Adaptation of the Kinetics of Glucose Transport to Environmental Conditions in the Yeast Candida utilis CBS 621: a Continuous-culture Study

Abstract

SUMMARY: The relation between the kinetic parameters of glucose transport and the physiology of Candida utilis CBS 621 was studied in chemostat cultures. In glucose-limited cultures the transport parameters were dependent on the growth rate of the yeast. Three different transport systems were found which differed by an order of magnitude in their affinity constants, namely a high-affinity (K m 25 μM), a medium-affinity (K m 190 μM), and a low-affinity uptake system (K m 2000 μM). Cells growing at a dilution rate of 0.45 h-1 or less had the high- and medium-affinity uptake systems. At a dilution rate of 0.52 h-1 the high-affinity system was absent and both the medium-and low-affinity systems were present. At a dilution rate close to μmax (0.57 h-1) only the low-affinity system was detected. The in situ contribution of each of the transport systems to glucose consumption in glucose-limited cultures was estimated on the basis of their kinetic parameters (K m and V max) and the residual glucose concentration in these cultures. The sum of the calculated rates of transport corresponded to the in situ rate of glucose consumption by the cultures as determined from the yield constant and the dilution rate. The dependence of the transport parameters on the growth rate and hence on the environmental sugar concentration was also evident in cells grown under nitrogen limitation. In contrast to carbon-limited cells, nitrogen-limited cultures growing at D = 0.15 h-1 did not exhibit the high-affinity glucose uptake system, whereas the medium- and low-affinity systems were present.