Use of a UF-membrane reactor for controlling selectively the nitrile hydratase–amidase system in Microbacterium imperiale CBS 498-74 resting cells: Case study: Benzonitrile conversion

The bioconversion of benzonitrile to benzamide and benzoic acid catalysed by resting cells of Microbacterium imperiale   CBS 498-74 was investigated in batch and UF-membrane reactors. The microorganism converts nitriles through a two-step reaction, catalysed by a nitrile hydratase (NHase)–amidase (AMase) system. The kinetic parameters, Kmappand Vmapp, tested in 50 mM sodium phosphate buffer, pH 7.0, for benzonitrile and benzamide bioconversion were evaluated in batch reactor at 20 °C. Kmapp resulted 1.34 and 0.042 (mM), and Vmapp 1.1 and 0.072 (μmol min−1 mgDCW−1) for NHase and AMase, respectively.Batch and UF-membrane reactors were used to study the effect of operating variables such as enzyme and substrate concentration, temperature and residence time. The appropriate choice of operating conditions allowed to selectively control the NHase/AMase system and consequently the reactor output. A UF-membrane bioreactor operating at 20 °C and a τ of 10.3 h, allowed 96.9% conversion into benzoic acid; in contrast, when operating at 5 °C and a τ of 22.5 h 70.5% benzamide accumulated in the bioreactor.