Organisms functioning best at high pressures are known as piezophiles. Piezophilic microorganisms, the main topic here, have a growth rate (
k
) maximum at high pressure, are prominent inhabitants of the cold ocean and found in warmer high pressure regions such as the deep waters of the Mediterranean and Sulu Seas, deep‐sea hydrothermal vent environments, the depths of sea floor sediments and the subsurface of continents. A
PTk
‐diagram shows values of k of a microorganism as a function of temperature (
T
) and pressure (
P
) either on a 3‐D surface or as isopleths on a 2‐D contour map and allows for comparing organisms from habitats of disparate temperatures and pressures. Laboratory studies of piezophilic eukaryotic organisms from the abyssal and hadal ocean are rare. At the present time, research on piezophilic prokaryotes offers the best opportunity for discovering adaptations for life in the deep sea, in deep‐earth environments and in extraterrestrial settings.
Key Concepts
Pressure is a force per unit area and at any given point in a fluid at rest is equal in every direction.
High‐pressure habitats are found in the deep sea, beneath the sea floor and in the depths of continents.
Collecting living organisms from extreme high‐pressure habitats requires specialised equipment.
Laboratory study of organisms from high‐pressure habitats also requires specialised equipment.
Temperature and pressure are two of the essential coordinate variables for describing a habitat or environment.