A BAROPHILIC RESPONSE BY 2 HYPERTHERMOPHILIC, HYDROTHERMAL VENT ARCHAEA - AN UPWARD SHIFT IN THE OPTIMAL TEMPERATURE AND ACCELERATION OF GROWTH-RATE AT SUPRA-OPTIMAL TEMPERATURES BY ELEVATED PRESSURE

The influence of elevated hydrostatic pressure on the growth rates of two hyperthermophilic Archaea isolated from hydrothermal vent environm ents (strains ES1 and ES4) was investigated over their entire temperat ure range for growth. Thermococcus celer, a shallow marine hyperthermo phile was included in the study for comparative purposes. For one stra in (ES4), the pressure at the site of collection (22 MPa) caused an up ward shift in the optimal growth temperature of about 6 degrees C comp ared to growth at 1 MPa. Although the optimal temperature for ES1 was unaffected by 22 MPa, elevated pressure stimulated the growth rate at supra-optimal temperatures. The temperature range for growth for both organisms was extended upward 2 degrees C at 22 MPa pressure. For both strains 22 MPa had little effect on growth rates at sub-optimal tempe ratures. Growth was observed at pressures as high as 89 MPa for ES1 an d 67 MPa for ES4, but with these higher pressures the temperature rang e for growth was narrowed, and the optimal temperature was shifted dow nward. Growth of Thermococcus celer was slightly stimulated by 22 MPa at its reported optimal temperature of 88 degrees C, but was inhibited by higher pressure.