High-yield continuous production of nicotinic acid via nitrile hydratase–amidase cascade reactions using cascade CSMRs

"High yields of nicotinic acid from 3cyanopyridine. bioconversion were obtained by exploiting the in situ. nitrile hydratase–amidase enzymatic cascade system of Microbacterium imperiale CBS 49874.. Experiments were carried out in continuously stirred tank UFmembrane. bioreactors (CSMRs) arranged. in series. This reactor configuration enables both enzymes, involved in the cascade reaction, to work with. optimized kinetics, without any purification, exploiting their differing temperature dependences. To this. end, the first CSMR, optimized for the properties of the NHase, was operated (i) at low temperature (5 ◦C),. limiting inactivation of the more fragile enzyme, nitrile hydratase, (ii) with a high residence time (24 h). to overcome reaction rate limitation. The second CSMR, optimized for the properties of the AMase, was. operated (i) at a higher temperature (50 ◦C), (ii) with a lower residence time (6 h), and (iii) with a lower. substrate (3cyanopyridine). concentration to control excess substrate inhibition. The appropriate choice. of operational conditions enabled total conversion of 3cyanpyridine. (up to 200mM) into nicotinic acid. to be achieved at steadystate. and for long periods. Higher substrate concentrations required two CSMRs. optimized for the properties of the NHase arranged in series to drive the first reaction to completion."