2-68: Metabolic analysis of the effect of acetic acid on the co-fermentation of glucose and xylose by S. cerevisiae 424A(LNH-ST)

Lignocellulosic biomass, primarily composed of cellulose, hemicellulose, and lignin, is a promising renewable feedstock for the microbial production of chemicals and fuels, especially ethanol via fermentation.  The major fermentable sugars released from the processing of the lignocellulose are glucose and xylose.  However, the primary processing steps required for this conversion also produce a range of compounds that can inhibit the subsequent microbial fermentation.  One such inhibitory compound is acetic acid, liberated from hemicelluloses during the pretreatment of the biomass.  We previously reported that acetic acid inhibited cell growth, substrate consumption, and ethanol productivity, while it improved metabolic ethanol yield.  To explore the effect of acetic acid on a cellular level, a comprehensive analysis of key intracellular metabolites involved in glycolysis and the pentose phosphate pathway was conducted.  The Global Isotope-labeled Internal Standard (GILISA) MS quantization method was used for the identification and quantification of the intracellular metabolites of glucose/xylose fermenting Saccharomyces cerevisiae 424A(LNH-ST).  Metabolic flux analyses were performed and compared between control co-fermentations and co-fermentations with acetic acid (7.5, 10, and 15 g/L) at a controlled pH of 5.5.