Multi-stage continuous culture fermentation of glucose-xylose mixtures to fuel ethanol using genetically engineered Saccharomyces cerevisiae 424A.

Multi-stage continuous (chemostat) culture fermentation (MCCF) with variable fermentor volumes was carried out to study the utilization of glucose and xylose for ethanol production via mixed sugar fermentation (MSF). Variable fermentor volumes were used to enable enhanced sugar utilization, accounting for differences in glucose and xylose utilization rates. Saccharomyces cerevisiae 424A-LNH-ST was used for fermentation of glucose-xylose mixtures. The dilution rates employed for continuous fermentation were based on earlier batch kinetic studies of ethanol production and sugar utilization. With a feed containing approximately 30 g L(-1) glucose and 15 g L(-1) xylose, cell washout was observed at a dilution rate of 0.8 h(-1). At dilution rates below 0.5 h(-1), complete glucose utilization was observed. Xylose consumption in the first-stage 1 L reactor was only 37% at the lowest dilution rate studied, 0.0 5h(-1). At this same flow rate, xylose consumption rose to 69% after subsequently passing through 3 and 1 L reactors in series, primarily due to the longer residence time in the 3 L reactor (0.0167 h(-1) dilution rate).