Metabolic flux redirection from a central metabolic pathway toward a synthetic pathway using a metabolic toggle switch

• A synthetic genetic circuit named “metabolic toggle switch” for the redirection of metabolic flux was constructed in E. coli.
• Excess carbon flux in the TCA cycle was redirected toward isopropanol production pathway by metabolic toggle switch.
• Using metabolic toggle switch, isopropanol production titer and yield improved up to 3.7 and 3.1 times, respectively.

Overexpression of genes in production pathways and permanent knockout of genes in competing pathways are often employed to improve production titer and yield in metabolic engineering. However, the deletion of a pathway responsible for growth and cell maintenance has not previously been employed, even if its competition with the production pathway is obvious. In order to optimize intracellular metabolism at each fermentation phase for bacterial growth and production, a methodology employing conditional knockout is required. We constructed a metabolic toggle switch in Escherichia coli as a novel conditional knockout approach and applied it to isopropanol production. The resulting redirection of excess carbon flux caused by interruption of the TCA cycle via switching gltA OFF improved isopropanol production titer and yield up to 3.7 and 3.1 times, respectively. This approach is a useful tool to redirect carbon flux responsible for bacterial growth and/or cell maintenance toward a synthetic production pathway.