Synthesis of Niacin from 3-Cyanopyridine with Recombinant Escherichia coli Carrying afnitA Nitrilase in a Deep Eutectic Solvent System

Niacin is a compound with a wide range of applications in pharmaceuticals, healthcare, food nutrition, animal breeding, cosmetics, etc. A recombinant Escherichia coli carrying the afnitA nitrilase gene was created to transform 3-cyanopyridine into niacin in this work. After analyzing the viscosity, surface tension, and Kamlet-Taft (K-T) parameters (π*, α, and β values) of certain deep eutectic solvents (DESs), Betaine:Acetic Acid (Betaine:AA) (1:2, mol/mol) was chosen as the bioreaction medium. Using response surface methodology (RSM), systematic biocatalytic optimization was performed. The optimum medium pH, cell loading, temperature, and DES (Betaine:AA) (1:2, mol/mol) dose were determined to be 7.75, 195 g/L, 44.24 °C, and 18.04 wt%. Under the optimized conditions, whole-cell catalysis facilitated the conversion of 3-cyanopyridine to niacin, achieving a high yield of 98.6% within 40 min. These results demonstrated that recombinant E. coli carrying the afnitA nitrilase gene may have practical value as a biocatalyst for the production of niacin, with promising prospects for future applications.