A novel route for valerolactam production in Corynebacterium glutamicum: metabolic engineering and bioprocess optimization

Valerolactam is a promising bio-based monomer for polyamide synthesis, but microbial production remains limited by inefficient 5-aminovalerate (5AVA) cyclization, by-product formation, and insufficient process optimization. In this study, Corynebacterium glutamicum was engineered for valerolactam production by expression of davBA from Pseudomonas putida and lysP from Escherichia coli, followed by conversion of 5AVA to valerolactam using the recently identified avaC gene from Collinsella intestinalis. Flask cultivations confirmed efficient valerolactam formation with only minor accumulation of the by-products L-lysine, 5AVA, and glutarate. Batch bioreactor experiments showed that higher glucose concentrations increased titers but also promoted by-product accumulation, whereas increasing the dissolved oxygen setpoint from 30% to 50% improved growth and volumetric productivity. Intracellular cofactor analysis revealed declining energy status and shifts in redox balance during production. Based on these findings, carbon-limited fed-batch cultivation at 50% rDO improved production performance, reaching 3.6 g/L valerolactam with a yield of 0.231 g/g and a volumetric productivity of 0.075 g/L/h, while minimizing by-product formation. These results establish AvaC-based C. glutamicum as a promising platform for sustainable valerolactam biosynthesis.