Heat shock response in psychrophilic and psychrotrophic yeast from Antarctica

The response to heat stress in six yeast species isolated from Antarctica was examined. The yeast were classified into two groups: one psychrophilic, with a maximum growth temperature of 20 degrees C, and the other psychrotrophic, capable of growth at temperatures above 20 degrees C. In addition to species-specific heat shock prote in (hsp) profiles, a heat shock (15 degrees C-25 degrees C for 3 h) induced the synthesis of a 110-kDa protein common to the psychrophiles, Mrakia stokesii, M. frigida, and M. gelida, but not evident in Leucosporidium antarcticum. Immunoblot analyses revealed heat shock inducible proteins (hsps) corresponding to hsps 70 and 90. Interestingly, no proteins corresponding to hsps 60 and 104 were observed in any of the psychrophilic species examined. In the psychrotrophic yeast, Leucosporidium fellii and L. scottii, in addition to the presence of hsps 70 and 90, a protein corresponding to hsp 104 was observed. In psychrotrophic yeast, as observed 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 Celsius degree increase in temperature above the growth temperature (15 degrees C) of psychrophiles and psychrotrophs was optimal for heat shock induced thermotolerance. On the other hand, in psychrotrophic yeast grown at 25 degrees C, only a 5 Celsius degree increase in temperature was necessary for heat shock induced thermotolerance. Induced thermotolerance in all yeast species was coincident with hsp synthesis and trehalose accumulation. It was concluded that psychrophilic and psychrotrophic yeast, although exhibiting a stress response similar to mesophilic Saccharomyces cerevisiae, nevertheless had distinctive stress protein profiles.