SIMULTANEOUS UTILIZATION OF GLUCOSE AND D-XYLOSE BY CANDIDA-SHEHATAE IN A CHEMOSTAT

The kinetics of biomass formation, D-xylose utilization, and mixed sub strate utilization were determined in a chemostat using the yeast Cand ida 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 p ure D-xylose, Mixtures of D-xylose and glucose (similar to 1:1) were s imultaneously 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 mu(max) and reduced the dilution r ate range over which D-xylose was utilized in the presence of glucose, At pH 4.5, mu(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 pro duction of value added products from renewable carbon sources, since s imultaneous mixed substrate utilization was observed over a wide range of growth rates on a 1:1 mixture of glucose and D-xylose.