2-03: Production of a xylose utilizing Zymomonas mobilis strain for ethanol production from high concentrations of mixed sugars

Maximizing yield of ethanol from C5 utilizing micro organisms requires both high rates of sugar utilization and minimizing the production of by products that detract from carbon yield to ethanol.  Zymomonas mobilis that has been engineered to utilize xylose by way of the pathway through xylose isomerase and xylulose kinase to the endogenous sugar phosphate pathway produces xylitol and xylitol phosphate as byproducts.  Xylitol production results in loss of ethanol yield and xylitol phosphate is a general metabolic inhibitor as a dead end phosphate sink.  In order to correct these deficiencies in xylose utilizing Z. mobilis, the pathway to xylitol and xylitol phosphate was determined and the gene for the enzyme at the head of the pathway was inactivated to produce a strain that has better fermentation properties and a higher ethanol yield.  Effective means for achieving osmotic balance in high initial sugar fermentations was also established for the mutant and parent strain.