Pressure as an environmental parameter for microbial life - A review

- High-pressure environments represent the largest habitat for microbial life on Earth.
- Pressure generally enhances microbial activity rates in deep environments.
- Pressure is potentially a limiting parameter for life at depth.
- The field of high-pressure geomicrobiology is to be expanded.

Microbial life has been prevailing in the biosphere for the last 3.8 Ga at least. Throughout most of the Earth's history it has experienced a range of pressures; both dynamic pressure when the young Earth was heavily bombarded, and static pressure in subsurface environments that could have served as a refuge and where microbial life nowadays flourishes. In this review, we discuss the extent of high-pressure habitats in early and modern times and provide a short overview of microbial survival under dynamic pressures. We summarize the current knowledge about the impact of microbial activity on biogeochemical cycles under pressures characteristic of the deep subsurface. We evaluate the possibility that pressure can be a limiting parameter for life at depth. Finally, we discuss the open questions and knowledge gaps that exist in the field of high-pressure geomicrobiology.