Fenpropathrin Biodegradation Pathway in Bacillus sp. DG-02 and Its Potential for Bioremediation of Pyrethroid-Contaminated Soils

The widely used insecticide fenpropathrin in agriculture has become a public concern because of its heavy environmental contamination and toxic effects on mammals, yet little is known about the kinetic and metabolic behaviors of this pesticide. This study reports the degradation kinetics and metabolic pathway of fenpropathrin in Bacillus sp. DG-02, previously isolated from the pyrethroid-manufacturing wastewater treatment system. Up to 93.3% of 50 mg L^–1 fenpropathrin was degraded by <i>Bacillus</i> sp. DG-02 within 72 h, and the degradation rate parameters <i>q</i>_max, <i>K</i>_s, and <i>K</i>_i were determined to be 0.05 h^–1, 9.0 mg L^–1, and 694.8 mg L^–1, respectively. Analysis of the degradation products by gas chromatography–mass spectrometry led to identification of seven metabolites of fenpropathrin, which suggest that fenpropathrin could be degraded first by cleavage of its carboxylester linkage and diaryl bond, followed by degradation of the aromatic ring and subsequent metabolism. In addition to degradation of fenpropathrin, this strain was also found to be capable of degrading a wide range of synthetic pyrethroids including deltamethrin, λ-cyhalothrin, β-cypermethrin, β-cyfluthrin, bifenthrin, and permethrin, which are also widely used insecticides with environmental contamination problems with the degradation process following the first-order kinetic model. Bioaugmentation of fenpropathrin-contaminated soils with strain DG-02 significantly enhanced the disappearance rate of fenpropathrin, and its half-life was sharply reduced in the soils. Taken together, these results depict the biodegradation mechanisms of fenpropathrin and also highlight the promising potentials of <i>Bacillus</i> sp. DG-02 in bioremediation of pyrethroid-contaminated soils

Effect of nitrogen source on bacterial growth and zeamine production by <i>D. zeae</i> EC1.

<p>Note: Each inorganic nitrogen source was tested at 15 mM/L (Concentration of nitrogen molecules) and amino acid was tested at 1 g·L⁻¹ in MM containing (per liter): 10.5 g K₂HPO₄, 4.5 g KH₂PO₄, 2 g mannitol, 2 g glycerol, 5 mg FeSO₄, 10 mg of CaCl₂, 2 mg MnCl₂, 0.2 g MgSO₄·7H₂O, pH 7.0. Data are the means ± standard errors from three replicates per treatment at 36 h after inoculation. The multiple comparisons of means were obtained using Duncan's multiple-range test with an overall of 0.01. The means differing from each other were indicated with different capital letter (<i>P</i><0.01).</p><p>Effect of nitrogen source on bacterial growth and zeamine production by <i>D. zeae</i> EC1.</p

Effect of over-expression of <i>zmsK</i> on zeamines production.

<p>Three <i>D. zeae</i> strains including ΔzmsK (<i>white diamond</i>), EC1 (<i>white square</i>), and EC1(zmsK) (<i>white triangle</i>), were inoculated in LS5 (A) and MM (B) media, respectively. Data are the means from three replicates per treatment.</p

Effect of carbon source on bacterial growth and zeamine production by <i>D. zeae</i> EC1.

<p>Note: Each carbon source was tested at 5 g·L⁻¹ in LS1 and LS2 medium. Data are the means ± standard errors from three replicates per treatment at 36h after inoculation. The multiple comparisons of means were obtained using Duncan's multiple-range test with an overall of 0.01. The means differing from each other were indicated with different capital letter (<i>P</i><0.01).</p><p>Effect of carbon source on bacterial growth and zeamine production by <i>D. zeae</i> EC1.</p

Uncoded and coded levels of independent variables of LS3 for zeamines production by <i>D. zeae</i> EC1.

<p>Uncoded and coded levels of independent variables of LS3 for zeamines production by <i>D. zeae</i> EC1.</p

Zeamines production of strain EC1(<i>zmsK</i>) in different media.

<p>Quantitative analysis and plate assay were shown in (A) and (B), respectively. Data (A) are the means from four replicates per treatment.</p

Effect of amino acid and vitamin supplements on growth and zeamine production by <i>D.zeae</i> EC1 in LS4 medium.

<p>Note: Data are the means ± standard errors from three replicates per treatment. The multiple comparisons of means were obtained using Duncan's multiple-range test with an overall of 0.01. The means differing from each other were indicated with different capital letter (<i>P</i><0.01).</p><p>Effect of amino acid and vitamin supplements on growth and zeamine production by <i>D.zeae</i> EC1 in LS4 medium.</p

Effect of Mineral elements on bacterial growth and zeamines production by <i>D. zeae</i> EC1.

<p>Note: LS3 medium contains (per liter): 3.6 g NH₄NO₃, 10.5 g K₂HPO₄, 4.5 g KH₂PO₄, 15 g sucrose, 5 mg FeSO₄, 10 mg of CaCl₂, 2 mg MnCl₂, 0.2 g MgSO₄·7H₂O, pH 7.0. Data are the means ± standard errors from three replicates per treatment. The multiple comparisons of means were obtained using Duncan's multiple-range test with an overall of 0.01. The means differing from each other were indicated with different capital letter (<i>P</i><0.01).</p><p>Effect of Mineral elements on bacterial growth and zeamines production by <i>D. zeae</i> EC1.</p

Effect of temperature (A, C) and rotation speed (B, D) on zeamines production (A, B) and growth (C, D) of strain EC1 inoculated in LS5.

<p>Data are the means from three replicates per treatment.</p

Response surface plot showing the effects of NH₄NO₃ and sucrose on zeamines production of strain EC1 with the value of phosphate being fixed at 64.67 mM·L⁻¹.

<p>Data are the means from three replicates per treatment.</p