Multidimensional metabolic engineering strategies for efficient production of branched-chain amino acids and their derivatives in Escherichia coli and Corynebacterium glutamicum.

Branched-chain amino acids (BCAAs), comprising L-valine, L-leucine, and L-isoleucine, are essential amino acids with extensive applications in food, feed, pharmaceuticals, and cosmetics. Escherichia coli and Corynebacterium glutamicum, the two predominant industrial workhorses have been extensively engineered for high-level BCAAs biosynthesis. This review presents a comprehensive analysis of recent advances in microbial BCAAs production through a Mechanism-Module-Process framework. From the mechanism dimension, the intricate BCAA biosynthetic architectures are delineated, encompassing allosteric feedback inhibition, transcriptional attenuation, and transport system. From the module dimension, modular metabolic engineering strategies are dissected, including precursor supply enhancement, NADPH cofactor rebalancing, biosensor-driven dynamic regulation, and adaptive laboratory evolution for strain robustness. From the process dimension, how oxygen availability reprograms cellular metabolism across aerobic, microaerobic, and anaerobic fermentation is systematically examined, and how two-stage fermentation coupled with cofactor rebalancing resolves the growth-production trade-off to achieve near-theoretical yields is discussed. Furthermore, the biosynthetic strategies and current production status of BCAAs derivatives are summarized, highlighting the importance of multidimensional framework engineering. Collectively, this Mechanism-Module-Process framework provides a holistic roadmap for constructing superior BCAAs cell factories and extending their metabolic potential toward derivative biosynthesis.