Glucose Transport in Crabtree-positive and Crabtree-negative Yeasts

Abstract

The kinetic parameters of glucose transport in four Crabtree-positive and four Crabtreenegative yeasts were determined. The organisms were grown in aerobic glucose-limited chemostats at a dilution rate of 0.1 h-l . The results show a clear correlation between the presence of high-affinity glucose transport systems and the absence of aerobic fermentation upon addition of excess glucose to steady-state cultures. The presence of these H+-symport systems could be established by determination of intracellular accumulation of 6-deo~y-[~H]glucose and alkalinization of buffered cell suspensions upon addition of glucose. In contrast, the yeasts that did show aerobic alcoholic fermentation during these glucose pulse experiments had low-affinity facilitated-diffusion carriers only. In the yeasts examined the capacity of the glucose transport carriers was higher than the actual glucose consumption rates during the glucose pulse experiments. The relationship between the rate of sugar consumption and the rate of alcoholic fermentation was studied in detail with Saccharomyces cereuisiae. When S . cerevisiae was pulsed with low amounts of glucose or mannose, in order to obtain submaximal sugar consumption rates, fermentation was already occurring at sugar consumption rates just above those which were maintained in the glucose-limited steady-state culture. The results are interpreted in relation with the Crabtree effect. In Crabtree-positive yeasts, an increase in the external glucose concentration may lead to unrestricted glucose uptake by facilitated diffusion and hence, to aerobic fermentation. In contrast, Crabtree-negative yeasts may restrict the entry of glucose by their regulated H+-symport systems and thus prevent the occurrence of overflow metabolism.

Optimization of Corn Steep Liquor Dosage and Other Fermentation Parameters for Ethanol Production by Saccharomyces cerevisiae Type 1 and Anchor Instant Yeast

“…However, the decrease in biomass and ethanol concentrations at 42 h and 18 h, respectively, and the increased cell masses which were maintained after 12 h in Figures 1 and 2 could be indicative of glucose limitation which may be synonymous with the crabtree effect; this cannot be ascertained at this stage [40,41]. The slow conversion of the reducing sugar was also observed with yeast extract as the nutrient source.…”

Kinetics of growth and sugar consumption in yeasts

“…Sugar transport in these yeasts is an energy-requiring process since such cells accumulate the non-metabolizable analogue 6-deoxyglucose (Table 2; Van Urk et al 1989a). In Crabtree-positive yeasts on the other hand, transport of glucose occurs via facilitated diffusion and 6-deoxyglucose is not accumulated.…”

Prolonged selection in aerobic, glucose-limited chemostat cultures of Saccharomyces cerevisiae causes a partial loss of glycolytic capacity

“…O 2 and CO 2 concentrations were determined with a Rosemount NGA2000 analyser. Determination of the exhaust gas flow rate and calculation of specific rates of CO 2 production and O 2 consumption were performed as described previously (van Urk et al, 1988;Weusthuis et al, 1994).…”