Layered and multi-input autonomous dynamic control strategies for metabolic engineering

Metabolic engineering seeks to reprogram cells to efficiently produce value-added chemicals. Traditionally, this is achieved by overexpressing the production pathway and/or knocking out competing endogenous pathways. However, limitations in some pathways are more effectively addressed through dynamic metabolic flux control to favor different cellular objectives over the course of the fermentation. Dynamic control circuits can autonomously actuate changes in metabolic fluxes in response to changing fermentation conditions, cell density, or metabolite concentrations. In this review, we discuss recent studies focused on multiplexed autonomous strategies which (1) combine regulatory circuits to control metabolic flux at multiple nodes or (2) respond to more than one input signal. These strategies have the potential to address challenging pathway scenarios, actuate more complex response profiles, and improve the specificity of the criteria that actuate the dynamic response.