Biodegradation of Acetonitrile and Benzonitrile by a Newly Isolated Rhodococcus Pyridionvorans Strain I-Benzo from Leather Tanning Waste

Nitriles are toxic organo-cyanide compounds, but extensively used in various industries as solvents, plastics, synthetic rubber, pharmaceuticals, herbicides, and starting materials for other industrially important chemicals. The wider use of these toxic compounds could lead to an environmental pollution, which have a negative impact on health. Some microbes are reported to be able to utilize both aliphatic and aromatic nitrile s as growth substrates and convert them into non-toxic compounds, some of which also have economic value as well. An indigenous bacterial isolate I-benzo, capable of growing on and utilizing of a high concentration of acetonitrile (CH3CN) and benzonitrile (C6H5CN), could be isolated from leather tanning waste by the enrichment-culture technique. Based on 16S rDNA sequence, the strain was identified as Rhodococcus pyridinivorans. These bacterium was shown to able to grow on acetonitrile (0.2-2.0 M) and on benzonitrile (5-25 mM), as a sole source of energy, carbon and nitrogen, respectively. The best growth of R. pyridinivorans strain I-benzo was on 500 mM acetonitrile and on 15 mM benzonitrile. During the degradation of both nitriles using whole cells of the bacterium, amide and carboxilic acid were detected in the reaction media, indicating that nitrile hydratase and amidase involved in the metabolism of the substrate. The involvement of both enzymes on the conversion of acetonitrile and benzonitrile was also proved by the ability of R. Pyridinivorans I-benzo to grow on their intermediate degradation products, acetamide (CH3CONH2) and benzamide (C6H5ONH2), respectively. Based on these results, R. pyridinivorans strain I-benzo could be expected as a potential candidate for biological treatment for nitriles-containing wastes, although further research is still needed before being applied on a field scale.