Optogenetic switch for controlling the central metabolic flux of Escherichia coli

Dynamically controlling cellular metabolism can improve a cell's yield and productivity towards a target compound. However, the application of this strategy is currently limited by the availability of reversible metabolic switches. Unlike chemical inducers, light can readily be applied and removed from the medium multiple times without causing chemical changes. This makes light-inducible systems a potent tool to dynamically control cellular metabolism. Here we describe the construction of a light-inducible metabolic switch to regulate flux distribution between two glycolytic pathways, the Embden-Meyerhof-Parnas (EMP) and oxidative pentose phosphate (oxPP) pathways. This was achieved by using chromatic acclimation sensor/regulator (CcaSR) optogenetic system to control the expression of pgi, a metabolic gene which expression determines flux distribution between EMP and oxPP pathways. Control over these pathways may allow us to maximize Escherichia cob's yield on highly-reduced compounds such as mevalonate. Background pgi expression of the initial CcaSR construct was too high to significantly reduce pgi expression during the OFF-state. Therefore, we attenuated the system's output leakage by adjusting plasmid copy number and by tagging Pgi with ssRA protein degradation signal. Using our CcaSR-pgi ver.3, we could control EMP:oxPP flux ratio to 50:49 and 0.5:99 (of total glycolytic flux) by exposure to green and red light, respectively.