Engineering of xylose reductase and overexpression of xylitol dehydrogenase and xylulokinase improves xylose alcoholic fermentation in the thermotolerant yeast hansenula polymorpha

Abstract

Recombinant genetic constructs and strains of H. polymorpha having significantly increased ethanol productivity with a simultaneous decreased production of xylitol during high-temperature xylose fermentation are disclosed. The constructs include a H. polymorpha XYL1 gene encoding xylose reductase mutated to decrease affinity of the enzyme toward NADPH. The modified version of XYL1 gene under control of a strong constitutive HpGAP promoter was overexpressed in a Δxyll background. A recombinant H. polymorpha strain overexpressing the mutated enzyme together with native xylitol dehydrogenase and xylulokinase in the Δxyll background was also constructed. Xylose consumption, ethanol and xylitol production by the constructed strain were evaluated during high-temperature xylose fermentation (48° C.). A significant increase in ethanol productivity (up to 7.4 times) was shown in the recombinant strain as compared with the wild type strain. Moreover, the xylitol production by the recombinant strain was reduced considerably: 0.9 mgχ (Lχh)−1 versus 4.2 mgχ (Lxh)−1 by the wild type strain.

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