Biosensor-driven adaptive laboratory evolution of l-valine production in Corynebacterium glutamicum

Adaptive laboratory evolution has proven a valuable strategy for metabolic engineering. Here, we established an experimental evolution approach for improving microbial metabolite production by imposing an artificial selective pressure on the fluorescent output of a biosensor using fluorescence-activated cell sorting. Cells showing the highest fluorescent output were iteratively isolated and (re-)cultivated. The l-valine producer Corynebacterium glutamicum ΔaceE was equipped with an L-valine-responsive sensor based on the transcriptional regulator Lrp of C. glutamicum. Evolved strains featured a significantly higher growth rate, increased l-valine titers (~25%) and a 3-4-fold reduction of by-product formation. Genome sequencing resulted in the identification of a loss-of-function mutation (UreD-E188*) in the gene ureD (urease accessory protein), which was shown to increase l-valine production by up to 100%. Furthermore, decreased l-alanine formation was attributed to a mutation in the global regulator GlxR. These results emphasize biosensor-driven evolution as a straightforward approach to improve growth and productivity of microbial production strains.