S148: Kinetic and stoichiometric modeling of the fermentative metabolism of glycerol in E. coli

Glycerol has become an abundant and inexpensive feedstock for the synthesis of fuels and chemicals due to its generation as a by-product of the biodiesel, oleo-chemical, and bioethanol industries. In order to fully realize the potentials of glycerol, the use of industrial organisms capable of fermenting this carbon source under anaerobic conditions is highly desirable. The discovery that E. coli, the workhorse of modern biotechnology, is able to utilize glycerol in a fermentative manner has provided a new platform for the implementation of metabolic engineering strategies aimed at fuel and chemical production from glycerol. This work focuses in the implementation of kinetic and genome-scale stoichiometric models to study the fermentative metabolism of glycerol in E. coli.

Using kinetic modeling and Metabolic Control Analysis (MCA), the control structure of the pathways involved in glycerol utilization and ethanol synthesis was elucidated. Glycerol dehydrogenase (glyDH) and dihydroxyacetone kinase (DHAK) were identified as the enzymatic steps controlling the glycolytic flux during the fermentative metabolism of glycerol in E. coli. The control structure predicted by the MCA was experimentally verified and the findings used to improve the anaerobic production of ethanol from crude glycerol.

Genome scale models allow the prediction of flux mass distribution using Flux Balance Analysis (FBA), a methodology that uses linear optimization of a stoichiometric model, with biomass production as objective function. This model was used to validate the proposed model for glycerol fermentation, in which the production of ethanol and 1,2-propanediol (1,2-PDO) are essential for ATP synthesis and to achieve redox-balance.