(380e) Improving Exogenous Sugar Utilization: a Survey of Xylose Molecular Transporters

Metabolic engineering is a powerful platform for improving cellular production of biomolecules. However, classical metabolic engineering tools do not address molecular transport across the cellular membrane ? the key first step in most pathways. Molecular transport exerts limited flux control when an organism utilizes its preferred carbon source, yet its limitation is clearly evident when altering the carbon source preferences of an organism. As an example, molecular transport limits pentose utilization in Saccharomyces cerevisiae , an important problem in lignocellulosic biomass conversion to biofuels. Due to the lack of a native xylose transport protein, S. cerevisiae transports xylose via its hexose transporters where low affinity and hexose inhibition cause low flux. To improve this utilization, xylose transporters in yeast must be imported and/or engineered. Here, we present the first step towards this goal, namely a survey of a large group of known and putative xylose transporters from yeast, bacteria, and plant. These transporters were cloned and expressed in recombinant xylose-utilizing S. cerevisiae . The conferred growth on xylose and glucose was measured, along with an analysis of substrate preference. This study provides insight into the relative performance of these heterologous proteins as well as candidates for further investigation and improvement. Moreover, this work establishes the basis for molecular transporter protein engineering.