Microbial degradation of fipronil by Bacillus thuringiensis

Fipronil, a phenyl pyrazole insecticide has been found to be effective for the control of various insect pests. Due to its higher persistence in soil bioremediation is a promising approach to degrade the pesticide from soil. Isolation and identification of soil microbes was conducted for bioremediation of fipronil contaminated soils. Soil samples collected from different sugarcane growing fields in Gurdaspur district with extensive use of pesticide history served as a source of pesticide degrading microbes. The microbe cultures were grown in Luria broth and maintained at 28°C. After that Dorn's broth enrichment culture supplemented with fipronil was used and Bacillus thuringiensis were isolated. Clay loam soil samples were fortified with fipronil @ 0.50, 0.75, 1.00, 1.25 and 1.50mgkg(-1) along with 45×10(7) microbe cells. Each treatment was replicated thrice and from each fortified (insecticide+microbes) sample, 50g soil sample was taken at 7, 14, 28, 35, 42, 49 and 56 days after initiation of this experiment. Residues were not detected after 28, 35, 35, 35 and 42 days in soil samples after fortification with fipronil @ 0.50, 0.75, 1.00, 1.25 and 1.50mgkg(-1). Among metabolites, sulfide was found to be the main metabolite followed by sulfone and amide. Desulfinyl metabolite was not produced in any of the sample. Total fipronil residues were not found to follow the first order kinetics.