Barophiles (Piezophiles)

Abstract

The deep-sea is regarded as an extreme environment with high hydrostatic pressures [up to 110 megapascal (MPa)], predominantly low temperatures (1°-2°C) but with occasional regions of extremely high temperature (up to 375°C) at hydrothermal vents, darkness, and low nutrient availability. It is accepted that deep-sea microbiology as a definable field did not exist before the middle of this century and was paid little attention except for the efforts of Certes and Portier (Jannasch and Taylor 1984). Certes, during the Travaillier and Talisman Expeditions (1882–1883), examined sediment and water collected from depths to 5000 m and found bacteria in almost every sample. He noted that bacteria survived at great pressure and might live in a state of suspended animation (Certes 1884). In 1904 Portier used a sealed and autoclaved glass tube as a bacteriological sampling device and reported colony counts from various depths and locations (Richard 1907). In 1949 ZoBell and Johnson started work on the effect of hydrostatic pressure on microbial activities. The term “barophilic” was first used, defined today as optimal growth at pressure higher than 0.1 MPa or by a requirement of increased pressure for growth. Many microorganisms in the deep-sea are extremophiles, such as halophiles, thermophiles, psychrophiles, barophiles, or piezophiles [the term piezophile was proposed as a replacement to barophile as the Greek translations of the prefixes baro and piezo mean weight and pressure, respectively (Yayanos 1995)], and some of these microorganisms cannot survive in “moderate” environments. In this chapter, we focus on the isolation and taxonomy of microorganisms adapted to the deep-sea, and the molecular bases of their high pressure adaptations.