Utilization of microbial community potential for removal of chlorpyrifos: a review

Emerging technologies for the removal of pesticides from contaminated soils and their reuse in agriculture

Pesticides are becoming more prevalent in agriculture to protect crops and increase crop yields. However, nearly all pesticides used for this purpose reach non-target crops and remain as residues for extended periods. Contamination of soil by widespread pesticide use, as well as its toxicity to humans and other living organisms, is a global concern. This has prompted us to find solutions and develop alternative remediation technologies for sustainable management. This article reviews recent technological developments for remediating pesticides from contaminated soil, focusing on the following major points: (1) The application of various pesticide types and their properties, the sources of pesticides related to soil pollution, their transport and distribution, their fate, the impact on soil and human health, and the extrinsic and intrinsic factors that affect the remediation process are the main points of focus. (2) Sustainable pesticide degradation mechanisms and various emerging nano- and bioelectrochemical soil remediation technologies. (3) The feasible and long-term sustainable research and development approaches that are required for on-site pesticide removal from soils, as well as prospects for applying them directly in agricultural fields. In this critical analysis, we found that bioremediation technology has the potential for up to 90% pesticide removal from the soil. The complete removal of pesticides through a single biological treatment approach is still a challenging task; however, the combination of electrochemical oxidation and bioelectrochemical system approaches can achieve the complete removal of pesticides from soil. Further research is required to remove pesticides directly from soils in agricultural fields on a large scale.

Biodegradation of chlorpyrifos pollution from contaminated environment - A review on operating variables and mechanism

Chlorpyrifos (CPF) is a highly toxic phosphate-rich organic pesticide (OP), identified as an emerging contaminant and used extensively in agricultural production. CPF persistence in the environment and its potential health hazards has become increasingly concerning worldwide in recent years due to exponential rise in food demand. Biodegradation of chlorpyrifos by microbial cultures is a promising approach to reclaiming contaminated soil and aquatic environments. The purpose of this review is to summarize the current understanding of microbiological aspects of xenobiotic chlorpyrifos biodegradation, including microbial diversity, metabolic pathways, and factors that modulate it. In both aerobic and anaerobic environments, CPF is biochemically broken down by a broad spectrum of bacteria and fungi. Hydrolysis, dehalogenation, and oxidation of chlorpyrifos are all enzymatic reactions that lead to its degradation. Biodegradation rate and efficiency are strongly influenced by parametric variables such as co-substrates abundance, pH, temperature, and initial chlorpyrifos concentration. The review provides evidence that microbial biodegradation is a viable method for remediating chlorpyrifos-contaminated sites in a sustainable and safe manner.

The role of insect gut microbiota in host fitness, detoxification and nutrient supplementation

Insects are incredibly diverse, ubiquitous and have successfully flourished out of the dynamic and often unpredictable nature of evolutionary processes. The resident microbiome has accompanied the physical and biological adaptations that enable their continued survival and proliferation in a wide array of environments. The host insect and microbiome's bidirectional relationship exhibits their capability to influence each other's physiology, behavior and characteristics. Insects are reported to rely directly on the microbial community to break down complex food, adapt to nutrient-deficit environments, protect themselves from natural adversaries and control the expression of social behavior. High-throughput metagenomic approaches have enhanced the potential for determining the abundance, composition, diversity and functional activities of microbial fauna associated with insect hosts, enabling in-depth investigation into insect-microbe interactions. We undertook a review of some of the major advances in the field of metagenomics, focusing on insect-microbe interaction, diversity and composition of resident microbiota, the functional capability of endosymbionts and discussions on different symbiotic relationships. The review aims to be a valuable resource on insect gut symbiotic microbiota by providing a comprehensive understanding of how insect gut symbionts systematically perform a range of functions, viz., insecticide degradation, nutritional support and immune fitness. A thorough understanding of manipulating specific gut symbionts may aid in developing advanced insect-associated research to attain health and design strategies for pest management.

Resilience of aerobic sludge biomass under chlorpyrifos stress and its recovery potential

Non-agricultural sources of pesticides in urban areas are responsible for their presence in domestic wastewater. Therefore, pesticides are typically found in sewage treatment plants in developed and developing countries as micro-pollutant. The presence of pesticides in the wastewater can impart stress on the aerobic sludge biomass and disrupt the functioning of the plant. However, there exists a knowledge gap regarding the resilience of aerobic sludge biomass towards stress due to the presence of pesticides in the wastewater. This study investigated the impact of chlorpyrifos (CPS) - a widely used pesticide, on sludge biomass and explored its recovery capability when CPS is discontinued in the influent. Four duplicate reactors were operated with different CPS concentrations ranging from 50 to 200 mg/L. Chemical oxygen demand (COD) removal for reactors has ranged within 18-73 % at the steady state of the stressed phase, whereas COD removal for the control reactor was 91 %. CPS stress slightly inhibited filamentous biomass growth. Biomass activity and cell viability have decreased significantly, whereas biochemical contents have varied slightly under CPS stress. The activities of the enzymes dehydrogenase and urease were significantly inhibited when compared to catalase and protease. Amplified ribosomal DNA restriction analysis reflected changes in the microbial community. The discontinuation of CPS has allowed aerobic sludge biomass to recover in its organic degradation capability (COD removal of more than 88 % at steady-state conditions of recovery phase operation), biomass growth, and cell viability. In addition, enzyme activities have retrieved to their original levels, and 78-93 % similarity of microbial community structure has been displayed between CPS-exposed and control reactor biomasses. Overall, the present study has indicated the orderly changes in the quality of aerobic sludge biomass under CPS stress through physico-chemical and biological characteristics. The study also has highlighted the self-recovery of sludge biomass characteristics stressed with different concentrations of CPS.

Degradation kinetics and physiological studies of organophosphates degrading microorganisms for soil bioremediation

Organophosphate compounds are widely used in agricultural activities to optimize food production. Contamination of field soil by these compounds may result in detrimental effects on soil biota. The aim of the present study was to isolate microorganisms from field soils and evaluate the strains on ability to degrade organophosphates as single isolate and as a consortium. Isolated strains were identified using both biochemical and molecular techniques. Results revealed that, out of the 46 isolated strains, three isolates herein referred to as S6, S36 and S37 showed an average diazinon degradation rate of 76.4%, 76.7% and 76.8% respectively, of the initial dose (50 ppm) within 11 days of incubation in mineral medium. Notably, isolates S36 and S37 were more effective than S6 in degrading diazinon by 40% in soil aliquot after 11 days and therefore were evaluated on biochemical reactions and molecular identification. The isolates showed variable biochemical characteristics. However, both isolates possessed catalase enzyme, but lacked oxidase enzyme. Molecular characterization showed that, the closest species for S36 and S37 were Priestia megaterium and P. arybattia, respectively, based on 16S rRNA gene similarity (> 99%). Combination of the strains increased diazinon degradation ability by 45% compared to single strain treatment. Chlorpyrifos was the most highly degraded organophosphate, compared to phorate and cadusafos. Therefore it is expected that the pesticide-degrading bacteria could be a solution to soil health improvement and contribution to the production of safe agricultural products.

The concentration of pesticides in tomato: a global systematic review, meta-analysis, and health risk assessment

To improve farming productivity, a large number of pesticides have been used worldwide in recent decades, leading to the pollution of soil, agri-products, and water, directly/indirectly affecting human health. In this regard, many studies were conducted in different countries on residual pesticides in the environment. In the current study, residual pesticides including chlorpyrifos, cypermethrin, diazinon, malathion, and metalaxyl in tomatoes were meta-analyzed and health risk of consumers was estimated. For this purpose, based on a systematic review, data from 47 studies were extracted and meta-analyzed, and the health impact of pooled concentrations was assessed via a health risk method. According to the results, metalaxyl had the most concentration followed by malathion, cypermethrin, diazinon, and chlorpyrifos, respectively. The non-carcinogenic risk (n-CR) was calculated from crop consumption also showed that exposure to malathion has the most risk. Among the investigated communities, Iranian consumers were in considerable health risk (THQ > 1). Considering that the potential for the use of pesticides will increase with the need for food in the future, hence, governments must manage the usage by governments via alternative methods such as cultural, biological, physical, and genetic modifications.

Insight into the environmental fate, hazard, detection, and sustainable degradation technologies of chlorpyrifos-an organophosphorus pesticide

Pesticides play a critical role in terms of agricultural output nowadays. On top of that, pesticides provide economic support to our farmers. However, the usage of pesticides has created a public health issue and environmental hazard. Chlorpyrifos (CPY), an organophosphate pesticide, is extensively applied as an insecticide, acaricide, and termiticide against pests in various applications. Environmental pollution has occurred because of the widespread usage of CPY, harming several ecosystems, including soil, sediment, water, air, and biogeochemical cycles. While residual levels in soil, water, vegetables, foodstuffs, and human fluids have been discovered, CPY has also been found in the sediment, soil, and water. The irrefutable pieces of evidence indicate that CPY exposure inhibits the choline esterase enzyme, which impairs the ability of the body to use choline. As a result, neurological, immunological, and psychological consequences are seen in people and the natural environment. Several research studies have been conducted worldwide to identify and develop CPY remediation approaches and its derivatives from the environment. Currently, many detoxification methods are available for pesticides, such as CPY. However, recent research has shown that the breakdown of CPY using bacteria is the most proficient, cost-effective, and sustainable. This current article aims to outline relevant research events, summarize the possible breakdown of CPY into various compounds, and discuss analytical summaries of current research findings on bacterial degradation of CPY and the potential degradation mechanism.

An inclusive outlook on the fate and persistence of pesticides in the environment and integrated eco-technologies for their degradation

Intensive and inefficient exploitation of pesticides through modernized agricultural practices has caused severe pesticide contamination problems to the environment and become a crucial problem over a few decades. Due to their highly toxic and persistent properties, they affect and get accumulated in non-target organisms, including microbes, algae, invertebrates, plants as well as humans, and cause severe issues. Considering pesticide problems as a significant issue, researchers have investigated several approaches to rectify the pesticide contamination problems. Several analyses have provided an extensive discussion on pesticide degradation but using specific technology for specific pesticides. However, in the middle of this time, cleaner techniques are essential for reducing pesticide contamination problems safely and environmentally friendly. As per the research findings, no single research finding provides concrete discussion on cleaner tactics for the remediation of contaminated sites. Therefore, in this review paper, we have critically discussed cleaner options for dealing with pesticide contamination problems as well as their advantages and disadvantages have also been reviewed. As evident from the literature, microbial remediation, phytoremediation, composting, and photocatalytic degradation methods are efficient and sustainable and can be used for treatment at a large scale in engineered systems and in situ. However, more study on the bio-integrated system is required which may be more effective than existing technologies.

New Insights into Baicalein's Effect on Chlorpyrifos-Induced Liver Injury in Carp: Involving Macrophage Polarization and Pyropto sis

Chlorpyrifos (CPF) is widely used in agriculture, plants, and buildings to kill pests and worms. Excessive environmental residues of CPF will result in soil and ecological contamination and toxicity to animals and humans. Baicalein (Bai), derived from the root of natural Scutellaria baicalensis, is a potent anti-inflammatory, antioxidant, and antitumor agent. The objective of this paper is to investigate the molecular mechanism by which Bai prevents CPF-induced hepatotoxic injury. Carp were kept in water containing CPF (23.2 μg/L) and/or fed diets containing Bai (0.15 g/kg). We found that Bai attenuated liver tissue damage and vacuolization caused by CPF. We confirmed that CPF causes M1/M2 polarization imbalance in macrophages and hepatocyte pyroptosis, which ultimately leads to liver injury. Further exploration of the internal mechanism shows that CPF participates in liver toxicity damage by destroying the AMPK/SIRT1/pGC-1α pathway and causing mitochondrial biogenesis and mitochondrial dynamics imbalance. Notably, Bai significantly attenuated CPF-induced inhibition of the AMPK/SIRT1/pGC-1α pathway. In summary, our results suggest that Bai alleviates CPF exposure-induced inhibition of the AMPK/SIRT1/pGC-1α pathway, thereby attenuating macrophage M1 hyperpolarization and pyroptosis by inhibiting the NF-κB pathway. These results may provide new insights into the detoxification mechanism of Bai on the same type of organophosphorus pesticides.

Precisely Navigated Biobot Swarms of Bacteria Magnetospirillum magneticum for Water Decontamination

Hybrid biological robots (biobots) prepared from living cells are at the forefront of micro-/nanomotor research due to their biocompatibility and versatility toward multiple applications. However, their precise maneuverability is essential for practical applications. Magnetotactic bacteria are hybrid biobots that produce magnetosome magnetite crystals, which are more stable than synthesized magnetite and can orient along the direction of earth's magnetic field. Herein, we used Magnetospirillum magneticum strain AMB-1 (M. magneticum AMB-1) for the effective removal of chlorpyrifos (an organophosphate pesticide) in various aqueous solutions by naturally binding with organic matter. Precision control of M. magneticum AMB-1 was achieved by applying a magnetic field. Under a programed clockwise magnetic field, M. magneticum AMB-1 exhibit swarm behavior and move in a circular direction. Consequently, we foresee that M. magneticum AMB-1 can be applied in various environments to remove and retrieve pollutants by directional control magnetic actuation.

Use of surfactants in biodegradation of hydrophobic compounds: A review

Industrial development has led to immense emission and accumulation of hydrophobic organic compounds (HOC) in the environment. Primarily, they include petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The extensive use of hydrophobic pesticides in agriculture led to the contamination of soil, air and water. Many of the hydrophobic substances are dangerous for the biota due to their high toxicity and carcinogenic and mutagenic activity. In addition to their widespread use, the possible adverse effects are also determined by their resistance to decomposition, including the biological one, which defines their long-term persistence in soil, water and other media. The impact of HOC on ecosystems poses a potential threat not only to the environment but also to human health. Numerous studies were devoted to the remediation of soils polluted with HOC. The approaches to remediation can be conditionally divided into mechanical, chemical and bio-methods, with the former two being widely used in the past. Bioremediation methods proved more efficient and, as a rule, more cost-effective and environmentally friendly. In recent years, the good efficiency of solubilizing agents in bioremediation processes has been demonstrated. Various surfactants have become widely popular due to their ability to increase desorption, water solubility and microbial bioavailability of HOC. In this brief review, state-of-the-art literature data on the biodegradation of hydrophobic organic compounds using surfactants were considered.

Biochar alleviated the toxicity of atrazine to soybeans, as revealed by soil microbial community and the assembly process

Atrazine has a detrimental effect on soybean growth in corn-soybean rotation systems. A knowledge gap exists regarding how rhizosphere microbial interactions respond to atrazine stress, and specifically, whether they may alleviate the detriment of atrazine on soybeans, this serving as a target to alleviate the adverse impact. Biochar are widely used for remediation in herbicide contamination soil, however, little is known about how biochar fuels the microbiomes in rhizosphere to improve soybean performance. We investigated the response of the microbial community to atrazine stress with and without biochar application to soybean cultivation in a greenhouse experiment. Atrazine had detrimental effects on soybeans and nodules, reshaping the microbial community in both the bulk and rhizosphere soil. Biochar application was able to ameliorate atrazine effects on soybean and nodule activity, with an increase in competition among microbes in the soybean rhizosphere soils. Biochar favored the probiotics such as the bacteria Lysobacter, Paenarthrobacter, and Sediminibacterium in the rhizosphere soils. The relative abundance of Lysobacter exhibited strong-negative correlations with potential pathogens. Elastic net regression with bioindicators and environmental factors accurately predicted the residual content of atrazine in soil. Collectively, our results provide a practical strategy of using biochar to improve soil quality for corn-soybean rotation that is contaminated with residual atrazine. Overall, beneficial plant microbes and changes in microbial interactions and assembly processes in the soybean rhizosphere are capable of alleviating atrazine stress on soybean growth.

Occurrence, Distribution, and Risk Assessment of Organophosphorus Pesticides in the Aquatic Environment of the Sele River Estuary, Southern Italy

The intensive use of organophosphorus pesticides (OPPs) causes concern among authorities in different countries, as many of them, remaining unchanged for a long time, pose a threat to environmental sustainability. This study assessed the spatio-temporal trends of nine OPPs in the water dissolved phase (WDP), suspended particulate matter (SPM), and sediment samples from the Sele River estuary, Southern Italy. Samples were collected in 10 sampling sites during four seasons. The highest levels were found at the mouth (mean value 28.25 ng L⁻¹ as WDP + SPM) and then decreased moving southwards to the Mediterranean Sea. Moreover, highest concentrations were detected in the warm season (July) with a mean value of 27.52 ng L⁻¹. The load contribution to the Mediterranean Sea was evaluated in about 61.5 kg year⁻¹, showing that the river was an important source of OPPs through discharge into the sea. The risk assessment revealed that no high-risk indices for the general-case scenario were observed, but for the worst-case scenario, potential risks were associated with chlorpyrifos, pyrimifos-methyl, and parathion, suggesting that OPP contamination should not be neglected. This study makes up the first record of OPPs in the surface waters of the Sele River and provides helpful data as a starting point for future studies.

Gene sdaB Is Involved in the Nematocidal Activity of Enterobacter ludwigii AA4 Against the Pine Wood Nematode Bursaphelenchus xylophilus

Bursaphelenchus xylophilus, a plant parasitic nematode, is the causal agent of pine wilt, a devastating forest tree disease. Essentially, no efficient methods for controlling B. xylophilus and pine wilt disease have yet been developed. Enterobacter ludwigii AA4, isolated from the root of maize, has powerful nematocidal activity against B. xylophilus in a new in vitro dye exclusion test. The corrected mortality of the B. xylophilus treated by E. ludwigii AA4 or its cell extract reached 98.3 and 98.6%, respectively. Morphological changes in B. xylophilus treated with a cell extract from strain AA4 suggested that the death of B. xylophilus might be caused by an increased number of vacuoles in non-apoptotic cell death and the damage to tissues of the nematodes. In a greenhouse test, the disease index of the seedlings of Scots pine (Pinus sylvestris) treated with the cells of strain AA4 plus B. xylophilus or those treated by AA4 cell extract plus B. xylophilus was 38.2 and 30.3, respectively, was significantly lower than 92.5 in the control plants treated with distilled water and B. xylophilus. We created a sdaB gene knockout in strain AA4 by deleting the gene that was putatively encoding the beta-subunit of L-serine dehydratase through Red homologous recombination. The nematocidal and disease-suppressing activities of the knockout strain were remarkably impaired. Finally, we revealed a robust colonization of P. sylvestris seedling needles by E. ludwigii AA4, which is supposed to contribute to the disease-controlling efficacy of strain AA4. Therefore, E. ludwigii AA4 has significant potential to serve as an agent for the biological control of pine wilt disease caused by B. xylophilus.

Molecular characterization of chlorpyrifos degrading bacteria isolated from contaminated dairy farm soils in Nakuru County, Kenya

Chlorpyrifos (CP) is an organophosphate widely used as an insecticide and acaricide. Extensive application of CP contaminates ecosystems, polluting the environment and food products, creating health complications to humans due to its neurotoxicity. The study evaluated CP bioremediation by bacteria isolated from dairy farm soils in Nakuru County, Kenya, through enrichment culture technique. The growth response of the bacteria and degradation of chlorpyrifos was monitored every five days using UV-VIS Spectrophotometer (600nm). Enrichment culture technique led to the isolation of eighteen (MA1-MA18) potential CP degraders belonging to the genera Pseudomonas, Stenotrophomonas, Bacillus, Alicaligenes, and Achromobacter. The efficacy of four (4) strains was further investigated using Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The results showed that all four strains significantly degraded chlorpyrifos in Minimum Salt Medium (MSM): Lysinibacillus sp.HBUM206408 (87.16 %), Stenotrophomonas maltophilia (82.04 %), Pseudomonas putida (89.52 %), and Achromobacter insuavis (91.08 %) within 16 days, producing 2-Hydroxy-3, 5, 6-trichloropyridine (TCP) as the main metabolite. Therefore, these strains can be used to degrade chlorpyrifos in contaminated soil. There is a need for further studies to determine the possible mechanisms and other metabolites of chlorpyrifos degradation by the isolates obtained in the study. Besides, future studies should explore the efficacy and survival of the organisms in the contaminated environment.

A review on the microbial degradation of chlorpyrifos and its metabolite TCP

Chlorpyrifos (CPF) falls under the category of organophosphorus pesticides which are in huge demand in the agricultural sector. Overuse of this pesticide has led to the degradation of the quality of terrestrial and aquatic life. The chemical is moderately persistent in the environment but its primary metabolite 3,5,6-trichloro-2-pyridinol (TCP) is comparatively highly persistent. Thus, it is important to degrade the chemical and there are many proposed techniques of degradation. Out of which bioremediation is considered to be highly cost-effective and efficient. Many previous studies have attempted to isolate appropriate microbial strains to degrade CPF which established the fact that chlorine atoms released while mineralising TCP inhibits further proliferation of microorganisms. Thus, it has been increasingly important to experiment with strains that can simultaneously degrade both CPF and TCP. In this review paper, the need for degrading CPF specifically the problems related to it has been discussed elaborately. Alongside these, the metabolism pathways undertaken by different kinds of microorganisms have been included. This paper also gives a detailed insight into the potential strains of microorganisms which has been confirmed through experiments conducted previously. It can be concluded that a wide range of microorganisms has to be studied to understand the possibility of applying bioremediation in wastewater treatment to remove pesticide residues. In addition to this, in the case of recalcitrant pesticides, options of treating it with hybrid techniques like bioremediation clubbed with photocatalytic biodegradation can be attempted.

Recent advancements in the detection of organophosphate pesticides: a review

Organophosphorus pesticides (OPPs) are generally utilized for the protection of crops from pests. Because the use of OPPs in various agricultural operations has expanded dramatically, precise monitoring of their concentration levels has become the critical issue, which will help in the protection of ecological systems and food supply. However, the World Health Organization (WHO) has classified them as extremely dangerous chemical compounds. Taking their immense use and toxicity into consideration, the development of easy, rapid and highly sensitive techniques is necessary. Despite the fact that there are numerous conventional ways for detecting OPPs, the development of portable sensors is required to make routine analysis considerably more convenient. Some of these advanced techniques include colorimetric sensors, fluorescence sensors, molecular imprinted polymer-based sensors, and surface plasmon resonance-based sensors. This review article specifically focuses on the colorimetric, fluorescence and electrochemical sensors. In this article, the sensing strategies of these developed sensors, analytical conditions and their respective limit of detection are compiled.

Chlorpyrifos in environment and food: a critical review of detection methods and degradation pathways

Chlorpyrifos (CP) is a class of organophosphorus (OP) pesticides, which find extensive applications as acaricide, insecticide and termiticide. The use of CP has been indicated in environmental contamination and disturbance in the biogeochemical cycles. CP has been reported to be neurotoxic and has a detrimental effect on immunological and psychological health. Therefore, it is necessary to design and develop effective degradation methods for the removal of CP from the environment. In the past few years, physicochemical (advanced oxidation process) and biological treatment approaches have been widely employed for the pesticide removal. However, the byproducts of this process are more toxic than the parent compound and along with an incomplete degradation of CP. This review focuses on the toxicity of CP, the sources of contamination, degradation pathways, physicochemical, biological, and nano-technology based methods employed for the degradation of CP. In addition, consolidated information on various detection methods and materials used for the detection have been provided in this review.

Pollutants affect algae-bacteria interactions: A critical review

With increasing concerns on the ecological risks of pollutants, many efforts have been devoted to revealing the toxic effects of pollutants on algae or bacteria in their monocultures. However, how pollutants affect algae and bacteria in their cocultures is still elusive but crucial due to its more environmental relevance. The present review outlines the interactions between algae and bacteria, reveals the influential mechanisms of pollutants (including pesticides, metals, engineered nanomaterials, pharmaceutical and personal care products, and aromatic pollutants) to algae and bacteria in their coexisted systems, and puts forward prospects for further advancing toxic studies in algal-bacterial systems. Pollutants affect the physiological and ecological functions of bacteria and algae by interfering with their relationships. Cell-to-cell adhesion, substrate exchange and biodegradation of organic pollutants, enhancement of signal transduction, and horizontal transfer of tolerance genes are important defense strategies in algal-bacterial systems to cope with pollution stress. Developing suitable algal-bacterial models, identifying cross-kingdom signaling molecules, and deciphering the horizontal transfer of pollutant resistant genes between algae and bacteria under pollution stress are the way forward to fully exploit the risks of pollutants in natural aquatic environments.

Effects of mancozeb on citrus rhizosphere bacterial community

Multiple and consecutive application of fungicide might damage the rhizosphere bacterial community of citrus. In order to evaluated effect of mancozeb on the chemical properties of citrus-cultivated soil and the richness and diversity of rhizosphere bacterial community. The abundance response of rhizosphere bacterial groups without application or with application of 1.333 g mg^-1 mancozeb for 2, 4, 6 and 8 times were investigated, and further studied the relationship between the rhizosphere bacterial community and chemical properties of citrus-cultivated soil. We found the rhizosphere bacterial composition and diversity were distinct between soil planted with citrus and without citrus, in addition, the abundance of rhizosphere-associated bacterial species in the soil planted with citrus increased significantly. Meanwhile, the chemical properties and the richness and diversity of rhizosphere bacterial community of the soil planted with citrus did not significantly change among different application frequence of mancozeb. Moreover, with the increased applying times of mancozeb, the relative abundance of Candidatus, Saccharibacteria, Parcubacteria, and Proteobacteria increased but the abundance of Nitrospirae decreased. In our one-year trial, there were less adverse effects of mancozeb on the citrus-cultivated rhizosphere by the repeated application of mancozeb. Therefore, mancozeb, as a fungicide, could be used multiple times to control citrus disease.

Insights into the microbial degradation and catalytic mechanisms of chlorpyrifos

Chlorpyrifos is extensively used worldwide as an insecticide to control various insect pests. Long-term and irregular applications of chlorpyrifos have resulted in large-scale soil, groundwater, sediment, and air pollution. Numerous studies have shown that chlorpyrifos and its major intermediate metabolite 3,5,6-trichloropyridinol (TCP) accumulate in non-target organisms through biomagnification and have a strong toxic effect on non-target organisms, including human beings. Bioremediation based on microbial metabolism is considered an eco-friendly and efficient strategy to remove chlorpyrifos residues. To date, a variety of bacterial and fungal species have been isolated and characterized for the biodegradation of chlorpyrifos and TCP. The metabolites and degradation pathways of chlorpyrifos have been investigated. In addition, the chlorpyrifos-degrading enzymes and functional genes in microbes have been reported. Hydrolases can catalyze the first step in ester-bond hydrolysis, and this initial regulatory metabolic reaction plays a key role in the degradation of chlorpyrifos. Previous studies have shown that the active site of hydrolase contains serine residues, which can initiate a catalytic reaction by nucleophilic attack on the P-atom of chlorpyrifos. However, few reviews have focused on the microbial degradation and catalytic mechanisms of chlorpyrifos. Therefore, this review discusses the deep understanding of chlorpyrifos degradation mechanisms with microbial strains, metabolic pathways, catalytic mechanisms, and their genetic basis in bioremediation.

Enhanced biodegradation of organophosphorus insecticides in industrial wastewater via immobilized Cupriavidus nantongensis X1T

Chlorpyrifos is an important organophosphorus insecticide. It is highly toxic to mammals and can pollute the environment. Cupriavidus nantongensis X1^T can efficiently degrade chlorpyrifos. Immobilization technology can also improve the viability, stability and catalytic ability of bacteria. In this study, strain X1^T was, therefore, captured on various composite immobilized carriers, sodium alginate (SA), diatomite (KLG), chitosan (CTS) and polyvinyl alcohol (PVA). The four types of immobilized beads (SA, SA + KLG, SA + CTS and SA + PVA) could form a slice and honeycomb structure to capture strain X1^T. The results showed that SA + CTS (SC) was an optimal material combination for the immobilization of strain X1^T to degrade chlorpyrifos. Compared with SA-X1^T, after adding CTS, the specific surface area and adsorption capacity for chlorpyrifos were increased 3.4 and 1.7 fold, respectively. SC-X1^T could degrade 96.6% of chlorpyrifos at 20 mg/L within 24 h and the degradation rate constant was 4.8 fold greater than immobilized strain LLBD2, a well-studied chlorpyrifos-degrading strain. The immobilized beads SC-X1^T also showed a more stable and greater degradation ability than X1^T free cells for chlorpyrifos in industrial wastewater. The synergy of adsorption and degradation of immobilized strain X1^T is suitable for in-situ remediation of chlorpyrifos contaminated environment.

Gut bacteria of the silkworm Bombyx mori facilitate host resistance against the toxic effects of organophosphate insecticides

Organophosphate insecticides that are heavily used in agriculture for pest control have caused growing environmental problems and public health concerns worldwide. Ironically, insecticide resistance develops quickly in major lepidopteran pests, partially via their microbial symbionts. To investigate the possible mechanisms by which the microbiota confers insecticide resistance to Lepidoptera, the model organism silkworm Bombyx mori (Lepidoptera: Bombycidae) was fed different antibiotics to induce gut dysbiosis (microbiota imbalance). Larvae treated with polymyxin showed a significantly lower survival rate when exposed to chlorpyrifos. Through high-throughput sequencing, we found that the abundances of Stenotrophomonas and Enterococcus spp. changed substantially after treatment. To assess the roles played by these two groups of bacteria in chlorpyrifos resistance, a germ-free (GF) silkworm rearing protocol was established to avoid the influence of natural microbiota and antibiotics. Monoassociation of GF silkworms with Stenotrophomonas enhanced host resistance to chlorpyrifos, but not in Enterococcus-fed larvae, consistent with larval detoxification activity. GC-μECD detection of chlorpyrifos residues in feces indicated that neither Stenotrophomonas nor Enterococcus degraded chlorpyrifos directly in the gut. However, gut metabolomics analysis revealed a highly species-specific pattern, with higher levels of essential amino acid produced in the gut of silkworm larvae monoassociated with Stenotrophomonas. This critical nutrient provisioning significantly increased host fitness and thereby allowed larvae to circumvent the deleterious effects of these toxic chemicals more efficiently. Altogether, our study not only suggests a new mechanism for insecticide resistance in notorious lepidopteran pests but also provides a useful template for investigating the interplay between host and gut bacteria in complex environmental systems.

Exploitation of Potential Extremophiles for Bioremediation of Xenobiotics Compounds: A Biotechnological Approach

Microorganisms that are capable of live and adapt in hostile habitats of different environmental factors such as extremes temperature, salinity, nutrient availability and pressure are known as extremophiles. Exposure to xenobiotic compounds is global concern influencing the world population as a health hazard. Hence their removal is warranted using biological means that is very sustainable, potentially cost-effective and eco-friendly. Due to adaptation in extreme environments and unique defense mechanisms, they are receiving more attention for the bioremediation of the xenobiotic compounds. They possess robust enzymatic and biocatalytic systems that make them suitable for the effective removal of pollutants from the contaminated environment. Additionally, the extremophiles act as microfactories having specific genetic and biotechnological potential for the production of biomolecules. This mini review will provide an overview of microbial degradation metabolic pathways for bioremediation along with the molecular and physiological properties of diverse extremophiles from variety of habitats. Furthermore, the factors affecting the bioremediation process is also summarized.

Enantioselective Uptake Determines Degradation Selectivity of Chiral Profenofos in Cupriavidus nantongensis X1T

Organophosphorus insecticides account for approximately 28% of the global commercial insecticide market, while 40% of them are chiral enantiomers. Chiral enantiomers differ largely in their toxicities. Enantiomers that are less active or inactive do not offer the needed efficacy but pollute the environment and cause toxicities to non-target species. Cupriavidus nantongensis X1^T, a recently isolated bacterial strain, could degrade S-profenofos 2.3-fold faster than R-profenofos, while the latter is the active enantiomer potently against pest insects and has greater mammalian safety. The degradation enzyme encoded by opdB was expressed via Escherichia coli and purified. The degradation kinetics of R- and S-profenofos showed that both the purified OpdB and crude enzyme extracts had no enantiomer degradation selectivity, which strongly indicated that the degradation selectivity occurred in the uptake process. Metabolite analyses suggested a novel dealkylation pathway. This is the first report of bacterial selective uptake of organophosphates. Selective degradation of S-profenofos over R-profenofos by the strain X1^T suggests a concept of co-application of racemic pesticides and degradation-selective bacteria to minimize contamination and non-target toxicity problems.

Ortho and para oxydehalogenation of dihalophenols catalyzed by the monooxygenase TcpA and NAD(P)H:FAD reductase Fre

Dihalophenols such as dichlorophenols (DCPs) are important industrial chemical intermediates, but also persistent pollutants in the environment. Oxidative dehalogenation by microbes is an efficient biological method to degrade halophenols, but the mechanism is unclear yet. Cupriavidus nantongensis X1^T was a type strain of genus Cupriavidus, and could degrade 2,4-dichlorophenol of 50 mg/L within 12 h. The degradation rate constant was approximately 84 fold greater than that by Bacillus endophyticus CP1R43, a well-studied 2,4-DCP-degrading bacterial strain. The genes encoding 2,4,6-trichlorophenol monooxygenase (TcpA) and NAD(P)H:FAD reductase (Fre) from strain X1^T were cloned and expressed. The expressed TcpA Fre were purified. The molecular docking of TcpA with DCPs and point mutation experiments showed that the degradation activity of TcpA was associated with the length of the hydrogen bond between the substrates and the amino acids in the active pocket. DCPs were degraded via a stepwise oxidative dechlorination in a positive relationship between the oxidation ability and the electron-withdrawing potential of the p-position group. In addition, TcpA has dual dehalogenation and denitration functions. The results demonstrate that either strain X1^T or TcpA and Fre can effectively dehalogenate dihalophenols, which can be useful for the treatment of dihalophenols in wastewaters and remediation of DCP-contaminated environments.

Aerobic and anoxic degradation and detoxification of profenofos insecticide by Pseudomonas plecoglossicida strain PF1

Profenofos insecticide is one of the most broadly used organophosphorus pesticides causing the contamination of soil and groundwater. Since dissolved oxygen concentration in groundwater is limited, this study aimed to investigate profenofos biodegradation and detoxification under aerobic and anoxic conditions using the profenofos-degrading Pseudomonas plecoglossicida strain PF1 (PF1). Anoxic biodegradation under the presence of nitrate was the focus. The results showed that profenofos at 10-150 mg/L was degraded under aerobic and anoxic conditions with removal efficiencies of 38-55% and 27-45%, respectively. Kinetic analysis following the Michaelis-Menten model revealed that the maximum substrate degradation rates and the Michaelis constants were 13.07 and 8.92 mg/L/d and 92.07 and 84.76 mg/L under aerobic and anoxic conditions, respectively. The culture preferred an aerobic environment resulting in better biodegradation performance. During the degradation experiment, 4-bromo-2-chlorophenol and 1,1-dimethylethylphenol were detected as profenofos biodegradation intermediate products. Microbial toxicity, phytotoxicity, and cytogenotoxicity assays showed that the toxicity of the contaminated water significantly decreased after both aerobic and anoxic biodegradation by PF1. The results from this study indicated that PF1 has the potential for bioremediation in a profenofos-contaminated environment under the presence or absence of oxygen.

Rapid Biodegradation of the Organophosphorus Insecticide Chlorpyrifos by Cupriavidus nantongensis X1T

Chlorpyrifos was one of the most widely used organophosphorus insecticides and the neurotoxicity and genotoxicity of chlorpyrifos to mammals, aquatic organisms and other non-target organisms have caused much public concern. Cupriavidus nantongensis X1^T, a type of strain of the genus Cupriavidus, is capable of efficiently degrading 200 mg/L of chlorpyrifos within 48 h. This is ~100 fold faster than Enterobacter B-14, a well-studied chlorpyrifos-degrading bacterial strain. Strain X1^T can tolerate high concentrations (500 mg/L) of chlorpyrifos over a wide range of temperatures (30–42 °C) and pH values (5–9). RT-qPCR analysis showed that the organophosphorus hydrolase (OpdB) in strain X1^T was an inducible enzyme, and the crude enzyme isolated in vitro could still maintain 75% degradation activity. Strain X1^T can simultaneously degrade chlorpyrifos and its main hydrolysate 3,5,6-trichloro-2-pyridinol. TCP could be further metabolized through stepwise oxidative dechlorination and further opening of the benzene ring to be completely degraded by the tricarboxylic acid cycle. The results provide a potential means for the remediation of chlorpyrifos- contaminated soil and water.

Enhanced diuron remediation by microorganism-immobilized silkworm excrement composites and their impact on soil microbial communities

In response to the potential threats stemming from the constantly increasing consumption of herbicides, bioremediation offers a beneficial technology for reducing the widespread herbicide contamination. In order to facilitate the in-situ degradation of diuron, Arthrobacter globiformis D47 is captured onto a biocompatible carrier to assemble the microorganism-immobilized silkworm excrement (MSE) composites. By characterization, bacterial cells are intensively entrapped in/onto the carriers, showing high survival and stable catalytic degradation of target pollutants. Meanwhile, MES composites display excellent adaptiveness and feasibility under different conditions, and the average half-life of diuron is shortened to 7.69 d in sugarcane field where diuron is regularly sprayed for weed management. Importantly, we assess that the use of MSE may generally boost the overall xenobiotic-degrading ability, likely due to the slight alternation of the diversity and composition of soil microbial communities. Taking together, the presented MSE provides an attractive in situ approach for the efficient diuron removal as well as for the more feasible utilization of various pollutant-degrading microorganisms.

Pollution status and bioremediation of chlorpyrifos in environmental matrices by the application of bacterial communities: A review

Pesticides currently play a significant role in enhancing agricultural production and offer economic assistance to our farmers. However, their indiscriminate and injudicious application has caused environmental problems and public health concerns. Chlorpyrifos, a pesticide of organophosphate category is used globally as an insecticide, acaricide, and termiticide in households, public health, and agriculture against pests of a wide range. The extensive application of chlorpyrifos has caused contamination of various ecosystems like soil, sediments, water, air and also leads to the disruption of biogeochemical cycles. Moreover, chlorpyrifos residues have been detected in sediments, soil, water, vegetables, foodstuff and even in human fluids. It has been confirmed that exposure to chlorpyrifos has created health complications due to the inhibition of choline esterase enzyme, which leads to neurotoxicity, immunological and psychological effects in humans plus to the natural ecosystem. Due to the higher toxicity of chlorpyrifos, research is conducted globally to design and develop effective and efficient approaches for the elimination of chlorpyrifos and its associated compounds from environmental settings. At present different techniques are available for detoxification of such pesticides, but the microbial degradation of chlorpyrifos especially by bacteria has proven to be highly efficient, economical and environmental friendly. Thus, this paper aims to provide an outline of research events on this issue and summarize the evidences of chlorpyrifos pollution, discuss the analytical summary of latest research results on bacterial degradation of chlorpyrifos and possible degradation pathways along with effects on its degradation by different environmental parameters.

Kinetics and Catabolic Pathways of the Insecticide Chlorpyrifos, Annotation of the Degradation Genes, and Characterization of Enzymes TcpA and Fre in Cupriavidus nantongensis X1T

Chlorpyrifos is one of the most used organophosphorus insecticides. It is commonly degraded to 3,5,6-trichloro-2-pyridinol (TCP), which is water-soluble and toxic. Bacteria can degrade chlorpyrifos and TCP, but the biodegradation mechanism has not been well-characterized. Recently isolated Cupriavidus nantongensis X1^T can completely degrade 100 mg/L chlorpyrifos and 20 mg/L TCP with half-lives of 6 and 8 h, respectively. We annotated a complete gene cluster responsible for TCP degradation in recently sequenced strain X1^T. Two key genes, tcpA and fre, were cloned from X1^T and transferred and expressed in Escherichia coli BL21(DE3). Degradation of TCP by X1^T whole cell was compared with that by the enzymes 2,4,6-trichlorophenol monooxygenase and NAD(P)H:flavin reductase expressed and purified from E. coli BL21(DE3). Novel metabolites of TCP were isolated and characterized, indicating stepwise dechlorination of TCP, which was confirmed by TCP disappearance, mass balance, and detection and formation kinetics of chloride ion from TCP.

Zirconium Metal-Organic Framework UiO-66: Stability in an Aqueous Environment and Its Relevance for Organophosphate Degradation

Zirconium-based metal-organic frameworks were recently investigated as catalysts for degradation of organophosphate toxic compounds, such as pesticides or chemical warfare agents. The most utilized UiO-66 is considered as a stable material for these applications in an aqueous environment. However, the presented results indicate that the properties of UiO-66 are changing considerably in aqueous media under common conditions used for organophosphate degradations, and therefore its catalytic activity is not related to the number of structural defects created during the material synthesis. We delineate the stability of UiO-66 in water of various pHs, the in situ formation of new catalytic sites, and the correlation of these two parameters with the degradation rate of a model organophosphate pollutant, dimethyl-4-nitrophenyl phosphate (methyl-paraoxon). The stability was quantified using high-performance liquid chromatography (HPLC) by measuring the amounts of leached terephthalic acid, the linker of UiO-66, and monocarboxylic acids, the modulators bound at UiO-66 defects. We demonstrate that the HPLC analysis is a more suitable method for metal-organic frameworks stability assessment than commonly used methods, e.g., powder X-ray diffraction, adsorption isotherms, or electron microscopy.

Strengthening calcium alginate microspheres using polysulfone and its performance evaluation: Preparation, characterization and application for enhanced biodegradation of chlorpyrifos

Bacterial cell immobilization offer considerable advantages over traditional biotreatment systems using free cells. Calcium alginate matrix usually used for bacterial immobilization is susceptible to biodegradation in harsh environment. Current study aimed to produce and characterize stable macrocapsules (MCs) of Chlorpyrifos (CP) degrading bacterial consortium using biocompatible calcium alginate matrix coupled with environmentally stable polysulfone. In current study bacterial consortium capable of CP biodegradation was immobilized using calcium alginate in a form of microcapsule (MC) reinforced by being coated with a synthetic polymer polysulfone (PSf) through phase inversion. Consortium comprised of five bacterial strains was immobilized using optimized concentration of sodium alginate (2.5gL^-1), calcium chloride (6gL^-1), biomass (600mgL^-1) and polysulfone (10gL^-1). It has been observed that MCs have high thermal, pH and chemical stability than CAMs. In synthetic media complete biodegradation of CP (100-600mgL^-1) was achieved using macrocapsules (MCs) within 18h. CAMs could be reused effectively only upto 5cycles, contrary to this MCs could be used 13 times to achieve more than >96% CP degradation. Shelf life and reusability studies conducted for MCs indicated unaltered biomass retention and CP biodegradation activity (95%) over 16weeks of storage. MCs achieved complete biodegradation of CP (536mgL^-1) in real industrial wastewater and reused several times effectively. Metabolites (3,5,6-trichloro-2-pyridinol (TCP), 3,5,6-trichloro-2-methoxypyridine (TMP) and diethyl-thiophosphate (DETP) were traced using GC-MS and possible metabolic pathway was constructed. Study indicated MCs could be used for cleanup of CP contaminated wastewater repeatedly, safely, efficiently for a longer period of time.

Toxicity assessment of chlorpyrifos-degrading fungal bio-composites and their environmental risks

Bioremediation techniques coupling with functional microorganisms have emerged as the most promising approaches for in-situ elimination of pesticide residue. However, the environmental safety of bio-products based on microorganisms or engineered enzymes was rarely known. Here, we described the toxicity assessment of two previously fabricated fungal bio-composites which were used for the biodegradation of chlorpyrifos, to clarify their potential risks on the environment and non-target organisms. Firstly, the acute and chronic toxicity of prepared bio-composites were evaluated using mice and rabbits, indicating neither acute nor chronic effect was induced via short-term or continuous exposure. Then, the acute mortality on zebrafish was investigated, which implied the application of fungal bio-composites had no lethal risk on aquatic organisms. Meanwhile, the assessment on soil organic matters suggested that no threat was posed to soil quality. Finally, by monitoring, the germination of cabbage was not affected by the exposure to two bio-products. Therefore, the application of fungal bio-composites for chlorpyrifos elimination cannot induce toxic risk to the environment and non-target organisms, which insured the safety of these engineered bio-products for realistic management of pesticide residue, and provided new insights for further development of bioremediation techniques based on functional microorganisms.

Bacteria contribute to pesticide degradation in cryoconite holes in an Alpine glacier

Organic contaminants deposited on glacier snow and ice are subject to partitioning and degradation processes that determine their environmental fate and, consequently, their accumulation in ice bodies. Among these processes, organic compound degradation by supraglacial bacteria has been investigated to a lesser extent than photo- and chemical degradation. We investigated biodegradation of the organophosphorus insecticide chlorpyrifos (CPF), a xenobiotic tracer that accumulates on glaciers after atmospheric medium- and long-range transport, by installing in situ microcosms on an Alpine glacier to simulate cryoconite hole systems. We found that biodegradation contributed to the removal of CPF from the glacier surface more than photo- and chemical degradation. The high concentration of CPF (2-3 μg g^-1 w.w.) detected in cryoconite holes and the estimated half-life of this compound (35-69 days in glacier environment) indicated that biodegradation can significantly reduce CPF concentrations on glaciers and its runoff to downstream ecosystems. The metabolic versatility of cryoconite bacteria suggests that these habitats might contribute to the degradation of a wide class of pollutants. We therefore propose that cryoconite acts as a "biofilter" by accumulating both pollutants and biodegradative microbial communities. The contribution of cryoconite to the removal of organic pollutants should be included in models predicting the environmental fate of these compounds in cold areas.

Tween 80 surfactant-enhanced bioremediation: toward a solution to the soil contamination by hydrophobic organic compounds

The occurrence of hydrophobic organic compounds (HOCs) in the soil has become a highly significant environmental issue. This problem has been exacerbated by the strong sorption of HOCs to the soils, which makes them unavailable for most remediation processes. More and more works show that surfactant-enhanced biological technologies offer a great potential to clear up HOCs-contaminated soils. This article is a critical review of HOCs removal from soils using Tween 80 (one of the mostly used nonionic surfactants) aided biological remediation technologies. The review begins with a discussion of the fundamentals of Tween 80-enhanced desorption of HOCs from contaminated soils, with special emphasis on the biotoxicity of Tween 80. Successful results obtained by Tween 80-enhanced microbial degradation and phytoremediation are documented and discussed in section 3 and section 4, respectively. Results show Tween 80-enhanced biotechnologies are promising for treating HOCs-contaminated soils. However, considering the fact that most of these scientific studies have only been conducted at the laboratory-scale, many improvements are required before these technologies can be scaled up to the full-scale level. Moreover, further research on mechanisms related to the interaction of Tween 80 with degrading microorganisms and the plants is in high demand.

Non-target effect of continuous application of chlorpyrifos on soil microbes, nematodes and its persistence under sub-humid tropical rice-rice cropping system

Application of pesticide in agricultural fields is "unnecessary evil" for non-target microflora and fauna. Hence, to identify the safer pesticide molecules against non-target microbes, a long-term pesticide experiment was initiated at National Rice Research Institute, Cuttack, India. In the present study, the effect of continuous application of chlorpyrifos (0.5kgha^-1) in rice fields on non-target groups of soil microbes and nematodes was studied for seven seasons (four wet and three dry seasons) during 2009-2013. Treatments were arranged in a randomized complete block design with four replications of chlorpyrifos-treated (0.5kg a.i. ha^-1) (CT) and untreated control (UT) plots. During seven seasons of experimentation, regular application of chlorpyrifos had no significant effect on population of heterotrophic aerobic, anaerobic, oligotrophic and copiotrophic bacteria in CT compared to UT, whereas, population of asymbiotic aerobic nitrogen fixer, nitrifiers, denitrifiers, gram positive and spore-forming bacteria were significantly reduced by nearly 0.25-2 fold in CT than UT. However, comparatively less deviation in population of actinomycetes, fungi, phosphate solubilizing and sulfur oxidizing bacteria were observed in CT than UT. Significant interactions were found between effects of chlorpyrifos with time in population dynamics of microbes. In plant parasitic nematode species, Meloidogyne graminicola (RRKN) and Hirschmanniella spp. (RRN), were significantly lower (p<0.01) in CT compared to UT after first year onwards. The overall observation of five years data indicated that the RRKN population showed a decreasing trend (R²=0.644) whereas RRN showed increasing trend (R²=0.932) in CT. The drastic chlorpyrifos dissipation was noticed after 15 days of application from the initial residue of 0.25mgkg^-1 soil, which indicated that chlorpyrifos residue in rice field soil was not persistent and its half-life was found to be 4.02 days. Overall, the present findings revealed that non-target effect of repetitive application of chloropyrifos (0.5kgha^-1) on soil microbes and nematodes was found less under rice-rice cropping system.