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Poster Presentation 2-23
A Metabolic Network Stoichiometry Analysis of Recombinant Zymomonas mobilis Fermenting a Mixture of Glucose and Xylose
M. Mete Altintas1, Qiang Gao1, Min Zhang2, James D. McMillan2, and Dhinakar S. Kompala1
1Department of Chemical Engineering, University of Colorado, Boulder, CO 80309-0424 USA
2Biotechnology Division for Fuels and Chemicals, National Renewable Energy Laboratory, Golden, CO 80401-3933 USA
Telephone: (303) 492-6530; Fax: (303) 492-4341; E-mail: altintas@colorado.edu
Zymomonas mobilis strains engineered to express two heterologous xylose utilization metabolic enzymes and two heterologous pentose phosphate pathway enzymes utilize glucose and xylose simultaneously but demonstrate a strong preference for glucose. Thus, mixed sugar fermentations can be separated into two metabolic regimes. In the first regime, glucose is rapidly consumed with only modest levels of xylose being utilized. In the second regime, sustained fermentation of xylose occurs. We have developed a stoichiometrically-based metabolic flux network based on the known hexose Entner-Doudoroff and ethanol fermentation pathways and the putative pentose assimilation pathway to better understand and quantify the shift in metabolism that occurs during batch fermentation of glucose-xylose mixtures to ethanol. At the core of the metabolic flux network is the assumed pentose phosphate pathway where xylose assimilation and conversion to the Entner-Doudoroff pathway intermediates are catalyzed by the four heterologous enzymes. Metabolic flux distributions within this network were calculated using experimental data from batch cultures of engineered Zymomonas mobilis grown on a medium containing glucose and xylose. The dramatic shifts observed in the metabolic flux distributions during the course of the fermentations highlight the need to develop a kinetic model capable of describing the dynamics of mixed hexose-pentose sugar metabolism.
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