Investigation of Temperature Tolerance in Saccharomyces cerevisiae under Anaerobic Conditions

Saccharomyces yeasts are common workhorses for the production of alcoholic beverage and bio-ethanol. In these production processes, temperature is one of the predominant factors determining the operational costs of the industrial fermentation processes and the quality of the products (alcoholic beverage) because it influences the functioning of cellular activities in yeast cells. Saccharomyces yeasts in natural habitats have a wide range of difference in temperature optimal due to the geographic difference of habitats. Saccharomyces yeasts in an artificial environment, such as industrial fermentation processes, adapt to the conditions and have a temperature optimal close to the condition of the production process. In chapter 2, various Saccharomyces yeasts were compared for their growth performance between 12°C and 40°C wherein we selected two industrial strains which grew the fastest at sub- (12-27°C) and supra-optimal (33-40°C) temperatures. A top-down holistic approach was used to evaluate the temperature impact on cell growth, meaning the substrate uptake rates, (by)products production rates, as well as cellular protein and storage carbohydrates accumulations were measured. To do so, the two selected industrial strains and a laboratory strain were grown in anaerobic chemostat cultures at 12, 30, and 39°C to separate the growth rate effect from temperature effect. Significant differences in biomass and ethanol yields on glucose, total biomass protein, storage carbohydrates contents were observed between strains and cultivation temperatures.