Biodegradation of Allethrin, a Pyrethroid Insecticide, by an Acidomonas Sp

Enhancing enantiomeric and diastereomeric separations: A single chromatograph approach for two-dimensional heart-cut methodology

A high-performance chromatograph was adapted and reconfigured to establish a two-dimensional methodology for separations that are not easily achievable using a single enantioselective column. Allethrin, a pyrethroid used widely as a pesticide in domestic environments, was chosen as the model analyte. With three chiral centers, it has eight stereoisomers and is considered one of the more difficult chiral separations. Diastereomeric separation was achieved in the first dimension using a shape-selective stationary phase based on ultrapure porous graphitic carbon (particle diameter, 3 μm) in the reversed phase mode. Advanced asymmetric bidirectional peak functions (half-Gaussian modified Gaussian and exponentially modified Gaussian) were employed to extract overlapping peak areas. The four diastereomeric peaks were heart-cut and sent to the second dimension online using a standard six-port 2-position rotary valve. Enantiomeric separation was attained in the second dimension using an immobilized-cellulose tris(3,5-dichlorophenylcarbamate) column (3 μm) with chromatographic resolutions >2.7 for all enantiomeric pairs. The second dimension method was developed using the information from circular dichroism detection. The baseline separation of seven peaks of allethrin in a single dimension was also demonstrated using (2-hydroxypropyl)-β-cyclodextrin. The enantiomeric purity of a purified formulation of allethrin in a commercial pesticide was validated using the developed 2D approach.

Novel mechanism and degradation kinetics of allethrin using Bacillus megaterium strain HLJ7 in contaminated soil/water environments

As a common pyrethroid insecticide, allethrin is widely used for various purposes in agriculture and home applications. At present, allethrin residues have been frequently detected worldwide, yet little is known about the kinetics and degradation mechanisms of this insecticide. In this study, a highly efficient allethrin-degrading bacterium, Bacillus megaterium strain HLJ7, was obtained through enrichment culture technology. Strain HLJ7 can remove 96.5% of 50 mg L^-1 allethrin in minimal medium within 11 days. The first-order kinetic analysis of degradation demonstrated that the half-life of allethrin degradation by strain HLJ7 was 3.56 days, which was significantly shorter than the 55.89 days of the control. The Box-Behnken design of the response surface method optimized the degradation conditions for strain HLJ7: temperature 32.18 °C, pH value 7.52, and inoculation amount 1.31 × 10⁷ CFU mL^-1. Using Andrews equation, the optimal concentration of strain HLJ7 to metabolize allethrin was determined to be 21.15 mg L^-1, and the maximum specific degradation rate (q_max), half-rate constant (K_s) and inhibition coefficient (K_i) were calculated to be 1.80 d^-1, 1.85 mg L^-1 and 68.13 mg L^-1, respectively. Gas chromatography-mass spectrometry identified five intermediate metabolites, suggesting that allethrin could be degraded firstly by cleavage of its carboxylester bond, followed by degradation of the five-carbon ring and subsequent metabolism. The results of soil remediation experiments showed that strain HLJ7 has excellent bioremediation potential in the soils. After 15 days of treatment, about 70.8% of the initial allethrin (50 mg kg^-1) was removed and converted into nontoxic intermediate metabolites, and its half-life was significantly reduced in the soils. Taken together, these findings shed light on the degradation mechanisms of allethrin and also highlight the promising potentials of B. megaterium HLJ7 in bioremediation of allethrin-comtaminated environment.

Advances and future prospects of pyrethroids: Toxicity and microbial degradation

Pyrethroids are a class of insecticides structurally similar to that of natural pyrethrins. The application of pyrethrins in agriculture and pest control lead to many kinds of environmental pollution affecting human health and loss of soil microbial population that affect soil fertility and health. Natural pyrethrins have been used since ancient times as insect repellers, and their synthetic versions especially type 2 pyrethroids could be highly toxic to humans. PBO (Piperonyl butoxide) is known to enhance the toxicity of prallethrin in humans due to the resistance in its metabolic degradation. Pyrethroids are also known to cause plasma biochemical profile changes in humans and they also lead to the production of high levels of reactive oxygen species. Further they are also known to increase SGPT activity in humans. Due to the toxicity of pyrethrins in water bodies, soils, and food products, there is an urgent need to develop sustainable approaches to reduce their levels in the respective fields, which are eco-friendly, economically viable, and socially acceptable for on-site remediation. Keeping this in view, an attempt has been made to analyse the advances and prospects in using pyrethrins and possible technologies to control their harmful effects. The pyrethroid types, composition and biochemistry of necessary pyrethroid insecticides have been discussed in detail, in the research paper, along with their effect on insects and humans. It also covers the impact of pyrethroids on different plants and soil microbial flora. The second part deals with the microbial degradation of the pyrethroids through different modes, i.e., bioaugmentation and biostimulation. Many microbes such as Acremonium, Aspergillus, Microsphaeropsis, Westerdykella, Pseudomonas, Staphylococcus have been used in the individual form for the degradation of pyrethroids, while some of them such as Bacillus are even used in the form of consortia.

Current insights into the microbial degradation for pyrethroids: strain safety, biochemical pathway, and genetic engineering

As a biologically inspired insecticide, pyrethroids (PYRs) exert evident toxic side effects on non-target organisms. PYRs and their general toxic intermediate 3-phenoxybenzoic acid (3-PBA) have shown high detection rates/levels in human beings recently, for which diet was identified as the major exposure route. Microbial mineralization has emerged as a versatile strategy in addressing such escalating concern. Herein, PYRs and 3-PBA biodegradation with regards to strain safety, application and surfactant were summarized. Numerous PYRs-degrading microbes have been reported yet with a minority focused on 3-PBA. Most isolates were from contaminated sites while several microbial food cultures (MFCs) have been investigated. MFCs such as Bacillus spp. and Aspergillus spp. that dominate in PYRs-degrading microbial pools are applicable candidates for agricultural by-products detoxification during the postharvest process. Subsequently, we discussed committed degradation steps, wherein hydrolase responsible for PYRs ester linkage cleavage and oxygenase for 3-PBA diphenyl ether bond rupture play vital roles. Finally, comprehensive information of the key enzyme genes is outlined along with methodologies concerning gene cloning. Cytochrome P450 monooxygenases (CYP) is competent for diphenyl ether scission. Newly-developed omics has become a feasible gene and enzyme mining technology. To achieve PYRs mineralization in feed and food commodities, the screening of MFCs rich in related enzymes and the construction of MFCs-derived genetically modified microbes (GMMs) exhibit great potential considering the safety issues.

Metagenome Sequencing Reveals the Midgut Microbiota Makeup of Culex pipiens quinquefasciatus and Its Possible Relationship With Insecticide Resistance

Midgut microbiota can participate in the detoxification and metabolism processes in insects, but there are few reports on the relationship between midgut microbiota and insecticide resistance in mosquitoes. In this study, we performed metagenomic sequencing on a susceptible strain (SS), a field-collected Hainan strain (HN), and a deltamethrin-resistant strain (RR) of Culex pipiens quinquefasciatus to understand the diversity and functions of their midgut microbiota. The results revealed differences in midgut microbiota among the three strains of Cx. pipiens quinquefasciatus. At the phylum level, Proteobacteria was the most prominent, accounting for nearly 70% of their midgut microbes. At the genus level, Aeromonas made up the highest proportion. In addition, Aeromonas, Morganella, Elizabethkingia, Enterobacter, Cedecea, and Thorsellia showed significant differences between strains. At the species level, Bacillus cereus, Enterobacter cloacae complex sp. 4DZ3-17B2, Streptomyces sp. CNQ329, and some species of Pseudomonas and Wolbachia were more abundant in the two resistant strains. Principal component analysis (PCA) showed that the SS strain had significantly different metagenomic functions than the two deltamethrin-resistant strains (HN and RR strain). The HN and RR strains differed from the SS strain in more than 10 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The analysis of species abundance and functional diversity can provide directions for future studies.

Binding interaction of allethrin with esterase: Bioremediation potential and mechanism

The main aim of this work was to study the allethrin binding interactions with esterase and its bioremediation potential using an isolated bacterial strain CW7, identified as Pseudomonas nitroreducens. The degradation conditions with strain CW7 were optimized using response surface methodology at pH 7.0, a temperature of 32 °C, and an inocula concentration of 150 mg·L^-1, with 96% allethrin degradation observed over 7 days. The kinetic parameters q_max, K_s, and K_i were calculated to be 0.512 day^-1, 4.97 mg·L^-1, and 317.13 mg·L^-1, respectively. Nine intermediate metabolites were identified after analysing the degradation products by gas chromatography-mass spectrometry. Strain CW7 effectively degraded a wide variety of pyrethroids as a carbon source. Molecular modeling, docking, and enzyme kinetics were used to investigate the binding pocket of the esterase containing amino acids such as alanine, arginine, valine, proline, cysteine, glycine, isoleucine, phenylalanine, serine, asparagine, and threonine, which play active roles in allethrin degradation.

Mechanism of allethrin biodegradation by a newly isolated Sphingomonas trueperi strain CW3 from wastewater sludge

The main aim of this study was to investigate and characterize the bacterial strain that has the potential to degrade allethrin. The isolated strain, Sphingomonas trueperi CW3, degraded allethrin (50 mg L-1) in batch experiments within seven days. The Box-Behnken design optimized allethrin degradation and had a confirmation of 93% degradation at pH 7.0, at a temperature of 30 °C and an inocula concentration of 100 mg L-1. The results from gas chromatography and mass spectrometry analysis confirmed the existence of nine metabolites from the degradation of allethrin with strain CW3. The cleavage of the ester bond, followed by the degradation of the five-carbon rings, was allethrin's primary degradation pathway. The strain CW3 also degraded other widely applied synthetic pyrethroids such as cyphenothrin, bifenthrin, permethrin, tetramethrin, β-cypermethrin and chlorempenthrin. Furthermore, in experiments performed with sterilized soil, strain CW3 based bioaugmentation effectively removed allethrin at a significantly reduced half-life.

Biodegradation of Allethrin by a Novel Fungus Fusarium proliferatum Strain CF2, Isolated from Contaminated Soils

Continuous use of allethrin has resulted in heavy environmental contamination and has raised public concern about its impact on human health, yet little is known about the kinetics and microbial degradation of this pesticide. This study reported the degradation kinetics in a novel fungal strain, Fusarium proliferatum CF2, isolated from contaminated agricultural fields. Strain CF2 utilized 50 mg·L-1 of allethrin as the sole carbon source for growth in minimal salt medium and tolerated high concentrations of allethrin of up to 1000 mg·L-1. The optimum degradation conditions for strain CF2 were determined to be a temperature of 26 °C and pH 6.0 using response surface methodology. Under optimum conditions, strain CF2 completely degraded allethrin within 144 hours. The degradation kinetics of allethrin followed first order reaction kinetics. Kinetics analysis showed that its half-life was substantially reduced by 507.1 hours, as compared to the uninoculated control. This study provides new insights into the microbial degradation of allethrin with fungal F. proliferatum CF2.

New insights into the microbial degradation and catalytic mechanism of synthetic pyrethroids

The significant applications of pyrethroid insecticides in agro-ecosystem and household environments have raised serious environmental concerns. Environmental bioremediation has emerged as an effective and eco-friendly approach to remove or neutralize hazardous compounds. Bioaugmentation accelerates pyrethroid degradation in liquid cultures and soil. Pyrethroid-degrading microorganisms have been extensively studied to cope with pyrethroid residues. Microorganisms primarily hydrolyze the ester bonds of pyrethroids, and their degradation pathways have been elaborated. The functional genes and enzymes involved in microbial degradation have also been screened and studied. Carboxylesterase plays a key role in pyrethroid degradation by cleaving its carboxylester linkage. The catalytic mechanism is dependent on a specific catalytic triad, consisting of three amino acid residues (glutamine, histidine, and serine) within the active site of the carboxylesterase enzyme. Pyrethroid-degrading strains and enzymes have proven to be effective for the bioremediation of pyrethroid-contaminated environments. In this review, we have summarized newly isolated pyrethroid-degrading strains and proposed the degradation pathways along with key functional genes/enzymes. To develop an efficient bioremediation strategy, pyrethroid-degrading microorganisms should be comprehensively explored.

Insight Into Microbial Applications for the Biodegradation of Pyrethroid Insecticides

Pyrethroids are broad-spectrum insecticides and presence of chiral carbon differentiates among various forms of pyrethroids. Microbial approaches have emerged as a popular solution to counter pyrethroid toxicity to marine life and mammals. Bacterial and fungal strains can effectively degrade pyrethroids into non-toxic compounds. Different strains of bacteria and fungi such as Bacillus spp., Raoultella ornithinolytica, Psudomonas flourescens, Brevibacterium sp., Acinetobactor sp., Aspergillus sp., Candida sp., Trichoderma sp., and Candia spp., are used for the biodegradation of pyrethroids. Hydrolysis of ester bond by enzyme esterase/carboxyl esterase is the initial step in pyrethroid biodegradation. Esterase is found in bacteria, fungi, insect and mammalian liver microsome cells that indicates its hydrolysis ability in living cells. Biodegradation pattern and detected metabolites reveal microbial consumption of pyrethroids as carbon and nitrogen source. In this review, we aim to explore pyrethroid degrading strains, enzymes and metabolites produced by microbial strains. This review paper covers in-depth knowledge of pyrethroids and recommends possible solutions to minimize their environmental toxicity.

Deltamethrin impact in a cabbage planted soil: Degradation and effect on microbial community structure

Synthetic pyrethroids (SPs) are one of the most common pesticides used worldwide. Their use has greatly increased in the last decades and its' continuous application lead to added pesticides concentration in soil. Consequently, SPs may enter the food chain, affecting the environment and human health. The degradation over time of the pyrethroid pesticide deltamethrin applied to cabbages was monitored. The evolution was followed both on cabbages and the surrounding soils, and the soil microbial community characterized by next-generation sequencing of the 16S rRNA gene. The main shift in the microbial community structure was observed during the first 30 days after pesticides' application. The modification in the microbial community composition, where an increased abundance of Nocardioides sp. and Sphingomonas sp. were observed, was correlated respectively with the conversions of deltamethrin and its metabolite, 3-phenoxybenzoic acid (3-PBA). Although deltamethrin was not found in any of the tested samples (soil and cabbage) after 180 days, it caused an environmental impact much further than the 7 days security interval. These findings suggest that deltamethrin application can disturb soil microbial community and that natural biodegradation can have an important part in pesticides soil decontamination.

Pyrethroid-Degrading Microorganisms and Their Potential for the Bioremediation of Contaminated Soils: A Review

Pyrethroid insecticides have been used to control pests in agriculture, forestry, horticulture, public health and for indoor home use for more than 20 years. Because pyrethroids were considered to be a safer alternative to organophosphate pesticides (OPs), their applications significantly increased when the use of OPs was banned or limited. Although, pyrethroids have agricultural benefits, their widespread and continuous use is a major problem as they pollute the terrestrial and aquatic environments and affect non-target organisms. Since pyrethroids are not degraded immediately after application and because their residues are detected in soils, there is an urgent need to remediate pyrethroid-polluted environments. Various remediation technologies have been developed for this purpose; however, bioremediation, which involves bioaugmentation and/or biostimulation and is a cost-effective and eco-friendly approach, has emerged as the most advantageous method for cleaning-up pesticide-contaminated soils. This review presents an overview of the microorganisms that have been isolated from pyrethroid-polluted sites, characterized and applied for the degradation of pyrethroids in liquid and soil media. The paper is focused on the microbial degradation of the pyrethroids that have been most commonly used for many years such as allethrin, bifenthrin, cyfluthrin, cyhalothrin, cypermethrin, deltamethrin, fenpropathrin, fenvalerate, and permethrin. Special attention is given to the bacterial strains from the genera Achromobacter, Acidomonas, Bacillus, Brevibacterium, Catellibacterium, Clostridium, Lysinibacillus, Micrococcus, Ochrobactrum, Pseudomonas, Serratia, Sphingobium, Streptomyces, and the fungal strains from the genera Aspergillus, Candida, Cladosporium, and Trichoderma, which are characterized by their ability to degrade various pyrethroids. Moreover, the current knowledge on the degradation pathways of pyrethroids, the enzymes that are involved in the cleavage of pesticide molecules, the factors/conditions that influence the survival of strains that are introduced into soil and the rate of the removal of pyrethroids are also discussed. This knowledge may be useful to optimize the environmental conditions of bioremediation and may be crucial for the effective removal of pyrethroids from polluted soils.

Potential of Biological Agents in Decontamination of Agricultural Soil

Pesticides are widely used for the control of weeds, diseases, and pests of cultivated plants all over the world, mainly since the period after the Second World War. The use of pesticides is very extensive to control harm of pests all over the globe. Persistent nature of most of the synthetic pesticides causes serious environmental concerns. Decontamination of these hazardous chemicals is very essential. This review paper elaborates the potential of various biological agents in decontamination of agricultural soils. The agricultural crop fields are contaminated by the periodic applications of pesticides. Biodegradation is an ecofriendly, cost-effective, highly efficient approach compared to the physical and chemical methods which are expensive as well as unfriendly towards environment. Biodegradation is sensitive to the concentration levels of hydrogen peroxide and nitrogen along with microbial community, temperature, and pH changes. Experimental work for optimum conditions at lab scale can provide very fruitful results about specific bacterial, fungal strains. This study revealed an upper hand of bioremediation over physicochemical approaches. Further studies should be carried out to understand mechanisms of biotransformation.

Isomerization and biodegradation of beta-cypermethrin by Pseudomonas aeruginosa CH7 with biosurfactant production

Pseudomonas aeruginosa CH7, isolated from activated sludge, was able not only to isomerize and degrade beta-cypermethrin but also to utilize it as the sole source of carbon and energy for growth and produce biosurfactant. The strain effectively degraded beta-cypermethrin with inocula biomass of 0.1-0.2 g L(-1) at 25-35°C, pH 6-9, and a final concentration of beta-cypermethrin 25-900 mg L(-1). Via response surface methodology analysis, we found the optimal condition was 29.4°C, pH 7.0, and inocula biomass of 0.15 g L(-1); under these conditions, about 90% of the beta-cypermethrin could be degraded within 12 days. Noticeably, biosurfactant was detected in the MSM culture of strain CH7, suggesting that the biosurfactant (rhamnolipid) could potentially enhance the degradation of beta-cypermethrin by promoting the dissolution, adsorption, and absorption of the hydrophobic compounds. Therefore, CH7 may serve as a promising strain in the bioremediation of wastewater and soil polluted by beta-cypermethrin.

Biodegradation of beta-cypermethrin and 3-phenoxybenzoic acid by a novel Ochrobactrum lupini DG-S-01

A newly isolated bacterium DG-S-01 from activated sludge utilized beta-cypermethrin (beta-CP) and its major metabolite 3-phenoxybenzoic acid (3-PBA) as sole carbon and energy source for growth in mineral salt medium (MSM). Based on the morphology, physio-biochemical characteristics, and 16S rDNA sequence analysis, DG-S-01 was identified as Ochrobactrum lupini. DG-S-01 effectively degraded beta-CP with total inocula biomass A(590 nm) = 0.1-0.8, at 20-40 °C, pH 5-9, initial beta-CP 50-400 mg L(-1) and metabolized to yield 3-PBA leading to complete degradation. Andrews equation was used to describe the special degradation rate at different initial concentrations. Degradation rate parameters q(max), K(s) and K(i) were determined to be 1.14 d(-1), 52.06 mg L(-1) and 142.80 mg L(-1), respectively. Maximum degradation was observed at 30 °C and pH 7.0. Degradation of beta-CP was accelerated when MSM was supplemented with glucose, beef extract and yeast extract. Studies on biodegradation in liquid medium showed that over 90% of the initial dose of beta-CP (50 mg L(-1)) was degraded under the optimal conditions within 5d. Moreover, the strain also degraded beta-cyfluthrin, fenpropathrin, cyhalothrin and deltamethrin. These results reveal that DG-S-01 may possess potential to be used in bioremediation of pyrethroid-contaminated environment.