Metabolic engineering of Klebsiella oxytoca M5A1 for ethanol production from xylose and glucose.

The efficient diversion of pyruvate from normal fermentative pathways to ethanol production in Klebsiella oxytoca M5A1 requires the expression of Zymomonas mobilis genes encoding both pyruvate decarboxylase and alcohol dehydrogenase. Final ethanol concentrations obtained with the best recombinant, strain M5A1 (pLOI555), were in excess of 40 g/liter with an efficiency of 0.48 g of ethanol (xylose) and 0.50 g of ethanol (glucose) per g of sugar, as compared with a theoretical maximum of 0.51 g of ethanol per g of sugar. The maximal volumetric productivity per hour for both sugars was 2.0 g/liter. This volumetric productivity with xylose is almost twice that previously obtained with ethanologenic Escherichia coli. Succinate was also produced as a minor product during fermentation.