(752d) Enabling Glucose-Xylose Co-Utilization in Yeast through Expression of Xylose-Specific Transporters

Co-utilization of glucose and xylose is highly desired for cost-effective industrial biofuel and biochemical production from lignocellulosic biomass. However, in yeast, xylose uptake is significantly repressed by glucose, which impedes the implementation of yeast as an efficient platform for biorenewables production. Most of the previous studies focused on engineering yeast hexose transporters to alleviate glucose inhibition as well as increase xylose affinity to improve co-sugar utilization. In contrast to Saccharamyces cerevisiae, which cannot naturally metabolize xylose, nearly all the yeasts from CUG clade possess the inherent capability to assimilate xylose. Taking advantage of this property, we were able to identify three xylose-specific transporters from CUG clade yeasts, which could efficiently transport xylose even in the presence of glucose. Among these three, the best transporter allowed simultaneous co-sugar utilization, and was able to assimilate 30 g/L xylose in the mixture of 70 g/L glucose and 40 g/L xylose. The transporters were characterized in an industrially relevant CUG clade strain, Scheffersomyces stipitis, which possesses a superior capability of producing ethanol from xylose. The performance of the best newly identified transporter was compared with the best reported transporters in S. stipitis. Our work demonstrates that besides reshaping hexose transporters, seeking naturally existing high-performance xylose-specific transporters free from glucose repression is practical. Our results further enhance the potential of S. stipitis as a platform strain for commodity and specialty chemicals production in industry.