Enhanced xylose utilization in an adapted S. cerevisiae strain expressing xylose isomerase

We analyzed the genome sequence of an engineered S. cerevisiae strain expressing codon-optimized Prevotella ruminicola XI and XK genes that was previously adapted for increased xylose fermentation. Tetrad analysis of haploid spores from the heterozygous diploid showed that of the seven mutations present in the adapted strain, only pbs2L363X and pho13G208C mutations improved xylose utilization. Strains carrying a single mutated or deleted PBS2 or PHO13 did not show improved growth on xylose, indicating that both mutations were necessary. Double deletion of PBS2 and PHO13 also improved xylose utilization for strains expressing the XR/XDH pathway. However, unlike strains expressing the XI pathway, these strains also showed a significant improvement from deletion of the PHO13 gene alone.