Subsurface environments, both marine and continental, represent the largest habitat on Earth for microbial life. These environments have one parameter in common – pressure. In a review published in press in Biophysical Chemistry, Aude Picard (University of Tübingen, Germany) and Isabelle Daniel (University of Lyon, France) focus on the pressure as a driving force in the distribution, activity and survival of microbial life throughout the Earth’s history .
On early Earth, oceans covered a larger area than at present day and emerged continents may have represented only 1/10 of Earth’s surface. Even today, 71% of Earth’s crust is under water. At the time life first appeared on Earth, therefore, high-pressure environments could have represented potential “incubators” for the emergence of microbial life. Such environments, as well as providing the chemical and physical necessities for life, would also have protected nascent organisms from harmful cosmic radiation and constant meteoritic bombardment.
The authors provide a literature survey of studies investigating the effects of pressure on microbial activities relevant for biogeochemical cycles. Most studies have looked at the effect of pressure on microbial aerobic activities in the deep sea, but few others have investigated pressure in sediments, under aerobic or anaerobic conditions.
Pressure generally has a positive effect on microbial activity rates in water or sediments collected at depth. Although the importance of pressure as an environmental parameter has been highlighted by the recognition of pressure-loving (piezophilic) microorganisms living in the deep sea, their significance for the functioning of subsurface microbial communities is still unknown. The authors highlight the importance of assessing the relative abundance of piezophilic vs. piezosensitive microorganisms at depth and systematically investigating the physiological and metabolic capabilities of subsurface isolates.
This review emphasizes not only the importance of pressure in today’s ecosystems, but also as a potentially critical part of the story of origins of life on Earth.
Photo credit: Aude Picard. A high-pressure vessel and associated pump designed to analyse piezophillic life in the lab.