Application of continuous stirred membrane reactor to 3-cyanopyridine bioconversion using the nitrile hydratase–amidase cascade system of Microbacterium imperiale CBS 498-74

The bioconversion of 3-cyanopyridine using the in situ nitrile hydratase–amidase cascade system of resting Microbacterium imperiale CBS 498-74 cells was investigated in an ultrafiltration-membrane reactor, operated in either batch or continuous mode. The effects of operating conditions such as the amount of biocatalyst, substrate concentration, substrate feeding rate, mean residence time, and enzyme-to-substrate ratio, were investigated with the aim of achieving almost 100% substrate conversion and high reactor productivity. As a result, it was found that the NHase–AMase cascade system could be adequately exploited in a continuous reactor configuration. The differing temperature dependence of nitrile hydratase and amidase kinetics enabled the operational parameters to be module d to ensure (i) nitrile hydratase operational stability (at 5 °C), and (ii) 100% conversion of 3-cyanopyridine into nicotinic acid, or, alternatively, (iii) enrichment of the effluent stream with the intermediate nicotinamide (up to 80% conversion). It was possible to select operating conditions that allowed long periods of operation (at least 100 h) at a constant flow-rate without enzyme activity loss.