(197c) Metabolic Flux Analysis of the Central Metabolism of Laboratory and Industrial Saccharomyces Cerevisiae Strains Using 13C-Labeling Experiments

Recombinant Saccharomyces cerevisiae capable of utilizing xylose as a carbon source contains fungal or bacterial xylose catabolic pathways. In fungal pathway, D-xylose is converted to D-xylulose-phosphate through a series of oxidation and reduction and D-xylulose-phosphate is introduced to the endogenous pentose phosphate pathway. Central metabolism of Saccharomyces cerevisiae is highly regulated in a cooperative manner and the metabolic responses to the exogenous metabolic pathway including cell growth and xylose utilization depend on the metabolic functionality of wild type Saccharomyces cerevisiae. Recombinant yeast strains expressing identical xylose catabolic pathway show differences in cell growth, xylose uptake, and ethanol production. To elucidate the metabolic background conferring those differences, the central metabolisms of a laboratory strain, CEN.PK113-7D, and an industrial strain are investigated and compared by determining metabolic fluxes. Two yeast strains are grown in chemostats under oxygen-limited condition on ¹³C-labeled substrate and mass isotopomer distributions of central metabolites are determined using GC-MS. Mass isotopomer distributions are simulated by solving isotopomer balance equations and fluxes are calculated by fitting simulated mass isotopomer distributions to those obtained experimentally. These two yeast strains showed distinctive flux distribution and partitioning in their central metabolic pathways. These results combined with the strain-dependent rearrangement of flux distribution in recombinant Saccharomyces cerevisae would provide valuable metabolic engineering strategies to create recombinant yeast strains efficiently utilizing xylose for bioethanol production.