Amidase-catalyzed production of nicotinic acid in batch and continuous stirred membrane reactors

The aim of the present study is to explore the potential use of Microbacterium imperiale CBS 498–74 resting cells as a catalyst for the bioconversion of nicotinamide into nicotinic acid. This strain converts nitrile into the corresponding acid following a two-step reaction catalysed by nitrile hydratase and amidase via an amide as intermediate. The effect of temperature, cell load and substrate feeding strategy were investigated with controlled continuous stirred membrane bioreactors (CSMR) in an attempt to improve reaction conversion as well as reactor performances. The temperature dependence of amidase activity was investigated in both batch reactors and CSMR. An activation energy of about 52.6/53.5 kJ mol−1 was determined, indicating absence of mass-transport phenomena. Amidase operated under mild conditions suitable for the synthesis of labile organic molecules and it was stable up to 50 ◦C. Nicotinamide (substrate) at concentrations of ≥300mM partially inhibited the enzyme. In the batch reactor, total conversion was achieved. In CSMR, the residence time was optimized to attain high conversion (up to 88%). These data indicate the potentiality of the continuous bioprocess for industrial application.