SYNTHESIS OF HEAT-SHOCK PROTEINS IN MYCELIA AND YEAST FORMS OF PARACOCCIDIOIDES-BRASILIENSIS

The induction of heat-shock proteins has been postulated to play a role not only in thermo-adaptation, but also in phase transition of the dimorphic fungi. In this study, we used yeast and mycelial forms of the thermally dimorphic fungus Paracoccidioides brasiliensis to evaluate the effect of temperature on the induction of the heat-shock response. We also evaluated protein synthesis by P. brasiliensis caused by exposure to low pH and H2O2. Analysis of protein synthesis by SDS-PAGE disclosed that P. brasiliensis mycelia increased synthesis of all major constitutive proteins when stressed at 37 degrees C and increased synthesis of three non-constitutive proteins of 134, 82 and 28 kDa at 40 degrees C. Yeasts incubated at 40 degrees C showed decreased synthesis of five constitutive proteins (136, 98, 62, 57 and 54 kDa) and the appearance of three new proteins (134, 82 and 28 kDa). There was a decrease in the synthesis of all major constitutive proteins except for three proteins of 141, 136 and 16 kDa when yeast cells were incubated at 25 degrees C. When stressed by low pH and H2O2, P. brasiliensis yeast increased synthesis of one (134 kDa) and five (134, 104, 82, 52 and 40 kDa) non-constitutive proteins, respectively. P. brasiliensis mycelia and yeast forms disclosed the same profile of protein synthesis when stressed at temperatures that trigger phase transition (37 degrees C for mycelia; 25 degrees C for yeast). The same profile of protein synthesis by both forms occurred when the fungi were incubated at 40 degrees C and was similar to that of yeast cells stressed by low pH or H2O2, but different from the patterns produced by mycelia incubated at 37 degrees C or yeast at 25 degrees C. These results suggest that synthesis of stress proteins by P. brasiliensis mycelia and yeast forms at 40 degrees C, low pH or exposed to H2O2 was associated with adaptation to hostile environments. In contrast, the overall increased and decreased synthesis of major constitutive proteins by mycelia and yeast forms at 37 degrees C and 25 degrees C was associated with phase transition. It is unlikely that the heat-shock proteins produced in these experiments are important in the maintenance of the morphology of yeast or mycelia at their usual temperatures of growth.