Bench scale production of nicotinic acid using a newly isolated Stenotrophomonas maltophilia AC21 producing highly-inducible and versatile nitrilase

Abstract

A novel bacterial named AC21 having nitrile-converting activity was gained with acetonitrile as sole source of nitrogen, which was recognized by morphology and 16S rDNA gene sequence as Stenotrophomonas maltophilia. This intracellular nitrilase induced by acetonitrile (0.3%) catalyses the conversion of 3-cyanopyridine to nicotinic acid without noticeable production of nicotinamide. Optimal pH and temperature of Nitrilase AC21 was obtained at pH 8.0 and 45 °C. Irreversible thermo-inactivation results showed that, enzyme half-life was 6 h at 80 °C. Several process factors, including quantity of enzyme and rate of substrate feeding, were considered with the goal of reaching whole substrate transformation. In a fed batch manner at 1 l scale using hyper-induced AC21 resting cells equivalent to 10 U ml⁻¹ nitrilase activity, a total of 945 mM of 3-cyanopyridine was formed at a rate of 3.32 g h⁻¹ g dcw⁻¹, which directed AC21 has ability of application in large scale nicotinic acid production.