Parathion degradation by Xanthomonas sp. and its crude enzyme extract in clay suspensions

The degradation of parathion by a Xanthomonas sp. and by its crude enzyme extract in the presence of Na-montmorillonite and albumin, were studied to determine the influence of both organic and inorganic macrospecies on the availability of parathion (O,O diethyl-O-p-nitrophenyl phosphorothioate) for biological degradation in soil and water. Parathion hydrolysis, both by the bacterium and by its crude enzyme extract, was retarded by the clay. Parathion was rapidly adsorbed by the clay, reaching equilibrium within 6 h at a Kd value of 76 L/kg, but parathion adsorption was considerably higher on the protein-loaded clay. Enzyme inactivation, due to its adsorption by the clay, was the dominant cause for the decrease in parathion degradation in the presence of clay, while parathion adsorption had a smaller effect. The parathion desorption rate was very high; therefore, sorbed parathion was readily available for bacterial and enzymatic hydrolysis in solution. Addition of albumin to the crude enzyme extract stabilized the enzymatic activity in clay-free solution, but did not prevent the inactivation of parathion hydrolase by the clay.