Fipronil biodegradation and metabolization by Bacillus megaterium strain E1

Abstract

BACKGROUND: Fipronil is a broad-spectrum insecticide that is used extensively due to its effective action in pest control. However, environmental studies have shown it has high toxicity towards non-target organisms as well. In addition, the degradation of fipronil can generate even more toxic and reactive metabolites in the environment. In the present study, bioprospecting for bacteria with the potential to degrade fipronil was performed using fipronil as the sole source of nitrogen and main source of carbon. From samples of corn culture soil with a history of fipronil application, isolation was performed using the microcosm enrichment method. RESULTS: Bacteria were isolated using fipronil (0.6 g L −1 ) as the sole nitrogen source and main carbon source. After preliminary tests, isolate E1 was selected and, following sequencing of 16S rRNA, it was found that the isolate E1 was a bacterium of the Bacillaceae family, Bacillus megaterium species. Growth was evaluated by dry biomass and degradation quantified by gas chromatography-mass spectrometry (GC-MS). Strain E1 presented a 94% degradation of fipronil, as well as 91% and 96% degradation of its metabolites fipronil-sulfide and fipronil-sulfone, respectively, in 14 days, reducing its initial concentration from 0.6 g L −1 to 0.036 mg L −1 . CONCLUSION: The results showed that bioprospecting of the E1 strain, isolated from soil, showed efficiency in the biodegradation process of fipronil. This strain is a potential candidate for use in bioremediation processes in areas contaminated with fipronil and for use in further studies on the elucidation of the metabolic pathways of fipronil degradation.

Fipronil Degradation in Soil by Enterobacter chengduensis Strain G2.8: Metabolic Perspective

“…To initiate the isolation process, ten grams of soil were suspended in 90 mL of 0.9% saline solution, and a serial dilution (ranging from 10 −1 to 10 −4 ) was carried out. Subsequently, 100 µL of each sample was spread-plated using the solid ATZ-R method, which is a procedure previously elucidated by Prado et al [ 6 ]. This medium was enriched with 0.6 g/L of fipronil.…”

“…The plated samples were then incubated at a constant temperature of 30 °C for a 48 h. After incubation, bacterial colonies displaying distinct characteristics were selected for further analysis. These bacterial colonies underwent purification through streak plating; subsequently, a Gram stain procedure, as detailed by Prado et al [ 6 ], was executed to ascertain the presence of spores and determine cell wall composition. For a more comprehensive understanding, the critical steps used in this work are described in detail in Figure 1 .…”

“…The experiments were performed as described by Prado et al [ 6 ]. Then, bacterial growth was measured by the dry biomass for 14 days.…”

“…This prohibition, in part, is related to the problem that only 1% of the pesticides applied in agriculture reach the crops, with the rest dispersed in the environment [ 5 ]. Prado and colleagues [ 6 ] reported that only 7% of the applied fipronil remains on crops. As it leaches through the soil due to natural factors (e.g., rain, leaching and wind), the presence of fipronil and its metabolites in soil, water bodies and sediments has become alarming [ 2 ].…”

“…These metabolites come from the mineralization process of the fipronil molecule, produced through its oxidation, reduction, hydrolysis and photolysis, producing fipronil-sulfone, fipronil-sulfide, fipronil-amide and fipronil-disulfenyl, respectively [ 1 ]. Due to its high harmfulness, especially of fipronil-sulfone, a metabolite even more toxic than fipronil, studies focused on the remediation of these molecules using microorganisms have become an approach widely used in order to minimize the impacts caused by environmental exposure to these compounds [ 2 , 3 , 6 , 7 , 13 , 14 ]. Given these approaches, biological processes are the most recommended [ 2 ] and the microorganisms selected from the environment contaminated with these compounds are capable of using fipronil as a source of carbon and nitrogen, making the biodegradation process more promising [ 6 , 15 ].…”