S77: Microbial nitrile metabolism: Regulation and utilization

Nitriles (R-CN) are widely manufactured and extensively used by the chemical industry. We have studied microbial degradation of toxic nitriles containing a cyano functional group. The microbial degradation of nitriles has been found to proceed through two enzymatic pathways; nitrile hydratase (NHase) catalyzes hydration of nitrile to amide (R-CONH₂) followed by its conversion to acid (R-COOH) plus ammonia by amidase, whereas nitrilase catalyzes hydrolysis of nitrile to acid plus ammonia. We have characterized both enzymes and their genes from several microorganisms. Particularly, we have focused on an actinomycete Rhodococcus rhodochrous J1. Although this strain produces only nitrilase when isovaleronitrile is added into the culture medium as an inducer, it also produces two NHases depending on each inducer in the presence of cobalt ions; when the strain is cultured in the medium containing urea and cyclohexanecarboxamide, high-molecular-mass- (H-) and low-molecular-mass- (L-) NHases are selectively induced, respectively. The industrial production of acrylamide and nicotinamide by H-NHase is under way. We clarified the overall pathway involving the nitrile-degrading enzymes and their transcriptional regulation mechanisms in R. rhodochrous J1. Based on the strong induction mechanisms, we developed hyper expression systems for Streptomyces and Rhodococcus genera. Nitrile metabolism in Pseudomonas also has been investigated.