Model of cellobiose phosphorylase-mediated cellobiose consumption in the presence of xylose. Cellobiose and xylose are simultaneously imported via the cellodextrin transporter CDT-1 (F213L) and endogenous hexose transporters, respectively. Cellobiose undergoes phosphorolytic cleavage via CBP, generating glucose and G1P, both of which enter glycolysis. However, some of the G1P and imported xylose are condensed by CBP to produce GX in its thermodynamically favorable reverse reaction. GX is then transported out of the cell and imported back into the cell by the cellodextrin transporter over the time course of fermentations. The intracellular GX is then cleaved to G1P and xylose by CBP when the intracellular cellobiose concentration drops in later times of the fermentation. Free xylose is then released back into the fermentation broth in the absence of the xylose consumption pathway. CDT-1 (F213L), cellodextrin transporter mutant; Hxt, hexose transporters; CBP, cellobiose phosphorylase; Pi, inorganic phosphate; Glc, glucose; GX, glucopyranosyl-xylose; G1P, glucose-1-phosphate.