Biodegradation of the neonicotinoid insecticide Acetamiprid by bacterium Pigmentiphaga sp. strain AAP-1 isolated from soil

Efficient Biodegradation of Multiple Aryloxyphenoxypropionate Herbicides by Corynebacterium sp. Z-1 and the Proposed Degradation Mechanism

Esterases are crucial for aryloxyphenoxypropionate herbicide (AOPP) biodegradation. However, the underlying molecular mechanisms of AOPP biodegradation by esterases are poorly understood. In the current work, Corynebacterium sp. Z-1 was isolated and found to degrade multiple AOPPs, including quizalofop-p-ethyl (QPE), haloxyfop-p-methyl (HPM), fenoxaprop-p-ethyl (FPE), cyhalofop-butyl (CYB), and clodinafop-propargyl (CFP). A novel esterase, QfeH, which catalyzes the cleavage of ester bonds in AOPPs to form AOPP acids, was identified from strain Z-1. The catalytic activities of QfeH toward AOPPs decreased in the following order: CFP > FPE > CYB > QPE > HPM. Molecular docking, computational analyses, and site-directed mutagenesis indicated the catalytic mechanisms of QfeH-mediated degradation of different AOPPs. Notably, the key residue S159 is essential for the activity of QfeH. Moreover, V222Y, T227M, T227A, A271R, and M275K mutants, exhibiting 2.9-5.0 times greater activity than QfeH, were constructed. This study facilitates the mechanistic understanding of AOPPs bioremediation by esterases.

RNA-Seq analysis of Phanerochaete sordida YK-624 degrades neonicotinoid pesticide acetamiprid

Acetamiprid (ACE) belongs to the group of neonicotinoid pesticides, which have become the most widely utilised pesticides around the world in the last two decades. The ability of Phanerochaete sordida YK-624 to degrade ACE under ligninolytic conditions has been demonstrated; however, the functional genes involved in ACE degradation have not been fully elucidated. In the present study, the differentially expressed genes of P. sordida YK-624 under ACE-degrading conditions and in the absence of ACE were elucidated by RNA sequencing (RNA-Seq). Based on the gene ontology enrichment results, the cell wall and cell membrane were significantly affected under ACE-degrading conditions. This result suggested that intracellular degradation of ACE might be mediated by this fungus. In addition, genes in metabolic pathways were the most enriched upregulated differentially expressed genes according to the KEGG pathway analysis. Eleven differentially expressed genes characterised as cytochrome P450s were upregulated, and these genes were determined to be particularly important for ACE degradation by P. sordida YK-624 under ligninolytic conditions.

The fecal bacterial microbiome of the Kuhl's pipistrelle bat (Pipistrellus kuhlii) reflects landscape anthropogenic pressure

BACKGROUND

Anthropogenic disturbance has the potential to negatively affect wildlife health by altering food availability and diet composition, increasing the exposure to agrochemicals, and intensifying the contact with humans, domestic animals, and their pathogens. However, the impact of these factors on the fecal microbiome composition of wildlife hosts and its link to host health modulation remains barely explored. Here we investigated the composition of the fecal bacterial microbiome of the insectivorous bat Kuhl's pipistrelle (Pipistrellus kuhlii) dwelling in four environmental contexts with different levels of anthropogenic pressure. We analyzed their microbiome composition, structure and diversity through full-length 16S rRNA metabarcoding using the nanopore long-read sequencer MinION™. We hypothesized that the bacterial community structure of fecal samples would vary across the different scenarios, showing a decreased diversity and richness in samples from disturbed ecosystems.

RESULTS

The fecal microbiomes of 31 bats from 4 scenarios were sequenced. A total of 4,829,302 reads were obtained with a taxonomic assignment percentage of 99.9% at genus level. Most abundant genera across all scenarios were Enterococcus, Escherichia/Shigella, Bacillus and Enterobacter. Alpha diversity varied significantly between the four scenarios (p < 0.05), showing the lowest Shannon index in bats from urban and intensive agriculture landscapes, while the highest alpha diversity value was found in near pristine landscapes. Beta diversity obtained by Bray-Curtis distance showed weak statistical differentiation of bacterial taxonomic profiles among scenarios. Furthermore, core community analysis showed that 1,293 genera were shared among localities. Differential abundance analyses showed that the highest differentially abundant taxa were found in near pristine landscapes, with the exception of the family Alcaligenaceae, which was also overrepresented in urban and intensive agriculture landscapes.

CONCLUSIONS

This study suggests that near pristine and undisturbed landscapes could promote a more resilient gut microbiome in wild populations of P. kuhlii. These results highlight the potential of the fecal microbiome as a non-invasive bioindicator to assess insectivorous bats' health and as a key element of landscape conservation strategies.

Response of microbial community to the remediation of neonicotinoid insecticide imidacloprid contaminated wetland soil by Phanerochaete chrysosporium

Imidacloprid (IMI), a typic neonicotinoid insecticide, is widely used and persist in soils with long half-time causing serious threat to ecosystem and human health. It is urgent to develop suitable and effective methods to accelerate it degradation and alleviate its negative impacts in soil. In this study, the introduction of functional microbe white-rot fungus Phanerochaete chrysosporium to remediate IMI contaminated wetland soil was carried out. The remediation performance and the response of the soil microbial community were examined. The results showed that P. chrysosporium could improve the degradation of IMI in soil no matter the soil was sterilized or not. The bioaugmentation was especially observed in non-sterilized soil under the inoculation patterns of FE and SP with the maximum IMI degradation rate of 91% and 93% in 7 days, respectively. The invertase activity in soil was also enhanced with P. chrysosporium inoculation. Microbial community analysis revealed that P. chrysosporium inoculation could increase the diversity and richness of bacterial community, and stimulate some IMI degraders genera including Ochrobactrum, Leifsonia, Achromobacter, and Bacillus. Moreover, the xenobiotic degradation and metabolism pathway was generally enhanced with P. chrysosporium inoculation based on PICRUSt analysis. These obtained results demonstrated that the introduction of white-rot fungus is of great potentially enabling the remediation of neonicotinoids contaminated soil.

A fluorescent aptasensor based on gold nanoparticles quenching the fluorescence of rhodamine B to detect acetamiprid

Pesticide residue detection is one of the main safety issues in the utilization of medicinal plants. In this work, a highly selective and sensitive aptasensor for acetamiprid determination was designed. The mechanism of the proposed method is based on the fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and rhodamine B (RB). Aptamers protect AuNPs from salt-induced aggregation, which causes fluorescence quenching of RB by the AuNPs via surface energy transfer. In the absence of acetamiprid, AuNPs were coated with aptamers on the surface and dispersed in NaCl solution. At this time, the dispersed AuNPs could perfectly quench the fluorescence intensity of RB. In contrast, in the presence of acetamiprid, aptamers specifically combine with acetamiprid to form a complex. With a high salt concentration, AuNPs would be aggregated without aptamer protection, weakening the RB quenching effect. Therefore, the concentration of acetamiprid could be obtained from the change in fluorescence intensity in the system. A fluorescent sensing method was established with a linear range from 0.1 to 3 μg mL^-1, and the LOD was 0.0285 μg mL^-1. The recoveries of acetamiprid in traditional Chinese medicine (TCM) samples were 96.23-105.75%. This method has great application value for the detection of acetamiprid in a complex sample matrix.

Current and emerging trends in bioaugmentation of organic contaminated soils: A review

Organic contaminated soils constitute an important environmental problem, whereas field applicability of existing physical-chemical methods has encountered numerous obstacles, such as high chemical cost, large energy consumption, secondary pollution, and soil degradation. Bioaugmentation is an environmentally friendly and potentially economic technology that efficiently removes toxic pollutants from organic contaminated soils by microorganisms or their enzymes and bioremediation additives. This review attempted to explore the recent advances in bioaugmentation of organic contaminated soils and provided a comprehensive summary of various bioaugmentation methods, including bacterial, fungus, enzymes and bioremediation additives. The practical application of bioaugmentation is frequently limited by soil environmental conditions, microbial relationships, enzyme durability and remediation cycles. To tackle these problems, the future of bioaugmentation can be processed from sustainability of broad-spectrum bioremediation carriers, microbial/enzyme agents targeting combined contaminants, desorption of environmentally friendly additives and small molecular biological stimulants. Findings of this research are expected to provide new references for bioaugmentation methods that are practically feasible and economically potential.

Genetic redundancy of 4-hydroxybenzoate 3-hydroxylase genes ensures the catabolic safety of Pigmentiphaga sp. H8 in 3-bromo-4-hydroxybenzoate-contaminated habitats

Genetic redundancy is prevalent in organisms and plays important roles in the evolution of biodiversity and adaptation to environmental perturbation. However, selective advantages of genetic redundancy in overcoming metabolic disturbance due to structural analogues have received little attention. Here, functional divergence of the three 4-hydroxybenzoate 3-hydroxylase (PHBH) genes (phbh1~3) was found in Pigmentiphaga sp. strain H8. The genes phbh1/phbh2 were responsible for 3-bromo-4-hydroxybenzoate (3-Br-4-HB, an anthropogenic pollutant) catabolism, whereas phbh3 was primarily responsible for 4-hydroxybenzoate (4-HB, a natural intermediate of lignin) catabolism. 3-Br-4-HB inhibited 4-HB catabolism by competitively binding PHBH3, and was toxic to strain H8 cells especially at high concentrations. The existence of phbh1/phbh2 not only enabled strain H8 to utilize 3-Br-4-HB, but also ensured the catabolic safety of 4-HB. Molecular docking and site-directed mutagenesis analyses revealed that Val199 and Phe384 of PHBH1/PHBH2 were required for the hydroxylation activity towards 3-Br-4-HB. Phylogenetic analysis indicated that phbh1 and phbh2 originated from a common ancestor and evolved specifically in strain H8 to adapt to 3-Br-4-HB-contaminated habitats, whereas phbh3 evolved independently. This study deepens our understanding of selective advantages of genetic redundancy in prokaryote's metabolic robustness and reveals the factors driving the divergent evolution of redundant genes in adaptation to environmental perturbation. This article is protected by copyright. All rights reserved.

Biodegradation of imidacloprid: Molecular and kinetic analysis

Imidacloprid (C₉H₁₀ClN₅O₂) is the most widely used insecticide. Its persistence and toxic nature have caused a detrimental effect on living biota. Thus its removal from the contaminated environment has become imperative. The present study aimed to isolate bacterial species from pesticide-contaminated sites and assess their potential for biodegradation of imidacloprid. The 16S rRNA analysis revealed the genetic relatedness of isolates to Sphingobacterium sp., Agrobacterium sp., Pseudomonas sp., and Bacillus sp. Batch biodegradation studies showed that Sphingobacterium sp. and Agrobacterium sp. were the most promising isolates as they degraded 81.0% and 84.9%, respectively, of imidacloprid at the concentration of 95 mg/L via co-metabolism. Kinetic study (V_max/K_s ratio) also suggested the high degradation efficiency of these isolates. Imidacloprid-guanidine (C₉H₁₁ClN₄) was identified as the metabolite. This report highlights the potential of bacteria for imidacloprid degradation and could be utilized for the formulation of strategies for the remediation of imidacloprid contaminated environments.

Microbial Technologies Employed for Biodegradation of Neonicotinoids in the Agroecosystem

Neonicotinoids are synthetic pesticides widely used for the control of various pests in agriculture throughout the world. They mainly attack the nicotinic acetylcholine receptors, generate nervous stimulation, receptor clot, paralysis and finally cause death. They are low volatile, highly soluble and have a long half-life in soil and water. Due to their extensive use, the environmental residues have immensely increased in the last two decades and caused many hazardous effects on non-target organisms, including humans. Hence, for the protection of the environment and diversity of living organism's the degradation of neonicotinoids has received widespread attention. Compared to the other methods, biological methods are considered cost-effective, eco-friendly and most efficient. In particular, the use of microbial species makes the degradation of xenobiotics more accessible fast and active due to their smaller size. Since this degradation also converts xenobiotics into less toxic substances, the various metabolic pathways for the microbial degradation of neonicotinoids have been systematically discussed. Additionally, different enzymes, genes, plasmids and proteins are also investigated here. At last, this review highlights the implementation of innovative tools, databases, multi-omics strategies and immobilization techniques of microbial cells to detect and degrade neonicotinoids in the environment.

Selected transformation products of neonicotinoid insecticides (other than imidacloprid) in drinking water

Several transformation products (or metabolites) of neonicotinoid insecticides (NNIs) have been detected in drinking water, such as desnitro-imidacloprid and imidacloprid-urea. However, data on the occurrences of the metabolites of NNIs (mNNIs) in drinking water are mainly limited to the imidacloprid metabolites. To identify whether the potential metabolites of other widely used NNIs (such as acetamiprid, clothianidin, and thiamethoxam) occur in drinking water and to characterize their distribution profiles, twelve selected (mainly urea and desnitro/decyano) metabolites of NNIs were measured in drinking water samples (n = 884, including n = 789 for tap water, and n = 95 for shallow groundwater) that were collected from 32 provinces in mainland China and Hong Kong. Nearly 90% of the drinking water samples contained the detected mNNI residues. Among the selected mNNIs, thiamethoxam-urea (THM-urea: 76%) and decyano-acetamiprid (decyano-ACE: 73%) were frequently detected (median: 0.94 and 0.25 ng/L, respectively), which were followed by clothianidin-urea (CLO-urea: 45%), desnitro-thiamethoxam (DN-THM: 38%), and other mNNIs (detected in less than 30% of the water samples). Surface-water-sourced tap water had an approximately 8-10 times higher median cumulative concentration (ng/L) of the selected mNNIs (ΣmNNIs: 3.88) than the deep groundwater-sourced tap water (0.53) and groundwater that was directly used as drinking water (0.38). Higher ratios of THM-urea accounted for ΣTHM in north and northwest China than in south China could be partly explained by the decreasing soil pH values from north to south in China. The higher ratios of decyano-ACE accounted for ΣACE in south China than in north and northwest China could be attributable to the lower soil pH levels, higher temperatures, and greater light intensities in south China. The THM-urea, decyano-ACE, and ΣmNNIs levels in cities were found to be significantly higher than those in nonurban areas. The THM-urea levels in seven drinking water samples from Guangxi and Henan Provinces exceeded the guideline limit (100 ng/L) of the European Union. This is the first study to identify THM-urea, decyano-ACE, CLO-urea, and DN-THM in drinking water. To better assess the mass loadings of NNIs in drinking water, mNNIs should be considered in further studies.

Bioaugmentation of acetamiprid-contaminated soil with Pigmentiphaga sp. strain D-2 and its effect on the soil microbial community

Bioaugmentation, a strategy based on microbiome engineering, has been proposed for bioremediation of pollutant-contaminated environments. However, the complex microbiome engineering processes for soil bioaugmentation, involving interactions among the exogenous inoculum, soil environment, and indigenous microbial microbiome, remain largely unknown. Acetamiprid is a widely used neonicotinoid insecticide which has caused environmental contaminations. Here, we used an acetamiprid-degrading strain, Pigmentiphaga sp. D-2, as inoculum to investigate the effects of bioaugmentation on the soil microbial community and the process of microbiome reassembly. The bioaugmentation treatment removed 94.8 and 92.5% of acetamiprid within 40 days from soils contaminated with 50 and 200 mg/kg acetamiprid, respectively. A decrease in bacterial richness and diversity was detected in bioaugmentation treatments, which later recovered with the removal of acetamiprid from soil. Moreover, the bioaugmentation treatment significantly influenced the bacterial community structure, whereas application of acetamiprid alone had little influence on the soil microbial community. Furthermore, the bioaugmentation treatment improved the growth of bacteria associated with acetamiprid degradation, and the inoculated and recruited taxa significantly influenced the keystone taxa of the indigenous microbiome, resulting in reassembly of the bacterial community yielding higher acetamiprid-degrading efficiency than that of the indigenous and acetamiprid-treated communities. Our results provide valuable insights into the mechanisms of microbiome engineering for bioaugmentation of acetamiprid-contaminated soils.

Nitrile Hydratases: From Industrial Application to Acetamiprid and Thiacloprid Degradation

The widespread application of neonicotinoid insecticides (NEOs) in agriculture causes a series of environmental and ecological problems. Microbial remediation is a popular approach to relieve these negative impacts, but the associated molecular mechanisms are rarely explored. Nitrile hydratase (NHase), an enzyme commonly used in industry for amide production, was discovered to be responsible for the degradation of acetamiprid (ACE) and thiacloprid (THI) by microbes. Since then, research into NHases in NEO degradation has attracted increasing attention. In this review, microbial degradation of ACE and THI is briefly described. We then focus on NHase evolution, gene composition, maturation mechanisms, expression, and biochemical properties with regard to application of NHases in NEO degradation for bioremediation.

An overview of neonicotinoids: biotransformation and biodegradation by microbiological processes

Neonicotinoids are a class of pesticides widely used in different phases of agricultural crops. Similar to other classes of pesticides, they can damage human and environmental health if overused, and can be resistent to degradation. This is especially relevant to insect health, pollination, and aquatic biodiversity. Nevertheless, application of pesticides is still crucial for food production and pest control, and should therefore be carefully monitored by the government to control or reduce neonicotinoid contamination reaching human and animal feed. Aware of this problem, studies have been carried out to reduce or eliminate neonicotinoid contamination from the environment. One example of a green protocol is bioremediation. This review discusses the most recent microbial biodegradation and bioremediation processes for neonicotinoids, which employ isolated microorganisms (bacteria and fungi), consortiums of microorganisms, and different types of soils, biobeds, and biomixtures.

Neonicotinoids in the agroecosystem: In-field long-term assessment on honeybee colony strength and microbiome

Bees can be severely affected by various plant protection products (PPP). Among these, neonicotinoid insecticides are of concern as they have been shown to be responsible for extensive honeybee colonies death when released into the environment. Also, sublethal neonicotinoid doses contaminating single honeybees and their colonies (e.g. through contaminated pollen) are responsible for honeybees physiological alterations with probable implication also on microbiome functionality. Honeybees show symbiotic interactions with specific gut bacteria that can enhance the adult host performances. Among the known mechanisms, the modulation of the immune system, the degradation of recalcitrant secondary plant metabolites, pollen digestion, and hormonal signaling, are the most important functional benefits for the host honeybee. To date, few research efforts have aimed at revealing the impact of PPP on the gut microbial community of managed and wild honeybees. The majority of the existing literature relays on cage or semifield tests of short duration for research investigating neonicotinoids-gut microbiome interactions. This research wanted to unravel the impact of two neonicotinoids (i.e. imidacloprid and thiacloprid) in natural field conditions up to 5 weeks of exposure. A long-term impact of neonicotinoids on gut microbial community of honeybees was observed. The alterations affected several microbial genera and species such as Frischella spp., lactobacilli and bifidobacteria, whose shifting is implicated in intestinal dysbiosis. Long-term impact leading to dysbiosis was detected in case of exposure to imidacloprid, whereas thiacloprid exposure stimulated temporary dysbiosis. Moreover, the microbial diversity was significantly reduced in neonicotinoid-treated groups. Overall, the reported results support a compromised functionality of the gut microbial community, that might reflect a lower efficiency in the ecosystemic functionality of honeybees.

Fate of selected neonicotinoid insecticides in soil-water systems: Current state of the art and knowledge gaps

The occurrence of emerging contaminants, such as: personal care products, medicines, pharmaceuticals, pesticides, and their transformation products in the environment is of concern for human health and aquatic ecosystems due to their high persistence, toxicity and potential to bioaccumulation. Among pesticides, the main attention and thus our focus is on neonicotinoids: acetamiprid, clothianidin, imidacloprid, thiacloprid and thiamethoxam, which are widely used classes of insecticides in agriculture. Determining the associated risk to humans and ecosystems from neonicotinoid insecticides requires detailed understanding of their fate and transport in the environment which is complex and includes diverse pathways and processes depending on environmental compartments in which they occur. This paper critically reviews the current state of the art about processes, parameters and phenomena influencing the fate of neonicotinoid insecticides in soil-water systems (i.e. soil and groundwater), and reveals existing knowledge gaps. Sorption, biodegradation, chemical transformations of neonicotinoid insecticides in the soil and leaching to the groundwater, as well as groundwater/surface water interactions are highlighted, as they determine their further migration from sources, through soils to groundwater systems and then to other environmental compartments posing ecological and human risks. A number of key knowledge gaps in fate of neonicotinoid insecticides in soil-water systems are identified, that concern mostly processes and pathways occurring in the groundwater, and require further research to assess the associated risk to humans and ecosystems.

Characterization of Acetamiprid Biodegradation by the Microbial Consortium ACE-3 Enriched From Contaminated Soil

Microbial consortia are ubiquitous in nature and exhibit several attractive features such as sophisticated metabolic capabilities and strong environmental robustness. This study aimed to decipher the metabolic and ecological characteristics of synergistic interactions in acetamiprid-degrading consortia, suggesting an optimal scheme for bioremediation of organic pollutants. The microbial consortium ACE-3 with excellent acetamiprid-degrading ability was enriched from the soil of an acetamiprid-contaminated site and characterized using high-throughput sequencing (HTS). Consortium ACE-3 was able to completely degrade 50 mg⋅L^–1 acetamiprid in 144 h, and was metabolically active at a wide range of pH values (6.0–8.0) and temperatures (20–42°C). Furthermore, plausible metabolic routes of acetamiprid biodegradation by the consortium were proposed based on the identification of intermediate metabolites (Compounds I, II, III and IV). The findings indicated that the consortium ACE-3 has promising potential for the removal and detoxification of pesticides because it produces downstream metabolites (Compounds I and II) that are less toxic to mammals and insects than acetamiprid. Finally, Illumina HTS revealed that β Proteobacteria were the dominant group, accounting for 85.61% of all sequences at the class level. Among the more than 50 genera identified in consortium ACE-3, Sphingobium, Acinetobacter, Afipia, Stenotrophomonas, and Microbacterium were dominant, respectively accounting for 3.07, 10.01, 24.45, and 49.12% of the total population.

A critical review on the potential impacts of neonicotinoid insecticide use: current knowledge of environmental fate, toxicity, and implications for human health

Neonicotinoid insecticides are widely used in both urban and agricultural settings around the world. Historically, neonicotinoid insecticides have been viewed as ideal replacements for more toxic compounds, like organophosphates, due in part to their perceived limited potential to affect the environment and human health. This critical review investigates the environmental fate and toxicity of neonicotinoids and their metabolites and the potential risks associated with exposure. Neonicotinoids are found to be ubiquitous in the environment, drinking water, and food, with low-level exposure commonly documented below acceptable daily intake standards. Available toxicological data from animal studies indicate possible genotoxicity, cytotoxicity, impaired immune function, and reduced growth and reproductive success at low concentrations, while limited data from ecological or cross-sectional epidemiological studies have identified acute and chronic health effects ranging from acute respiratory, cardiovascular, and neurological symptoms to oxidative genetic damage and birth defects. Due to the heavy use of neonicotinoids and potential for cumulative chronic exposure, these insecticides represent novel risks and necessitate further study to fully understand their risks to humans.

Insights Into the Microbial Degradation and Biochemical Mechanisms of Neonicotinoids

Neonicotinoids are derivatives of synthetic nicotinoids with better insecticidal capabilities, including imidacloprid, nitenpyram, acetamiprid, thiacloprid, thiamethoxam, clothianidin, and dinotefuran. These are mainly used to control harmful insects and pests to protect crops. Their main targets are nicotinic acetylcholine receptors. In the past two decades, the environmental residues of neonicotinoids have enormously increased due to large-scale applications. More and more neonicotinoids remain in the environment and pose severe toxicity to humans and animals. An increase in toxicological and hazardous pollution due to the introduction of neonicotinoids into the environment causes problems; thus, the systematic remediation of neonicotinoids is essential and in demand. Various technologies have been developed to remove insecticidal residues from soil and water environments. Compared with non-bioremediation methods, bioremediation is a cost-effective and eco-friendly approach for the treatment of pesticide-polluted environments. Certain neonicotinoid-degrading microorganisms, including Bacillus, Mycobacterium, Pseudoxanthomonas, Rhizobium, Rhodococcus, Actinomycetes, and Stenotrophomonas, have been isolated and characterized. These microbes can degrade neonicotinoids under laboratory and field conditions. The microbial degradation pathways of neonicotinoids and the fate of several metabolites have been investigated in the literature. In addition, the neonicotinoid-degrading enzymes and the correlated genes in organisms have been explored. However, few reviews have focused on the neonicotinoid-degrading microorganisms along with metabolic pathways and degradation mechanisms. Therefore, this review aimed to summarize the microbial degradation and biochemical mechanisms of neonicotinoids. The potentials of neonicotinoid-degrading microbes for the bioremediation of contaminated sites were also discussed.

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).

Pigmentiphaga sp. Strain D-2 Uses a Novel Amidase To Initiate the Catabolism of the Neonicotinoid Insecticide Acetamiprid

Acetamiprid, a chloronicotinyl neonicotinoid insecticide, is among the most commonly used insecticides worldwide, and its environmental fate has caused considerable concern. The compound 1-(6-chloropyridin-3-yl)-N-methylmethanamine (IM 1-4) has been reported to be the main intermediate during acetamiprid catabolism in microorganisms, honeybees, and spinach. However, the molecular mechanism underlying the hydrolysis of acetamiprid to IM 1-4 has not yet been elucidated. In this study, a novel amidase (AceAB) that initially hydrolyzes the C-N bond of acetamiprid to generate IM 1-4 was purified and characterized from the acetamiprid-degrading strain Pigmentiphaga sp. strain D-2. Based on peptide profiling of the purified AceAB and the draft genome sequence of strain D-2, aceA (372 bp) and aceB (2,295 bp), encoding the α and β subunits of AceAB, respectively, were cloned and found to be necessary for acetamiprid hydrolysis in strain D-2. The characteristics of AceAB were also systematically investigated. Though AceA and AceB showed 35% to 56% identity to the α and β subunits of the N,N-dimethylformamidase from Paracoccus aminophilus, AceAB was specific for the hydrolysis of acetamiprid and showed no activities to N,N-dimethylformamide or its structural analogs.IMPORTANCE Acetamiprid, among the top neonicotinoid insecticides used worldwide, is one of the most important commercial insecticides. Due to its extensive use, the environmental fate of acetamiprid, especially its microbial degradation, has caused considerable concern. Although the catabolic pathways of acetamiprid in microorganisms have been extensively studied, the molecular mechanisms underlying acetamiprid biodegradation (except for a nitrile hydratase) remain largely unknown, and the enzyme responsible for the biotransformation of acetamiprid into its main intermediate, IM 1-4, have not yet been elucidated. The amidase AceAB and its encoding genes, aceA and aceB, characterized in this study, were found to be necessary and specific for the initial hydrolysis of the C-N bond of acetamiprid to generate IM 1-4 in Pigmentiphaga sp. strain D-2. The finding of the novel amidase AceAB will greatly enhance our understanding of the microbial catabolism of the widely used insecticide acetamiprid at the molecular level.

Identification of the cytochrome P450 involved in the degradation of neonicotinoid insecticide acetamiprid in Phanerochaete chrysosporium

We previously reported that cytochrome P450 s play critical roles in neonicotinoid insecticide biodegradation by white-rot fungi. Here, we investigated the biodegradation of acetamiprid (ACET) by Phanerochaete chrysosporium to identify the cytochrome P450 involved in this degradation process. During a 20-day incubation period, P. chrysosporium degraded 21% and 51% of ACET in ligninolytic and nonligninolytic media, respectively. The degradation rate of ACET was markedly decreased by the addition of cytochrome P450 inhibitors. Recombinant cytochrome P450s in P. chrysosporium (PcCYP) were heterologously expressed in Saccharomyces cerevisiae strain AH22, and the PcCYP involved in ACET degradation was identified. The results showed that CYP5147A3 can degrade ACET, and two ACET metabolites, N'-cyano-N-methyl acetamidine and 6-chloro-3-pyridinemethanol, were identified. To the best of our knowledge, this study provides the first characterization of the fungal cytochrome P450 that is responsible for the degradation and detoxification of ACET.

Biodegradation of the Neonicotinoid Insecticide Acetamiprid by Actinomycetes Streptomyces canus CGMCC 13662 and Characterization of the Novel Nitrile Hydratase Involved

Neonicotinoid insecticide pollution in soil and water poses serious environmental risks. Microbial biodegradation is an important neonicotinoid insecticide degradation pathway in the environment. In this study, 70.0% of the acetamiprid in a 200 mg/L solution was degraded by actinomycetes Streptomyces canus CGMCC 13662 (isolated from soil) in 48 h, and the acetamiprid degradation half-life was 27.7 h. Acetamiprid was degraded to IM-1-2 (( E)-1-(1-(((6-chloropyridin-3-yl)methyl)(methyl) amino)ethylidene)urea) through hydrolysis of the cyanoimine moiety. Gene cloning and overexpression indicated that a novel nitrile hydratase with three unusual subunits (AnhD, AnhE, and AnhA) without accessory protein mediated IM-1-2 formation. The purified nitrile hydratase responsible for degrading acetamiprid had a K_m of 5.85 mmol/L and a V_max of 15.99 U/mg. A homology model suggested that AnhD-Glu56 and AnhE-His21 play important roles in the catalytic efficiency of the nitrile hydratase. S. canus CGMCC 13662 could be used to remediate environments contaminated with acetamiprid.

Aerobic Degradation of Clothianidin to 2-Chloro-methyl Thiazole and Methyl 3-(Thiazole-yl) Methyl Guanidine Produced by Pseudomonas stutzeri smk

Overuse of pesticides in agriculture may harm environmental and agricultural yields. Sustainable maintenance of soil fertility and management of the environment have become a concern due to the persistence of pesticides in the soil. Microbes have various mechanisms for the bioremediation of persistent organic pollutants from the environment. A bacterium that degrades clothianidin was isolated from the pesticide and applied to agricultural soil by the enrichment technique. The identity of the bacterium was determined by studying morphological, cultural, and biochemical characteristics and 16S rRNA gene sequences. The ability to metabolize clothianidin was confirmed using UV-visible spectrophotometric, chromatographic, and spectroscopic analyses. A Gram-negative bacterium, designated smk, isolated from clothianidin-contaminated soil was confirmed to be a member of Pseudomonas stutzeri. The biodegradation of clothianidin was studied using P. stutzeri smk. Approximately 62% degradation of clothianidin was achieved within two weeks when grown at 30°C and pH 7. The effects of various physicochemical parameters, including pH, temperature, and clothianidin concentrations, on catabolic rates were studied. The biodegradation studies using UV-Vis spectrophotometry, HPLC, FTIR, and LC-MS indicated the production of the following metabolites: 2-chloro-5-methyl thiazole (CMT), methyl nitroguanidine (MNG), methyl 3-[thiazole-yl], and methyl guanidine (TMG). Identification of specific degradation metabolites indicates that bioremediation of toxic neonicotinoid insecticides may be achieved by application of P. stutzeri smk.

Quantum Dots-Based Immunochromatographic Strip for Rapid and Sensitive Detection of Acetamiprid in Agricultural Products

In this study, a rapid and sensitive immunochromatographic strip (ICS) assay, based on quantum dots (QDs), was developed for the qualitative and quantitative detection of acetamiprid in agricultural samples. Acetamiprid-ovalbumin conjugates (ACE-OVA) and goat anti-mouse IgG were sprayed onto a nitrocellulose membrane as a test and control line. Two kinds of anti-acetamiprid monoclonal antibodies (mAb) obtained in our lab were characterized by the ELISA and surface plasmon resonance assay. The competitive immunoassay was established using a QDs-mAb conjugate probe. The visual detection limit of acetamiprid for a qualitative threshold was set as 1 ng/mL to the naked eye. In the quantitative test, the fluorescence intensity was measured by a portable strip reader and a standard curve was obtained with a linear range from 0.098 to 25 ng/mL, and the half maximal inhibitory concentration of 1.12 ng/mL. The developed method showed no evident cross-reactivities with other neonicotinoid insecticides except for thiacloprid (36.68%). The accuracy and precision of the developed QDs-ICS were further evaluated. Results showed that the average recoveries ranged from 78.38 to 126.97% in agricultural samples. Moreover, to test blind tea samples, the QDs-ICS showed comparable reliability and a high correlation with ultra-performance liquid chromatography-tandem mass spectrometry. The whole sample detection could be accomplished within 1 h. In brief, our data clearly manifested that QDs-ICS was quite qualified for the rapid and sensitive screening of acetamiprid residues in an agricultural product analysis and paves the way to point-of-care testing for other analytes.

A Novel Nutrient Deprivation-Induced Neonicotinoid Insecticide Acetamiprid Degradation by Ensifer adhaerens CGMCC 6315

Biodegradation of pesticide pollution is often restricted by environmental pressures, such as nutrient deprivation. Ensifer adhaerens CGMCC 6315 could overcome this issue and degrade neonicotinoid acetamiprid (ACE) efficiently under low nutrient stimuli. The ACE degradation rate improved by 33.1-fold when the lysogeny broth content for cell culture was decreased to 1/15-fold. Resting cells of CGMCC 6315 degraded 94.4% of 200 mg/L ACE in 12 h and quickly eliminated 87.8% of 5 mg/kg of residual soil ACE within 2 d. ACE degradation by CGMCC 6315 was via a nitrile hydratase (NHase) pathway. Genome sequencing showed that CGMCC 6315 had two NHase genes ( cnhA and pnhA). PnhA had the highest reported activity of 28.8 U/mg for ACE. QPCR and proteomic analysis showed that the improved ACE degradation ability was attributed to the up-regulated expression of PnhA. This biodegradation system of CGMCC 6315 has great potential for use in pesticide pollution remediation.

Sorption, desorption and degradation of neonicotinoids in four agricultural soils and their effects on soil microorganisms

In this study, the sorption, desorption and degradation of three neonicotinoids, imidacloprid (IMI), clothianidin (CLO) and thiacloprid (THI), and their effects on microorganisms in four different agricultural soils were systematically evaluated. The sorption of neonicotinoids on the soils was generally low with distribution coefficients (K_d) up to 16.2L/kg at C_e of 0.05mg/L following the order THI>IMI≈CLO, and the sorption were mainly influenced by the soil organic carbon content. The percentage degradation rates of the pesticides in different soils ranged from 25.4% to 80.9%, all following the order THI>IMI≈CLO. All the three neonicotinoids degraded much faster under non-sterilized conditions than sterilized conditions, indicating considerable contribution of biodegradation. The total degradation or biodegradation of neonicotinoids was the fastest in the soil with the highest organic carbon content, and the neonicotinoids' bioavailability was not the primary influencing factor due to their weak sorption. The chemical degradation was mainly affected by pH and cation exchange capacity. The degradation of neonicotinoids occurred mainly via nitrate reduction, cyano hydrolysis and chloropyridinyl dechlorination. High-throughput sequencing data showed that the microbial community structure and abundance changed greatly in neonicotinoid-spiked soils as compared to the control, which might influence their degradation pathways. Some microbe families associated with the biodegradation of neoniconoids were found, which were all belonging to Proteobacteria and Actinobacteria. The degradation of neoniconoids influenced the soil nitrifying process. The present study provides valuable information for comprehensively understanding the fate of neonicotinoids in soils.

Characterization and mechanism analysis of lincomycin biodegradation with Clostridium sp. strain LCM-B isolated from lincomycin mycelial residue (LMR)

Lincomycin mycelial residue (LMR) is the restricted resource because it contains residual lincomycin, which is producing potential risks to the environment and human health. In this study, lincomycin-degrading strain LCM-B was isolated and identified as Clostridium sp. in the LMR. Strain LCM-B was able to degrade 62.03% of lincomycin at the initial concentration of 100 mg L^-1 after incubation for 10 d, while only 15.61% of lincomycin was removed at the initial concentration of 500 mg L^-1. The removal efficiency of lincomycin by strain LCM-B decreased as the initial concentration increased. Gene lnuB (which encodes the nucleotidyl transferase) was detected in the isolated strain, and it was proven to participate in lincomycin biodegradation based on the analysis of degradation products and pathway. The results provide a relatively complete understanding of lincomycin biodegradation mechanism. Strain LCM-B is promising to eliminate lincomycin from the LMR.

Purification and properties of a novel quizalofop-p-ethyl-hydrolyzing esterase involved in quizalofop-p-ethyl degradation by Pseudomonas sp. J-2

Quizalofop-p-ethyl (QPE) is a post-emergence herbicide that effectively controls grass weeds and is often detected in the environment. However, the biochemical and molecular mechanisms of QPE degradation in the environment remains unclear. In this study, a highly effective QPE-degrading bacterial strain J-2 was isolated from acclimated activated sludge and identified as a Pseudomonas sp., containing the QPE breakdown metabolite quizalofop acid (QA) identified by Liquid Chromatography-Ion Trap-Mass Spectrometry (LC-IT-MSⁿ) analysis. A novel QPE hydrolase esterase-encoding gene qpeH was cloned from strain J-2 and functionally expressed in Escherichia coli BL21 (DE3). The specific activity of recombinant QpeH was 198.9 ± 2.7 U mg⁻¹ for QPE with K_m and K_cat values of 41.3 ± 3.6 μM and 127.3 ± 4.5 s⁻¹. The optimal pH and temperature for the recombinant QpeH were 8.0 and 30 °C, respectively and the enzyme was activated by Ca²⁺, Cd²⁺, Li⁺, Fe³⁺ and Co²⁺ and inhibited by Ni²⁺, Fe²⁺, Ag⁺, DEPC, SDS, Tween 80, Triton X, β-mercaptoethanol, PMSF, and pCMB. In addition, the catalytic efficiency of QpeH toward different AOPP herbicides in descending order was as follows: fenoxaprop-P-ethyl > quizalofop-P-tefuryl > QPE > haloxyfop-P-methyl > cyhalofopbutyl > clodinafop-propargyl. On the basis of the phylogenetic analysis and multiple sequence alignment, the identified enzyme QpeH, was clustered with esterase family V, suggesting a new member of this family because of its low similarity of amino acid sequence with esterases reported previously.

Biodegradation of the neonicotinoid insecticide acetamiprid in surface water by the bacterium Variovorax boronicumulans CGMCC 4969 and its enzymatic mechanism

The plant growth-promoting rhizobacterium Variovorax boronicumulans CGMCC4969 was used to degrade the neonicotinoid insecticide, acetamiprid (AAP), in surface water, and the enzymatic mechanisms of AAP degradation were explored.

Aerobic versus Anaerobic Microbial Degradation of Clothianidin under Simulated California Rice Field Conditions

Microbial degradation of clothianidin was characterized under aerobic and anaerobic California rice field conditions. Rate constants (k) and half-lives (DT50) were determined for aerobic and anaerobic microcosms, and an enrichment experiment was performed at various nutrient conditions and pesticide concentrations. Temperature effects on anaerobic degradation rates were determined at 22 ± 2 and 35 ± 2 °C. Microbial growth was assessed in the presence of various pesticide concentrations, and distinct colonies were isolated and identified. Slow aerobic degradation was observed, but anaerobic degradation occurred rapidly at both 25 and 35 °C. Transformation rates and DT50 values in flooded soil at 35 ± 2 °C (k = -7.16 × 10(-2) ± 3.08 × 10(-3) day(-1), DT50 = 9.7 days) were significantly faster than in 25 ± 2 °C microcosms (k= -2.45 × 10(-2) ± 1.59 × 10(-3) day(-1), DT50 = 28.3 days). At the field scale, biodegradation of clothianidin will vary with extent of oxygenation.

Co-transport of Pesticide Acetamiprid and Silica Nanoparticles in Biochar-Amended Sand Porous Media

The role of biochar as a soil amendment on the transport of acetamiprid, a widely used neonicotinoid pesticide, is little known. We conducted saturated column experiments to examine cotransport of acetamiprid and silica nanoparticles (NPs) in pure and biochar-amended sands. Retention of acetamiprid was minor in the pure sand, whereas application of biochar in the sand significantly increased retention. Retention was greater at lower ionic strengths and near neutral pH values and was attributed to biodegradation and sorption through π-π interaction and pore filling. The convection-diffusion equation with inclusion of first-order sorption, desorption, and degradation well described the transport of acetamiprid in the biochar-amended sand. The simulation results show that the sorption rate did not change with pH. This is because the acetamiprid is nonionic and cannot be bonded with the biochar by protonation or deprotonation. The desorption rate was independent of variation of solution chemistry, indicating that desorption was a physical process (i.e., pore diffusion). Application of biochar in the sand had little influence on the transport of silica NPs in NaCl but caused complete attachment in CaCl. Energy dispersive X-ray spectroscopy suggested that the enhanced attachment was due to cation bridging between silica NPs and functional groups in biochar by the Ca. The co-presence of acetamiprid and silica NPs in the solutions enhanced transport of acetamiprid and NPs in the biochar-amended sand by competing for the binding sites on the biochar surfaces.

Construction and analysis of an intergeneric fusion from Pigmentiphaga sp. strain AAP-1 and Pseudomonas sp. CTN-4 for degrading acetamiprid and chlorothalonil

Pseudomonas sp. CTN-4 degrades chlorothalonil (CTN) but not acetamiprid (AAP), and Pigmentiphaga sp. strain AAP-1 degrades AAP but not CTN. A functional strain, AC, was constructed through protoplast fusion of two parental strains (Pseudomonas sp. CTN-4 and Pigmentiphaga sp. strain AAP-1) in order to simultaneously improve the degradation efficiency of AAP and CTN. Fusant-AC with eight transfers on plates containing two antibiotics and CTN was obtained. For the purpose of identifying and confirming the genetic relationship between fusant-AC and its parents, randomly amplified polymorphic DNA (RAPD), scanning electron microscopy (SEM), and 16S ribosomal DNA (rDNA) analysis were performed. In toto, RAPD fingerprint analysis produced 194 clear bands with 9 primers, which not only had bands in common with strains CTN-4 and AAP-1, but also had its own novel fusant-specific bands. The genetic similarity indices between fusant-AC and parental strains CTN-4 and AAP-1 were 0.40 and 0.69, respectively. The result of SEM indicated that the cell morphology of fusant-AC differed from both its parents. The fusant strain AC possesses a strong capability for AAP and CTN degradation. At AAP concentration (50-300 mg L(-1)), the degradation was achieved within 5 h. At the initial dose of 50 and 100 mg L(-1) CTN, the percentages reached 96 and 91 % over a 36-h incubation period. The present study indicates that the protoplast-fusion technique may have possible applications in environmental pollution control.

Metabolic Pathway Involved in 6-Chloro-2-Benzoxazolinone Degradation by Pigmentiphaga sp. Strain DL-8 and Identification of the Novel Metal-Dependent Hydrolase CbaA

6-Chloro-2-benzoxazolinone (CDHB) is a precursor of herbicide, insecticide, and fungicide synthesis and has a broad spectrum of biological activity. Pigmentiphaga sp. strain DL-8 can transform CDHB into 2-amino-5-chlorophenol (2A5CP), which it then utilizes as a carbon source for growth. The CDHB hydrolase (CbaA) was purified from strain DL-8, which can also hydrolyze 2-benzoxazolinone (BOA), 5-chloro-2-BOA, and benzamide. The specific activity of purified CbaA was 5,900 U · mg protein(-1) for CDHB, with Km and kcat values of 0.29 mM and 8,500 s(-1), respectively. The optimal pH for purified CbaA was 9.0, the highest activity was observed at 55°C, and the inactive metal-free enzyme could be reactivated by Mg(2+), Ni(2+), Ca(2+), or Zn(2+) Based on the results obtained for the CbaA peptide mass fingerprinting and draft genome sequence of strain DL-8, cbaA (encoding 339 amino acids) was cloned and expressed in Escherichia coli BL21(DE3). CbaA shared 18 to 21% identity with some metal-dependent hydrolases of the PF01499 family and contained the signature metal-binding motif Q127XXXQ131XD133XXXH137 The conserved amino acid residues His288 and Glu301 served as the proton donor and acceptor. E. coli BL21(DE3-pET-cbaA) resting cells could transform 0.2 mM CDHB into 2A5CP. The mutant strain DL-8ΔcbaA lost the ability to degrade CDHB but retained the ability to degrade 2A5CP, consistent with strain DL-8. These results indicated that cbaA was the key gene responsible for CDHB degradation by strain DL-8.

IMPORTANCE

2-Benzoxazolinone (BOA) derivatives are widely used as synthetic intermediates and are also an important group of allelochemicals acting in response to tissue damage or pathogen attack in gramineous plants. However, the degradation mechanism of BOA derivatives by microorganisms is not clear. In the present study, we reported the identification of CbaA and metabolic pathway responsible for the degradation of CDHB in Pigmentiphaga sp. DL-8. This will provide microorganism and gene resources for the bioremediation of the environmental pollution caused by BOA derivatives.

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.

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

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.

Systemic insecticides (neonicotinoids and fipronil): trends, uses, mode of action and metabolites

Since their discovery in the late 1980s, neonicotinoid pesticides have become the most widely used class of insecticides worldwide, with large-scale applications ranging from plant protection (crops, vegetables, fruits), veterinary products, and biocides to invertebrate pest control in fish farming. In this review, we address the phenyl-pyrazole fipronil together with neonicotinoids because of similarities in their toxicity, physicochemical profiles, and presence in the environment. Neonicotinoids and fipronil currently account for approximately one third of the world insecticide market; the annual world production of the archetype neonicotinoid, imidacloprid, was estimated to be ca. 20,000 tonnes active substance in 2010. There were several reasons for the initial success of neonicotinoids and fipronil: (1) there was no known pesticide resistance in target pests, mainly because of their recent development, (2) their physicochemical properties included many advantages over previous generations of insecticides (i.e., organophosphates, carbamates, pyrethroids, etc.), and (3) they shared an assumed reduced operator and consumer risk. Due to their systemic nature, they are taken up by the roots or leaves and translocated to all parts of the plant, which, in turn, makes them effectively toxic to herbivorous insects. The toxicity persists for a variable period of time-depending on the plant, its growth stage, and the amount of pesticide applied. A wide variety of applications are available, including the most common prophylactic non-Good Agricultural Practices (GAP) application by seed coating. As a result of their extensive use and physicochemical properties, these substances can be found in all environmental compartments including soil, water, and air. Neonicotinoids and fipronil operate by disrupting neural transmission in the central nervous system of invertebrates. Neonicotinoids mimic the action of neurotransmitters, while fipronil inhibits neuronal receptors. In doing so, they continuously stimulate neurons leading ultimately to death of target invertebrates. Like virtually all insecticides, they can also have lethal and sublethal impacts on non-target organisms, including insect predators and vertebrates. Furthermore, a range of synergistic effects with other stressors have been documented. Here, we review extensively their metabolic pathways, showing how they form both compound-specific and common metabolites which can themselves be toxic. These may result in prolonged toxicity. Considering their wide commercial expansion, mode of action, the systemic properties in plants, persistence and environmental fate, coupled with limited information about the toxicity profiles of these compounds and their metabolites, neonicotinoids and fipronil may entail significant risks to the environment. A global evaluation of the potential collateral effects of their use is therefore timely. The present paper and subsequent chapters in this review of the global literature explore these risks and show a growing body of evidence that persistent, low concentrations of these insecticides pose serious risks of undesirable environmental impacts.

Risks of large-scale use of systemic insecticides to ecosystem functioning and services

Large-scale use of the persistent and potent neonicotinoid and fipronil insecticides has raised concerns about risks to ecosystem functions provided by a wide range of species and environments affected by these insecticides. The concept of ecosystem services is widely used in decision making in the context of valuing the service potentials, benefits, and use values that well-functioning ecosystems provide to humans and the biosphere and, as an endpoint (value to be protected), in ecological risk assessment of chemicals. Neonicotinoid insecticides are frequently detected in soil and water and are also found in air, as dust particles during sowing of crops and aerosols during spraying. These environmental media provide essential resources to support biodiversity, but are known to be threatened by long-term or repeated contamination by neonicotinoids and fipronil. We review the state of knowledge regarding the potential impacts of these insecticides on ecosystem functioning and services provided by terrestrial and aquatic ecosystems including soil and freshwater functions, fisheries, biological pest control, and pollination services. Empirical studies examining the specific impacts of neonicotinoids and fipronil to ecosystem services have focused largely on the negative impacts to beneficial insect species (honeybees) and the impact on pollination service of food crops. However, here we document broader evidence of the effects on ecosystem functions regulating soil and water quality, pest control, pollination, ecosystem resilience, and community diversity. In particular, microbes, invertebrates, and fish play critical roles as decomposers, pollinators, consumers, and predators, which collectively maintain healthy communities and ecosystem integrity. Several examples in this review demonstrate evidence of the negative impacts of systemic insecticides on decomposition, nutrient cycling, soil respiration, and invertebrate populations valued by humans. Invertebrates, particularly earthworms that are important for soil processes, wild and domestic insect pollinators which are important for plant and crop production, and several freshwater taxa which are involved in aquatic nutrient cycling, were all found to be highly susceptible to lethal and sublethal effects of neonicotinoids and/or fipronil at environmentally relevant concentrations. By contrast, most microbes and fish do not appear to be as sensitive under normal exposure scenarios, though the effects on fish may be important in certain realms such as combined fish-rice farming systems and through food chain effects. We highlight the economic and cultural concerns around agriculture and aquaculture production and the role these insecticides may have in threatening food security. Overall, we recommend improved sustainable agricultural practices that restrict systemic insecticide use to maintain and support several ecosystem services that humans fundamentally depend on.

Assessment of imidacloprid degradation by soil-isolated Bacillus alkalinitrilicus

Imidacloprid is extensively used on a broad range of crops worldwide as seed dressing, soil treatment, and foliar application. Hence, the degradation potential of bacterial strains from sugarcane-growing soils was studied in liquid medium for subsequent use in bioremediation of contaminated soils. The microbe cultures degrading imidacloprid were isolated and enriched on Dorn's broth containing imidacloprid as sole carbon source maintained at 28 °C and Bacillus alkalinitrilicus showed maximum potential to degrade imidacloprid. Clay loam soil samples were fortified with imidacloprid at 50, 100, and 150 mg kg(-1) along with 45 × 10(7) microbe cells under two opposing sets of conditions, viz., autoclaved and unautoclaved. To study degradation and metabolism of imidacloprid under these two conditions, samples were drawn at regular intervals of 7, 14, 28, 35, 42, 49, and 56 days. Among metabolites, three metabolites were detected, viz., 6-chloronicotinic acid, nitrosimine followed by imidacloprid-NTG under both the conditions. Total imidacloprid residues were not found to follow the first-order kinetics in both types of conditions. This paper reports for the first time the potential use of pure cultures of soil-isolated native bacterium B. alkalinitrilicus and also its use along with natural soil microflora for remediation of imidacloprid-contaminated soils.

Degradation of the neonicotinoid insecticide acetamiprid via the N-carbamoylimine derivate (IM-1-2) mediated by the nitrile hydratase of the nitrogen-fixing bacterium Ensifer meliloti CGMCC 7333

The metabolism of the widely used neonicotinoid insecticide acetamiprid (ACE) has been extensively studied in plants, animals, soils, and microbes. However, hydration of the N-cyanoimine group in ACE to the N-carbamoylimine derivate (IM-1-2) by purified microbes, the enzyme responsible for this biotransformation, and further degradation of IM-1-2 have not been studied. The present study used liquid chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy to determine that the nitrogen-fixing bacterium Ensifer meliloti CGMCC 7333 transforms ACE to IM-1-2. CGMCC 7333 cells degraded 65.1% of ACE in 96 h, with a half-life of 2.6 days. Escherichia coli Rosetta (DE3) overexpressing the nitrile hydratase (NHase) from CGMCC 7333 and purified NHase converted ACE to IM-1-2 with degradation ratios of 97.1% in 100 min and 93.9% in 120 min, respectively. Interestingly, IM-1-2 was not further degraded by CGMCC 7333, whereas it was spontaneously hydrolyzed at the N-carbamoylimine group to the derivate ACE-NH, which was further converted to the derivative ACE-NH2. Then, ACE-NH2 was cleaved to the major metabolite IM-1-4. IM-1-2 showed significantly lower insecticidal activity than ACE against the aphid Aphis craccivora Koch. The present findings will improve the understanding of the environmental fate of ACE and the corresponding enzymatic mechanisms of degradation.

Influence of short-time imidacloprid and acetamiprid application on soil microbial metabolic activity and enzymatic activity

The influence of two neonicotinoids, i.e., imidacloprid (IMI) and acetamiprid (ACE), on soil microbial activities was investigated in a short period of time using a combination of the microcalorimetric approach and enzyme tests. Thermodynamic parameters such as Q T (J g(-1) soil), ∆H met (kJ mol(-1)), J Q/S (J g(-1) h(-1)), k (h(-1)), and soil enzymatic activities, dehydrogenase, phosphomonoesterase, arginine deaminase, and urease, were used to evaluate whole metabolic activity changes and acute toxicity following IMI and ACE treatment. Various profiles of thermogenic curves reflect different soil microbial activities. The microbial growth rate constant k, total heat evolution Q T (expect for IMI), and inhibitory ratio I show linear relationship with the doses of IMI and ACE. Q T for IMI increases at 0.0-20 μg g(-1) and then decreases at 20-80 μg g(-1), possibly attributing to the presence of tolerant microorganisms. The 50 % inhibitory ratios (IC50) of IMI and ACE are 95.7 and 77.2 μg g(-1), respectively. ACE displays slightly higher toxicity than IMI. Plots of k and Q T against microbial biomass-C indicate that the k and Q T are growth yield-dependent. IMI and ACE show 29.6; 40.4 and 23.0; and 23.3, 21.7, and 30.5 % inhibition of dehydrogenase, phosphomonoesterase, and urease activity, respectively. By contrast, the arginine deaminase activity is enhanced by 15.2 and 13.2 % with IMI and ACE, respectively. The parametric indices selected give a quantitative dose-response relationship of both insecticides and indicate that ACE is more toxic than IMI due to their difference in molecular structures.

The metabolism of neonicotinoid insecticide thiamethoxam by soil enrichment cultures, and the bacterial diversity and plant growth-promoting properties of the cultured isolates

A soil enrichment culture (SEC) rapidly degraded 96% of 200 mg L(-1) neonicotinoid insecticide thiamethoxam (TMX) in MSM broth within 30 d; therefore, its metabolic pathway of TMX, bacterial diversity and plant growth-promoting rhizobacteria (PGPR) activities of the cultured isolates were studied. The SEC transformed TMX via the nitro reduction pathway to form nitrso, urea metabolites and via cleavage of the oxadiazine cycle to form a new metabolite, hydroxyl CLO-tri. In addition, 16S rRNA gene-denaturing gradient gel electrophoresis analysis revealed that uncultured rhizobacteria are predominant in the SEC broth and that 77.8% of the identified bacteria belonged to uncultured bacteria. A total of 31 cultured bacterial strains including six genera (Achromobacter, Agromyces, Ensifer, Mesorhizobium, Microbacterium and Pseudoxanthomonas) were isolated from the SEC broth. The 12 strains of Ensifer adhaerens have the ability to degrade TMX. All six selected bacteria showed PGPR activities. E. adhaerens TMX-23 and Agromyces mediolanus TMX-25 produced indole-3-acetic acid, whereas E. adhaerens TMX-23 and Mesorhizobium alhagi TMX-36 are N2-fixing bacteria. The six-isolated microbes were tolerant to 200 mg L(-1) TMX, and the growth of E. adhaerens was significantly enhanced by TMX, whereas that of Achromobacter sp. TMX-5 and Microbacterium sp.TMX-6 were enhanced slightly. The present study will help to explain the fate of TMX in the environment and its microbial degradation mechanism, as well as to facilitate future investigations of the mechanism through which TMX enhances plant vigor.

Microbial degradation of acetamiprid by Ochrobactrum sp. D-12 isolated from contaminated soil

Neonicotinoid insecticides are one of the most important commercial insecticides used worldwide. The potential toxicity of the residues present in environment to humans has received considerable attention. In this study, a novel Ochrobactrum sp. strain D-12 capable of using acetamiprid as the sole carbon source as well as energy, nitrogen source for growth was isolated and identified from polluted agricultural soil. Strain D-12 was able to completely degrade acetamiprid with initial concentrations of 0–3000 mg·L⁻¹ within 48 h. Haldane inhibition model was used to fit the special degradation rate at different initial concentrations, and the parameters q_max, K_s and K_i were determined to be 0.6394 (6 h)⁻¹, 50.96 mg·L⁻¹ and 1879 mg·L⁻¹, respectively. The strain was found highly effective in degrading acetamiprid over a wide range of temperatures (25–35°C) and pH (6–8). The effects of co-substrates on the degradation efficiency of acetamiprid were investigated. The results indicated that exogenously supplied glucose and ammonium chloride could slightly enhance the biodegradation efficiency, but even more addition of glucose or ammonium chloride delayed the biodegradation. In addition, one metabolic intermediate identified as N-methyl-(6-chloro-3-pyridyl)methylamine formed during the degradation of acetamiprid mediated by strain D-12 was captured by LC-MS, allowing a degradation pathway for acetamiprid to be proposed. This study suggests the bacterium could be a promising candidate for remediation of environments affected by acetamiprid.

Co-metabolic biodegradation of acetamiprid by Pseudoxanthomonas sp. AAP-7 isolated from a long-term acetamiprid-polluted soil

An AAP-degrading bacterium, AAP-7, was isolated from AAP-polluted soil. AAP-7 was identified as Pseudoxanthomonas sp. on the basis of the comparative analysis of 16S rDNA sequences. The strain was able to transformate more than 80% AAP by means of co-metabolism and degraded AAP via hydrolysis or demethylation to form (E)-3-(((6-chloropyridin-3yl)methyl)(methyl)amino)acrylonitrile and N-((6-chloropyridin-3yl)methyl)-N-methylprop-1-en-2-amine, both of which transformed into ultimate product, which was 1-(6-chloropyridin-3yl)-N-methylmethanamine. A novel degradation pathway was proposed based on these metabolites. AAP could be transformed with a maximum specific degradation rate, half-saturation constant and inhibit constant of 1.775/36 h, 175.3 mg L(-1), and 396.5 mg L(-1), respectively, which proved that the degradation rate of AAP could be restrained at high AAP concentration. This paper highlights a significant potential use of co-metabolic cultures of microbial cells for the cleanup of AAP-contaminated soil.