The Mystery of Piezophiles: Understudied Microorganisms from the Deep, Dark Subsurface

Abstract

Microorganisms that can withstand high pressure within an environment are termed piezophiles. These organisms are considered extremophiles and inhabit the deep marine or terrestrial subsurface. Because these microorganisms are not easily accessed and require expensive sampling methods and laboratory instruments, advancements in this field have been limited compared to other extremophiles. This review summarizes the current knowledge on piezophiles, notably the cellular and physiological adaptations that such microorganisms possess to withstand and grow in high-pressure environments. Based on existing studies, organisms from both the deep marine and terrestrial subsurface show similar adaptations to high pressure, including increased motility, an increase of unsaturated bonds within the cell membrane lipids, upregulation of heat shock proteins, and differential gene-regulation systems. Notably, more adaptations have been identified within the deep marine subsurface organisms due to the relative paucity of studies performed on deep terrestrial subsurface environments. Nevertheless, similar adaptations have been found within piezophiles from both systems, and therefore the microbial biogeography concepts used to assess microbial dispersal and explore if similar organisms can be found throughout deep terrestrial environments are also briefly discussed.

Temperature-dependent iron motion in extremophile rubredoxins – no need for ‘corresponding states’

“…Organisms have been found that can function down to -25 °C (psychrophiles) and up to 122 °C (hyperthermophiles) 3 . Microbial activity has been demonstrated at GPa pressures 4 , and growth at 100 MPa can has also been demonstrated (piezophiles) 5 , 6 , as well as over a wide range of pH values (acidophiles and alkaliphiles) 7 , ionic strengths (halophiles) 8 , and other stressors and even combinations thereof 9 . These living systems must modulate their protein properties to function best in their preferred environment.…”