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Hxt2 is a glucose repressed, high affinity glucose transporter of the yeast Saccharomyces cerevisiae and is subjected to high glucose induced degradation. Hxt11 is a sugar transporter that is stably expressed at the membrane irrespective the sugar concentration. To transfer this property to Hxt2, the N-terminal tail of Hxt2 was replaced by the corresponding region of Hxt11 yielding a chimeric Hxt11/2 transporter. This resulted in the stable expression of Hxt2 at the membrane and improved the growth on 8% D-glucose and 4% D-xylose. Mutation of N361 of Hxt11/2 into threonine reversed the specificity for D-xylose over D-glucose with high D-xylose transport rates. This mutant supported efficient sugar fermentation of both D-glucose and D-xylose at industrially relevant sugar concentrations even in the presence of the inhibitor acetic acid which is normally present in lignocellulosic hydrolysates. Biotechnol. (C) 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

Hxt2 is a glucose repressed, high affinity glucose transporter of the yeast Saccharomyces cerevisiae and is subjected to high glucose induced degradation. Hxt11 is a sugar transporter that is stably expressed at the membrane irrespective the sugar concentration. To transfer this property to Hxt2, the N-terminal tail of Hxt2 was replaced by the corresponding region of Hxt11 yielding a chimeric Hxt11/2 transporter. This resulted in the stable expression of Hxt2 at the membrane and improved the growth on 8% D-glucose and 4% D-xylose. Mutation of N361 of Hxt11/2 into threonine reversed the specificity for D-xylose over D-glucose with high D-xylose transport rates. This mutant supported efficient sugar fermentation of both D-glucose and D-xylose at industrially relevant sugar concentrations even in the presence of the inhibitor acetic acid which is normally present in lignocellulosic hydrolysates. Biotechnol. (C) 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

Hxt2 is a glucose repressed, high affinity glucose transporter of the yeast Saccharomyces cerevisiae and is subjected to high glucose induced degradation. Hxt11 is a sugar transporter that is stably expressed at the membrane irrespective the sugar concentration. To transfer this property to Hxt2, the N-terminal tail of Hxt2 was replaced by the corresponding region of Hxt11 yielding a chimeric Hxt11/2 transporter. This resulted in the stable expression of Hxt2 at the membrane and improved the growth on 8% D-glucose and 4% D-xylose. Mutation of N361 of Hxt11/2 into threonine reversed the specificity for D-xylose over D-glucose with high D-xylose transport rates. This mutant supported efficient sugar fermentation of both D-glucose and D-xylose at industrially relevant sugar concentrations even in the presence of the inhibitor acetic acid which is normally present in lignocellulosic hydrolysates. Biotechnol. (C) 2017 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

Background The yeast Saccharomyces cerevisiae is unable to ferment pentose sugars like d-xylose. Through the introduction of the respective metabolic pathway, S. cerevisiae is able to ferment xylose but first utilizes d-glucose before the d-xylose can be transported and metabolized. Low affinity d-xylose uptake occurs through the endogenous hexose (Hxt) transporters. For a more robust sugar fermentation, co-consumption of d-glucose and d-xylose is desired as d-xylose fermentation is in particular prone to inhibition by compounds present in pretreated lignocellulosic feedstocks. Results Evolutionary engineering of a d-xylose-fermenting S. cerevisiae strain lacking the major transporter HXT1–7 and GAL2 genes yielded a derivative that shows improved growth on xylose because of the expression of a normally cryptic HXT11 gene. Hxt11 also supported improved growth on d-xylose by the wild-type strain. Further selection for glucose-insensitive growth on d-xylose employing a quadruple hexokinase deletion yielded mutations at N366 of Hxt11 that reversed the transporter specificity for d-glucose into d-xylose while maintaining high d-xylose transport rates. The Hxt11 mutant enabled the efficient co-fermentation of xylose and glucose at industrially relevant sugar concentrations when expressed in a strain lacking the HXT1–7 and GAL2 genes. Conclusions Hxt11 is a cryptic sugar transporter of S. cerevisiae that previously has not been associated with effective d-xylose transport. Mutagenesis of Hxt11 yielded transporters that show a better affinity for d-xylose as compared to d-glucose while maintaining high transport rates. d-glucose and d-xylose co-consumption is due to a redistribution of the sugar transport flux while maintaining the total sugar conversion rate into ethanol. This method provides a single transporter solution for effective fermentation on lignocellulosic feedstocks. Electronic supplementary material The online version of this article (doi:10.1186/s13068-015-0360-6) contains supplementary material, which is available to authorized users.