Thermal association and dissociation in thermosensitive mutants ofSaccharomyces cerevisiae

Conditioning by mitochondria and energy source of thermal death parameters in yeast

Two strains of Saccharomyces cerevisiae of opposite mating type (a and alpha), with different resistance to thermal death, and their respective mitochondrial respiratory-deficient mutants (petites ap and alpha p) were used to prepare the following diploid strains: a alpha, a alpha p and ap alpha. Specific thermal death rates were determined at supramaximum temperatures for growth, under conditions of mitochondrial derepression (glycerol medium). Comparison of the entropies of activation of thermal death showed that diploids a alpha and ap alpha behaved like the more resistant haploid alpha, and diploid a alpha p like haploid a. In glucose medium strains alpha and a alpha became even more thermoresistant. The results favour the concept that thermal death determinants are located in the mitochondrial genome, and that mitochondria repressed cells repair thermal injuries more efficiently.

Comparative study of the temperature profiles of growth and death of the pathogenic yeast Cryptococcus neoformans and the non-pathogenic Cryptococcus albidus

The temperature profiles of two species of Cryptococcus were compared. The pathogenic Cr. neoformans had a maximum temperature for growth of 39.8 degrees C and the non-pathogenic Cr. albidus, of 30.2 degrees C. The specific growth rates measured in the former were of an order of magnitude higher than in the latter, whereas the Arrhenius plots of the specific thermal death rates did not show a significant difference.

The temperature profile of the pathogenic yeast Candida albicans

A strain of Candida albicans was found to have an associative temperature profile with respect to growth, thermal death and yield on glucose. The ARRHENIUS plot of sustained exponential growth displayed two branches in the supraoptimal temperature range with the optimum temperature for growth around 33 degrees C, the final maximum temperature for growth around 38 degrees C and the initial maximum temperature for growth around 42 degrees C. The yield on glucose was temperature dependent in the supraoptimal range and declined linearly to zero between the optimum and the initial maximum temperature for growth.