AN INVESTIGATION OF THE KINETICS OF YEAST GROWTH ON MIXTURES OF D-GLUCOSE, D-XYLULOSE AND D-XYLOSE (SCHIZOSACCHAROMYCES, POMBE)
Abstract
When the yeast Schizosaccharomyces pombe is grown on mixtures of D-glucose, D-xylulose, and D-xylose, simultaneous utilization of D-glucose and D-xylulose is observed. The kinetics of the utilization of these sugars have been examined under steady state conditions using a computer coupled fermentor which was operated as a turbidostat. At steady state, specific rates of sugar utilization were calculated based upon the nutrient feed, residual sugar and cell dry mass concentrations, and the dilution rate. The effects of the concentration of each of the sugars upon the utilization of the other were observed. Based upon the single substrate and mixed substrate fermentations, it was determined that levels of xylulose had no observable effect upon specific rates of glucose utilization. In contrast, glucose was observed to have a significant effect upon xylulose utilization. The extent of this effect was related to the glucose concentration in the fermentor. The pattern of attenuation was observed to be too complex to be attributed to simple competitive or non-competitive substrate inhibition. The effect has been tentatively attributed to either catabolite repression or catabolite inactivation. For the growth of this yeast on the sugar mixtures simple linear relationships were observed to exist between the specific growth rate and the total specific sugar uptake rate and between the specific rate of ethanol production and the total specific sugar uptake rate. These relationships along with models for sugar utilization and results from a mass balance analysis of the fermentor have provided the basis for the formulation of a steady state model for yeast growth on mixtures of glucose and xylulose. Excellent correlation between the experimental data and values calculated from the model was observed.
Degree
Ph.D.
Subject Area
Chemical engineering
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