Bifunctional\nOptogenetic Switch Powered NADPH Availability\nfor Improving l‑Valine Production in <i>Escherichia\ncoli</i>

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