Degradation of fipronil by Stenotrophomonas acidaminiphila isolated from rhizospheric soil of Zea mays.

Shivani Uniyal,R K Sharma,Rashmi Paliwal,J P N Rai

doi:10.1007/s13205-015-0354-x

Abstract

Fipronil is a widely used insecticide in agriculture and can cause potential health hazards to non-target soil invertebrates and nearby aquatic systems. In the present study, a fipronil degrading bacterium was isolated from fipronil contaminated soil, i.e. rhizospheric zone of Zea mays. Morphological, biochemical and molecular characterization of strain indicated that it clearly belongs to Stenotrophomonas acidaminiphila (accession no. KJ396942). A three-factor Box–Behnken experimental design combined with response surface modeling was employed to predict the optimum conditions for fipronil degradation. The optimum pH, temperature and total inocula biomass for the degradation of fipronil were 7.5, 35 °C and 0.175 g L−1, respectively. The bacterial strain was able to metabolize 25 mg L−1 fipronil with 86.14 % degradation in Dorn’s broth medium under optimum conditions. Metabolites formed as a result of fipronil degradation were characterized with gas liquid chromatograph. A novel fipronil degradation pathway was proposed for S. acidaminiphila on the basis of metabolites formed. Non-sterilized soil inoculated with S. acidaminiphila was found to follow first order kinetics with a rate constant of 0.046 d−1. Fipronil sulfone, sulfide and amide were formed as the metabolites and were degraded below the quantifiable limit after 90 days of time period. Given the high fipronil degradation observed in the present study, S. acidaminiphila may have potential for use in bioremediation of fipronil contaminated soils.

Highlights

The widespread use of increasing number of pesticides in agriculture has acquired great importance due to direct and indirect hazards to human health and environment
A three-factor Box–Behnken experimental design combined with response surface modeling was employed to predict the optimum conditions for fipronil degradation
An indigenous bacterial strain capable of utilizing fipronil as a sole carbon and energy source was eventually isolated from the fipronil contaminated soil

Summary

Introduction

The widespread use of increasing number of pesticides in agriculture has acquired great importance due to direct and indirect hazards to human health and environment. Fipronil [5Amino-3-cyano-1-(2, 6-dichloro 4 trifluoromethylphenyl)-4trifluoromethyl sulfinyl pyrazole] is a phenyl pyrazole insecticide first synthesized by Rhone Poulenc Ag Company ( Bayer Crop Science) in 1987, introduced for use in 1993 and registered in the U.S in 1996 (Tomlin 2000; Ware 2000; Tingle et al 2003). It is one of the most persistent, lipophilic and toxic insecticides licensed for use since dieldrin, lindane and DDT (Mohapatra et al 2010). Fipronil elicits its toxicity by blocking the GABA-gated chloride channel in the

Objectives

Methods

Results

Conclusion