Isolation and characterization of a chlorpyrifos and 3,5,6-trichloro-2-pyridinol degrading bacterium

Enhanced remediation of chlorpyrifos-contaminated soil by immobilized strain Bacillus H27

Chlorpyrifos is a pesticide widely used in agricultural production with a relatively long residual half-life in soil. Addressing the problem of residual chlorpyrifos is of universal concern. In this study, rice hull biochar was used as an immobilized carrier to prepare the immobilized strain H27 for the remediation of chlorpyrifos-contamination soil. Soil microorganisms after remediation were investigated by ecotoxicological methods. The immobilized strain H27 had the highest removal rate of chlorpyrifos when 10% bacterial solution was added to the liquid medium containing 0.075-0.109 mm diameter biochar cultured for 22 hr. This study on the removal of chlorpyrifos by immobilized strain H27 showed that the initial concentration of chlorpyrifos in solution was 25 mg/L, and the removal rate reached 97.4% after 7 days of culture. In the soil, the removal rate of the immobilized bacteria group increased throughout the experiment, which was significantly higher than that of the free bacteria and biochar treatment groups. The Biolog-ECO test, T-RFLP and RT-RCR were used to study the effects of the soil microbial community and nitrogen cycling functional genes during chlorpyrifos degradation. It was found that ICP group had the highest diversity index among the four treatment groups. The microflora of segment containing 114 bp was the dominant bacterial community, and the dominant microflora of the immobilized bacteria group was more evenly distributed. The influence of each treatment group on ammonia-oxidizing bacteria (AOB) was greater than on ammonia-oxidizing archaea (AOA). This study offers a sound scientific basis for the practical application of immobilized bacteria to reduce residual soil pesticides.

Effects of cylindrospermopsin, chlorpyrifos and their combination in a SH-SY5Y cell model concerning developmental neurotoxicity

The cyanotoxin cylindrospermopsin (CYN) has been postulated to cause neurotoxicity, although the studies in this concern are very few. In addition, some studies in vitro indicate its possible effects on development. Furthermore, pesticides can be present in the same environmental samples as cyanotoxins. Therefore, chlorpyrifos (CPF) has been one of the most common pesticides used worldwide. The aim of this report was to study the effects of CYN, isolated and in combination with CPF, in a developmental neurotoxicity in vitro model. The human neuroblastoma SH-SY5Y cell line was exposed during 6 days of differentiation to both toxics to study their effects on cell viability and neurite outgrowth. To further evaluate effects of both toxicants on cholinergic signaling, their agonistic and antagonistic activities on the α7 homomeric nicotinic acetylcholine receptor (nAChR) were studied upon acute exposure. Moreover, a transcriptomic analysis by qPCR was performed after 6 days of CYN-exposure during differentiation. The results showed a concentration-dependent decrease on both cell viability and neurite outgrowth for both toxics isolated, leading to effective concentration 20 (EC20) values of 0.35 µM and 0.097 µM for CYN on cell viability and neurite outgrowth, respectively, and 100 µM and 58 µM for CPF, while the combination demonstrated no significant variations. In addition, 95 µM and 285 µM CPF demonstrated to act as an antagonist to nicotine on the nAChR, although CYN up to 2.4 µM had no effect on the efficacy of these receptors. Additionally, the EC20 for CYN (0.097 µM) on neurite outgrowth downregulated expression of the 5 genes NTNG2 (netrin G2), KCNJ11 (potassium channel), SLC18A3 (vesicular acetylcholine transporter), APOE (apolipoprotein E), and SEMA6B (semaphorin 6B), that are all important for neuronal development. Thus, this study points out the importance of studying the effects of CYN in terms of neurotoxicity and developmental neurotoxicity.

Microbiology and Biochemistry of Pesticides Biodegradation

Pesticides are chemicals used in agriculture, forestry, and, to some extent, public health. As effective as they can be, due to the limited biodegradability and toxicity of some of them, they can also have negative environmental and health impacts. Pesticide biodegradation is important because it can help mitigate the negative effects of pesticides. Many types of microorganisms, including bacteria, fungi, and algae, can degrade pesticides; microorganisms are able to bioremediate pesticides using diverse metabolic pathways where enzymatic degradation plays a crucial role in achieving chemical transformation of the pesticides. The growing concern about the environmental and health impacts of pesticides is pushing the industry of these products to develop more sustainable alternatives, such as high biodegradable chemicals. The degradative properties of microorganisms could be fully exploited using the advances in genetic engineering and biotechnology, paving the way for more effective bioremediation strategies, new technologies, and novel applications. The purpose of the current review is to discuss the microorganisms that have demonstrated their capacity to degrade pesticides and those categorized by the World Health Organization as important for the impact they may have on human health. A comprehensive list of microorganisms is presented, and some metabolic pathways and enzymes for pesticide degradation and the genetics behind this process are discussed. Due to the high number of microorganisms known to be capable of degrading pesticides and the low number of metabolic pathways that are fully described for this purpose, more research must be conducted in this field, and more enzymes and genes are yet to be discovered with the possibility of finding more efficient metabolic pathways for pesticide biodegradation.

Identification of two possible metabolic pathways responsible for the biodegradation of 3, 5, 6-trichloro-2-pyridinol in Micrococcus luteus ML

3, 5, 6-Trichloro-2-pyridinol (TCP) is a metabolite of the insecticide chlorpyrifos and the herbicide triclopyr, and it is higher toxic than the parent compounds. Microbially-mediated mineralization appears to be the primary degradative pathway and the important biological process of detoxification. However, little information is available on TCP complete metabolic pathways and mechanisms. In this study, the degradation of TCP was studied with a novel strain Micrococcus luteus ML isolated from a stable TCP degrading microbiota. Strain ML was capable of degrading 61.6% of TCP (50 mg/L) and 35.4% of chlorpyrifos (50 mg/L) at 24 h and 48 h under the optimal conditions (temperature: 35 °C; pH: 7.0), respectively. It could also degrade 3, 5-dichloro-2-pyridone, 6-chloropyridin-2-ol, 2-hydroxypyridine and phoxim when provided as sole carbon and energy sources. Seven TCP intermediate metabolites were detected in strain ML and two possible degradation pathways of TCP were proposed on the basis of LC-MS analysis. Both the hydrolytic-oxidative dechlorination pathway and the denitrification pathway might be involved in TCP biodegradation by strain ML. To the best of our knowledge, this is the first report on two different pathways responsible for TCP degradation in one strain, and this finding also provides novel information for studying the metabolic mechanism of TCP in pure culture.

Evidence for enhanced dissipation of chlorpyrifos in an agricultural soil inoculated with Serratia rubidaea strain ABS 10

The insecticide ¹⁴C-chlorpyrifos was found mineralized in a Tunisian soil with repeated exposure to it. From this soil, a bacterial strain was isolated that was able to grow in a minimal salt medium (MSM) supplemented with 25 mg L^-1 of chlorpyrifos. It was characterized as Serratia rubidaea strain ABS 10 using morphological and biochemical analyses, as well as 16S rRNA sequencing. In a liquid culture, the S. rubidaea strain ABS 10 was able to dissipate chlorpyrifos almost entirely within 48 h of incubation. Although the S. rubidaea strain ABS 10 was able to grow in an MSM supplemented with chlorpyrifos and dissipate it in a liquid culture, it was not able to mineralize ¹⁴C-chlorpyrifos. Therefore, it can be concluded that the dissipation capability of this bacteria might be attributed to its capacity to adsorb CHL. It can also be ascribed to other reasons such as the formation of biogenic non-extractable residues. In both non-sterile and sterile soil inoculated with S. rubidaea strain ABS 10, chlorpyrifos was more rapidly dissipated than in controls with DT₅₀ of 1.38 and 1.05 days, respectively.

Degradation insight of organophosphate pesticide chlorpyrifos through novel intermediate 2,6-dihydroxypyridine by Arthrobacter sp. HM01

Organophosphates (OPs) are hazardous pesticides, but an indispensable part of modern agriculture; collaterally contaminating agricultural soil and surrounding water. They have raised serious food safety and environmental toxicity that adversely affect the terrestrial and aquatic ecosystems and therefore, it become essential to develop a rapid bioremediation technique for restoring the pristine environment. A newly OPs degrading Arthrobacter sp. HM01 was isolated from pesticide-contaminated soil and identified by a ribotyping (16S rRNA) method. Genus Arthrobacter has not been previously reported in chlorpyrifos (CP) degradation, which shows 99% CP (100 mg L-1) degradation within 10 h in mMSM medium and also shows tolerance to a high concentration (1000 mg L-1) of CP. HM01 utilized a broad range of OPs pesticides and other aromatic pollutants including intermediates of CP degradation as sole carbon sources. The maximum CP degradation was obtained at pH 7 and 32 °C. During the degradation, a newly identified intermediate 2,6-dihydroxypyridine was detected through TLC/HPLC/LCMS analysis and a putative pathway was proposed for its degradation. The study also revealed that the organophosphate hydrolase (opdH) gene was responsible for CP degradation, and the opdH-enzyme was located intracellularly. The opdH enzyme was characterized from cell free extract for its optimum pH and temperature requirement, which was 7.0 and 50 °C, respectively. Thus, the results revealed the true potential of HM01 for OPs-bioremediation. Moreover, the strain HM01 showed the fastest rate of CP degradation, among the reported Arthrobacter sp.

Microbial detoxification of dimethoate through mediated hydrolysis by Brucella sp. PS4: molecular profiling and plant growth-promoting traits

High toxicity of dimethoate requires efficient ways for detoxification and removal of its residues in contaminated environments. Microbial remediation is a process that utilizes the degradation potential of microbes to provide a cost-effective and reliable approach for pesticide abatement. For this purpose, a dimethoate-degrading bacterium Brucella sp. was isolated from a contaminated agricultural soil sample in Multan, Pakistan. This isolate was found to tolerate up to 100 ppm of dimethoate in minimal salt medium and was further evaluated for plant growth-promoting traits. The strain gave positive results for amylase, ammonia, and catalase production, while other traits such as indole acetic acid production and potassium solubilization were also confirmed. Thus, the strain could play an important role for plant nutrient transmission in the plant rhizosphere. Optimization of growth parameters (i.e., pH and temperature) depicted the potential of PS4 to be best tolerating dimethoate, with maximum cell density at λ 600 nm. Optimum pH and temperature for growth were found to be 6 and 35 °C, respectively. Based on optimization results as well as different attributes, the rhizospheric bacterial isolate PS4 was further subjected to a batch degradation experiment under different concentrations of dimethoate (25, 50, 75, and 100 ppm). This promising dimethoate-degrading isolate was found to degrade 83% of dimethoate (at 100 ppm) within a period of 7 days. In addition, it degraded 88% of dimethoate at 50 ppm, indicating that the bacterial isolate utilized dimethoate solely as a source of energy. The strain followed the first order reaction kinetics, depicting its dependence on dimethoate as energy and carbon source. Molecular profiling further supported its role in plant growth promotion and multi-stress tolerance. This research showed that Brucella sp. is capable of degrading dimethoate, and therefore, it would be useful in the investigation of novel bioremediation techniques at pesticide-polluted sites.

Growth, respiratory activity and chlorpyrifos biodegradation in cultures of Azotobacter vinelandii ATCC 12837

This study aimed to evaluate the growth, respiratory activity, and biodegradation of chlorpyrifos in cultures of Azotobacter vinelandii ATCC 12837. A strategy based on the modification of culture media and aeration conditions was carried out to increase the cell concentration of A. vinelandii, in order to favor and determine its tolerance to chlorpyrifos and its degradation ability. The culture in shaken flasks, using sucrose as a carbon source, significantly improved the growth compared to media with mannitol. When the strain was cultivated under oxygen-limited (5.5, 11.25 mmol L⁻¹ h⁻¹) and no-oxygen-limited conditions (22 mmol L⁻¹ h⁻¹), the growth parameters were not affected. In cultures in a liquid medium with chlorpyrifos, the bacteria tolerated a high pesticide concentration (500 ppm) and the growth parameters were improved even under conditions with a reduced carbon source (sucrose 2 g L⁻¹). The strain degraded 99.6% of chlorpyrifos at 60 h of cultivation, in co-metabolism with sucrose; notably, A. vinelandii ATCC 12837 reduced by 50% the initial pesticide concentration in only 6 h (DT₅₀).

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.

Environmental Occurrence, Toxicity Concerns, and Degradation of Diazinon Using a Microbial System

Diazinon is an organophosphorus pesticide widely used to control cabbage insects, cotton aphids and underground pests. The continuous application of diazinon in agricultural activities has caused both ecological risk and biological hazards in the environment. Diazinon can be degraded via physical and chemical methods such as photocatalysis, adsorption and advanced oxidation. The microbial degradation of diazinon is found to be more effective than physicochemical methods for its complete clean-up from contaminated soil and water environments. The microbial strains belonging to Ochrobactrum sp., Stenotrophomonas sp., Lactobacillus brevis, Serratia marcescens, Aspergillus niger, Rhodotorula glutinis, and Rhodotorula rubra were found to be very promising for the ecofriendly removal of diazinon. The degradation pathways of diazinon and the fate of several metabolites were investigated. In addition, a variety of diazinon-degrading enzymes, such as hydrolase, acid phosphatase, laccase, cytochrome P450, and flavin monooxygenase were also discovered to play a crucial role in the biodegradation of diazinon. However, many unanswered questions still exist regarding the environmental fate and degradation mechanisms of this pesticide. The catalytic mechanisms responsible for enzymatic degradation remain unexplained, and ecotechnological techniques need to be applied to gain a comprehensive understanding of these issues. Hence, this review article provides in-depth information about the impact and toxicity of diazinon in living systems and discusses the developed ecotechnological remedial methods used for the effective biodegradation of diazinon in a contaminated environment.

Degradation studies of pendimethalin by indigenous soil bacterium Pseudomonas strain PD1 using spectrophotometric scanning and FTIR

In this study pendimethalin degrading indigenous soil bacterium was isolated from rice field (supplemented with pendimethalin) and identified as, Pseudomonas strain PD1 on the basis of 16S rRNA phylogenetic analysis. Biodegradation of pendimethalin by this strain was evaluated by spectrophotometric scanning and FTIR analysis of degraded compounds in minimal salt media. Decrease in concentration of pendimethalin at λ_max (430 nm) under spectrophotometric scanning is a measurement of time taken by bacterium strain PD1 to degrade pendimethalin. Degraded products were further analyzed by comparing stretching and bending pattern of chemical groups attached to compounds using FTIR spectroscopy. FTIR profile represented disappearance of nitrate group in degraded product by bacterium strain PD1 in minimal salt medium. Molecular docking of pendimethalin on nitro-reductase was done to suggest first enzyme of pathway used by bacterium strain PD1 to degrade pendimethalin. Analysis on degradation by strain PD1 shows that newly isolated strain PD1 can degrade 77.05% of pendimethalin at 50 mgL^-1 concentration in 30 h incubation under room temperature. Thus, the study here shed a light on degradation potential of Pseudomonas.

Beneficial microbiomes for bioremediation of diverse contaminated environments for environmental sustainability: present status and future challenges

Over the past few decades, the rapid development of agriculture and industries has resulted in contamination of the environment by diverse pollutants, including heavy metals, polychlorinated biphenyls, plastics, and various agrochemicals. Their presence in the environment is of great concern due to their toxicity and non-biodegradable nature. Their interaction with each other and coexistence in the environment greatly influence and threaten the ecological environment and human health. Furthermore, the presence of these pollutants affects the soil quality and fertility. Physicochemical techniques are used to remediate such environments, but they are less effective and demand high costs of operation. Bioremediation is an efficient, widespread, cost-effective, and eco-friendly cleanup tool. The use of microorganisms has received significant attention as an efficient biotechnological strategy to decontaminate the environment. Bioremediation through microorganisms appears to be an economically viable and efficient approach because it poses the lowest risk to the environment. This technique utilizes the metabolic potential of microorganisms to clean up contaminated environments. Many microbial genera have been known to be involved in bioremediation, including Alcaligenes, Arthrobacter, Aspergillus, Bacillus, Burkholderia, Mucor, Penicillium, Pseudomonas, Stenotrophomonas, Talaromyces, and Trichoderma. Archaea, including Natrialba and Haloferax, from extreme environments have also been reported as potent bioresources for biological remediation. Thus, utilizing microbes for managing environmental pollution is promising technology, and, in fact, the microbes provide a useful podium that can be used for an enhanced bioremediation model of diverse environmental pollutants.

Potential of formulated Dyadobacter jiangsuensis strain 12851 for enhanced bioremediation of chlorpyrifos contaminated soil

Chlorpyrifos (O, O-diethyl O-3, 5, 6-trichloropyridin-2-yl phosphorothioate) is a toxic and chlorinated organic contaminant in soils across the globe. The present study examines the chlorpyrifos (CP) degrading potential of gram-negative bacterium Dyadobacter jiangsuensis (MTCC 12851), to be a promising and sustainable remedial approach. The proliferation of D. jiangsuensis in the chlorpyrifos spiked minimal salt media indicated the ability of this strain to utilize CP as a sole carbon source and also confirmed the utilization of 3,5,6- trichloro-2-pyridinyl (TCP) through silver nitrate assay. The strain 12851 degraded 80.36% and 76.93% chlorpyrifos (CP) in aqueous medium and soil environment, respectively. The water dispersible granules (WDG) of 45% (v/w) inoculum (bacterial suspension) were developed using talcum powder, acacia gum and alginic acid as key ingredients. The formulated strain (12851) achieved 21.13% enhanced CP degradation in soil under microcosm condition as compared to the unformulated one on 15th day of the treatment. The intermediate metabolites namely 3,5,6-trichloro-2-pyridinol (TCP), tetrahydropyridine, thiophosphate and phenol, 1, 3-bis (1,1-dimethylethyl) were detected during the CP degradation. The current investigation reveals D. jiangsuensis as a potential microbe for CP degradation and opens up the possibility of exploiting its formulations to remediate the CP polluted soils.

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.

Novel degradation pathways for Chlorpyrifos and 3, 5, 6-Trichloro-2-pyridinol degradation by bacterial strain Bacillus thuringiensis MB497 isolated from agricultural fields of Mianwali, Pakistan

Over use of organophosphate pesticides including Chlorpyrifos (CPF) has led to contamination of soil and water resources, resulting in serious health problems in humans along with other non-target organisms. The current study was aimed to investigate Chlorpyrifos as well as 3, 5, 6-Trichloro-2-pyridinol (TCP) biodegradation tendency of bacterial strain Bacillus thuringiensis MB497 isolated from wheat/cotton fields of Dera Saleemabad, Mianwali, Pakistan, having a history of heavy Organophosphate pesticides application. HPLC analysis revealed almost 99% degradation of the spiked CPF (200 mg L^-1) in M-9 broth, soil slurry and soil microcosm by MB497 after 9 days of incubation. Strain MB497 was also able to degrade and transform TCP (28 mg L^-1), up to 90.57% after 72 h of incubation in M-9 broth. A novel compound Di-isopropyl methanephosphonate along with known products of 3, 5, 6-Trichloro-2-pyridinol (TCP), Diethyl thiophospsphate and Phosphorothioic acid were detected as metabolites of CPF by GCMS analysis. Three novel metabolites of TCP (p-Propyl phenol, 2-Ethoxy-4, 4, 5, 5-tetramethyloxazoline and 3-(2, 4, 5-Trichlorophenoxy)-1-propyne) were identified after 72 h. Based on these metabolites, new/amended metabolic pathways for CPF and TCP degradation in these bacteria has been suggested.

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.

Biodegradation of CP/TCP by a constructed microbial consortium after comparative bacterial community analysis of long-term CP domesticated activated sludge

The objective of this study was to construct a microbial consortium for effective biodegradation of chlorpyrifos (CP) and its hydrolysis product, 3,5,6-Trichloro-2-pyridinol (TCP). A activated sludge from an organophosphorus pesticide factory was domesticated under long-term (20 weeks) CP stress, and the dynamic change in bacterial communities was analyzed by high-throughput sequencing. Then, a microbial consortium MC-BSPK was constructed of Bacillus sp. MC-B, Serratia sp. MC-S, Pseudomonas sp. MC-P, and Klebsiella sp. MC-K, which were significantly enriched during the domestication process. The biodegradation capacities of the microbial consortium MC-BSPK reached 100% for CP within 9 days and 88.61% for TCP within 15 days under the optimized degradation conditions (pH 8.0 and 31 °C). High-performance liquid chromatography (HPLC) revealed that CP could be degraded by the microbial consortium MC-BSPK into TCP, probably through hydrolysis of the P-O ester bond, and further degraded into other small molecules. A bioassay revealed that the virulence of CP toward Drosophila melanogaster W1118 was clearly reduced by the microbial consortium MC-BSPK biodegradation. Thus, the easily constructed microbial consortium MC-BSPK with high CP/TCP degradation capacities has the potential for application in pesticide-contaminated bioremediation.

Mitigation of organophosphate pesticide pollution in agricultural watersheds

Adsorption and biodegradation processes for four organophosphate pesticides (chlorpyrifos, diazinon, fenthion, dichlorvos) in wetlands and agricultural drains in Meric-Ergene Basin, Turkey have been investigated. K_oc (organic carbon normalized partition coefficient) values for all pesticides except diazinon were higher in more aromatic Pamuklu Drain sediments, indicating the possible influence of aromaticity on the extent of adsorption. The average half-lives of pesticides in Gala Lake sediments and Pamuklu agricultural drain sediments ranged from 2.25 to 69.31 days with chlorpyrifos exhibiting the slowest biotransformation rate and dichlorvos having the fastest biotransformation rate. The presence of humic substances and hydroperiod of wetlands have been identified as possible factors that affected the behavior of organophosphate pesticides in this study. The results from this study provide insight into the constructed wetland design offered for the mitigation of organophosphate pesticides in the basin.

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.

Ligninolytic behavior of the white-rot fungus Stereum ostrea under influence of culture conditions, inducers and chlorpyrifos

The production of three ligninolytic enzymes, laccase (LAC), manganese peroxidase (MnP) and lignin peroxidase (LiP) by the white-rot fungus, Stereum ostrea, was significantly more in Koroljova liquid medium in the presence of chlorpyrifos under shaking conditions than under stationary conditions. These enzymes were secreted into the broth to the extent of 214.37, 82.75 and 8.05 U/ml under influence of chlorpyrifos on 10th day of incubation in comparison with 138.06, 51.85 and 6.44 U/ml, respectively, under similar conditions in control. Maximum production of LAC, MnP and LiP on liquid medium with/without chlorpyrifos under stationary conditions did not exceed 80-85, 33-40, 0.6-0.7 U/ml, respectively. Among lignosulfonic acid, veratryl alcohol (VA), gallic acid (GA) and tannic acid tested, GA induced maximum production of LAC (300.53 U/ml) and MnP (181.66 U/ml) after 10 days of growth in the presence of chlorpyriphos, while maximum LiP (1.134 U/ml) was produced when grown with the inducer VA during this period. Our data suggest that chlorpyrifos and inducers interacted positively in producing higher amounts of the ligninolytic enzymes in S. ostrea.

Rapid degradation of the organophosphate pesticide - Chlorpyrifos by a novel strain of Pseudomonas nitroreducens AR-3

The indiscriminate use of pesticides leads to serious food safety and toxicity issues and threatens the environment and biodiversity. Pseudomonas nitroreducens AR-3 isolated from pesticide contaminated agricultural soil removed 97% of chlorpyrifos (CP) in just 8 h, in a mineral salt medium (MSM) containing glucose (1.0 g/L) and yeast extract (0.5 g/L) at 30 °C and 2% (v/v) inoculum when challenged with 100 mg/L CP. 3, 5, 6-trichloro 2-pyridinol (TCP), the degradation product of CP was detected only in low levels, indicating its further degradation. Organophosphate hydrolase (OPH), the enzyme considered responsible for CP degradation, had an intracellular localization. Crude OPH (1 mg/ml) removed 42% of 100 mg/L chlorpyrifos in just 2 h, indicating a rapid rate of degradation. Ultra-fast degradation of chlorpyrifos with an inducible OPH marks the potential of P. nitroreducens AR-3 for bioremediation of organophosphates. The strain AR-3 has the fastest rate of organophosphate degradation reported till date among Pseudomonads.

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.

Biodegradation of chlorpyrifos and 3,5,6-trichloro-2-pyridinol by the epiphytic yeasts Rhodotorula glutinis and Rhodotorula rubra

The possible involvement of the epiphytic yeasts Rhodotorula glutinis and Rhodotorula rubra in the biodegradation of the insecticide chlorpyrifos and its metabolite 3,5,6-trichloro-2-pyridinol (TCP), in pure cultures and in plant surfaces (tomato fruits) was investigated. Higher biodegradation rates were observed as the concentration of chlorpyrifos and the inoculum of the microorganisms were increased, while the yeasts proved to be more active at 25 and 15 °C. The presence of glucose in the mineral nutrient medium, as an extra source of carbon, delayed the biodegradation by Rhodotorula glutinis, while Rhodotorula rubra proved to be more active. The detection and quantification of the parent compound and TCP was successfully achieved using a LC/MS/MS chromatographic system. The in vitro enzymatic assays applied suggested that esterases may be involved in the biodegradation of chlorpyrifos, a fact that was further enhanced after the addition of the synergists triphenyl phosphate, diethyl maleate and piperonyl butoxide in the biodegradation trials. The decrease of chlorpyrifos residues on tomato fruits confirmed the corresponding on pure cultures, resulting in the suggestion that the yeasts R. glutinis and R. rubra can possibly be used successfully for the removal or detoxification of chlorpyrifos residues on tomatoes.

Combined effects of antimony and sodium diethyldithiocarbamate on soil microbial activity and speciation change of heavy metals. Implications for contaminated lands hazardous material pollution in nonferrous metal mining areas

The combined effects of antimony (Sb) and sodium diethyldithiocarbamate (DDTC), a common organic flotation reagent, on soil microbial activity and speciation changes of heavy metals were investigated for the first time. The results showed that the exchangeable fraction of Sb was transformed to a stable residual fraction during the incubation period, and the addition of DDTC promoted the transformation compared with single Sb pollution, probably because DDTC can react with heavy metals to form a complex. In addition, the presence of DDTC and Sb inhibited the soil microbial activity to varying degrees. The growth rate constant k of different interaction systems was in the following order on the 28th day: control group ≥ single DDTC pollution > combined pollution > single Sb pollution. A correlation analysis showed that the concentration of exchangeable Sb was the primary factor that affected the toxic reaction under combined pollution conditions, and it significantly affected the characteristics of the soil microorganisms. All the observations provide useful information for a better understanding of the toxic effects and potential risks of combined Sb and DDTC pollution in antimony mining areas.

Simultaneous biodegradation of bifenthrin and chlorpyrifos by Pseudomonas sp. CB2

The degradation of bifenthrin (BF) and chlorpyrifos (CP), either together or individually, by a bacterial strain (CB2) isolated from activated sludge was investigated. Strain CB2 was identified as belonging to genus Pseudomonas based on the morphological, physiological, and biochemical characteristics and a homological analysis of the 16S rDNA sequence. Strain CB2 has the potential to degrade BF and CP, either individually or in a mixture. The optimum conditions for mixture degradation were as follows: OD_600nm = 0.5; incubation temperature = 30°C; pH = 7.0; BF-CP mixture (10 mg L^-1 of each). Under these optimal conditions, the degradation rate constants (and half-lives) were 0.4308 d^-1 (1.61 d) and 0.3377 d^-1 (2.05 d) for individual BF and CP samples, respectively, and 0.3463 d^-1 (2.00 d) and 0.2931 d^-1 (2.36 d) for the BF-CP mixture. Major metabolites of BF and CP were 2-methyl-3-biphenylyl methanol and 3,5,6-trichloro-2-pyridinol, respectively. No metabolite bioaccumulation was observed. The ability of CB2 to efficiently degrade BF and CP, particularly in a mixture, may be useful in bioremediation efforts.

Simultaneous hydrolysis of carbaryl and chlorpyrifos by Stenotrophomonas sp. strain YC-1 with surface-displayed carbaryl hydrolase

Many sites are often co-contaminated with multiple pesticides. To date, there are no reports on simultaneous degradation of different classes of pesticides by a natural microorganism. In this work, we aim at constructing a live biocatalyst able to simultaneously hydrolyze carbaryl and chlorpyrifos. For this purpose, carbaryl hydrolase (CH) was displayed on the cell surface of a chlorpyrifos-degrading bacterium Stenotrophomonas sp. strain YC-1 using N- and C-terminal domain of ice nucleation protein (INPNC) from Pseudomonas syringae INA5 as an anchoring motif. The localization of INPNC-CH fusion protein in the outer membrane fraction was demonstrated by cell fractionation followed by Western blot analysis. Surface display of INPNC-CH was further confirmed by proteinase accessibility experiment and immunofluorescence microscope. CH was present in an active form on cell surface without causing any growth inhibition, suggesting that the INP-based display system is a useful tool for surface expression of macromolecular heterologous proteins on the bacterial cell surface. Because surface-displayed CH has free access to pesticides, this bacterium can be used as a whole-cell biocatalyst for efficient hydrolysis of pesticides.

Biodegradation of Quinalphos by a Soil Bacterium-Bacillus subtilis

BACKGROUND AND OBJECTIVE

A widely used pesticide quinalphos (O, O-diethyl O-quinoxalin-2-yl phosphorothioate) may be an undesirable and persistent pollutant to non-target environments like rivers and other ecosystems. The objective of this study was to isolate a potential degradant bacterium of quinalphos from polluted soils and test its fitness under various culture conditions.

MATERIALS AND METHODS

A soil bacterium strain, capable of utilizing quinalphos as its sole source of carbon and energy was isolated from soil by enrichment method on a minimal salts medium (MSM). On the basis of morphological, biochemical and 16S rRNA gene sequence analysis the bacterium is a species of the genus Bacillus and it was closely related to Bacillus subtilis. Quinalphos degrading capabilities of this bacterium were assessed under different culture conditions. Quinalphos degradation data were analysed byusing a two-way ANOVA analysis with the Statistica v.10.

RESULTS

Bacillus subtilis grew on quinalphos with a generation time of 32.34 min or 0.54 h in the logarithmic phase. Maximum degradation of quinalphos was observed with an inoculum of 1.0 optical density, around pH-7.5 and at an optimum temperature of 35-37°C. Among the additional carbon and nitrogen sources, carbon source-glucose and nitrogen source-yeast extract marginally improved the rate of degradation of quinalphos. Gas chromatography-mass spectrometry (GC-MS) analysis of the culture of B. subtilis grown on quinalphos indicated the formation of one main metabolite-quinoxaline.

CONCLUSION

The B. subtilis strain discovered in this study has a unique combination of abilities to degrade quinalphos and it is therefore suitable candidate bioremediator of quinalphos polluted environments.

Solvent-dependent binding interactions of the organophosphate pesticide, chlorpyrifos (CPF), and its metabolite, 3,5,6-trichloro-2-pyridinol (TCPy), with Bovine Serum Albumin (BSA): A comparative fluorescence quenching analysis

Analysis of the interaction of pesticides and their metabolites with the cellular proteins has drawn considerable attention in past several years to understand the effect of pesticides on environment and mankind. In this study, we have investigated the binding interaction of Bovine Serum Albumin (BSA) with a widely used organophosphorous insecticide chlorpyrifos (CPF), and its stable metabolite, 3,5,6-trichloro-2-pyridinol (TCPy) to provide a comparative analysis of the two molecules by employing various spectroscopic techniques viz., UV-vis absorption, Circular Dichroism (CD), and Fluorescence spectroscopy. The fluorescence quenching studies of BSA emission in two different solvents viz., water and methanol in presence of CPF and TCPy have led to the revelation of several interesting facts about the pesticide-protein interaction. It has been found that both the molecules cause static quenching of BSA emission as seen from the Stern-Volmer constant (K_sv) irrespective of the solvent used for the analysis. While TCPy is a stronger quencher in water, it exhibits comparable quenching capacity with CPF in methanol. The solvent dependent differential binding interaction of the two molecules finally indicates possibility of diverse bio-distribution of the pesticides within human body. The UV-vis and CD spectra of BSA in presence of the test molecules have unravelled that the molecules formed ground state complex that are highly reversible in nature and have minimal effect on the protein secondary structure. Furthermore it is also understood that structural changes of BSA in presence of CPF is significantly higher compared to that in presence of TCPY.

Isolation and Molecular Characterization of Novel Chlorpyrifos and 3,5,6-trichloro-2-pyridinol-degrading Bacteria from Sugarcane Farm Soils

Chlorpyrifos (CP) is one of the most widely used organophosphate pesticides in agriculture worldwide, but its extensive use has led to the contamination of various soil and water systems. Microbial bioremediation is considered to be one of the most viable options for the removal of CP from the environment; however, little is known about the soil bacterial diversity that degrade CP. Sequential soil and liquid culture enrichments enabled the isolation of bacterial CP degraders with sequence homologies to Xanthomonas sp., Pseudomonas sp., and Rhizobium sp. The efficacy of the three isolated strains: Xanthomonas sp. 4R3-M1, Pseudomonas sp. 4H1-M3, and Rhizobium sp. 4H1-M1 was further investigated for biodegradation of CP and its primary metabolic product, 3,5,6-trichloro-2-pyridinol (TCP). The results indicate that all three bacterial strains almost completely metabolized CP (10 mg/L) and TCP, occurring as a metabolic degradation product, in mineral salt media as a sole source of carbon and nitrogen. The isolated bacterial strains Xanthomonas sp. 4R3-M1 and Pseudomonas sp. 4H1-M3 could also degrade TCP (10 mg/L) as a sole carbon and nitrogen source, when provided externally. Thus, these bacterial strains may be effective in practical application of bioremediation of both CP and TCP.

Bioaugmentation as a strategy for the remediation of pesticide-polluted soil: A review

Bioaugmentation, a green technology, is defined as the improvement of the degradative capacity of contaminated areas by introducing specific microorganisms, has emerged as the most advantageous method for cleaning-up soil contaminated with pesticides. The present review discusses the selection of pesticide-utilising microorganisms from various sources, their potential for the degradation of pesticides from different chemical classes in liquid media as well as soil-related case studies in a laboratory, a greenhouse and field conditions. The paper is focused on the microbial degradation of the most common pesticides that have been used for many years such as organochlorinated and organophosphorus pesticides, triazines, pyrethroids, carbamate, chloroacetamide, benzimidazole and derivatives of phenoxyacetic acid. Special attention is paid to bacterial strains from the genera Alcaligenes, Arthrobacter, Bacillus, Brucella, Burkholderia, Catellibacterium, Pichia, Pseudomonas, Rhodococcus, Serratia, Sphingomonas, Stenotrophomonas, Streptomyces and Verticillum, which have potential applications in the bioremediation of pesticide-contaminated soils using bioaugmentation technology. Since many factors strongly influence the success of bioaugmentation, selected abiotic and biotic factors such as pH, temperature, type of soil, pesticide concentration, content of water and organic matter, additional carbon and nitrogen sources, inoculum size, interactions between the introduced strains and autochthonous microorganisms as well as the survival of inoculants were presented.

Influence of environmental factors on biodegradation of quinalphos by Bacillus thuringiensis

BACKGROUND

The extensive and intensive uses of organophosphorus insecticide-quinalphos in agriculture, pose a health hazard to animals, humans, and environment because of its persistence in the soil and crops. However, there is no much information available on the biodegradation of quinalphos by the soil micro-organisms, which play a significant role in detoxifying pesticides in the environment; so research is initiated in biodegradation of quinalphos.

RESULTS

A soil bacterium strain, capable of utilizing quinalphos as its sole source of carbon and energy, was isolated from soil via the enrichment method on minimal salts medium (MSM). On the basis of morphological, biochemical and 16S rRNA gene sequence analysis, the bacterium was identified as to be Bacillus thuringiensis. Bacillus thuringiensis grew on quinalphos with a generation time of 28.38 min or 0.473 h in logarithmic phase. Maximum degradation of quinalphos was observed with an inoculum of 1.0 OD, an optimum pH (6.5-7.5), and an optimum temperature of 35-37 °C. Among the additional carbon and nitrogen sources, the carbon source-sodium acetate and nitrogen source-a yeast extract marginally improved the rate of degradation of quinalphos.

CONCLUSIONS

Display of degradation of quinalphos by B. thuringiensis in liquid culture in the present study indicates the potential of the culture for decontamination of quinalphos in polluted environment sites.

Effect of chlorpyrifos on soil microbial diversity and its biotransformation by Streptomyces sp. HP-11

The application of pesticides in agricultural fields not only reaches the target pests but also with soil where it interacts with soil microorganisms resulting in change of microbial diversity. Chlorpyrifos (CP) is one such organophosphorous insecticide most widely used against various insects, termites, and beetles throughout the globe. In the present work, the effect of CP on soil microbial population was assessed by the cultivable method. The fertile soil which does not have a history of any pesticide application was treated with 100 and 200 µg/g of CP along with control which received only sterile water and incubated for 1, 7, and 14 days. The soil amended with the insecticide showed decrease in the number of colony forming units (CFU) of bacteria and fungi. However, Streptomyces sp. HP-11 which tolerated high concentration and also inhibited fungal population was further selected for biodegradation studies. After 14 days of incubation in Mineral salt media (MSM), the strain HP-11 biotransformed CP into 3, 5, 6-trichloro-2-pyridinol (TCP) and Diethyl Phosphorothioate (DETP), and its formation was confirmed by the m/z peak of LC-MS analysis, which was later metabolized to unknown polar metabolites. The results obtained highlights that the application of chlorpyrifos favored the Actinomycete growth in the soil, thereby inhibiting other microorganisms and the strain HP-11 harbors metabolic pathway for detoxification of CP and its hydrolysis product TCP into polar metabolites, thus suggesting the strain HP-11 will be a potential bioaugmenting agent for the bioremediation of chlorpyrifos contaminated soil and water.

Determination of organophosphorus pesticides and their major degradation product residues in food samples by HPLC-UV

A simple method based on dispersive solid-phase extraction (DSPE) and dispersive liquid-liquid microextraction method based on solidification of floating organic droplets (DLLME-SFO) was developed for the extraction of chlorpyrifos (CP), chlorpyrifos-methyl (CPM), and their main degradation product 3,5,6-trichloro-2-pyridinol (TCP) in tomato and cucumber samples. The determination was carried out by high performance liquid chromatography with ultraviolet detection (HPLC-UV). In the DSPE-DLLME-SFO, the analytes were first extracted with acetone. The clean-up of the extract by DSPE was carried out by directly adding activated carbon sorbent into the extract solution, followed by shaking and filtration. Under the optimum conditions, the proposed method was sensitive and showed a good linearity within a range of 2-500 ng/g, with the correlation coefficients (r) varying from 0.9991 to 0.9996. The enrichment factors ranged from 127 to 138. The limit of detections (LODs) were in the range of 0.12-0.68 ng/g, and the relative standard deviations (RSDs) for 50 ng/g of each analytes in tomato samples were in the range of 3.25-6.26 % (n = 5). The proposed method was successfully applied for the extraction and determination of the mentioned analytes residues in tomato and cucumber samples, and satisfactory results were obtained.

Perspectives of using fungi as bioresource for bioremediation of pesticides in the environment: a critical review

Pesticides are used for controlling the development of various pests in agricultural crops worldwide. Despite their agricultural benefits, pesticides are often considered a serious threat to the environment because of their persistent nature and the anomalies they create. Hence removal of such pesticides from the environment is a topic of interest for the researchers nowadays. During the recent years, use of biological resources to degrade or remove pesticides has emerged as a powerful tool for their in situ degradation and remediation. Fungi are among such bioresources that have been widely characterized and applied for biodegradation and bioremediation of pesticides. This review article presents the perspectives of using fungi for biodegradation and bioremediation of pesticides in liquid and soil media. This review clearly indicates that fungal isolates are an effective bioresource to degrade different pesticides including lindane, methamidophos, endosulfan, chlorpyrifos, atrazine, cypermethrin, dieldrin, methyl parathion, heptachlor, etc. However, rate of fungal degradation of pesticides depends on soil moisture content, nutrient availability, pH, temperature, oxygen level, etc. Fungal strains were found to harbor different processes including hydroxylation, demethylation, dechlorination, dioxygenation, esterification, dehydrochlorination, oxidation, etc during the biodegradation of different pesticides having varying functional groups. Moreover, the biodegradation of different pesticides was found to be mediated by involvement of different enzymes including laccase, hydrolase, peroxidase, esterase, dehydrogenase, manganese peroxidase, lignin peroxidase, etc. The recent advances in understanding the fungal biodegradation of pesticides focusing on the processes, pathways, genes/enzymes and factors affecting the biodegradation have also been presented in this review article.

Complete biodegradation of chlorpyrifos by engineered Pseudomonas putida cells expressing surface-immobilized laccases

The long-term abuse use of chlorpyrifos-like pesticides in agriculture and horticulture has resulted in significant soil or water contamination and a worldwide ecosystem threat. In this study, the ability of a solvent-tolerant bacterium, Pseudomonas putida MB285, with surface-displayed bacterial laccase, to biodegrade chlorpyrifos was investigated. The results of compositional analyses of the degraded products demonstrate that the engineered MB285 was capable of completely eliminating chlorpyrifos via direct biodegradation, as determined by high-performance liquid chromatography and gas chromatography-mass spectrometry assays. Two intermediate metabolites, namely 3,5,6-trichloro-2-pyridinol (TCP) and diethyl phosphate, were temporarily detectable, verifying the joint and stepwise degradation of chlorpyrifos by surface laccases and certain cellular enzymes, whereas the purified free laccase incompletely degraded chlorpyrifos into TCP. The degradation reaction can be conducted over a wide range of pH values (2-7) and temperatures (5-55 °C) without the need for Cu(2+). Bioassays using Caenorhabditis elegans as an indicator organism demonstrated that the medium was completely detoxified of chlorpyrifos by degradation. Moreover, the engineered cells exhibited a high capacity of repeated degradation and good performance in continuous degradation cycles, as well as a high capacity to degrade real effluents containing chlorpyrifos. Therefore, the developed system exhibited a high degradation capacity and performance and constitutes an improved approach to address chlorpyrifos contamination in chlorpyrifos-remediation practice.

Optimization study of 2-hydroxyquinoxaline (2-HQ) biodegradation by Ochrobactrum sp. HQ1

A novel aerobic gram-negative bacterial strain capable of utilizing 2-hydroxyquinoxaline (2-HQ) as sole source of carbon and energy was isolated from Indian agricultural soil and named as HQ1. Strain HQ1 was identified as Ochrobactrum sp. on the basis of morphology, physico-biochemical characteristics and 16S rRNA sequence analysis. The generation time of Ochrobactrum sp. HQ1 on 2-HQ at log phase is 0.71 h or 42.6 min. The degradation of 2-HQ by HQ1 under various physico-chemical parameters was analysed by HPLC and observed to be optimum with a high inoculum density (1.0 OD) at pH 7–8, temperatures 37–40°C and a high concentration of 2-HQ (500 ppm). Degradation of 2-HQ was also improved when additional nitrogen sources were used and this was attributed to the enhanced growth of the bacterium on the readily available nitrogen sources. Analysis of 2-HQ degradation by GC–MS resulted in elucidation of the degradation pathway for HQ1, a novel observation for aerobic Gram-negative bacteria. These findings are a possible indication of the application of HQ1 in the bioremediation of pesticide/metabolite contamination.

Biodegradation of Chlorpyrifos by Pseudomonas Resinovarans Strain AST2.2 Isolated from Enriched Cultures

A bacterial strain AST2.2 with chlorpyrifos degrading ability was isolated by enrichment technique from apple orchard soil with previous history of chlorpyrifos use. Based on the morphological, biochemical tests and 16S rRNA sequence analysis, AST2.2 strain was identified as Pseudomonas resinovarans. The strain AST2.2 utilized chlorpyrifos as the sole source of carbon and energy. This strain exhibited growth upto 400mg/l concentration of chlorpyrifos and exhibited high extracellular organophosphorus hydrolase (OPH) activity. Gas chromatography-flame ionization detector (GC-FID) studies revealed that Pseudomonas resinovarans AST2.2 degraded 43.90 % of chlorpyrifos (400 mg/l) within 96 hrs. Intermediates of chlorpyrifos degradation were identified using GC-MS. This strain have potential to degrade chlorpyrifos and thus can be used for bioremediation and ecological restoration of sites contaminated with chlorpyrifos

Effect of three typical sulfide mineral flotation collectors on soil microbial activity

The sulfide mineral flotation collectors are wildly used in China, whereas their toxic effect on soil microbial activity remains largely unexplored. In this study, isothermal microcalorimetric technique and soil enzyme assay techniques were employed to investigate the toxic effect of typical sulfide mineral flotation collectors on soil microbial activity. Soil samples were treated with different concentrations (0-100 μg•g - 1 soil) of butyl xanthate, butyl dithiophosphate, and sodium diethyldithiocarbamate. Results showed a significant adverse effect of butyl xanthate (p < 0.05), butyl dithiophosphate, and sodium diethyldithiocarbamate (p < 0.01) on soil microbial activity. The growth rate constants k decreased along with the increase of flotation collectors concentration from 20.0 to 100.0 μg•g(-1). However, the adverse effects of these three floatation collectors showed significant difference. The IC 20 of the investigated flotation reagents followed such an order: IC 20 (butyl xanthate) > IC 20 (sodium diethyldithiocarbamate) > IC 20 (butyl dithiophosphate) with their respective inhibitory concentration as 47.03, 38.36, and 33.34 μg•g(-1). Besides, soil enzyme activities revealed that these three flotation collectors had an obvious effect on fluorescein diacetate hydrolysis (FDA) enzyme and catalase (CAT) enzyme. The proposed methods can provide meaningful toxicological information of flotation reagents to soil microbes in the view of metabolism and biochemistry, which are consistent and correlated to each other.

Biodegradation of chlorpyrifos and its hydrolysis product 3,5,6-trichloro-2-pyridinol using a novel bacterium Ochrobactrum sp. JAS2: A proposal of its metabolic pathway

Biodegradation of chlorpyrifos and its major metabolite 3,5,6-trichloro-2-pyridinol (TCP) were studied with a novel bacterial strain JAS2 isolated from paddy rhizosphere soil. The molecular characterization based on 16S rRNA gene sequence homology confirmed its identity as Ochrobactrum sp. JAS2. The JAS2 strain degraded 300mgl(-1) of chlorpyrifos within 12h of incubation in the aqueous medium and it produced the TCP metabolite. However, after 72h of incubation TCP was also completely degraded by the JAS2 strain. A tentative degradation pathway of chlorpyrifos by Ochrobactrum sp. JAS2 has been proposed on basis of GC-MS analysis. The complete degradation of chlorpyrifos occurred within 24h in the soil spiked with and without addition of nutrients inoculated with Ochrobactrum sp. JAS2. TCP was obtained in both the studies which was degraded completely by 96h in the soil spiked with nutrients and whereas 120h in absence of nutrients in the soil. The mpd gene which is responsible for organophosphorus hydrolase production was identified. The isolates Ochrobactrum sp. JAS2 also exhibited a time dependent increase in the amount of tricalcium phosphate solubilization in Pikovskaya's medium. Further screening of the strain JAS2 for auxiliary plant growth promoting activities revealed its remarkable capability of producing the indole acetic acid (IAA), hydrogen cyanide (HCN) and ammonia.

Chemotaxis and degradation of organophosphate compound by a novel moderately thermo-halo tolerant Pseudomonas sp. strain BUR11: evidence for possible existence of two pathways for degradation

An organophosphate (OP) degrading chemotactic bacterial strain BUR11 isolated from an agricultural field was identified as a member of Pseudomonas genus on the basis of its 16S rRNA gene sequence. The strain could utilize parathion, chlorpyrifos and their major hydrolytic intermediates as sole source of carbon for its growth and exhibited positive chemotactic response towards most of them. Optimum concentration of parathion for its growth was recorded to be 200 ppm and 62% of which was degraded within 96 h at 37 °C. Growth studies indicated the strain to be moderately thermo-halo tolerant in nature. Investigation based on identification of intermediates of parathion degradation by thin layer chromatography (TLC), high performance liquid chromatography (HPLC), gas chromatography (GC) and liquid chromatography mass spectrometry (LC-MS/MS) provided evidence for possible existence of two pathways. The first pathway proceeds via 4-nitrophenol (4-NP) while the second proceeds through formation of 4-aminoparathion (4-APar), 4-aminophenol (4-AP) and parabenzoquinone (PBQ). This is the first report of chemotaxis towards organophosphate compound by a thermo-halo tolerant bacterium.

Biodegradation of nicosulfuron by a novel Alcaligenes faecalis strain ZWS11

A bacterial strain ZWS11 was isolated from sulfonylurea herbicide-contaminated farmland soil and identified as a potential nicosulfuron-degrading bacterium. Based on morphological and physicochemical characterization of the bacterium and phylogenetic analysis of the 16S rRNA sequence, strain ZWS11 was identified as Alcaligenes faecalis. The effects of the initial concentration of nicosulfuron, inoculation volume, and medium pH on degradation of nicosulfuron were investigated. Strain ZWS11 could degrade 80.56% of the initial nicosulfuron supplemented at 500.0mg/L under the conditions of pH7.0, 180r/min and 30°C after incubation for 6days. Strain ZWS11 was also capable of degrading rimsulfuron, tribenuron-methyl and thifensulfuron-methyl. Four metabolites from biodegradation of nicosulfuron were identified, which were 2-aminosulfonyl-N, N-dimethylnicotinamide (M1), 4, 6-dihydroxypyrimidine (M2), 2-amino-4, 6-dimethoxypyrimidine (M3) and 2-(1-(4,6-dimethoxy-pyrimidin-2-yl)-ureido)-N,N-dimethyl-nicotinamide (M4). Among the metabolites detected, M2 was reported for the first time. Possible biodegradation pathways of nicosulfuron by strain ZWS11 were proposed. The degradation proceeded mainly via cleavage of the sulfonylurea bridge, O-dealkylation, and contraction of the sulfonylurea bridge by elimination of a sulfur dioxide group. The results provide valuable information for degradation of nicosulfuron in contaminated environments.