HEAT-SHOCK RESPONSE IN PSYCHROPHILIC AND PSYCHROTROPHIC YEAST FROM ANTARCTICA

The response to heat stress in six yeast species isolated from Antarct ica was examined. The yeast were classified into two groups: one psych rophilic, with a maximum growth temperature of 20 degrees C, and the o ther psychrotrophic, capable of growth at temperatures above 20 degree s C. In addition to species-specific heat shock prote in (hsp) profile s, a heat shock (15 degrees C-25 degrees C for 3 h) induced the synthe sis of a 110-kDa protein common to the psychrophiles, Mrakia stokesii, M. frigida, and M. gelida, but not evident in Leucosporidium antarcti cum. Immunoblot analyses revealed heat shock inducible proteins (hsps) corresponding to hsps 70 and 90. Interestingly, no proteins correspon ding to hsps 60 and 104 were observed in any of the psychrophilic spec ies examined. In the psychrotrophic yeast, Leucosporidium fellii and L . scottii, in addition to the presence of hsps 70 and 90, a protein co rresponding to hsp 104 was observed. In psychrotrophic yeast, as obser ved in psychrophilic yeast, the absence of a protein corresponding to hsp 60 was noted. Relatively high endogenous levels of trehalose which were elevated upon a heat shock were exhibited by all species. A 10 C elsius degree increase in temperature above the growth temperature (15 degrees C) of psychrophiles and psychrotrophs was optimal for heat sh ock induced thermotolerance. On the other hand, in psychrotrophic yeas t grown at 25 degrees C, only a 5 Celsius degree increase in temperatu re was necessary for heat shock induced thermotolerance. Induced therm otolerance in all yeast species was coincident with hsp synthesis and trehalose accumulation. It was concluded that psychrophilic and psychr otrophic yeast, although exhibiting a stress response similar to mesop hilic Saccharomyces cerevisiae, nevertheless had distinctive stress pr otein profiles.