Membrane-Based Adaptations of Deep-Sea Piezophiles

Abstract

Pressure is an important thermodynamic variable of particular significance when comparing biological processes that take place at different depths. Most of what is known about high pressure habitats has come from studies of deep-sea environments. When one considers the tremendous diversity of deep-sea benthic invertebrates (Rex et al., 1993), and the propensity of marine microorganisms to establish symbiotic associations, the combined diversity of free-living and host-associated deep-sea microorganisms must surely be immense. Add to these microorganisms those dwelling in the deep-earth (Kerr, 1997), and high pressure environments are seen to encompass a diverse biota as well as represent the vast majority of the biosphere by volume. Within both marine and terrestrial environments pressure usually increases by about 10 megapascal (MPa, 1 MPa = 10 bar ≈ 9.87 atmospheres ≈ 145 pounds per square inch) per kilometer depth, however, great variation in this rule is found within the deep earth. In contrast to the deep sea where an isothermal temperature near freezing (2°C) predominates, subterranean temperatures generally increase by 20–30°C per kilometer. The highest pressure environment yet sampled for microorganisms is within the Challenger Deep of the Mariana Trench at a depth of 10,898 m and a pressure of 110 MPa. The current upper pressure limit for microbial growth is about 130 MPa (Yayanos, 1986).