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An enrichment culture technique was used for the isolation of bacteria capable of utilizing fipronil as a sole source of carbon and energy. Based on morphological, biochemical characteristics and phylogenetic analysis of 16S rRNA sequence, the bacterial strains were identified as Acinetobacter calcoaceticus and Acinetobacter oleivorans. Biodegradation experiments were conducted in loamy sand soil samples fortified with fipronil (50 µg kg(-1)) and inoculated with Acinetobacter sp. cells (45 × 10(7) CFU mL(-1)) for 90 days. Soil samples were periodically analyzed by gas liquid chromatography equipped with electron capture detector. Biodegradation of fipronil fitted well with the pseudo first-order kinetics, with rate constant value between 0.041 and 0.051 days(-1). In pot experiments, fipronil and its metabolites fipronil sulfide, fipronil sulfone and fipronil amide were found below quantifiable limit in soil and root, shoot and leaves of Zea mays. These results demonstrated that A. calcoaceticus and A. oleivorans may serve as promising strains in the bioremediation of fipronil-contaminated soils.

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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.

Two indigenous bacterial strains, Bacillus megaterium ETLB-1 (accession no. KC767548) and Pseudomonas plecoglossicida ETLB-3 (accession no. KC767547), isolated from soil contaminated with paper mill effluent, were co-immobilized on corncob cubes to investigate their biodegradation potential against black liquor (BL). Results exhibit conspicuous reduction in color and lignin of BL upto 913.46 Co-Pt and 531.45 mg l(-1), respectively. Reduction in chlorophenols up to 12 mg l(-1) was recorded with highest release of chloride ions, i.e., 1290 mg l(-1). Maximum enzyme activity for lignin peroxidase (LiP), manganese peroxidase (MnP), and laccase (LAC) was recorded as 5.06, 8.13, and 8.23 U ml(-1), respectively, during the treatment. Scanning electron microscopy (SEM) revealed successful immobilization of bacterial strains in porous structures of biomaterial. Gas chromatography/mass spectroscopy (GC/MS) showed formation of certain low molecular weight metabolites such as 4-hydroxy-benzoic acid, 3-hydroxy-4-methoxybenzaldehyde, ferulic acid, and t-cinnamic acid and removal of majority of the compounds (such as teratogenic phthalate derivatives) during the period of treatment. Results demonstrated that the indigenous bacterial consortium possesses excellent decolorization and lignin degradation capability which enables its commercial utilization in effluents treatment system.