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, K-m(app) and V-m(app), tested in 50mM sodium phosphate buffer, pH 7.0, for benzonitrile and benzamide bioconversion were evaluated in batch reactor at 20 degrees C. K-m(app) resulted 1.34 and 0.042 (mM), and V-m(app) 1.1 and 0.072 (mu mol min(-1) Mg-DCW(-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 degrees C and a tau of 10.3 h, allowed 96.9% conversion into benzoic acid; in contrast, when operating at 5 degrees C and a tau of 22.5 h 70.5% benzamide accumulated in the bioreactor. (c) 2005 Elsevier Inc. All rights reserved.