This study characterizes the sugar transport systems underlying fructophily (preference for fructose over glucose) in Zygosaccharomyces bailii, a yeast that spoils food products. Researchers measured initial uptake rates of fructose and glucose in cells grown on different carbon sources. Fructose is transported by a specific low-affinity, high-capacity system (Km 65.6 mM, Vmax 67 mmol g⁻¹ h⁻¹), while glucose uses a separate transporter with higher affinity but lower capacity (Km 7 mM, Vmax 1.7 mmol g⁻¹ h⁻¹). The glucose transporter also accepts fructose as a substrate. Three mechanisms favor fructose utilization: the fructose transporter has higher capacity, fructose inactivates the glucose transporter in a concentration-dependent manner, and fructose can compete for glucose transport. Both transporters are partially inducible. Metabolic measurements confirmed transport kinetics observations. Uranyl ion experiments demonstrated the two transporters are distinct—uranyl inhibited glucose transport but not fructose transport in cells grown on high fructose. The study reveals that transport kinetics and regulation, rather than metabolism, explain Z. bailii's fructophilic behavior, providing insight into why this yeast dominates in fructose-rich food environments.

Key findings

• Zygosaccharomyces bailii has two distinct sugar transporters: a specific fructose transporter with low affinity/high capacity and a glucose transporter that also accepts fructose
• Fructose inactivates the glucose transporter in a concentration-dependent manner, progressively inhibiting glucose uptake
• The fructose-specific transporter shows high specificity and is not inhibited by uranyl ions, distinguishing it from the glucose transporter
• Both transport systems are partially inducible, with expression dependent on growth substrate
• Transport kinetics and regulation, not metabolic enzymes, explain Z. bailii's fructophilic phenotype and its ecological success in fructose-rich environments