Simultaneous utilization of glucose and D-xylose by Candida shehatae in a chemostat

Abstract

The kinetics of biomass formation, D-xylose utilization, and mixed substrate utilization were determined in a chemostat using the yeast Candida shehatae. The maximum growth rate of C. shehatae grown aerobically on D- xylose was 0.42 h-1 and the Monod constant, K(s), was 0.06 g L-1. The biomass yield, Y({X/S}), ranged from 0.40 to 0.50 g g-1 over a dilution rate range of 0.2-0.3 h-1, when C. shehatae was grown on pure D-xylose. Mixtures of D-xylose and glucose (~1: 1) were simultaneously utilized over a dilution rate from 0.15 to 0.35 h-1 at pH 3.5 and 4.5, but pH 3.5 reduced μ(max) and reduced the dilution rate range over which D-xylose was utilized in the presence of glucose. At pH 4.5, μ(max) was not reduced with the mixed sugar feed and the overall or lumped K (s)value was not significantly increased (0.058 g L-1 vs 0.06 g L-1), when compared to a pure D-xylose feed. Kinetic data indicate that C. shehatae is an excellent candidate for chemostat production of value added products from renewable carbon sources, since simultaneous mixed substrate utilization was observed over a wide range of growth rates on a 1 : 1 mixture of glucose and D-xylose.