Isolation and identification of a nitrile hydrolyzing bacterium and simultaneous utilization of aromatic and aliphatic nitriles

Abstract

Rhodococcus sp. MTB5, a bacterial strain capable of utilizing benzonitrile as the sole source of carbon and nitrogen was isolated from a nitrile-contaminated agricultural soil sample by selective enrichment culture technique. This bacterial strain is capable of utilizing both aliphatic and aromatic nitriles. The production of ammonia was noticed during the growth of this strain in the medium supplemented with benzonitrile. The enzyme assay and GC studies revealed that benzonitrile degradation by Rhodococcus sp. MTB5 follows a NHase/amidase pathway involving benzamide and benzoic acid as metabolic intermediates. The resting cells grown on benzonitrile showed NHase and amidase activities of 0.155 and 0.261 units, respectively. The strain utilized 30 mM benzonitrile completely and could tolerate and grow in benzonitrile at concentration up to 60 mM. The cells grown on glucose and ammonium nitrate did not show the above enzymatic activities indicating the inducible nature of these enzymes. In addition to benzonitrile, the isolate was also able to utilize indole-3-acetonitrile and aliphatic nitriles, namely, propionitrile, butyronitrile and valeronitrile. Furthermore, the bacterium simultaneously utilizes different combinations of aromatic and aliphatic nitriles. These novel features make the bacterium a suitable candidate for the in-situ application of sites contaminated with both aliphatic and aromatic nitriles.