Physiological and Molecular Analyses of Stress Responses in Psychrophilic Psychrotrophic, Mesophilic and Thermophilic Yeast

Abstract

The response to heat and oxidative stress in seven yeast species isolated from Antarctica was examined. The yeast were classified into two groups, one psychrophilic, with a maximum growth temperature of 20°C and the other psychrotrophic. capable of growth at temperatures above 20°C. In addition to species specific heat shock protein (hsp) profiles, a heat shock (15°C to 25°C for 3 h) induced the synthesis of a 110 kDa protein common to the psychrophiles. 'Candida psychrophila', 'Mrakia stokesii', 'M. frigida' and 'M. gelida', but not in 'Leucosporidium antarcticum'. Preliminary amino acid sequence characterization of hsp 110 revealed similarity to fructose-2,6-bisphosphatase. Immunoblot analyses revealed heat shock inducible proteins corresponding to 'Saccharomyces cerevisiae' hsps 70 and 90 in psychrophilic and psychrotrophic yeast ('L. fellii' and 'L. scottii'). Interestingly, no protein corresponding to 'S. cerevisiae' hsp 104 was observed in any of the psychrophilic species examined, however a hsp 104 homologue was identified in psychrotrophic yeast. In psi chrotrophic yeast, as observed in psychrophilic yeast, there was a noticeable absence of a protein corresponding to hsp 60 with the notable exception of a hsp 60 homologue detected in 'C. psychrophila'. A 10°C increase in temperature above the growth temperature (15°C) of psychrophiles and psychrotrophs induced thermotolerance. On the other hand in psychrotrophic yeast grown at 25°C. only a 5°C increase in temperature was necessary for heat shock induced thermotolerance. Induced thermotolerance in all psychrophilic and psychrotrophic yeast species was coincident with hsp synthesis and trehalose accumulation.