1-19: Effect of cations and anions on glucose/xylose co-fermentation and the distribution of intracellular metabolites of recombinant S. cerevisiae 424A(LNH-ST)

The commercialization of cellulosic ethanol has faced a number of different technical hurdles.  One major challenge is the negative impact of inhibitors on the fermentative performance of industrial microorganisms.  Most inhibition studies have focused on furan derivatives and weak acids; however, potential fermentation inhibitors also include cations and anions.  Cations and anions are present in cellulosic biomass and are also used for pH adjustment prior to and during fermentation.  To characterize the inhibitory effect of cations (potassium, sodium, ammonium) and anions (chloride and sulfate), a series of lab-scale fermentations were completed using S. cerevisiae 424A(LNH-ST), a recombinant yeast strain that can effectively co-ferment glucose and xylose.  The concentration of the cations and anions tested ranged from 0.1M to 0.5M.  Preliminary analysis of these fermentations showed xylose fermentation to be more sensitive to the presence of cations and anions than glucose fermentation.  Results also found sodium to be the most inhibitory cation.  To further explore the effect of sodium, a comprehensive analysis of 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 intracellular metabolites at key metabolic stages during fermentation.