Bifunctional Optogenetic Switch Powered NADPH Availability for Improving <scp>l</scp>-Valine Production in <i>Escherichia coli</i>

l-Valine is a key amino acid in the food and feed industries, but the efficiency of its microbial production is often hindered by limited intracellular NADPH availability. To address this issue, a bifunctional optogenetic switch (BOS) was developed by combining the light-inducible transcriptional regulator LEVI mutant with the chemical-inducible repressor LacI. The BOS demonstrated high composability, enabling precise control of intracellular NADPH levels by regulating the expression of pgi (encoding glucose 6-phosphate isomerase) and zwf (encoding glucose 6-phosphate dehydrogenase) in response to blue light. To evaluate its potential in optimizing l-valine production, we introduced BOS into an engineered Escherichia coli strain, LYD-V1, designed for l-valine production. The resulting strain, E. coli LYD-V5, achieved enhanced NADPH synthesis without compromising cell growth, leading to an 18% increase in l-valine titer (59 g/L) and a 34% improvement in yield (0.39 g/g glucose). These findings highlight the potential of BOS for improving microbial production of value-added chemicals.