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

Quantitative analysis of TCE biodegradation pathway in landfill cover utilizing continuous monitoring, droplet digital PCR and multi-omics sequencing technology

The remediation of volatile chlorinated hydrocarbons in the quasi-vadose zone has become a significant challenge. We applied an integrated approach to assess the biodegradability of trichloroethylene to identify the biotransformation mechanism. The formation of the functional zone biochemical layer was assessed by analyzing the distribution of landfill gas, physical and chemical properties of cover soil, spatial-temporal variations of micro-ecology, biodegradability of landfill cover soil and distributional difference metabolic pathway. Real-time online monitoring showed that trichloroethylene continuously undergoes anaerobic dichlorination and simultaneous aerobic/anaerobic conversion-aerobic co-metabolic degradation on the vertical gradient of the landfill cover system and reduction in trans-1,2-dichloroethylene in the anoxic zone but not 1,1-dichloroethylene. PCR and diversity sequencing revealed the abundance and spatial distribution of known dichlorination-related genes within the landfill cover, with 6.61 ± 0.25 × 104-6.78 ± 0.09 × 106 and 1.17 ± 0.78 × 103-7.82 ± 0.07 × 105 copies per g/soil of pmoA and tceA, respectively. In addition, dominant bacteria and diversity were significantly linked with physicochemical factors, and Mesorhizobium, Pseudoxanthomonas and Gemmatimonas were responsible for biodegradation in the aerobic, anoxic and anaerobic zones. Metagenome sequencing identified 6 degradation pathways of trichloroethylene that may occur in the landfill cover; the main pathway was incomplete dechlorination accompanied by cometabolic degradation. These results indicate that the anoxic zone is important for trichloroethylene degradation.

Bioremediation of Neonicotinoid Pesticide, Imidacloprid, Mediated by Bacillus cereus

Imidacloprid, a toxic pesticide of the chloronicotinyl category, is employed extensively in agricultural fields, and its exposure causes serious health issues. Biodegradation is considered to be a green and economical approach to remediate pesticides. Herein, imidacloprid degradation efficiency of Bacillus sp. is highlighted, among which Bacillus cereus exhibited the greatest degradation; optimization of experimental variables (pH, imidacloprid and agitation time) via Box-Behnken factorial design and analysis of variance (ANOVA) revealed 92% biodegradation at the initial substrate concentration of 0.03 mM, aerobically in 11 days under favorable pH 7. The subsequent metabolites, identified through liquid chromatography-mass spectrometry, were 5-hydroxy imidacloprid, imidacloprid-guanidine and 6-chloronicotinic acid.

Remediation technologies for neonicotinoids in contaminated environments: Current state and future prospects

Neonicotinoids (NEOs) are synthetic insecticides with broad-spectrum insecticidal activity and outstanding efficacy. However, their extensive use and persistence in the environment have resulted in the accumulation and biomagnification of NEOs, posing significant risks to non-target organisms and humans. This review provides a summary of research history, advancements, and highlighted topics in NEOs remediation technologies and mechanisms. Various remediation approaches have been developed, including physiochemical, microbial, and phytoremediation, with microbial and physicochemical remediation being the most extensively studied. Recent advances in physiochemical remediation have led to the development of innovative adsorbents, photocatalysts, and optimized treatment processes. High-efficiency degrading strains with well-characterized metabolic pathways have been successfully isolated and cultured for microbial remediation, while many plant species have shown great potential for phytoremediation. However, significant challenges and gaps remain in this field. Future research should prioritize isolating, domesticating or engineering high efficiency, broad-spectrum microbial strains for NEO degradation, as well as developing synergistic remediation techniques to enhance removal efficiency on multiple NEOs with varying concentrations in different environmental media. Furthermore, a shift from pipe-end treatment to pollution prevention strategies is needed, including the development of green and economically efficient alternatives such as biological insecticides. Integrated remediation technologies and case-specific strategies that can be applied to practical remediation projects need to be developed, along with clarifying NEO degradation mechanisms to improve remediation efficiency. The successful implementation of these strategies will help reduce the negative impact of NEOs on the environment and human health.

Characterization of a new chlorimuron-ethyl-degrading strain Cedecea sp. LAM2020 and biodegradation pathway revealed by multiomics analysis

The widespread use of the herbicide chlorimuron-methyl is hazard to rotational crops and causes soil degradation problems. Biodegradation is considered a promising way for removing herbicide residues from the environment. Here, a new isolated strain, Cedecea sp. LAM2020, enabled complete degradation of 100 mg/L chlorimuron-methyl within five days. Transcriptome analysis revealed that ABC transporters, atrazine degradation and purine metabolism were enriched in the KEGG pathway. Integrating GO and KEGG classification with related reports, we predict that carboxylesterases are involved in the biodegradation of chlorimuron-methyl by LAM2020. Heterologous expression of the carboxylesterase gene carH showed 26.67% degradation of 50 mg/L chlorimuron-methyl within 6 h. The intracellular potential biological response and extracellular degradation process of chlorimuron-ethyl were analyzed by the nontarget metabolomic and mass spectrometry respectively, and the biodegradation characteristics and complete mineralization pathway was revealed. The cleavage of the sulfonylurea bridge and the ester bond achieved the first step in the degradation of chlorimuron-methyl. Together, these results reveal the presence of acidolysis and enzymatic degradation of chlorimuron-methyl by strain LAM2020. Hydroponic corn experiment showed that the addition of strain LAM2020 alleviated the toxic effects of chlorimuron-ethyl on the plants. Collectively, strain LAM2020 may be a promising microbial agent for plants chlorimuron-ethyl detoxification and soil biofertilizer.

An amidase and a novel phenol hydroxylase catalyze the degradation of the antibacterial agent triclocarban by Rhodococcus rhodochrous

Triclocarban (TCC) is an emerging and intractable environmental contaminant due to its hydrophobicity and chemical stability. However, the antibacterial property of TCC limits its biodegradation, and only the functional enzyme TccA involved in TCC degradation has been characterized to date. In this study, we report a highly efficient TCC-degrading bacterium, Rhodococcus rhodochrous BX2, that could degrade and mineralize TCC (10 mg/L) by 76.8% and 56.5%, respectively, within 5 days. Subsequently, the TCC biodegradation pathway was predicted based on the detection of metabolites using modern mass spectrometry techniques. Furthermore, an amidase (TccS) and a novel phenol hydroxylase (PH_IND) encoded by the tccS and PH_IND genes, respectively, were identified by genomic and transcriptomic analyses of strain BX2, and these enzymes were further unequivocally proven to be the key enzymes responsible for the metabolism of TCC and its intermediate 4-chloroaniline (4-CA) by using a combination of heterologous expression and gene knockout. Our results shed new light on the mechanism of TCC biodegradation and better utilization of microbes to remediate TCC contamination.

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.

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.

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.

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.

Characterization and genome functional analysis of an efficient nitrile-degrading bacterium, Rhodococcus rhodochrous BX2, to lay the foundation for potential bioaugmentation for remediation of nitrile-contaminated environments

Nitriles are a class of extremely toxic chemicals with extensive applications, and these compounds pose potential risks to humans and ecosystems. The activated sludge isolate Rhodococcus rhodochrous BX2 efficiently metabolizes aliphatic nitriles. However, the molecular underpinnings of the degradation mechanism of aliphatic nitriles by BX2 remain unknown, and the metabolic fate of aliphatic nitriles also has not been elucidated. Here, strain BX2 was capable of completely mineralizing three aliphatic nitriles. Bioinformatic analysis yielded a deeper insight into the genetic basis of BX2 for efficient degradation of aliphatic nitriles and adaptation to harsh environments. Transcriptional, enzyme activity and metabolite analyses confirmed that the intracellular inducible nitrile hydratase/amidase pathway is the preferred metabolic pathway. Our findings provide an in-depth understanding of the environmental fate of aliphatic nitriles and, most importantly, offer a new perspective on the potential applications of the genus Rhodococcus in bioremediation and the development of degradation enzyme resources.

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.

Cometabolic biotransformation and impacts of the anti-inflammatory drug diclofenac on activated sludge microbial communities

This study evaluated the removal of diclofenac (DCF) in activated sludge and its long-term exposure effects on the function and structure of the microbial community. Activated sludge could remove <50% of 50 μg/L DCF. The removal decreased significantly to below 15% when DCF concentrations increased to 500 and 5000 μg/L. Quantitative assessment of the fate of DCF showed that its main removal routes were biodegradation (21%) and adsorption (7%), with other abiotic removals being insignificant (<5%). The biodegradation occurred through cometabolic mechanisms. DCF exposure in the range of 50-5000 μg/L did not disrupt the major functions of the activated sludge ecosystem (e.g. biomass yield and heterotrophic activity) over two months of DCF exposure. Consistently, 16S rRNA gene-based community analysis revealed that the overall community diversity (e.g. species richness and diversity) and structure of activated sludge underwent no significant alterations. The analysis did uncover a significant increase in several genera, Nitratireductor, Asticcacaulis, and Pseudacidovorax, which gained competitive advantages under DCF exposure. The enrichment of Nitratireductor, Asticcacaulis, and Pseudacidovorax genus might contribute to DCF biodegradation and emerge as a potential microbial niche for the removal of DCF.

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.

Background Nutrients Affect the Biotransformation of Tetracycline by Stenotrophomonas maltophilia as Revealed by Genomics and Proteomics

Certain bacteria are resistant to antibiotics and can even transform antibiotics in the environment. It is unclear how the molecular mechanisms underlying the resistance and biotransformation processes vary under different environmental conditions. The objective of this study is to investigate the molecular mechanisms of tetracycline resistance and biotransformation by Stenotrophomonas maltophilia strain DT1 under various background nutrient conditions. Strain DT1 was exposed to tetracycline for 7 days with four background nutrient conditions: no background (NB), peptone (P), peptone plus citrate (PC), and peptone plus glucose (PG). The biotransformation rate follows the order of PC > P > PG > NB ≈ 0. Genomic analysis showed that strain DT1 contained tet(X1), a gene encoding an FAD-binding monooxygenase, and eight peroxidase genes that could be relevant to tetracycline biotransformation. Quantitative proteomic analyses revealed that nodulation protein transported tetracycline outside of cells; hypoxanthine-guanine phosphoribosyltransferase facilitated the activation of the ribosomal protection proteins to prevent the binding of tetracycline to the ribosome and superoxide dismutase and peroxiredoxin-modified tetracycline molecules. Comparing different nutrient conditions showed that the biotransformation rates of tetracycline were positively correlated with the expression levels of superoxide dismutase.

Efficient degradation of chlorimuron-ethyl by a bacterial consortium and shifts in the aboriginal microorganism community during the bioremediation of contaminated-soil

Excessive application of chlorimuron-ethyl has led to soil contamination and limited crop rotation; therefore, tactics to decrease and eliminate residual chlorimuron-ethyl in the environment have attracted increasing attention. In this study, two chlorimuron-ethyl-degrading bacterial strains (Rhodococcus sp. D310-1; Enterobacter sp. D310-5) were used to ferment and prepare a chlorimuron-ethyl-degrading bacterial consortium. To improve the degradation efficiency of the bacterial consortium, the cultivation conditions were optimized using response surface methodology (RSM). The maximum biodegradation rate (87.42%) was obtained under optimal conditions (carbon concentration, 9.21gL^-1; temperature, 26.15°C; pH, 6.95). The rate of chlorimuron-ethyl degradation by the bacterial consortium in the chlorimuron-ethyl-contaminated soil was monitored and reached 80.02% at the end of a 60-d incubation period. Illumina MiSeq sequencing results showed that microbial diversity was high, and 33 phyla were identified in the analyzed samples. Proteobacteria, Acidobacteria, Acidobacteria, Firmicutes and Bacteroidetes were present in relatively high abundances in the samples. The bacterial consortium made a positive impact on the remediation of chlorimuron-ethyl-contaminated soil and somewhat altered the composition of the bacterial community in the chlorimuron-ethyl-contaminated soil. These findings provide highly valuable information on the production of bacterial consortium for the remediation of chlorimuron-ethyl and other sulfonylurea-herbicide-contaminated soil.

A key esterase required for the mineralization of quizalofop-p-ethyl by a natural consortium of Rhodococcus sp. JT-3 and Brevundimonas sp. JT-9

A natural consortium, named L1, of Rhodococcus sp. JT-3 and Brevundimonas sp. JT-9 was obtained from quizalofop-p-ethyl (QE) polluted soil. The consortium was able to use QE as a sole carbon source for growth and degraded 100mgL^-1 of QE in 60h. Strain JT-3 initiated the catabolism of QE to quizalofop acid (QA), which was used by strain JT-9 as carbon source for growth and to simultaneously feed strain JT-3. A novel esterase EstS-JT, which was responsible for the transformation of QE to QA and essential for the mineralization of QE by the consortium, was cloned from strain JT-3. EstS-JT showed low amino acid identity to other reported esterases from esterase family VIII and represents a new member of this family. The deduced amino acid sequence contained the esterase family VIII conserved motifs S-X-X-K, YSV and WAG. The purified recombinant EstS-JT displayed maximal esterase activity at 35°C and pH 7.5. An inhibitor assay, site-directed mutagenesis and 3D modeling analysis revealed that S₆₄, K₆₇ and Y₁₇₅ were essential for catalysis and probably comprised the catalytic center of EstS-JT. Additionally, EstS-JT had broad substrate specificity and was capable of hydrolyzing p-nitrophenyl esters (C₂-C₈) and various AOPP herbicides.

Diazinon degradation by a novel strain Ralstonia sp. DI-3 and X-ray crystal structure determination of the metabolite of diazinon

Diazinon is a widely used organophosphorus insecticide often detected in the environment. A highly effective diazinon-degrading Ralstonia sp. strain DI-3 was isolated from agricultural soil. Strain DI-3 can utilize dimethoate as its sole carbon source for growth and degrade an initial concentration of 100 mg L-1 diazinon to non-detectable levels within 60 h in liquid culture. A small amount of second carbon source as co-substrate could slightly enhance the biodegradation of diazinon. In addition, a less toxic metabolic intermediate formed during the degradation of diazinon mediated by strain DI-3 was purified using thin-layer chromatography (TLC) and identified based on single-crystal Xray diffraction analysis, allowing a degradation pathway for diazinon by pure culture to be proposed. Finally, this is the first providing authentic evidence to describe the metabolite.

Application of acclimated sewage sludge as a bio-augmentation/bio-stimulation strategy for remediating chlorpyrifos contamination in soil with/without cadmium

This experiment was performed to investigate the effects of acclimated sewage sludge (ASS) and sterilized ASS on the fates of chlorpyrifos (CP) in soil with or without cadmium (Cd), as well as the improvement of soil biochemical properties. Results showed that both ASS and sterilized ASS could significantly promote CP dissipation, and the groups with ASS had the highest efficiency on CP removal, whose degradation rates reached 71.3%-85.9% at the 30th day (40.4%-50.2% higher than non-sludge groups). Besides, the degradation rate of CP was not severely influenced by the existence of Cd, and the population of soil microorganism dramatically increased after adding sludge. The soil enzyme activities (dehydrogenase, acid phosphatase and FDA hydrolase activities) ranked from high to low were as follows: groups with sterilized ASS>groups with ASS>groups without sludge. Simultaneously, 16S rRNA gene sequencing revealed that ASS changed bacterial community structure and diversity in soil. In addition, alkali-hydrolyzable nitrogen and Olsen- phosphorus increased after application of sludge, indicating that the addition of ASS (or sterilized ASS) could effectively improve soil fertility.

Biodemulsifiers produced by Achromobacter sp. and their features in improving the biodegradation of phenanthrene

The application of biodemulsifiers plays an essential role in oil recovery and demulsification.

Biotransformation of tetracycline by a novel bacterial strain Stenotrophomonas maltophilia DT1

Although several abiotic processes have been reported that can transform antibiotics, little is known about whether and how microbiological processes may degrade antibiotics in the environment. This work isolated one tetracycline degrading bacterial strain, Stenotrophomonas maltophilia strain DT1, and characterized the biotransformation of tetracycline by DT1 under various environmental conditions. The biotransformation rate was the highest when the initial pH was 9 and the reaction temperature was at 30°C, and can be described using the Michaelis-Menten model under different initial tetracycline concentrations. When additional substrate was present, the substrate that caused increased biomass resulted in a decreased biotransformation rate of tetracycline. According to disk diffusion tests, the biotransformation products of tetracycline had lower antibiotic potency than the parent compound. Six possible biotransformation products were identified, and a potential biotransformation pathway was proposed that included sequential removal of N-methyl, carbonyl, and amine function groups. Results from this study can lead to better estimation of the fate and transport of antibiotics in the environment and has the potential to be utilized in designing engineering processes to remove tetracycline from water and soil.

Bacterial biodegradation of neonicotinoid pesticides in soil and water systems

Neonicotinoids are neurotoxic systemic insecticides used in plant protection worldwide. Unfortunately, application of neonicotinoids affects both beneficial and target insects indiscriminately. Being water soluble and persistent, these pesticides are capable of disrupting both food chains and biogeochemical cycles. This review focuses on the biodegradation of neonicotinoids in soil and water systems by the bacterial community. Several bacterial strains have been isolated and identified as capable of transforming neonicotinoids in the presence of an additional carbon source. Environmental parameters have been established for accelerated transformation in some of these strains. Studies have also indicated that enhanced biotransformation of these pesticides can be accomplished by mixed microbial populations under optimised environmental conditions. Substantial research into the identification of neonicotinoid-mineralising bacterial strains and identification of the genes and enzymes responsible for neonicotinoid degradation is still required to complete the understanding of microbial biodegradation pathways, and advance bioremediation efforts.

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.

Biodegradation of chlorimuron-ethyl and the associated degradation pathway by Rhodococcus sp. D310-1

Chlorimuron-ethyl is a typical long-term residual sulfonylurea herbicide, and strategies for its removal have attracted increasing attention. Microbial degradation is considered the most acceptable dissipation method. In this study, we optimized the cultivation conditions (substrate concentration, pH, inoculum concentration, and temperature) of the chlorimuron-ethyl-degrading bacterium Rhodococcus sp. D310-1 using response surface methodology (RSM) to improve the biodegradation efficiency. A maximum biodegradation rate of 88.95 % was obtained. The Andrews model was used to describe the changes in the specific degradation rate as the substrate concentration increased. Chlorimuron-ethyl could be transformed with a maximum specific degradation rate (q max), half-saturation constant (K S), and inhibition constant (K i) of 0.4327 day(-1), 63.50045 mg L(-1), and 156.76666 mg L(-1), respectively. Eight biodegradation products (2-amino-4-chloro-6-methoxypyrimidine, ethyl 2-sulfamoyl benzoate, 2-sulfamoyl benzoic acid, o-benzoic sulfimide, 2-[[(4-chloro-6-methoxy-2-pyrimidinyl) carbamoyl] sulfamoyl] benzoic acid, ethyl 2-carbonyl sulfamoyl benzoate, ethyl 2-benzenesulfonyl isocyanate benzoate, and N,N-2(ethyl formate)benzene sulfonylurea) were identified, and three possible degradation pathways were proposed based on the results of high performance liquid chromatography HPLC, liquid chromatography tandem mass spectroscopy (LC-MS/MS), and Fourier transform infrared spectroscopy (FTIR) analyses and the relevant literature. This systematic study is the first to examine the chlorimuron-ethyl degradation pathways of the genus Rhodococcus.

Binding and detoxification of chlorpyrifos by lactic acid bacteria on rice straw silage fermentation

This investigation examined the reduction of pesticide residues on straw inoculated with lactic acid bacteria (LAB) during ensiling. Lactobacillus casei WYS3 was isolated from rice straw that contained pesticide residues. Non-sterilized rice straw, which was inoculated with L. casei WYS3, showed increased removal of chlorpyrifos after ensiling, compared with rice straw that was not inoculated with L. casei WYS3 or sterilized rice straw. In pure culture, these strains can bind chlorpyrifos as indicated by high-performance liquid chromatography analysis. Viable L. casei WYS3 was shown to bind 33.3-42% of exogenously added chlorpyrifos. These results are similar to those of acid-treated cells but less than those of heat-treated cells, which were found to bind 32.0% and 77.2% of the added chlorpyrifos respectively. Furthermore, gas chromatography-mass spectrometry analysis determined that L. casei WYS3 detoxified chlorpyrifos via P-O-C cleavage. Real-time polymerized chain reaction analysis determined that organophosphorus hydrolase gene expression tripled after the addition of chlorpyrifos to LAB cultures, compared with the control group (without chlorpyrifos). This paper highlights the potential use of LAB starter cultures for the detoxification and removal of chlorpyrifos residues in the environment.

Insights into the degradation of chlorimuron-ethyl by Stenotrophomonas maltophilia D310-3

In this study, the effects of cultivation conditions on the degradation of chlorimuron-ethyl by Stenotrophomonas maltophilia D310-3, which exhibits a high chlorimuron-ethyl-degrading capability, were investigated. To improve the biodegradation efficiency, the cultivation conditions were optimized using response surface methodology (RSM) based on Box-Behnken design (BBD). The maximum biodegradation rate (89.9%) was obtained at the optimal conditions (culture time, 6 d; substrate concentration, 50.21 mg L(-1); pH, 5.95; temperature, 30.15 °C). The Andrews model was used to describe the dynamic change regularity of the specific degradation rate as the substrate concentration increased, and the values of the maximum specific degradation rate (q(max)), half-saturation constant (K(S)) and inhibition constant (K(i)) were 78.87 d(-1), 9180.97 mg L(-1) and 0.28 mg L(-1), respectively. Eight degradation products were captured and identified by liquid chromatography-mass spectrometry (LC-MS) and Fourier transform infrared (FTIR) spectrometry, and three possible degradation pathways are proposed based on the results of high-performance liquid chromatography (HPLC), LC-MS and FTIR analyses as well as results reported in relevant literature. To the best of our knowledge, this is the first systematic study of the degradation pathway of chlorimuron-ethyl by S. maltophilia D310-3. This study provides valuable information for further exploration of the microbial degradation of other sulfonylurea herbicides.

Using co-metabolism to accelerate synthetic starch wastewater degradation and nutrient recovery in photosynthetic bacterial wastewater treatment technology

Starch wastewater is a type of nutrient-rich wastewater that contains numerous macromolecular polysaccharides. Using photosynthetic bacteria (PSB) to treat starch wastewater can reduce pollutants and enhance useful biomass production. However, PSB cannot directly degrade macromolecular polysaccharides, which weakens the starch degradation effect. Therefore, co-metabolism with primary substances was employed in PSB wastewater treatment to promote starch degradation. The results indicated that co-metabolism is a highly effective method in synthetic starch degradation by PSB. When malic acid was used as the optimal primary substrate, the chemical oxygen demand, total sugar, macromolecules removal and biomass yield were considerably higher than when primary substances were not used, respectively. Malic acid was the primary substrate that played a highly important role in starch degradation. It promoted the alpha-amylase activity to 46.8 U and the PSB activity, which induced the degradation of macromolecules. The products in the wastewater were ethanol, acetic acid and propionic acid. Ethanol was the primary product throughout the degradation process. The introduction of co-metabolism with malic acid to treat wastewater can accelerate macromolecules degradation and bioresource production and weaken the acidification effect. This method provides another pathway for bioresource recovery from wastewater. This approach is a sustainable and environmentally friendly wastewater treatment technology.

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.

Experimental and kinetic study on the cometabolic biodegradation of phenol and 4-chlorophenol by psychrotrophic Pseudomonas putida LY1

This study investigated the kinetics of phenol and 4-chlorophenol (4-CP) biodegradation by a cold-adapted bacteria, Pseudomonas putida LY1, isolated from Songhua River sediment. The results showed that P. putida LY1 cannot grow on 4-CP as a sole carbon source. P. putida LY1 had the potential to cometabolic biodegrade phenol and 4-CP in a wide range of temperature (varying from 5 to 35 °C) with the optimal temperature around 25 °C. Mixture of phenol and 4-CP were completely removed at two 4-CP concentrations (15 and 40 mg/L) over a wide range of phenol (20-400 mg/L) concentrations, whereby the ratio of 4-CP/biomass (S 2/X) was lower than 0.03. The kinetic models of cometabolic biodegradation of phenol and 4-CP were proposed, considering the growth and nongrowth substrate inhibition. These models successfully simulate the processes of cometabolic degradation of phenol and 4-CP.

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.

Co-metabolic transformation of the neonicotinoid insecticide imidacloprid by the new soil isolate Pseudoxanthomonas indica CGMCC 6648

A new imidacloprid (IMI) degrading bacterium Z-9 (deposited number CGMCC 6648) was isolated and identified as Pseudoxanthomonas indica by 16S rRNA gene analysis. Two metabolites were identified as olefin and 5-hydroxy IMI by liquid chromatography-mass spectrometry and nuclear magnetic resonance analysis. P. indica CGMCC 6648 degraded 70.1% of IMI (1.22 mmol L(-1)) and formed 0.93 mmol L(-1) 5-hydroxy IMI and 0.05 mmol L(-1) olefin IMI in 6 days and in the presence of 100 mmol L(-1) glucose. The half-life of IMI degradation was 3.6 days. P. indica CGMCC 6648 transforms IMI via a co-metabolism mechanism and different carbohydrates have significant effects on 5-hydroxy IMI formation, whereas different organic acids have substantial effects on olefin IMI production. Lactose is the best co-substrate for IMI degradation and 5-hydroxy IMI formation with 0.77 mmol L(-1) degraded and 0.67 mmol L(-1) formed in 48 h, respectively. Pyruvate is the best co-substrate for olefin IMI formation with 0.17 mmol L(-1) produced in 96 h for all carbon sources tested. Pyruvate significantly stimulates the conversion of 5-hydroxy IMI to olefin IMI, whereas glucose slightly inhibits this reaction. P. indica CGMCC 6648 rapidly degrades IMI and forms olefin IMI, which may enhance its potential for biodegradation of IMI and increase its insecticidal activity, which can decrease the IMI dosage required.