Modeling simultaneous glucose and xylose uptake in Saccharomyces cerevisiae from kinetics and gene expression of sugar transporters.

A kinetic model for glucose and xylose co-substrate uptake in Saccharomyces cerevisiae is presented. The model couples the enzyme kinetics with the glucose-dependent genetic expression of the individual transport proteins. This novel approach implies several options for optimizing the co-substrate utilization. Interestingly, the simulations predict a maximum xylose uptake rate at a glucose concentration >0 g/L, which suggests that the genetic expressions of the considered transport proteins are of importance when optimizing the xylose uptake. This was also evident in fed-batch simulations, where a distinct optimal glucose addition rate >0 g/L x h was found. Strategies for improving the co-substrate utilization by genetic engineering of the transport systems are furthermore suggested based on simulations.