Microbes with high metabolic activity found in deep, hot subseafloor environment
- About 25 percent of the world’s seabed sediment can be found at a depth where temperature is more than 80 °C.
- Scientists previously proposed that 80 °C is the thermal barrier for life in the strata below the Earth’s surface.
- Researchers discovered a population of methanogenic and sulfate-reducing organisms in deep buried marine sediment.
- Methanogenic organisms produce methane as a metabolic byproduct in low oxygen conditions.
- Sulfate-reducing organisms can perform anaerobic respiration by using sulfate as terminal electron acceptor and reducing it to hydrogen sulfide.
- The IODP (International Ocean Discovery Program) Expedition 370 drilled and collected sediment cores in the Nankai Trough subduction zone just south of Japan.
- The Nankai Trough subduction zone can reach temperatures of about 120 °C.
- Subduction zone is the place where two plates of the Earth come together, one is found over the other.
- Researchers utilized a considerable suite of radiotracer experiments.
- Radiotracers is a compound that contains a radioactive element and can be used to study the mechanism of chemical reactions.
- The small microbes discovered from the Nankai Trough subduction zone survived with high potential cell-specific rates of energy metabolism, similar to the rates in active surface microbes and laboratory cultures.
- Researchers initially expected that the metabolic rates in the deep subseafloor will be extremely low.
- The cells appear to expend almost all of their energy to repair damages from the high temperature.
- At the same time, the cells are forced to balance between supporting themselves at a minimum level near the thermal barrier for life and a rich source of substrates and energy from the reactions of the sedimentary organic matter caused by the high temperature environment.
Beulig, F., Schubert, F., Adhikari, R.R. et al. Rapid metabolism fosters microbial survival in the deep, hot subseafloor biosphere. Nat Commun 13, 312 (2022). https://doi.org/10.1038/s41467-021-27802-7