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 enz yme extract in the presence of Na-montmorillonite and albumin, were st udied to determine the influence of both organic and inorganic macrosp ecies on the availability of parathion (O,O diethyl-O-p-nitrophenyl ph osphorothioate) for biological degradation in soil and water. Parathio n hydrolysis, both by the bacterium and by its crude enzyme extract, w as retarded by the clay. Parathion was rapidly adsorbed by the clay, r eaching equilibrium within 6 h sit a Kd value of 76 L/kg, but parathio n adsorption was considerably higher on the protein-loaded clay. Enzym e inactivation, due to its adsorption by the clay, was the dominant ca use for the decrease in parathion degradation in the presence of clay, while parathion adsorption had a smaller effect. The parathion desorp tion rate was very high; therefore, sorbed parathion was readily avail able for bacterial and enzymatic hydrolysis in solution. Addition of a lbumin to the crude enzyme extract stabilized the enzymatic activity i n clay-free solution, but did not prevent the inactivation of parathio n hydrolase by the clay.