” We propose that the organisms are forced to maintain a high metabolic turnover, which approaches the activity of microorganisms living in surface area sediments and in lab cultures, to supply the energy needed to repair thermal cell damage,” stated Felix Beulig from the University of Bayreuth, who is the lead author of the research study. “The energy needed to repair thermal damage to cellular parts increases steeply with temperature level, and most of this energy is likely needed to counteract the constant alteration of amino acids and loss of protein function,” stated the study leader, Tina Treude, UCLA professor of marine geomicrobiology.
It is far from insignificant to spot microbial metabolic activity in sediments with less than 500 cells per cubic centimeter sediment, which is seven orders of magnitude lower than in the average surface area sediment. “We worked under incredibly managed, sterilized conditions and carried out a great deal of control experiments simultaneously with the sample incubations,” stated Florian Schubert from the German Research Centre for Geosciences, who conducted these analyses as part of his Ph.D. research studies. “We even nurtured sediment decontaminated with high gamma radiation, in addition to drill fluid from the drill hole, to identify any potential non-biological responses or contamination-induced microbial activity,” said Jens Kallmeyer, who is the coach of Florian Schubert.
Due to the fact that the metabolic rate determinations were conducted under laboratory conditions, some uncertainty stayed whether the microorganisms would reveal the exact same metabolic activity in their natural environment. The researchers for that reason compared the measured metabolic sulfate reduction rates to the computed exhaustion time of dissolved sulfate in the deep sediment. “Given that we are comparing 2 really various methodological techniques that act on time scales of days versus countless years, the arrangement between the experimental rate decision and the determined exhaustion time is gratifyingly good,” said Arthur Spivack from the University of Rhode Island.
The high per-cell activity of sulfate reducers and methanogens in the deepest and most popular sediment is apparently sustained by hydrogen and acetate from the sediment porewater. “Acetate, which is a little natural particle that is also present in vinegar, is of specific interest as a potential food source,” stated Verena Heuer from MARUM in Germany, who was the co-chief researcher of the exploration. “Acetate reaches concentrations of more than 10 mmol per liter in the sediment porewater, which is incredibly high for marine sediments.”
For Bo Barker Jørgensen from Aarhus University, who is one of the pioneers of deep biosphere research study, the detection of high cell-specific rates in the deep biosphere is a remarkable discovery. “We always found that microorganisms in the deep biosphere are an exceptionally sluggish neighborhood that gradually munches on the last remains of million-year-old, buried natural matter. The deep biosphere is complete of surprises. To discover life growing with high metabolic rates at these heats in the deep seabed nourishes our creativity of how life might evolve or endure in comparable environments on planetary bodies beyond Earth.”
Fumio Inagaki and Yuki Morono from JAMSTEC in Japan were the other two co-chief researchers of the expedition and accountable for the detection of cells in the sediment. When asked what they considered the reality that the expedition did not identify the upper temperature level limitation of the deep biosphere, both said, “We need to go back and drill deeper. The supreme limitations of the biosphere inside the Earth stay unknown. As shown by this task, the border lives someplace in the oceanic crust below the sediments. It will be explored in the future through scientific ocean drilling.”.
Referral: “Rapid metabolic process cultivates microbial survival in the deep, hot subseafloor biosphere” by F. Beulig, F. Schubert, R. R. Adhikari, C. Glombitza, V. B. Heuer, K.-U. Hinrichs, K. L. Homola, F. Inagaki, B. B. Jørgensen, J. Kallmeyer, S. J. E. Krause, Y. Morono, J. Sauvage, A. J. Spivack and T. Treude, 25 January 2022, Nature Communications.DOI: 10.1038/ s41467-021-27802-7.
Sediment samples from the deep, hot subseafloor biosphere were collected during the IODP 370 expedition onboard the Japanese scientific drilling ship. Credit: JAMSTEC
Since the discovery of the deep subseafloor biosphere in the mid-1990s, researchers have actually studied the conditions under which organisms grow in this isolated and typically food-deprived environment and wondered which conditions set a limitation to the existence of life. In 2016, a group of international researchers set out to sea on board the Japanese scientific drillship, Chikyu, to study the temperature limitation of the deep subseafloor biosphere. Sediment samples were gathered from a drill hole that cut through the geological subduction zone of the Nankai Trough off Japan.
At this site, temperature increases steeply with depth to reach 120 ° C, a temperature level suggested near to the limit for life, at 1200 meters underneath the seafloor. To their surprise, the researchers found a very small, but extremely active microbial neighborhood growing under these deep and hot conditions.
The scientists figured out the number of cells in the sediment and determined their metabolic rates by highly delicate radiotracer measurements of methane production and sulfate reduction. They found that the metabolic rates per cell were extraordinarily high for the deep biosphere. New findings, released on January 25, 2022, in the journal Nature Communications, about the samples gathered in 2016 are shedding light on the survival strategies of organisms living in this harsh environment.
The researchers determined the number of cells in the sediment and measured their metabolic rates by highly delicate radiotracer measurements of methane production and sulfate decrease. It is far from unimportant to identify microbial metabolic activity in sediments with less than 500 cells per cubic centimeter sediment, which is seven orders of magnitude lower than in the typical surface area sediment. The scientists therefore compared the measured metabolic sulfate reduction rates to the determined depletion time of dissolved sulfate in the deep sediment. The high per-cell activity of sulfate reducers and methanogens in the deepest and most popular sediment is apparently sustained by hydrogen and acetate from the sediment porewater. “Acetate reaches concentrations of more than 10 mmol per liter in the sediment porewater, which is extremely high for marine sediments.”
