Identification and characterization of chlorpyrifos-methyl and 3,5,6-trichloro-2-pyridinol degrading Burkholderia sp. strain KR100

Proximal discrepancies in intrinsic atomic interaction determines comparative in vivo biotoxicity of Chlorpyrifos and 3,5,6-trichloro-2-pyridinol in embryonic zebrafish

Bioaccumulation of Chlorpyrifos (CP) as pesticides due to their aggrandized use in agriculture has raised serious concern on the health of ecosystem and human beings. Moreover, their degraded products like 3,5,6-trichloro-2-pyridinol (TCP) has enhanced the distress due to their unpredictable biotoxicity. This study evaluates and deduce the comparative in vivo mechanistic biotoxicity of CP and TCP with zebrafish embryos through experimental and computational approach. Experimental cellular and molecular analysis showed higher induction of morphological abnormalities, oxidative stress and apoptosis in TCP exposed embryos compared to CP exposure due to upregulation of metabolic enzymes like Zhe1a, Sod1 and p53. Computational analysis excavated the differential discrepancies in intrinsic atomic interaction as a reason of disparity in biotoxicity of CP and TCP. The mechanistic differences were deduced due to the differential accumulation and internalisation leading to variable interaction with metabolic enzymes for oxidative stress and apoptosis causing physiological and morphological abnormalities. The study unravelled the information of in vivo toxicity at cellular and molecular level to advocate the attention of taking measures for management of CP as well as TCP for environmental and human health.

Rapid Biodegradation of the Organophosphorus Insecticide Acephate by a Novel Strain Burkholderia sp. A11 and Its Impact on the Structure of the Indigenous Microbial Community

The acephate-degrading microbes that are currently available are not optimal. In this study, Burkholderia sp. A11, an efficient degrader of acephate, presented an acephate-removal efficiency of 83.36% within 56 h (100 mg·L^-1). The A11 strain has a broad substrate tolerance and presents a good removal effect in the concentration range 10-1600 mg·L^-1. Six metabolites from the degradation of acephate were identified, among which the main products were methamidophos, acetamide, acetic acid, methanethiol, and dimethyl disulfide. The main degradation pathways involved include amide bond breaking and phosphate bond hydrolysis. Moreover, strain A11 successfully colonized and substantially accelerated acephate degradation in different soils, degrading over 90% of acephate (50-200 mg·kg^-1) within 120 h. 16S rDNA sequencing results further confirmed that the strain A11 gradually occupied a dominant position in the soil microbial communities, causing slight changes in the diversity and composition of the indigenous soil microbial community structure.

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.

Isolation and characterization of cyromazine degrading Acinetobacter sp. ZX01 from a Chinese ginger cultivated soil

Cyromazine, a symmetrical triazine insecticide, is used to control dipteran larvae in chicken manure by feeding to the poultry, flies on animals, and leafminers in vegetables. Its extensive use has resulted in the widespread contamination in the environment. In the current study, a cyromazine degrading bacterium (designated strain ZX01) was isolated and characterized from a Chinese ginger cultivated soil by selective enrichment culture method. On the basis of morphological, biochemical characteristics, and 16S rRNA gene sequence, this bacterium showed strong similarity to the Pseudomonadales members and was closely related to the Acinetobacter baumannii group. Spectrophotometric and HPLC analyses revealed that strain ZX01 degraded cyromazine and utilized it as the sole carbon source for its growth. This process hydrolyzes cyromazine to melamine. Strain ZX01 degraded most of the cyromazine in 60 h. Besides, its substrate specificity against four symmetrical triazine herbicides, one triazinone herbicide, as well as 10 insecticides and its antibiotic sensitivity towards eight commercial antibiotics were also tested. At the concentration of 100 µg/mL for 60 h, it could effectively degrade a variety of different pesticides, including atrazine, prometon, simazine, prometryn, enitrothion, diazinon, cypermethrin, and acetamiprid, and the degradation was in the range of 71-87%. In particular, melamine, the main degradation product of cyromazine, was degraded by 47.3%. This microorganism was sensitive to chloramphenicol and tetracycline and intermediate to amoxicillin and trimethoprim. These results highlight that strain ZX01 can be used as a potential biological agent for the remediation of soil, water, or crop contaminated with cyromazine and other symmetrical triazine insecticides.

Toxicity and detoxification of monocrotophos from ecosystem using different approaches: A review

Monocrotophos (MCP) is an organophosphate insecticide with broad application in agricultural crops like rice, maize, sugarcane, cotton, soybeans, groundnut and vegetables. MCP solubilize in water readily and thus reduced sorption occurs in soil. This leads to MCP leaching into the groundwater and pose a significant threat of contamination. The MCP's half-life depends on the temperature and pH value and estimated as 17-96 d. But the half-life of technical grade MCP can exceed up to 2500 days if properly stored at 38 °C in a glass or polyethylene container in a stable condition. It causes abnormality, ranging from mild to severe confusion, agitation, hypersalivation, convulsion, pulmonary failure, senescence in mammals and insects. MCP affects humans by inhibiting the activity of the acetylcholine esterase enzyme. MCP is accountable for the catalytic degradation of acetylcholine and affects the neurotransmission between neurons. This review discusses MCP's various aspects and fate on aquatic and terrestrial life forms, quantification methods for monitoring, various degradation processes, and their mechanisms. Different case studies related to its impact on the human population in different parts of the world have been discussed. Efforts have also been made to summarize and present different microbial population's role in its degradation and mineralization.

Effects of the insecticide fipronil in freshwater model organisms and microbial and periphyton communities

Fipronil is a broad-spectrum insecticide whose release in the environment damages many non-target organisms. This study evaluated the toxicity of fipronil at two biological levels using in vivo conditions and environmentally relevant concentrations: the first based on two model organisms (aquatic invertebrate Daphnia magna and the unicellular freshwater alga Chlamydomonas reinhardtii) and a second based on three natural communities (river periphyton and freshwater and soil microbial communities). The physicochemical properties of fipronil make it apparently unstable in the environment, so its behaviour was followed with high performance liquid chromatography (HPLC) under the different test conditions. The most sensitive organism to fipronil was D. magna, with median lethal dose (LC₅₀) values from 0.07 to 0.38 mg/L (immobilisation test). Toxicity was not affected by the media used (MOPS or river water), but it increased with temperature. Fipronil produced effects on the photosynthetic activity of C. reinhardtii at 20 °C in MOPS (EC₅₀ = 2.44 mg/L). The freshwater periphyton presented higher sensitivity to fipronil (photosynthetic yield EC₅₀ of 0.74 mg/L) in MOPS and there was a time-dependent effect (toxicity increased with time). Toxicity was less evident when periphyton and C. reinhardtii tests were performed in river water, where the solubility of fipronil is poor. Finally, the assessment of the metabolic profiles using Biolog EcoPlates showed that bacteria communities were minimally affected by fipronil. The genetic identification of these communities based on 16S rRNA gene sequencing revealed that many of the taxa are specialists in degrading high molecular weight compounds, including pesticides. This work allows us to better understand the impact of fipronil on the environment at different levels of the food chain and in different environmental conditions, a necessary point given its presence in the environment and the complex behaviour of this compound.

In vitro interaction of organophosphate metabolites with bovine serum albumin: A comparative 1H NMR, fluorescence and molecular docking analysis

Since the exposure of organophosphate pesticides are known to cause severe health consequences, it is important to understand the molecular interaction of these pesticides metabolites with vital biomolecules, especially with the proteins. Here, considering bovine serum albumin (BSA) as a model protein, we have examined its interaction with two selected organophosphate metabolites, 3,5,6-trichloro-2-pyridinol (TCPy) and paraoxon methyl (PM). TCPy and PM are resultant metabolites of two most widely used organophosphate pesticides chlorpyrifos and parathion respectively. ¹H NMR line broadening, selective spin-lattice relaxation rate measurements, saturation transfer difference (STD) NMR of both TCPy and PM were carried out in the presence and absence of BSA. The obtained values of the affinity index (A), binding constants (K_a) and thermodynamic parameters indicated strong organophosphates-BSA interaction. Further, fluorescence quenching data on TCPy-BSA and PM-BSA interactions strongly supported the NMR results, besides providing the stoichiometry of these complexes. Molecular docking analysis unraveled viable, strong hydrogen bonds and electrostatic interactions in TCPy-BSA and PM-BSA complexes. This study also revealed substantial time-dependent changes in the ¹H NMR intensity of PM in the presence of BSA, which suggests faster degradation of PM with increasing protein concentration during protein-metabolite interactions. The hydrolysis is attributed to the esterase-like action of BSA. The result provides key insights into the direct interaction of the organophosphate metabolites with a biologically important carrier protein, serum albumin.

NanoFe3O4 accelerates anoxic biodegradation of 3, 5, 6-trichloro-2-pyridinol

3, 5, 6-trichloro-2-pyridinol (TCP) is a widespread organic pollutant with persistent, mobile and high antimicrobial effects. Here, nanoFe₃O₄ was firstly introduced into the anoxic biodegradation of TCP. It was found that nanoFe₃O₄ significantly accelerated TCP biodegradation. The removal rate of TCP (100 mg L^-1) increased from 83.03% to 98.74% within 12 h in the presence of nanoFe₃O₄, and the addition of nanoFe₃O₄ also promoted the accumulation of CO₂. Reductive dechlorination mechanism was involved in anoxic biodegradation of TCP. Molecular approaches further revealed that nanoFe₃O₄ distinctly induced the shifts of bacterial community. The dominant genus Ochrobactrum was converted to genus Delftia in nanoFe₃O₄ treatment, and the relative abundance of Delftia increased from 10.26% to 44.62%. Meanwhile, the total relative abundance of bacteria related to TCP dechlorination and degradation significantly increased in the presence of nanoFe₃O₄. These results indicated that nanoFe₃O₄ induced the enrichment of TCP-degrading bacteria to promote the anoxic biodegradation of TCP.

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.

Isolation and Characterization of 2,4-D Butyl Ester Degrading Acinetobacter sp. ZX02 from a Chinese Ginger Cultivated Soil

Strain ZX02 was isolated from Chinese ginger cultivated soil contaminated with various pesticides, which could utilize 2,4-dichlorophenoxyacetic acid butyl ester (2,4-D butyl ester) as the sole carbon source. On the basis of the sequence analysis of 16S rRNA gene as well as the morphological, biochemical, and physiological characteristics of strain ZX02, the organism belonged to Gram-negative bacterium and was identified as Acinetobacter sp. ZX02. The strain ZX02 showed a remarkable performance in 2,4-D butyl ester degradation (100% removal in <96 h) in pure culture. Strain ZX02 was sensitive to tetracycline and resistant to amoxicillin and chloramphenicol in an antibiotic sensitivity test. The curing study indicates that the gene for degradation of 2,4-D butyl ester was encoded on a single plasmid of 23 kb. The gene encoding resistance to polymixin B sulfate was also located on this plasmid. On the basis of its greater biodegradation activity, this bacterium is a potential candidate as a bioremediation agent in soils contaminated with 2,4-D butyl ester.

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.

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

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

Diazinon dissipation in pesticide-contaminated paddy soil: kinetic modeling and isolation of a degrading mixed bacterial culture

Dissipation kinetics of diazinon was investigated in soils culled from a paddy field with a long history of the pesticide application. Goodness of fit statistical indices derived from several fitted mono- and bi-exponential kinetic models revealed a bi-phasic pattern of the diazinon dissipation curve at 15 and 150 mg kg^-1 spiking levels, which could be described best by the first-order double exponential decay (FODED) model. Parameters obtained from this model were able to describe the enhanced dissipation of diazinon as the result of repeated soil applications, where a larger fraction of the pesticide readily available in the solution phase was dissipated with a fast rate. Cluster and principal component analysis (PCA) of denaturing gradient gel electrophoresis (DGGE) obtained from soil bacterial populations revealed that they were only affected at the 150 mg kg^-1 diazinon concentration. This was also supported by the phylogenetic tree obtained from sequences of the main gel bands. Accordingly, bacterial populations belonging to Proteobacteria were enriched in the soil following three treatments with diazinon at 150 mg kg^-1. The Shannon's index revealed a nonsignificant increase (P ≤ 0.05) in overall diversity of soil bacteria following diazinon application. Diazinon-degrading bacteria were isolated from the paddy soils in a mineral salt medium. Results showed that the isolated mixed culture was able to remove 90% of the pesticide at two concentrations of 50 and 100 mg L^-1 by 16.81 and 19.60 days, respectively. Sequencing the DGGE bands confirmed the role of Betaproteobacteria as the main components of the isolated mixed culture in the degradation of diazinon.

Biodegradation of propiconazole by newly isolated Burkholderia sp. strain BBK_9

The isolation of propiconazole (PCZ) degrading bacterium BBK_9 strain was done from paddy soil, and it was identified as Burkholderia sp. based on the morphological characteristics and biochemical properties combined with 16S rRNA gene sequencing analysis. It has been seen that the factors such as temperature and pH influence the biodegradation process. The role of plasmid was studied in the degradation process by plasmid curing method. The PCZ acts as the sole carbon source and as energy substrate which can be utilized by the strain for its growth in Mineral salt medium and degraded 8.89 µg ml^-1 of PCZ at 30 °C and pH 7 within 4 days. During the bioconversion process of PCZ, three metabolite were formed such as 1-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-yl) ethanone, 1-[2-(4-chlorophenyl) ethyl]-1H-1,2,4-triazole and 1-ethyl-1H-1,2,4-triazole. The LD50 value of BBK_9 strain was determined with acridine orange which resulted in 40 µg ml^-1 at cell density of 0.243 at 660 nm. Furthermore, plasmid curing was done using LD50 concentration and from that three plasmids got cured in the sixth generation. It was found that, cured strain was able to degrade 7.37 µg ml^-1 of PCZ, indicating the plasmid encoded gene were not responsible for the PCZ degradation. On the source of these outcomes, strain BBK_9 can be used as potential strain for bioremediation of contaminated sites.

Rapid biodegradation of organophosphorus pesticides by Stenotrophomonas sp. G1

Organophosphorus insecticides have been widely used, which are highly poisonous and cause serious concerns over food safety and environmental pollution. A bacterial strain being capable of degrading O,O-dialkyl phosphorothioate and O,O-dialkyl phosphate insecticides, designated as G1, was isolated from sludge collected at the drain outlet of a chlorpyrifos manufacture plant. Physiological and biochemical characteristics and 16S rDNA gene sequence analysis suggested that strain G1 belongs to the genus Stenotrophomonas. At an initial concentration of 50 mg/L, strain G1 degraded 100% of methyl parathion, methyl paraoxon, diazinon, and phoxim, 95% of parathion, 63% of chlorpyrifos, 38% of profenofos, and 34% of triazophos in 24 h. Orthogonal experiments showed that the optimum conditions were an inoculum volume of 20% (v/v), a substrate concentration of 50 mg/L, and an incubation temperature in 40 °C. p-Nitrophenol was detected as the metabolite of methyl parathion, for which intracellular methyl parathion hydrolase was responsible. Strain G1 can efficiently degrade eight organophosphorus pesticides (OPs) and is a very excellent candidate for applications in OP pollution remediation.

Isolation and characterization of a highly efficient chlorpyrifos degrading strain of Cupriavidus taiwanensis from sludge

In this study, a highly effective chlorpyrifos (CP)-degrading bacterium (termed strain X1) was isolated from the sludge of drain outlet of a chlorpyrifos manufacturer. Strain X1 was identified as Cupriavidus taiwanensis based upon the analysis of the 16S rDNA gene and biochemical characteristics, which is capable of transforming CP into 3,5,6-trichloro-2-pyridinol (TCP), and the resulting TCP was further metabolized when performed in an aqueous medium. Degradation experiments were carried out under different conditions at the range of pH (5.0∼9.0) and temperature (22∼42 °C), and the optimized pH and temperature were 7.0 and 32 °C respectively. Biotransformation of high concentration of CP was also determined; 400 mg l(À1) of CP was completely transformed within 36 h; approximately 95% of CP was removed within 48 h when concentration of CP was up to 500 mg l(À1) . A genomic library was successfully constructed to clone the gene encoding the CP hydrolase, and a positive transformant with clear hydrolytic zones was obtained and analyzed. The insert gene sequence exhibited close relationship with 99% similar to opdB gene encoding parathion hydrolase, whereas, transformant failed in degrading the accumulated TCP. These results highlight the potential of this bacterium to be used in the cleanup of CP.

Bacterial population succession and adaptation affected by insecticide application and soil spraying history

Although microbial communities have varying degrees of exposure to environmental stresses such as chemical pollution, little is known on how these communities respond to environmental disturbances and how past disturbance history affects these community-level responses. To comprehensively understand the effect of organophosphorus insecticide application on microbiota in soils with or without insecticide-spraying history, we investigated the microbial succession in response to the addition of fenitrothion [O,O-dimethyl O-(3-methyl-p-nitrophenyl) phosphorothioate, abbreviated as MEP] by culture-dependent experiments and deep sequencing of 16S rRNA genes. Despite similar microbial composition at the initial stage, microbial response to MEP application was remarkably different between soils with and without MEP-spraying history. MEP-degrading microbes more rapidly increased in the soils with MEP-spraying history, suggesting that MEP-degrading bacteria might already exist at a certain level and could quickly respond to MEP re-treatment in the soil. Culture-dependent and -independent evaluations revealed that MEP-degrading Burkholderia bacteria are predominant in soils after MEP application, limited members of which might play a pivotal role in MEP-degradation in soils. Notably, deep sequencing also revealed that some methylotrophs dramatically increased after MEP application, strongly suggesting that these bacteria play a role in the consumption and removal of methanol, a harmful derivative from MEP-degradation, for better growth of MEP-degrading bacteria. This comprehensive study demonstrated the succession and adaptation processes of microbial communities under MEP application, which were critically affected by past experience of insecticide-spraying.

Kinetics of biotransformation of chlorpyrifos in aqueous and soil slurry environments

The attenuation of chlorpyrifos (CPF) by the enriched indigenous soil microorganism was studied in 15 d aerobic and 60 d anaerobic batch experiments in aqueous and soil slurry (1:3 w/w) media. At the end of the batch experiments, 2.78 ± 0.11 μM of CPF was degraded by 82% in aerobic and 66% in anaerobic aqueous environments, while 12.4 ± 0.5 μM of CPF was degraded by 48% in aerobic and 31% in anaerobic soil slurries. The reduced degradation in the soil slurries was due to the significantly (2-10 times) slower rate of degradation of soil phase CPF compared with its degradation rate in water. The pathways of degradation of CPF were identified, including a partial anaerobic degradation pathway that is constructed for the first time. The simulation of the various conversions in the degradation pathways using first order kinetics was used to analyze relative persistence of metabolites. The common metabolite 3,5,6-trichloro-2-pyridinol (TCP) accumulated (increased monotonically during the period of experiments) in aerobic soil slurry and in anaerobic aqueous as well as soil slurry systems but did not accumulate in aerobic aqueous system. The most toxic compound in the pathway, chlorpyrifos oxon (CPFO) was not detected in anaerobic environment. In aerobic environment, CPFO was short lived in aqueous medium, but accumulated slowly in the soils.

Novel gene clusters and metabolic pathway involved in 3,5,6-trichloro-2-pyridinol degradation by Ralstonia sp. strain T6

3,5,6-Trichloro-2-pyridinol (TCP) is a widespread pollutant. Some bacteria and fungi have been reported to degrade TCP, but the gene clusters responsible for TCP biodegradation have not been characterized. In this study, a fragment of the reduced flavin adenine dinucleotide (FADH2)-dependent monooxygenase gene tcpA was amplified from the genomic DNA of Ralstonia sp. strain T6 with degenerate primers. The tcpA disruption mutant strain T6-ΔtcpA could not degrade TCP but could degrade the green intermediate metabolite 3,6-dihydroxypyridine-2,5-dione (DHPD), which was generated during TCP biodegradation by strain T6. The flanking sequences of tcpA were obtained by self-formed adaptor PCR. tcpRXA genes constitute a gene cluster. TcpR and TcpX are closely related to the LysR family transcriptional regulator and flavin reductase, respectively. T6-ΔtcpA-com, the complementation strain for the mutant strain T6-ΔtcpA, recovered the ability to degrade TCP, and the strain Escherichia coli DH10B-tcpRXA, which expressed the tcpRXA gene cluster, had the ability to transform TCP to DHPD, indicating that tcpA is a key gene in the initial step of TCP degradation and that TcpA dechlorinates TCP to DHPD. A library of DHPD degradation-deficient mutants of strain T6 was obtained by random transposon mutagenesis. The fragments flanking the Mariner transposon were amplified and sequenced, and the dhpRIJK gene cluster was cloned. DhpJ could transform DHPD to yield an intermediate product, 5-amino-2,4,5-trioxopentanoic acid (ATOPA), which was further degraded by DhpI. DhpR and DhpK are closely related to the AraC family transcriptional regulator and the MFS family transporter, respectively.

Identification of two combined genes responsible for dechlorination of 3,5,6-trichloro-2-pyridinol (TCP) in Cupriavidus pauculus P2

Dehalogenation is an important mechanism for degrading and detoxifying halogenated aromatics in microbes. However, the biochemical and molecular mechanisms of dehalogenation of 3,5,6-trichloro-2-pyridinol (TCP) are still unknown. In this study, a novel 6012 bp gene cluster was cloned from TCP-degrading strain P2, which was responsible for the dehalogenation of TCP. The cluster included a monooxygenase gene (tcpA1), a flavin reductase gene (tcpB1), tcpR1, orf1 and orf2. TcpA1 and TcpB1 were indispensable for the dehalogenation of TCP. They worked together to catalyze the dehalogenation of three chlorine of TCP, and generated a more readily biodegradable product of 3,6-dihydroxypyridine-2,5-dione. TcpA1 displayed the highest activity against TCP at 40°C and at pH 8.0. Cu(2+), Zn(2+), and Hg(2+) significantly inhibited enzyme activity. To the best of our knowledge, this is the first report on a gene cluster responsible for TCP degradation.

Biodegradation of methyl parathion and p-nitrophenol by a newly isolated Agrobacterium sp. strain Yw12

Strain Yw12, isolated from activated sludge, could completely degrade and utilize methyl parathion as the sole carbon, phosphorus and energy sources for growth in the basic salt media. It could also completely degrade and utilize p-nitrophenol as the sole carbon and energy sources for growth in the minimal salt media. Phenotypic features, physiological and biochemical characteristics, and phylogenetic analysis of 16S rRNA sequence showed that this strain belongs to the genus of Agrobacterium sp. Response surface methodology was used to optimize degradation conditions. Under its optimal degradation conditions, 50 mg l(-1) MP was completely degraded within 2 h by strain Yw12 and the degradation product PNP was also completely degraded within 6 h. Furthermore, strain Yw12 could also degrade phoxim, methamidophos, chlorpyrifos, carbofuran, deltamethrin and atrazine when provided as the sole carbon and energy sources. Enzymatic analysis revealed that the MP degrading enzyme of strain Yw12 is an intracellular enzyme and is expressed constitutively. These results indicated that strain Yw12 might be used as a potential and effective organophosphate pesticides degrader for bioremediation of contaminated sites.

Isolation of a novel gene encoding a 3,5,6-trichloro-2-pyridinol degrading enzyme from a cow rumen metagenomic library

3,5,6-trichloro-2-pyridinol (TCP) is a major metabolite of the insecticide chlorpyrifos and is hazardous to human and animal health. A gene encoding a TCP degrading enzyme was cloned from a metagenomic library prepared from cow rumen. The gene (tcp3A) is 2.5 kb in length, encoding a protein (Tcp3A) of 599 amino acid residues. Tcp3A has a potential signal sequence, as well as a putative ATP/GTP binding site, and a likely amidation site. The molecular weight of the enzyme is 62 kDa by SDS-PAGE. Comparison of Tcp3A with the NCBI database using BLASTP revealed homology to amidohydrolase proteins. Recombinant Escherichia coli harboring the tcp3A gene could utilize TCP as the sole source of carbon. TLC and HPLC revealed that TCP was degraded by recombinant E. coli harboring tcp3A. This is the first report of a gene encoding a TCP degrading enzyme.