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.[1]
- Sulfate-reducing organisms can perform anaerobic respiration by using sulfate as terminal electron acceptor and reducing it to hydrogen sulfide.[2]
- 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.[3]
- 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.[4]
- 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.
Sources:
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
[1] https://en.wikipedia.org/wiki/Methanogen
[2] https://en.wikipedia.org/wiki/Sulfate-reducing_microorganism
[3] https://earthquake.usgs.gov/learn/glossary/?term=subduction%20zone
