Determination of Bio-kinetic Parameters and Elucidation of Butachlor Metabolic Pathway by Serratia ureilytica Sp. AS1

Abstract

The present study reports the biotransformation of butachlor and other herbicides by a hyper butachlor-tolerant bacterial strain Serratia ureilytica strain AS1 isolated previously from the pesticide-contaminated agricultural soil. Under optimal conditions, the bacterial strain AS1 has the capacity to degrade up to 500 mg/L of butachlor completely within 240 hours in aqueous medium and within 288 hours at a rate constant of 0.2 day-1 following a first-order rate kinetics in agricultural soil at laboratory conditions. Since, the substrate is inhibitory in nature, fitting the biodegradation data in to Haldane model, the following bio-kinetic parameters are obtained: qmax= 3.83 mg/L/h, KS = 99.109 mg/L and Ki = 434.16 mg/L (R2 = 0.9906). The microbial strain has the potential to degrade other herbicides such as alachlor and glyphosate up to a concentration of 1000 mg/L efficiently. In order to overcome the substrate inhibition phenomenon at high butachlor concentration, the microbial strain AS1 was immobilized in calcium alginate beads and it was observed that on being immobilized, the biodegradation efficiency of the microbial strain increases many fold thus increasing its tolerance limit to 2000 mg/L. EI-MS analysis to determine the butachlor degradation pathway reveals that biodegradation of butachlor by the strain involves production of intermediates such as Alachlor, 2-chloro-N-(2,6-dimethylphenyl) acetamide, DEA, etc. The study reveals that the strain completely utilizes the herbicide leaving no toxic intermediates which may result in secondary pollution thus proving that the bacterial isolate Serratia ureilytica strain AS1 is a promising candidate for the remediation of herbicides from the environment.