Effects of hydrostatic pressure and temperature on physiological traits ofThermococcus guaymasensis and Thermococcus aggregans growing on starch

The effects of temperature and hydrostatic pressure on growth of two novel Thermococcus species, T. guaymasensis and T. aggregans, were investigated. These archaea, isolated from the Guaymas Basin hydrothermal vent site at 20 00 meters depth, are able to grow on starch in sulfur-depleted medium produ cing significant amounts of amylases and pullulanases. At 85 degrees C, T. guaymasensis exhibited a barophilic response at 20 and 35 MPa but inhibitio n of growth occurred at 50 MPa; at 50 MPa, cell replication was repressed, the mean cell size increased, and production of starch-hydrolysing enzymes was significantly stimulated. Barophily was also expressed by T. guaymasens is under 20 MPa at sub-optimal temperature (70 degrees C) but morphological alterations of cells were observed earlier (35 MPa). No barophily was exhibited by T. aggregans at 85 degrees C. In this case, c ell replication was repressed at 20 MPa and remarkable inhibition of growth occurred at 50 MPa. Only when T. aggregans was cultivated at 75 degrees C, a significant barophilic response was exhibited at 20 MPa, as shown by the rate of replication and metabolism. These results show that Thermococcus s pecies, although isolated from the same ecosystem, differ with regard to th e effects of pressure and temperature on cell physiology. The metabolic res ponses and their significance for potential biotechnological applications a re also discussed.