P157: Metabolome analysis of recombinant industrial Saccharomyces cerevisiae with xylose-fermenting ability

Little is known about how the differences in anaerobic ethanol production from glucose and xylose affect the metabolism of recombinant xylose-utilizing Saccharomyces cerevisiae. In the present study, we carried out comprehensive, quantitative metabolome analysis using capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS) on the recombinant glucose/xylose-cofermenting S. cerevisiae strain MA-R4 during fermentation with different carbon sources (glucose, xylose, glucose/xylose mixtures) to determine the intracellular pools of metabolites from the central carbon pathways and the levels of other biopolymers such as the twenty amino acids and purine nucleotides. We found that when xylose instead of glucose was metabolized, glycolytic metabolites were dramatically reduced, while conversely, most pentose phosphate pathway (PPP) metabolites were greatly increased. These results suggest that low carbon flux through glycolysis from the PPP is one of the limiting factors in xylose utilization. We further demonstrated that during xylose fermentation, many amino acids decreased and energy charges tended to decrease due to the selective reduction of ATP/AMP and GTP/GMP ratios. Associated with these lower energy states, fermentation with xylose alone drastically increased the level of citrate in the tricarboxylic acid cycle and increased the aromatic amino acids, strongly supporting the view that the fermentation of xylose leads to carbon and energy starvation. Thus, differences in carbon substrates, including glucose and xylose in the fermentation medium, widely affected the dynamic metabolism of MA-R4. These results provide us with a basis for better understanding of how the lack of efficiency with which recombinant S. cerevisiae strains ferment xylose influences the yeast metabolome.