Biotransformation of 3-cyanopyridine to nicotinic acid by free and immobilized cells of recombinant Escherichia coli

• 1 M 3-cyanopyridine was converted to nicotinic acid by recombinant nitrilase.
• Mild reaction conditions were used with no nicotinamide formation.
• No substrate or product inhibition was observed.
• Complete conversion was achieved within 5 h with yield of up to 93%.
• The immobilized biocatalyst was reused for continuous production of nicotinic acid.

An efficient biocatalytic process for the production of nicotinic acid (niacin) from 3-cyanopyridine was developed using cells of recombinant Escherichia coli JM109 harboring the nitrilase gene from Alcaligenes faecalis MTCC 126. The freely suspended cells of the biocatalyst were found to withstand higher concentrations of the substrate and the product without any signs of substrate inhibition. Immobilization of the cells further enhanced their substrate tolerance, stability and reusability in repetitive cycles of nicotinic acid production. Under optimized conditions (37 °C, 100 mM Tris buffer, pH 7.5) for the immobilized cells, the recombinant biocatalyst achieved a 100% conversion of 1 M 3-cyanopyridine to nicotinic acid within 5 h at a cell mass concentration (fresh weight) of 500 mg/mL. The high substrate/product tolerance and stability of the immobilized whole cell biocatalyst confers its potential industrial use.