Yield and maintenance relations of yeast growth in the chemostat at superoptimal temperatures

A model is proposed that accounts for the decreases in yield which occur in chemostat cultures of mesophilic yeasts at superoptimal growth temperatures. Two yield depressing effects were identified, one due to increased maintenance requirements by the viable fraction of the population, the other due to energy substrate dissipation by the nonviable function. The two effects are functions of the dilution rate, as is the fraction of nonviable cells. Experimental results were obtained on the yield, maintenance, and dissipation of energy substrate in a glucose-limited chemostat culture of a respiration-deficient mutant of Saccharomyces cerevisiae at 39 degrees C. The rates of glucose utilization for maintenance and for dissipation constituted, respectively, 33-28% and 15-9% of the total glucose utilization rate over the range of dilution rates tested (0.038-0.064 hr-1), while the yield varied over this range from 0.066-0.085 g of biomass (dry wt) per gram of glucose.