said Florian Schubert of the German Research Center for Geosciences, who performed these analyzes as part of his doctoral thesis. studies. “We even incubated the sediments sterilized with high gamma radiation, as well as drilling fluid from the drilling hole, to detect any potential non-biological interactions or potential microbial activity due to contamination,” said Jens Calmer, mentor for Florian Schubert.

Since the metabolic rate determination was performed under laboratory conditions, some uncertainty remained as to whether microbes would exhibit the same metabolic activity in their natural environment. So the scientists compared metabolic sulfate reduction rates measured with the calculated depletion time for dissolved sulfate in deep sediments. “Given that we are comparing two very different methodological approaches that operate on time scales of days versus millions of years, the agreement between setting the experimental rate and the calculated time to exhaustion is very good,” said Arthur Spivak of the University of Rhode Island.

The higher per-cell activity of sulfate reducers and methanogens in the deeper and hotter sediments appears to be fueled by hydrogen and acetate from the pore waters. “Acetate, a small organic molecule also found in vinegar, is of particular interest as a potential food source,” said Verena Heuer of Marum in Germany, who was the chief scientist involved in the expedition. “Acetate reaches concentrations greater than 10 mmol per liter in sedimentary pore water, which is exceptionally high for marine sediments.”

For Bo Barker Jorgensen of Aarhus University, one of the pioneers of deep biosphere research, the discovery of high cell-specific rates in the deep biosphere is a fascinating discovery. “We have always found that microbes in the deep biosphere are a very slow community that is slowly nibbling on the last remains of buried 1 million year old organic matter. But the deep biosphere is full of surprises. To find life thriving with high metabolic rates at these high temperatures on the deep sea floor nourishes Our imaginations about how life evolved or survived in similar environments on extraterrestrial planetary bodies.”

Fumio Inagaki and Yuki Morono of JAMSTEC in Japan were the other two co-chairs of the expedition responsible for discovering cells in the sediments. When asked what they thought of the fact that the expedition had not detected the upper temperature limit of the deep biosphere, they both said, “We have to go back and dig deeper. The final limit of the biosphere within the Earth is still unknown. As shown through this project, it lies The boundary is somewhere in the oceanic crust under the sediments. It will be explored in the future by scientific ocean drilling.”


How hot is it out of proportion to life at the bottom of the ocean?


more information:
Tina Triod, Rapid Metabolism Promotes Survival of Microbes in the Deep Undersea Biosphere, Nature Communications (2022). DOI: 10.1038/s41467-021-27802-7. www.nature.com/articles/s41467-021-27802-7

Provided by University of California, Los Angeles

the quote: New research discovers surprising activity among organisms thriving in an extremely deep and hot seabed floor (2022, Jan 25) Retrieved Jan 26, 2022 from https://phys.org/news/2022-01-extremely-deep-hot- subseafloor.html

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