| Extremophiles are found in environments spanning the extremes of temperature, pH, osmolarity, and pressure. Among these environments, deep-sea hydrothermal vents combine two extremes, high temperature and pressure. Methanocaldococcus jannaschii was collected from a "white smoker" chimney on the East Pacific Rise at 2,600 m (ca. 260 atm). This organism is a barophile, a "lover of pressure." At 86°C, M. jannaschii grows nearly five times faster at 750 atm than at 7.8 atm.; M. jannaschii appears to thrive under extreme conditions. Several enzymes in this barophile have been shown to be stabilized and/or activated by pressures of up to 500 atm. Additional mechanisms for high pressure and temperature adaptation can be elucidated using cDNA microarrays. Microarrays allow us to monitor the expression level of RNA corresponding to all the genes in an organism. Using microarrays, RNA expression profiles of M. jannaschii in response to temperature shock and growth at 500 atm, temperature shock at 7.8 atm and 500 atm, and pressure shock from 7.8 atm to 500 atm with helium in a high-temperature and high-pressure bioreactor have been examined.; A high-temperature and high-pressure bioreactor with a total volume of 1.15 L that can operate up to 880 atm and 200°C was developed to cultivate M. jannaschii. However, barophilic growth of M. jannaschii in this reactor only occurred when hydrogen consumption was physiologically limited and not when growth was gas-substrate mass-transfer limited. A stress response was exhibited under mass-transfer limitations at both 500 atm and 7.8 atm. Between 58--90°C and under conditions where mass transfer did not limit growth, the specific growth rate increased 3-fold as the pressure was raised from 7.8, atm to 500 atm. At 88°C and 500 atm, a gene encoding a replication protein A-related protein that may limit DNA recombination at high pressure was up-regulated (compared to 7.8 atm), as were several genes encoding proteins that regulate glutamine production.; Cells were also lethally heat shocked at 500 atm, which resulted in depression of the pressure effect for genes that were differentially-expressed at 500 atm without heat shock. In addition, several genes encoding transport proteins and genes involved in nucleotide and amino acid synthesis were up-regulated after heat shock at 500 atm relative to the expression levels after heat shock at 7.8 atm. Pressure shock of M. jannaschii from 7.8 atm to 500 atm at 88°C did not result in pressure-accelerated growth. Gene expression analysis revealed a heat shock and cold shock response for pressure-shocked cells that was not apparent in cells cultivated at 500 atm. |
