The yeast glucose-oxygen phenotypic phase plane (PhPP). (a) The three-dimensional S. cerevisiae PhPP drawn with Statistica™ (Statsoft, Tulsa, OK). The x and y axes represent the glucose uptake rate and oxygen uptake rate, respectively. The third dimension is the cellular growth rate. (b) A two-dimensional projection of the 3-D polytope in panel (a). The two lines of optimality are shown in red. LOgrowth represents optimal aerobic glucose-limited growth and LOethanol corresponds to maximum ethanol production under microaerobic conditions. P1 - P7 represent phases with various metabolic phenotypes. The hatched regions correspond to infeasible growth conditions. The orange line (glucose uptake flux = 5 mmol/gDCW/hr) represents the conditions which were used for the simulations in Figure 2.