Biosensor-guided directed evolution of aldehyde dehydrogenase for improved adipic acid production from caprolactone

Abstract Biological production of adipic acid, a crucial building block in nylon and polymer manufacturing, from renewable feedstocks has attracted attention as a sustainable alternative to the traditional petrochemical production. The enzymatic conversion of ε-caprolactone into adipic acid via alcohol dehydrogenase (ADH2) and aldehyde dehydrogenase (ALDH) represents a promising route due to its short pathway and high theoretical yield. To optimize this conversion route in Escherichia coli and enhance conversion efficiency, we constructed an adipic acid-responsive biosensor for high-throughput screening. By systematically optimizing the biosensor system, we achieved a 7.15-fold dynamic range. Using this biosensor system, we performed directed evolution of the low-activity ALDH and identified variants with improved conversion performance. The K23Q mutant showed a 2.33-fold increase in adipic acid conversion efficiency and subsequent fed-batch fermentation achieved 30.1 g/L of adipic acid production from ε-caprolactone with 92.7% of theoretical maximum yield. These results demonstrate the potential of biosensor-guided enzyme engineering to enhance catalytic efficiency and support the sustainable biological production of adipic acid.