Studies on bacterial biodegradation of benzonitrile

Despite the widespread use of herbicides containing nitrile groups, comparatively little is known about the microbial metabolism of nitriles, in particular, the mechanism of cleavage of the cyanide bond by microorganisms. Soil samples were collected from different areas like agricultural land and area surrounding pharmaceutical industries. By adaptation and acclimatization, sixty bacterial cultures were isolated. All isolates were capable of growing on mineral medium containing benzonitrile, as the sole source of carbon and nitrogen. Out of these 60 isolates, 17 bacterial strains were screened based on maximum production of ammonia. Secondary screening was carried out based on benzonitrile biodegradation at various pH.Three strains were selected showing maximum biodegradation in terms of ammonia production at basic, acidic, and alkaline pH, strain C8 at pH 7 (7.78 µmole), strain S14 at pH 9 (5.45 µmole), and strain S15 at pH 4 (10.31µmole). The presence of nitrilase was confirmed qualitatively by detecting non-occurrence of benzamide during hydrolysis. In both strains, the enzyme activity was found to be maximum in cell supernatant as compaired to cell lyzate.The strain S15 was used further for optimization of growth parameters.The intact cells of S15 showed maximum benzonitrile biodegradation at pH 4 and 30 °C temperature. The presence of casein as a nitrogen source and fructose as carbon source were found to enhance the benzonitrile hydrolysis.