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

Insights into the biodegradation of fipronil through soil microcosm-omics analyses of Pseudomonas sp. FIP_ A4

Fipronil, a phenylpyrazole insecticide, is used to kill insects resistant to conventional insecticides. Though its regular and widespread use has substantially reduced agricultural losses, it has also caused its accumulation in various environmental niches. The biodegradation is an effective natural process that helps in reducing the amount of residual insecticides. This study deals with an in-depth investigation of fipronil degradation kinetics and pathways in Pseudomonas sp. FIP_A4 using multi-omics approaches. Soil-microcosm results revealed ∼87% degradation within 40 days. The whole genome of strain FIP_A4 comprises 4.09 Mbp with 64.6% GC content. Cytochrome P450 monooxygenase and enoyl-CoA hydratase-related protein, having 30% identity with dehalogenase detected in the genome, can mediate the initial degradation process. Proteome analysis revealed differential enzyme expression of dioxygenases, decarboxylase, and hydratase responsible for subsequent degradation. Metabolome analysis displayed fipronil metabolites in the presence of the bacterium, supporting the proposed degradation pathway. Molecular docking and dynamic simulation of each identified enzyme in complex with the specific metabolite disclosed adequate binding and high stability in the enzyme-metabolite complex. This study provides in-depth insight into genes and their encoded enzymes involved in the fipronil degradation and formation of different metabolites during pollutant degradation. The outcome of this study can contribute immensely to developing efficient technologies for the bioremediation of fipronil-contaminated soils.

Biodegradation of fipronil: molecular characterization, degradation kinetics, and metabolites

Fipronil (C12H4Cl2F6N4OS) is a commonly used insecticide effective against numerous insects and pests. Its immense application poses harmful effects on various non-target organisms as well. Therefore, searching the effective methods for the degradation of fipronil is imperative and logical. In this study, fipronil-degrading bacterial species are isolated and characterized from diverse environments using a culture-dependent method followed by 16S rRNA gene sequencing. Phylogenetic analysis showed the homology of organisms with Acinetobacter sp., Streptomyces sp., Pseudomonas sp., Agrobacterium sp., Rhodococcus sp., Kocuria sp., Priestia sp., Bacillus sp., Aeromonas sp., and Pantoea sp. The bacterial degradation potential for fipronil was analyzed through high-performance liquid chromatography (HPLC). Incubation-based degradation studies revealed that Pseudomonas sp. and Rhodococcus sp. were found to be the most potent isolates that degraded fipronil at 100 mg L-1 concentration, with removal efficiencies of 85.9 and 83.6%, respectively. Kinetic parameter studies, following the Michaelis-Menten model, also revealed the high degradation efficiency of these isolates. Gas chromatography-mass spectrometry (GC-MS) analysis revealed fipronil sulfide, benzaldehyde, (phenyl methylene) hydrazone, isomenthone, etc., as major metabolites of fipronil degradation. Overall investigation suggests that native bacterial species isolated from the contaminated environments could be efficiently utilized for the biodegradation of fipronil. The outcome derived from this study has immense significance in formulating an approach for bioremediation of fipronil-contaminated surroundings.

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

Fipronil is an insecticide widely used in the agricultural and veterinary sectors for its efficacy in pest control. The presence of fipronil in the environment is mainly due to agricultural and domestic practices and is frequently found in different types of environmental matrices in concentrations ranging from µg/L to mg/L and can be hazardous to non-target organisms due to its high toxicity. This study was carried out to obtain and characterize microorganisms from soil which are capable of biodegrading fipronil that could be of great biotechnological interest. For this purpose, bioprospecting was carried out using fipronil (0.6 g/L) as the main source of carbon and nitrogen for growth. Once obtained, the strain was identified by sequencing the 16S ribosomal RNA (rRNA) gene and the capacity to degrade fipronil was monitored by GC-MS. Our study showed a presence in soil samples of the strain identified as Enterobacter chengduensis, which was able to metabolize fipronil and its metabolites during the mineralization process. Enterobacter chengduensis was able to biodegrade fipronil (96%) and its metabolites fipronil-sulfone (92%) and fipronil-sulfide (79%) in 14 days. Overall, the results of this study provided a bacterium with great potential that could contribute to the degradation of fipronil in the environment.

Impact of per- and polyfluorinated alkyl substances (PFAS) on the marine environment: Raising awareness, challenges, legislation, and mitigation approaches under the One Health concept

Per- and polyfluorinated alkyl substances (PFAS) have long been known for their detrimental effects on the ecosystems and living organisms; however the long-term impact on the marine environment is still insufficiently recognized. Based on PFAS persistence and bioaccumulation in the complex marine food network, adverse effects will be exacerbated by global processes such as climate change and synergies with other pollutants, like microplastics. The range of fluorochemicals currently included in the PFAS umbrella has significantly expanded due to the updated OECD definition, raising new concerns about their poorly understood dynamics and negative effects on the ocean wildlife and human health. Mitigation challenges and approaches, including biodegradation and currently studied materials for PFAS environmental removal are proposed here, highlighting the importance of ongoing monitoring and bridging research gaps. The PFAS EU regulations, good practices and legal frameworks are discussed, with emphasis on recommendations for improving marine ecosystem management.

Metabolism of an insecticide fipronil by soil fungus Cunninghamella elegans ATCC36112

In this study, the metabolic pathway of the phenylpyrazole insecticide fipronil in Cunninghamella elegans (C. elegans) was investigated. Approximately 92% of fipronil was removed within 5 days, and seven metabolites were accumulated simultaneously. The structures of the metabolites were completely or tentatively identified by GC-MS and ¹H, ¹³C NMR. To determine the oxidative enzymes involved in metabolism, piperonyl butoxide (PB) and methimazole (MZ) were used, and the kinetic responses of fipronil and its metabolites were determined. PB strongly inhibited fipronil metabolism, while MZ weakly inhibited its metabolism. The results suggest that cytochrome P450 (CYP) and flavin-dependent monooxygenase (FMO) may participate in fipronil metabolism. Integrated metabolic pathways can be inferred from the control and inhibitor experiments. Several novel products from the fungal transformation of fipronil were identified, and similarities between C. elegans transformation and mammalian metabolism of fipronil were compared. Therefore, these results will help to gain insight into the fungal degradation of fipronil and potential applications in fipronil bioremediation. At present, microbial degradation of fipronil is the most promising approach and maintains environmental sustainability. In addition, the ability of C. elegans to mimic mammalian metabolism will assist in illustrating the metabolic fate of fipronil in mammalian hepatocytes and assess its toxicity and potential adverse effects.

Biodegradation of fipronil: Molecular characterization, degradation kinetics, and metabolites

Fipronil (C12H4Cl2F6N4OS), is a commonly used insecticide effective against numerous insects and pests. Its immense application poses harmful effects on various non-target organisms as well. Therefore, searching the effective methods for the degradation of fipronil is imperative and logical. In this study, fipronil-degrading bacterial species are isolated and characterized from diverse environments using a culture-dependent method followed by 16S rRNA gene sequencing. Phylogenetic analysis showed the homology of organisms with Acinetobacter sp., Streptomyces sp., Pseudomonas sp., Agrobacterium sp., Rhodococcus sp., Kocuria sp., Priestia sp., Bacillus sp., Pantoea sp. The bacterial degradation potential for fipronil was analyzed through High-Performance Liquid Chromatography. Incubation-based degradation studies revealed that Pseudomonas sp. and Rhodococcus sp. were found to be the most potent isolates that degraded fipronil at 100 mg L-1 concentration, with removal efficiencies of 85.97 % and 83.64 %, respectively. Kinetic parameter studies, following the Michaelis-Menten model, also revealed the high degradation efficiency of these isolates. Gas Chromatography-Mass Spectrometry (GC-MS) analysis revealed fipronil sulfide, benzaldehyde, (phenyl methylene) hydrazone, isomenthone, etc., as major metabolites of fipronil degradation. Overall investigation suggests that native bacterial species isolated from the contaminated environments could be efficiently utilized for the biodegradation of fipronil. The outcome derived from this study has immense significance in formulating an approach for bioremediation of fipronil-contaminated surroundings.

Biodegradation of the Pesticides Bifenthrin and Fipronil by Bacillus Isolated from Orange Leaves

The pyrethroid bifenthrin and the phenylpyrazole fipronil are widely employed insecticides, and their extensive use became an environmental issue. Therefore, this study evaluated their biodegradation employing bacterial strains of Bacillus species isolated from leaves of orange trees, aiming at new biocatalysts with high efficiency for use singly and in consortium. Experiments were performed in liquid culture medium at controlled temperature and stirring (32 °C, 130 rpm). After 5 days, residual quantification by HPLC-UV/Vis showed that Bacillus amyloliquefaciens RFD1C presented 93% biodegradation of fipronil (10.0 mg.L^-1 initial concentration) and UPLC-HRMS analyses identified the metabolite fipronil sulfone. Moreover, Bacillus pseudomycoides 3RF2C showed a biodegradation of 88% bifenthrin (30.0 mg.L^-1 initial concentration). A consortium composed of the 8 isolated strains biodegraded 81% fipronil and 51% bifenthrin, showing that this approach did not promote better results than the most efficient strains employed singly, although high rates of biodegradation were observed. In conclusion, bacteria of the Bacillus genus isolated from leaves of citrus biodegraded these pesticides widely applied to crops, showing the importance of the plant microbiome for degradation of toxic xenobiotics.

New Insights into the Effect of Fipronil on the Soil Bacterial Community

Fipronil is a broad-spectrum insecticide with remarkable efficacy that is widely used to control insect pests around the world. However, its extensive use has led to increasing soil and water contamination. This fact is of concern and makes it necessary to evaluate the risk of undesirable effects on non-target microorganisms, such as the microbial community in water and/or soil. Studies using the metagenomic approach to assess the effects of fipronil on soil microbial communities are scarce. In this context, the present study was conducted to identify microorganisms that can biodegrade fipronil and that could be of great environmental interest. For this purpose, the targeted metabarcoding approach was performed in soil microcosms under two environmental conditions: fipronil exposure and control (without fipronil). After a 35-day soil microcosm period, the 16S ribosomal RNA (rRNA) gene of all samples was sequenced using the ion torrent personal genome machine (PGM) platform. Our study showed the presence of Proteobacteria, Actinobacteria, and Firmicutes in all of the samples; however, the presence of fipronil in the soil samples resulted in a significant increase in the concentration of bacteria from these phyla. The statistical results indicate that some bacterial genera benefited from soil exposure to fipronil, as in the case of bacteria from the genus Thalassobacillus, while others were affected, as in the case of bacteria from the genus Streptomyces. Overall, the results of this study provide a potential contribution of fipronil-degrading bacteria.

A novel strain of Stenotrophomonas acidaminiphila produces thermostable alkaline peptidase on agro-industrial wastes: process optimization, kinetic modeling and scale-up

Bacterial alkaline peptidases, especially from Bacillus species, occupy the frontline in global enzyme market, albeit with poor production economics. Here, we report the deployment of response surface methodology approximations to optimize fermentation parameters for enhanced yield of alkaline peptidase by the non-Bacillus bacterium; Stenotrophomonas acidaminiphila. Shake flask production under optimized conditions was scaled up in a 5-L bench-scale bioreactor. Logistic and modified Gompertz models revealed significant fits for biomass formation, total protein, and substrate consumption models. Maximum specific growth rate (µ_max = 0.362 h^-1) of the bacterium in the optimized medium did not differ significantly from those in Luria-Bertani and trypticase soy broths. The aqueous two-phase system-purified 45.7 kDa alkaline protease retained 83% activity which improved with increasing sodium dodecyl sulfate concentration thus highlighting potential laundry application. Maximum enzyme activity occurred at 75ºC and pH 10.5 but was inhibited by 5 mM phenyl-methyl-sulfonyl fluoride suggesting a serine-protease nature.

Atlas of the microbial degradation of fluorinated pesticides

Fluorine-based agrochemicals have been benchmarked as the golden standard in pesticide development, prompting their widespread use in agriculture. As a result, fluorinated pesticides can now be found in the environment, entailing serious ecological implications due to their harmfulness and persistence. Microbial degradation might be an option to mitigate these impacts, though environmental microorganisms are not expected to easily cope with these fluoroaromatics due to their recalcitrance. Here, we provide an outlook on the microbial metabolism of fluorinated pesticides by analyzing the degradation pathways and biochemical processes involved, while also highlighting the central role of enzymatic defluorination in their productive metabolism. Finally, the potential contribution of these microbial processes for the dissipation of fluorinated pesticides from the environment is also discussed.

Biodegradation of fipronil: current state of mechanisms of biodegradation and future perspectives

Fipronil is a broad-spectrum phenyl-pyrazole insecticide that is widely used in agriculture. However, in the environment, its residues are toxic to aquatic animals, crustaceans, bees, termites, rabbits, lizards, and humans, and it has been classified as a C carcinogen. Due to its residual environmental hazards, various effective approaches, such as adsorption, ozone oxidation, catalyst coupling, inorganic plasma degradation, and microbial degradation, have been developed. Biodegradation is deemed to be the most effective and environmentally friendly method, and several pure cultures of bacteria and fungi capable of degrading fipronil have been isolated and identified, including Streptomyces rochei, Paracoccus sp., Bacillus firmus, Bacillus thuringiensis, Bacillus spp., Stenotrophomonas acidaminiphila, and Aspergillus glaucus. The metabolic reactions of fipronil degradation appear to be the same in different bacteria and are mainly oxidation, reduction, photolysis, and hydrolysis. However, the enzymes and genes responsible for the degradation are somewhat different. The ligninolytic enzyme MnP, the cytochrome P450 enzyme, and esterase play key roles in different strains of bacteria and fungal. Many unanswered questions exist regarding the environmental fate and degradation mechanisms of this pesticide. The genes and enzymes responsible for biodegradation remain largely unexplained, and biomolecular techniques need to be applied in order to gain a comprehensive understanding of these issues. In this review, we summarize the literature on the degradation of fipronil, focusing on biodegradation pathways and identifying the main knowledge gaps that currently exist in order to inform future research. KEY POINTS: • Biodegradation is a powerful tool for the removal of fipronil. • Oxidation, reduction, photolysis, and hydrolysis play key roles in the degradation of fipronil. • Possible biochemical pathways of fipronil in the environment are described.

A comprehensive review of environmental fate and degradation of fipronil and its toxic metabolites

The use of pesticides to increase crop production has become one of the inevitable components of modern agriculture. Fipronil, a phenylpyrazoles insecticide, is one of the most widely used, systemic, broad-spectrum insecticides. Owing to its unique mode of action and selective toxicity, it was once regarded as safer alternatives to more toxic and persistent organochlorine insecticides. However, with the increased use, many studies have reported the toxicity of fipronil and its metabolites in various non-target organisms during the last two decades. Currently, it is regarded as one of the most persistent and lipophilic insecticides in the market. In the environment, fipronil can undergo oxidation, reduction, hydrolysis, or photolysis to form fipronil sulfone, fipronil sulfide, fipronil amide, or fipronil desulfinyl respectively. These metabolites except fipronil amide are more or less toxic and persistent than fipronil and have been reported from diverse environmental samples. Recently many studies have focused on the degradation and removal of fipronil residues from the environment. However, a comprehensive review summarizing and combining these recent findings is lacking. In the present review, we evaluate, summarize, and combine important findings from recent degradation studies of fipronil and its metabolites. An attempt has been made to elucidate the possible mechanism and pathways of degradation of fipronil and its toxic metabolites.

Effects of the insecticide fipronil in freshwater model organisms and microbial and periphyton communities

Fipronil is a broad-spectrum insecticide whose release in the environment damages many non-target organisms. This study evaluated the toxicity of fipronil at two biological levels using in vivo conditions and environmentally relevant concentrations: the first based on two model organisms (aquatic invertebrate Daphnia magna and the unicellular freshwater alga Chlamydomonas reinhardtii) and a second based on three natural communities (river periphyton and freshwater and soil microbial communities). The physicochemical properties of fipronil make it apparently unstable in the environment, so its behaviour was followed with high performance liquid chromatography (HPLC) under the different test conditions. The most sensitive organism to fipronil was D. magna, with median lethal dose (LC₅₀) values from 0.07 to 0.38 mg/L (immobilisation test). Toxicity was not affected by the media used (MOPS or river water), but it increased with temperature. Fipronil produced effects on the photosynthetic activity of C. reinhardtii at 20 °C in MOPS (EC₅₀ = 2.44 mg/L). The freshwater periphyton presented higher sensitivity to fipronil (photosynthetic yield EC₅₀ of 0.74 mg/L) in MOPS and there was a time-dependent effect (toxicity increased with time). Toxicity was less evident when periphyton and C. reinhardtii tests were performed in river water, where the solubility of fipronil is poor. Finally, the assessment of the metabolic profiles using Biolog EcoPlates showed that bacteria communities were minimally affected by fipronil. The genetic identification of these communities based on 16S rRNA gene sequencing revealed that many of the taxa are specialists in degrading high molecular weight compounds, including pesticides. This work allows us to better understand the impact of fipronil on the environment at different levels of the food chain and in different environmental conditions, a necessary point given its presence in the environment and the complex behaviour of this compound.

Efficient degradation of Fipronil in water by microwave-induced argon plasma: Mechanism and degradation pathways

Fipronil and its metabolites are potentially harmful to the ecological environment and have chronic neurotoxic effects, which makes it to be classified as class C carcinogens. Fipronil has been banned from agricultural use in China since 2009, but its residue remains in the environment. Therefore, an efficient and economical method is urgently needed to degrade fipronil residues in the environment. Herein, the degradation of fipronil in water solution using argon microwave-induced plasma (MIP) system was studied and a plausible reaction pathway was proposed in combination with Density Functional Theory (DFT) calculations. The degradation of fipronil by MIP system was optimized in terms of input power, plasma-sample distance, initial concentration and gas flow rate. After short time MIP treatment with an input power of 150 W, as high as 85.62% degradation efficiency was achieved for the fipronil at concentration of 20 mg·L^--1 under the optimized conditions, and the corresponding energy efficiency was 1334.8 mg·kwh^-1. Optical emission spectrometry (OES) was employed to characterize the distribution and intensity of OH, H and O species which play key roles in the degradation of fipronil by plasma, and it revealed that the degradation reaction mainly occurs at gas-liquid interface where the highest intensity of OH, H and O species was observed. High resolution mass spectrometric analysis in combination quantum chemical calculations indicate that a wide diversity of reaction processes occurred for fipronil degradation under MIP treatment, involving oxidation or reduction, nitro reduction, oxidative dichlorination, reductive dichlorination, hydration, dehydration and thiourea to urea. The possible degradation mechanism and pathways were proposed based on the degrading species identified by high resolution Mass Spectrometry (HRMS) and the thermodynamic profiles.

Optimization studies on biodegradation of atrazine by Bacillus badius ABP6 strain using response surface methodology

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Atrazine is widely used herbicide that causes harmful effects to living organisms.

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A bacterial isolate Bacillus badius ABP6 strain was used in the study.

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Optimization parameters showed better influence on the Biodegradation process of atrazine.

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Response surface methodology is a promising approach for Biodegradation enhancement by optimizing process parameters.

In this study, the optimization of distinctive environmental factors such as pH, temperature, agitation-speed and atrazine-concentration on atrazine degradation by utilizing Bacillus badius ABP6 strain, has been done through response-surface-methodology (RSM). The optimum-conditions after analysis for the maximum atrazine degradation were: pH 7.05, temperature 30.4 °C, agitation-speed 145.7 rpm, and atrazine-concentration 200.9 ppm. The prescribed model was approved for high F-value (95.92), very low P-value (<0.01) and non- significant lack of fit (0.1627). It was observed that under the optimized-conditions, the R² value of regression models for all the response variables was 0.9897 and the maximum atrazine degradation i.e. 89.7 % was found. Finally for graphical representation, the validated optimum-conditions of variables and responses were simulated using three dimensional plots (3D). The confirmation of the model is successful to suggest the optimization parameters of atrazine degradation under in-situ condition by bacterial isolate employing response-surface-methodology optimization tool of Design expert software (new version 10.0.1).

Isolation and Characterization of Fipronil Degrading Acinetobacter calcoaceticus and Acinetobacter oleivorans from Rhizospheric Zone of Zea mays

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.