Overexpression of bacterial xylose isomerase and yeast host xylulokinase improves xylose alcoholic fermentation in the thermotolerant yeast Hansenula polymorpha

Abstract

The thermotolerant methylotrophic yeast Hansenula polymorpha is able to ferment xylose to ethanol. To improve characteristics of xylose fermentation, the recombinant strain Δxyl1 Δxyl2-A Δxyl2-B, with deletions of genes encoding first enzymes of xylose utilization (NAD(P)H-dependent xylose reductase and NAD-dependent xylitol dehydrogenases, respectively), was constructed and used as a recipient for co-overexpression of the Escherichia coli xylA gene coding for xylose isomerase and endogenous XYL3 gene coding for xylulokinase. The expression of both genes was driven by the H. polymorpha glyceraldehyde-3-phosphate dehydrogenase promoter. Xylose isomerase activities of obtained transformants amounted to ∼80% of that of the bacterial host strain. Xylulokinase activities of the transformants increased twofold when compared with the parental strain. The recombinant strains displayed improved ethanol production during the fermentation of xylose. © 2007 Federation of European Microbiological Societies.