The relationship between transport kinetics and glucose uptake by Saccharomyces cerevisiae in aerobic chemostat cultures

The steady-state residual glucose concentrations in aerobic chemostat cultu res of Saccharomyces cerevisiae ATCC 4126, grown in a complex medium, incre ased sharply in the respiro-fermentative region, suggesting a large increas e in the apparent k(s) value. By contrast, strain CBS 8066 exhibited much l ower steady-state residual glucose concentrations in this region. Glucose t ransport assays were conducted with these strains to determine the relation ship between transport kinetics and sugar assimilation. With strain CBS 806 6, a high-affinity glucose uptake system was evident up to a dilution rate of 0.41 h(-1), with a low-affinity uptake system and high residual glucose levels only evident at the higher dilution rates. With strain ATCC 4126, th e high-affinity uptake system was present up to a dilution rate of about 0. 38 h(-1), but a low-affinity uptake system was discerned already from a dil ution rate of 0.27 h(-1), which coincided with the sharp increase in the re sidual glucose concentration. Neither of the above yeast strains had an abs olute vitamin requirement for aerobic growth. Nevertheless, in the same med ium supplemented with vitamins, no low-affinity uptake system was evident i n cells of strain ATCC 4126 even at high dilution rates and the steady-stat e residual glucose concentration was much lower. The shift in the relative proportions of the high and low-affinity uptake systems of strain ATCC 4126 , which might have been mediated by an inositol deficiency through its effe ct on the cell membrane, may offer an explanation for the unusually high st eady-state residual glucose concentrations observed at dilution rates above 52% of the wash-out dilution rate.