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Chapter 46 : Extreme High-Pressure Marine Environments
The observation that the vast majority of Earth’s microorganisms reside in extreme aquatic environments, given the immense volume of the deep ocean, is a simple fact. Some combination of extreme temperature, pressure, food supply, acidity, redox conditions, or even water activity describes the norm, not the rarity, for aquatic microbial habitats. This chapter provides some history, current trends, and specific examples of strategies and experimental protocols for studying microorganisms (Bacteria and Archaea) that inhabit the largest volume of extreme (or any inhabited) environment on the planet, the pressurized deep ocean and its sub-seafloor realm. Although few scientists have ready access to submersible operations in the deep sea or even to standard sampling expeditions by surface ships, the new investigator can find established researchers forthcoming with expertise, field samples, or cultured strains. Yet another variant on the theme of end-point experiments at high temperatures and pressures is the recent development in the Jørgensen laboratory of a high-pressure thermal gradient block, generally patterned after the system described for low-temperature, high-pressure research. The problem for extreme deep-sea environments, as elsewhere, lies with the available approaches to measuring activity, not with limitations to deep-sea sampling or seafloor experimentation. The latter are limited only by resources (and perhaps motivation), since a wide variety of sampling gear and instrumentation, including pressure retaining devices, are available for in situ study of deep-sea extremophiles.
Examples of typical equipment for conducting microbial studies at elevated hydrostatic pressures, including a stainless steel hand pump, gauge, and fluid reservoir (Enerpac Division, Applied Power, Inc.), high-pressure valves and flexible capillary tubing (HIP, Erie, Pa.), and a quickly disconnecting, threadless pressure vessel and threadless cap (custom-built by Tem-Pres Division, Leco Corp., modeled on the work of Yayanos [ 165 ] and Yayanos and Van Boxtel [ 170 ]). See the text for additional details.
Examples of sample containers used at elevated hydrostatic pressures, i.e., with pressure-responsive (moveable) parts (containers A to D) or a completely flexible design (containers E and F). Containers A and D double as sample collectors in the field for fluid and sediment, respectively. Containers B and C (when filled with solid media [ 45 , 172 ]) and container F ( 106 ) allow for colony formation under pressure. Container C, which can be of any length, is used in the pressure-temperature gradient instrument of Yayanos et al. ( 172 ). See Table 1 for examples of container use in selected studies; see the text for additional details.
Examples a of studies of microbial community activity in the cold deep sea conducted under in situ conditions or at simulated in situ temperatures and pressures b
Examples a of microbial community measurements on samples recovered from the hot (>90°C) deep sea, made directly or after incubation in situ or at laboratory-simulated in situ temperatures and pressures