CAN HIGH PRESSURES ENHANCE THE LONG-TERM SURVIVAL OF MICROORGANISMS?

Purported instances of long-term bacterial dormancy and survival have been ascribed to a variety of environmental factors, including desiccation, freezing, hypersalinity, or anoxia. Here we outline an experimental approach to investigate whether high pressures on the order of 0.1 to 1.0 GPa (1000 to 10,000 atmospheres) might also promote microbial stasis and longevity in some geological environments.

Experiments and field observations support the contention that microbes survive in a dormant state under high-pressure conditions. Sharma et al. (2002) documented significantly reduced microbial activity, but sustained viability, in strains of Escherichia coli (MG1655) and Shewanella oneidensis (MR1) at pressures to 1.6 GPa. Onstott and coworkers have recovered viable microorganisms from a variety of deep subsurface environments, including sedimentary basins and South African gold mines (e.g., Onstott et al. 1998). In each of these systems metabolic rates are extremely slow.

Principal impediments to microbial longevity include racemization of amino acids and depurination of DNA – processes that lead to cell death in the absence of an effective repair mechanism. By constraining the volume and restricting molecular vibrations, pressure may increase the activation energy for amino acid racemization, DNA degradation, and other harmful reactions. A further advantage to high-pressure environments is the increased relative permeability of hydrogen, which has been proposed as a likely energy source for cellular upkeep under these physiologically adverse conditions (Morita 2000).

We will describe experiments that employ a new array of large-volume (~0.1 mL), opposed-moissanite-anvil environmental pressure cells to explore microbial physiology and associated biogeochemistry under high pressure conditions. The relatively simple, low-cost, easy-to-use construction of the units is amenable to conducting multiple, parallel experiments. The ability to monitor microbial processes in real time will make these systems valuable experimental tools in our continued exploration of the slow, deep biosphere.

RY Morita (2000) Microbial Ecology 38:307-320. TC Onstott et al. (1998) Geomicrobiology Journal 15:353-386. A Sharma et al. (2002) Science 295:1514-1516.