5-Cyanovaleramide (5-CVAM) is an important intermediate of a herbicide and chemical raw material. Herein, we found a novel nitrile hydratase from the strain Rhodococcus erythropolis CCM2595, exhibiting high regioselectivity with higher substrate specificity toward dinitriles than mononitriles. In the past, the strain was shown to degrade only phenol, hydroxybenzoate, p -chlorophenol, aniline, and other aromatic compounds. In our study, 20 mM adiponitrile was completely consumed within 10 min with 95% selectivity to 5-CVAM and 5% selectivity to adipamide. In addition to its high regioselectivity, our recombinant Escherichia coli showed a higher substrate tolerance of up to 200 mM adiponitrile even after 3 h when compared with two reported strains with their cyano-tolerance concentrations of up to 100 mM, which is considered to be the highest cyano-tolerance. Such a robust biocatalyst is a desirable attribute of a biocatalyst intended for use in commercial applications of 5-CVAM.

In our previous study, we firstly cloned the gene of a novel ReNHase (NHase from Rhodococcus erythropolis CCM2595), and the strain was shown to degrade only phenol, hydroxybenzoate, p-chlorophenol, aniline and other aromatic compounds. Here in, we further purified the ReNHase from R. erythropolis CCM2595 and detected its properties of biodegradation. We constructed a plasmid with the gene of ReNHase with His-tag. The encoding ReNHase was cloned and overexpressed in recombinant Escherihia coli and confirmed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The substrate scope of the new heterologous ReNHase was tested and the efficiency of degradation of nitriles by the ReNHase was also investigated by high efficiency liquid chromatography. We also studied the effect of temperature and pH on the catalysis of adiponitrile by the purified ReNHase. The recombinant E.coli showed high catalytic regioselectivity with high substrate affinity towards dinitriles (especially for adiponitrile) whereas lower affinity towards mononitriles. Compared to whole-cell catalysis, the catalytic time was shortened significantly with the purified ReNHase. The enzyme activity of crude recombinant E.coli was 635 U g −1 (DCW), while the specific activity of purified ReNHase was 63.107 U mg −1 . The apparent Km value for the purified ReNHase is 6.6252 mmol L −1 , which revealed the good affinity between the purified ReNHase and adiponitrile. The reaction Kcat is 82.77 s −1 and Kcat/Km is 1.249 × 10 4 (mol −1 L s −1 ), which showed high catalytic activity towards adiponitrile. We propose that this purified ReNHase may be applied for the industry and sewage treatment for environmental protection.