Development and Validation of Yeast Biosensors for Signaling Pathways

Sammanfattning: Efficient bioconversion of the pentose xylose is vital for the development of competent lignocellulose biorefineries. Although many proper attempts of metabolic engineering for recombinant xylose utilization have been made in Saccharomyces cerevisiae, growth on xylose is still far from being optimal. Previous findings point out a more complex explanation to this feature involving interactions between xylose and signaling pathways. To assess this question we have developed and validated a panel of GFP yeast biosensor strains for the characterization of three signaling pathways (Snf3/Rgt2, Snf1/Mig1, cAMP/PKA) when subjected to different xylose conditions. Interestingly, the presence of 50 g/L xylose alone did not trigger any effect on these signaling pathways, however, when having a mixed condition of 50 g/L xylose and 5 g/L glucose higher induction patterns were observed than in glucose 5 g/L for the low affinity hexose transporters (HXT2 and HXT4) and the SUC2 gene. Together these results support the hypothesis that xylose alone produces a true starvation response in non-engineered W303 S. cerevisiae strains instead of a non-fermentable carbon response. Furthermore, sufficient information has been acquired to propose that mixed conditions of glucose and xylose produce a more profound effect in signaling that should be investigated further.