Enhancement Strategy for Protocatechuic Acid Production Using Corynebacterium glutamicum with Focus on Continuous Fermentation Scale-Up and Cytotoxicity Management

Protocatechuate acid (PCA) is a phenolic acid naturally synthesized by various organisms. Protocatechuic acid is synthesized by plants for physiological, metabolic functions, and self-defense, but extraction from plants is less efficient compared to the microbial culture process. The microbial synthesis of protocatechuic acid is sustainable and, due to its high yield, can save energy consumption when producing the same amount. To enhance PCA production using Corynebacterium glutamicum, a statistical optimization of the production medium was performed using full factorial design, the steepest ascent method, and the response surface method. The optimized production medium enabled a PCA production of over 5 g/L in a 72 h batch culture. However, PCA cytotoxicity affected the strain growth and PCA production rate, with an inhibitory concentration of approximately 5 g/L in the fermentation broth. Finally, continuous fermentation was operated for 150 h in the steady-state mode, maintaining the concentration of PCA below 5 g/L. The optimization method established in this study successfully increased PCA production levels, and the findings presented herein are anticipated to contribute to the industrialization of PCA production using C. glutamicum.