Methods for increasing nitrile biotransformation into amides using Mesorhizobium sp.

Abstract

Nitriles are potential soil pollutants from industrial wastewater. There has been increased demand for efficient process for nitrile degradation process. Nitrile hydratase (NHase) has been extensively used in the production of acrylamide and treatment of organocyanide contaminated industrial effluents. The NHase of Mesorhizobium sp., isolated from polyacrylonitrile activated sludge from fiber manufacturing wastewater treatment systems was studied in the whole bacterial cells. Different chemicals were added to observe the variation in the percentage of acrylonitrile converted into acrylamide. The result indicated that cobalt ions were the NHase cofactor and could increase the NHase activity. The addition of propionaldehyde, or butyraldehyde could enhance the acrylonitrile conversion rate. Therefore, acrylamide could be accumulated effectively and the percentage of acrylonitrile converted into acrylamide increased. Propionaldehyde was the most effective NHase activator. The percentage of acrylonitrile converted into acrylamide was nearly 100% at 3.8 h when propionaldehyde was added at about 207.4 mg/l. The addition of benzaldehyde was unable to increase the percentage of acrylonitrile converted into acrylamide. EDTA and acrylamide showed no effect on NHase activity. However, 0.1 mg/l of Ag2SO4 would slightly inhibit NHase activity, producing an acrylonitrile conversion rate of 492.9 mg/l with 54.9% converted at 29.1 h. The ability of the acrylonitrile biotransformation was completely inhibited if the Ag2SO4 concentration was above 0.5 mg/l.