Aspects of cell death and autolysis in Saccharomyces cerevisae : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University

Abstract

The kinetics of cell death and autolysis of twenty two haploid yeast strains were examined over a period of eight months in wine and synthetic media. Eight distinct patterns of cell death were observed using methylene blue staining and sample plating for viable cells. The rate of death was both yeast strain dependent and influenced by environmental factors such as temperature, nutrient supply and the presence or absence of ethanol. The activity of extracellular killer yeast toxin concentrated by ultrafiltration was examined under various environmental conditions. Toxin activity was pH and temperature dependent. Concentrations of ethanol greater than 2% completely inhibited killer toxin activity. A difference of 12 hours was detected between a yeast ce71 becoming incapable of reproduction as the result of killer toxin action and this inability becoming discern­ible by methylene blue staining. A maximum kill of 97 - 99% was obtained independent of cell or toxin concentration. Toxin induced death was accompanied by the release of arginine and lysine. A bioassay was developed to quantify the amounts of arginine and lysine released.