17-30: Systems biology approach to understanding the effect of acetic acid on the co-fermentation of glucose and xylose by S. cerevisiae 424A(LNH-ST)

Tuesday, May 1, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
Elizabeth Casey1, Nathan Mosier1, Jiri Adamec2, Amber Jannasch3, Nancy W. Y. Ho4 and Miroslav Sedlak1, (1)LORRE/Ag. and Bio. Engineering, Purdue University, West Lafayette, IN, (2)Department of Biochemistry, University of Nebraska Lincoln, Lincoln, NE, (3)Bindley Bioscience Center, Purdue University, West Lafayette, IN, (4)LORRE/Chemical Engineering, Purdue University, West Lafayette, IN
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.  One such inhibitory compound is acetic acid, liberated from hemicellulose during the pretreatment of the biomass. 

To study the effect of acetic acid on glucose/xylose co-fermentation by S. cerevisiae 424A(LNH-ST), a genetically engineered yeast strain that can effectively co-ferment both glucose and xylose to ethanol, we first determined the impact of the acetic acid on various yeast performance characteristics.  Results showed acetic acid to be inhibitory to cell growth, substrate consumption (especially xylose), and ethanol productivity, and stimulatory to the metabolic ethanol yield. 

To further explore and understand these effects of acetic acid, we took a systems biology approach by analyzing intracellular metabolite levels and gene expression levels.  Reverse-phase liquid chromatography-mass spectrometry and in vitro 13C labeling was used for the identification and quantification of key intracellular glycolytic and pentose phosphate pathway metabolites.  Initial results show significant differences in the concentration of the selected intracellular metabolites between fermentations with and without acetic acid.  Microarray technology was used to determine the expression levels of the full yeast genome (with the exception of the genes inserted to allow for xylose fermentation).  Preliminary analysis shows minimal differences in the expression of central carbon metabolism genes during glucose fermentation; however, significant differences were seen during xylose fermentation.  Relationships between metabolomic, transcriptomic, and fermentation performance will be presented.

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