Engineering Transaldolase in <i>Pichia stipitis</i> to Improve Bioethanol Production

In our effort to improve the efficiency and yield of xylose-to-ethanol bioconversion in <i>Pichia stipitis</i>, the transaldolase (TAL) in the pentose phosphate pathway was identified as a rate-limiting enzyme for improvement. A mutant containing the Q263R change was first obtained by directed evolution with 5-fold increase of activity, which was then incorporated into <i>P. stipites</i> <i>via</i> the pYDS vector to produce a genetically stable strain for fermentation on xylose. In comparison with the parental strain, TAL-Q263R­(+) increases ethanol prodcution by 36% and 100% as measured by volumetric production rate and specific production rate, respectively. Thus improving the transaldolase activity in <i>P. stipitis</i> can significantly increase the rate and yield of xylose conversion to ethanol