Degradation of monocrotophos in soil, microbial versus enzymatic method

Abstract

Rachna Jain, Veena Garg

Aim: The present study has been designed to compare two commonly used methods viz. microbial and enzymatic for the degradation of monocrotophos (MCP) in sandy loam soil of Rajasthan. Materials and Methods: Methodology involves the use of molecularly characterized fungal strain Aspergillus niger JQ660373. For the microbial method spore suspension (1 × 108 spores/ml) was used as inoculum. Enzymatic method employ the use isolated, purified extracellular fungal hydrolases as inoculum. %age of MCP degradation was assessed in the form of residual MCP concentration and hence degradation kinetics was calculated. The results were confirmed by using analytical tools, high pressure thin layer chromatography (HPTLC) and Fourier transform infrared spectroscopy (FTIR). Results: The results of this study demonstrated that extracellular fungal hydrolase composed of two different subunits of 33 and 67 Kd. Both subunits synergistically degrade MCP. Residual MCP concentration was found to be 64.94 ± 0.42 and 16.95 ± 0.55 μg/ml after 15 days of incubation for microbial and enzymatic method, respectively. Degradation of MCP followed first order kinetics with rate constants of 0.002 and 0.136/day and hence the calculated half-life was found to be 12.64 and 5.14 days, respectively. HPTLC chromatograms clearly indicate the significant decrease in the standard MCP peak (rf 0.19-0.21) with increasing incubation duration. Molecular insight of MCP degradation was studied by FTIR. Degradation proceeded with hydrolytic cleavage of MCP resulting in the formation of inorganic phosphates (−PO4). Conclusion: The study concludes that enzymatic method of degradation was more efficient than the microbial method.