Nitrile Degradation by Rhodococcus: Useful Microbial Metabolism for Industrial Productions

Nitrile can be degraded by nitrile hydratase (NHase) to the corresponding amide, which is then converted to the acid plus ammonium by amidase. Nitrile can also be directly hydrolyzed to the corresponding acid plus ammonium by nitrilase. NHases and nitrilases are widely distributed among genus Rhodococcus, and two types of NHases (Fe-type and Co-type) and versatile nitrilases have been isolated from several Rhodococcus species. NHases are composed of α- and β-subunits, which differ in size from each other, and two kinds of Co-type NHases, high-molecular-mass (H-NHase) and low-molecular-mass (L-NHase) ones, have been discovered in R. rhodochrous J1. Characterization of their enzymes at the molecular level has provided new insights into how the molecular structures determine these enzyme functions, and how the regulatory systems control the expression of the enzyme genes to improve the enzymes. The practical use of Rhodococcus in biotechnology, and the application of Rhodococcus NHase and nitrilase for the industrial production of useful compounds such as acrylamide, nicotinamide and several vitamins have been recognized and developed.