15C13 Advances in Metabolic Engineering
Controlling Central Carbon Metabolism for Improved Pathway Yields
Sue Zanne Tan & Kristala L. J. Prather
Microbial fermentation has the potential to produce valuable compounds, such as pharmaceuticals, fragrances, and fuel-like compounds, from simple and inexpensive starting materials. One of the challenges in manufacturing molecules with microbes is achieving sufficient titers and yields, such that the overall process can be economically feasible. Some common methods to improve pathway yields include overexpression of pathway enzymes, deleting competing pathways, and engineering redox and energy balances. However, these methods are not always successful due to the interconnectivity of metabolic pathways and the finite nature of cellular resources. Alternative to these traditional approaches is to control and regulate metabolic pathways in a dynamic manner. This method enables flux balance between growth and production, such that production is maximized while still maintaining high cell viability. As a proof-of-concept, we have successfully constructed a metabolite valve in Saccharomyces cerevisiae that provides the control of central carbon metabolism and redirection of carbon flux into a heterologous pathway. Using the tetracycline transactivator protein (tTA) system, we saw a 50-fold increase in yields of a model compound, gluconate. By varying different induction times and inducer concentrations, we obtained strains with different growth rates and gluconate titers, demonstrating the control of glucose flux either to growth or production. In addition, the successful redirection of carbon flux away from glycolysis significantly reduced the accumulation of ethanol, even in the presence of high glucose concentrations.