Niacin Synthesis from 3-Cyanopyridine by Recombinant Escherichia coli: Optimization and Immobilization

Niacin (vitamin B3) is a high-value chemical widely used in the pharmaceutical and food industries. In this study, a recombinant Escherichia coli strain expressing nitrilase from Pseudomonas putida CGMCC3830 was evaluated for the whole-cell biotransformation of high-concentration 3-cyanopyridine to niacin. Molecular docking predicted important substrate-interacting residues, including T135, K131, F202, and W166. Under optimized conditions (160 g/L wet cells, pH 8.5), free whole cells completely hydrolyzed 3.0 M 3-cyanopyridine within 8 h. To enhance operational stability, the cells were immobilized in sodium alginate beads containing green zeolite. The resulting catalyst achieved complete conversion of 1.4 M 3-cyanopyridine within 4 h and maintained 96.5% conversion after six cycles. These findings demonstrate the potential of this system for future industrial applications.