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

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.

Use of Bacillus thuringiensis supernatant from a fermentation process to improve bioremediation of chlorpyrifos in contaminated soils

The aim of this research was to investigate the potential of a nutrient-rich organic waste, namely the cell-free supernatant of Bacillus thuringiensis (BtS) gathered from fermentation, as a biostimulating agent to improve and sustain microbial populations and their enzymatic activities, thereby assisting in the bioremediation of chlorpyrifos-contaminated soil at a high dose (70 mg kg(-1)). Experiments were performed for up to 80 d. Chlorpyrifos degradation and its major metabolic product, 3,5,6-trichloro-2-pyridinol (TCP), were quantified by high-performance liquid chromatography (HPLC); total microbial populations were enumerated by direct counts in specific medium; and fluorescein diacetate (FDA) hydrolysis was measured as an index of soil microbial activity. Throughout the experiment, there was higher chlorpyrifos degradation in soil supplemented with BtS (83.1%) as compared to non-supplemented soil. TCP formation and degradation occurred in all soils, but the greatest degradation (30.34%) was observed in soil supplemented with BtS. The total microbial populations were significantly improved by supplementation with BtS. The application of chlorpyrifos to soil inhibited the enzymatic activity; however, this negative effect was counteracted by BtS, inducing an increase of approximately 16% in FDA hydrolysis. These results demonstrate the potential of B. thuringiensis supernatant as a suitable biostimulation agent for enhancing chlorpyrifos and TCP biodegradation in chlorpyrifos-contaminated soils.

Effects of chemical and biological pesticides on plant growth parameters and rhizospheric bacterial community structure in Vigna radiata

With increasing application of pesticides in agriculture, their non-target effects on soil microbial communities are critical to soil health maintenance. The present study aimed to evaluate the effects of chemical pesticides (chlorpyrifos and cypermethrin) and a biological pesticide (azadirachtin) on growth parameters and the rhizospheric bacterial community of Vigna radiata. Qualitative and quantitative analysis by PCR-denaturing gradient gel electrophoresis (DGGE) and q-PCR, respectively, of the 16S rRNA gene and transcript were performed to study the impact of these pesticides on the resident and active rhizospheric bacterial community. While plant parameters were not affected significantly by the pesticides, a shift in the bacterial community structure was observed with an adverse effect on the abundance of 16S rRNA gene and transcripts. Chlorpyrifos showed almost complete degradation toward the end of the experiment. These non-target impacts on soil ecosystems and the fact that the effects of the biopesticide mimic those of chemical pesticides raise serious concerns regarding their application in agriculture.

Degradation of chlorpyrifos in tropical rice soils

Chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridinol) phosphorothioate] is used worldwide as an agricultural insecticide against a broad spectrum of insect pests of economically important crops including rice, and soil application to control termites. The insecticide mostly undergoes hydrolysis to diethyl thiophosphoric acid (DETP) and 3,5,6-trichloro-2-pyridinol (TCP), and negligible amounts of other intermediate products. In a laboratory-cum-greenhouse study, chlorpyrifos, applied at a rate of 10 mg kg(-1) soil to five tropical rice soils of wide physico-chemical variability, degraded with a half-life ranging from 27.07 to 3.82 days. TCP was the major metabolite under both non-flooded and flooded conditions. Chlorpyrifos degradation had significant negative relationship with electrical conductivity (EC), cation exchange capacity (CEC), clay and sand contents of the soils under non-flooded conditions. Results indicate that degradation of chlorpyrifos was accelerated with increase in its application frequency, across the representative rice soils. Management regimes including moisture content and presence or absence of rice plants also influenced the process. Biotic factors also play an important role in the degradation of chlorpyrifos as demonstrated by its convincing degradation in mineral salts medium inoculated with non-sterile soil suspension.

Cloning and expression of ophB gene encoding organophosphorus hydrolase from endophytic Pseudomonas sp. BF1-3 degrades organophosphorus pesticide chlorpyrifos

Chlorpyrifos is an organophosphate pesticide that has adverse effect on animals and plants. We isolated endophytic bacterial strain, Pseudomonas sp. BF1-3, from balloon flower root which can hydrolyze chlorpyrifos. A gene (ophB) encoding a protein involved in chlorpyrifos degradation from this strain was cloned into Escherichia coli DH5α for confirming enzyme activity. After sequencing, total 1024bp nucleotide sequences were found in the open reading frame of ophB. The chlorpyrifos degradation patterns by E. coli DH5α (ophB) were observed. During incubation in minimal salt (M9) medium supplemented with chlorpyrifos (100mgL(-1)), the E. coli DH5α harboring ophB degraded about 97% initial chlorpyrifos (100mgL(-1)) and accumulated 86mgL(-1) 3,5,6-trichloro-2-pyridinol (TCP) within 9 days. In addition, optical density (OD) of E. coli DH5α (ophB) culture at 600nm was increased from 0.172 to 1.118 within 2 days of inoculation in the chlorpyrifos supplemented M9 medium. The estimated molecular weight of purified OphB protein was determined to be 31.4kDa by SDS-PAGE. The OphB enzyme was most active at pH 8 and an optimal temperature around 35°C. These results indicate that endophytic bacteria are supposed to be useful for biological control of environments contaminated with pesticides.

Biodegradation of 2-hydroxyquinoxaline (2-HQ) by Bacillus sp

An aerobic Gram +ve bacterial strain capable of utilizing 2-Hydroxyquinoxaline (2-HQ) as sole source of carbon and energy was isolated from Chrysanthemum indicum Indian agricultural soil and named as HQ2. On the basis of morphology, physico-biochemical characteristics and 16S rRNA sequence analysis, strain HQ2 was identified as Bacillus sp. The generation time of Bacillus sp. in log phase during growth on 2-HQ is 0.79 h or 47.4 min. The optimal conditions for 2-HQ degradation by Bacillus sp. were inoculum density of 1.0 OD, pH of 6-8, temperature of 37-45 °C and 2-HQ concentration of 500 ppm. Among the additional carbon and nitrogen sources, carbon sources did not influence the degradation rate of 2-HQ, but nitrogen sources-yeast extract marginally enhanced the rate of degradation of 2-HQ. GC-MS analysis of the culture Bacillus sp. grown on 2-HQ indicated the formation of dimers from 2 molecules of 2-hydroxyquinoxaline. The formation of dimer for degradation of 2-HQ by the culture appears to be the first report to our scientific knowledge.

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.

Cytotoxic effect of chlorpyrifos ethyl and its degradation derivatives by Pseudomonas peli strain isolated from the Oued Hamdoun River (Tunisia)

A bacterium was isolated from the river of Oued Hamdoun (Tunisia), and its phenotypic features, physiological and chemotaxonomic characteristics and phylogenetic analysis of 16S ribosomal RNA sequence revealed it as Pseudomonas peli ( P. peli). Chlorpyrifos ethyl (CP) was used as the sole source of carbon and energy by P. peli, and it was cometabolised in the presence of glucose. CP was completely degraded by P. peli after 96 h of shake incubation. High-performance liquid chromatography analysis indicated that the biodegradation kinetics was not affected by the addition of glucose into the culture medium. In the present study, only transient accumulation of one major no-identified product was observed after 48 h of incubation, with no other persistent metabolites detected. Cytotoxicity of CP, before and after biodegradation with P. peli, was evaluated in vitro using the MTT-colorimetric assay against three human cancer cell lines (A549, lung cell carcinoma, HT29, colon adenocarcinoma and MCF7, breast adenocarcinoma). CP reduced viability of all human cell lines in a dose-dependent manner. Its activity was very remarkable against A549 cell line. However, cytotoxicity strongly decreased in CP obtained after incubation with P. peli. Hence, we conclude that when incubated under appropriate conditions, P. peli has a metabolism that completely detoxifies CP.

Improving methyl parathion hydrolase to enhance its chlorpyrifos-hydrolysing efficiency

Methyl parathion hydrolase (MPH) can degrade a wide range of organophosphorus compounds, but its efficiency in hydrolysing chlorpyrifos, one of the most popular pesticides applied for crop protection, is much lower than that in hydrolysing the preferred substrate methyl parathion. In this study, random mutagenesis was adopted to improve MPH to enhance its efficiency in hydrolysing the poorly hydrolysed substrate chlorpyrifos. Rapid screening of the improved MPH variants was carried out using Bacillus subtilis WB800 secretory expression system to investigate the distribution of improved MPH variants based on the size of clear haloes as a result of chlorpyrifos hydrolysis. Four improved MPH variants were isolated, and one variant K3, in particular, showed a 5-fold increase in kcat value for chlorpyrifos hydrolysis. Furthermore, most of the MPH variants obtained in this study possessed enhanced thermostability and pH stability. The approaches adopted in this study could be extended to create other MPH variants with increased activity for hydrolysing other poorly hydrolysed substrates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Chlorpyrifos is one of the toxic organophosphorus compounds (OP compounds) widely used for insecticides control. Water, soil and foodstuff have been contaminated seriously by chlorpyrifos in some areas. It is urgent to find effective methods to remove its contamination. This work contributes to improve methyl parathion hydrolase (MPH) to enhance its efficiency in hydrolysing the poorly hydrolysed substrate chlorpyrifos. Our study brings new insights for enzymatic strategy for the decontamination of toxic OP compounds.

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.

Biotransformation of chlorpyrifos in riparian wetlands in agricultural watersheds: implications for wetland management

Biodegradation of the organophosphate insecticide chlorpyrifos (O,O-diethyl O-(3,5,6-trichloropyridin-2-yl) phosphorothioate) in sediments from wetlands and agricultural drains in San Joaquin Valley, CA was investigated. Sediments were collected monthly, spiked with chlorpyrifos, and rates of chlorpyrifos degradation were measured using a standardized aerobic biodegradation assay. Phosphoesterase enzyme activities were measured and phosphotriesterase activity was related to observed biodegradation kinetics. First-order biodegradation rates varied between 0.02 and 0.69 day(-1), after accounting for abiotic losses. The average rate of abiotic chlorpyrifos hydrolysis was 0.02 d(-1) at pH 7.2 and 30 °C. Sediments from the site exhibiting the highest chlorpyrifos degradation capacity were incubated under anaerobic conditions to assess the effect of redox conditions on degradation rates. Half-lives were 5 and 92 days under aerobic and anaerobic conditions, respectively. There was a consistent decrease in observed biodegradation rates at one site due to permanently flooded conditions prevailing during one sampling year. These results suggest that wetland management strategies such as allowing a wet-dry cycle could enhance degradation rates. There was significant correlation between phosphotriesterase (PTE) activity and the chlorpyrifos biotransformation rates, with this relationship varying among sites. PTE activities may be useful as an indicator of biodegradation potential with reference to the previously established site-specific correlations.

Biodegradation of chlorpyrifos and 3,5,6-trichloro-2-pyridinol by Cupriavidus sp. DT-1

A bacterial strain, Cupriavidus sp. DT-1, capable of degrading chlorpyrifos and 3,5,6-trichloro-2-pyridinol (TCP) and using these compounds as sole carbon source was isolated and characterized. Investigation of the degradation pathway showed that chlorpyrifos was first hydrolyzed to TCP, successively dechlorinated to 2-pyridinol, and then subjected to the cleavage of the pyridine ring and further degradation. The mpd gene, encoding the enzyme responsible for chlorpyrifos hydrolysis to TCP, was cloned and expressed in Escherichia coli BL21. Inoculation of chlorpyrifos-contaminated soil with strain DT-1 resulted in a degradation rate of chlorpyrifos and TCP of 100% and 94.3%, respectively as compared to a rate of 28.2% and 19.9% in uninoculated soil. This finding suggests that strain DT-1 has potential for use in bioremediation of chlorpyrifos-contaminated environments.

Degradation kinetics of chlorpyrifos and 3,5,6-trichloro-2-pyridinol (TCP) by fungal communities

Fungal isolates obtained from soil were used for degrading chlorpyrifos (CP) and TCP. The percentage degradation ranged from 69.4 to 89.8 for CP and 62.2 to 92.6 for TCP after one week. The values of K(s) and V(max) were different for different isolates. The K(s) ranged from 66.66 to 169.5mg/L and V(max) from 6.56 to 40.4 mg/L/d for CP and from 53.19 to 163.9 mg/L and 3.41 to 40.40 mg/L/d, respectively, for TCP. Fungal community showed high affinity for both CP and TCP. The genetic relatedness of isolate F1 to Aspergillus sp., F2 and F3 to Penicillium sp., F4 to Eurotium sp. and F5 to Emericella sp. were confirmed. The degradation potential was in the order: F1>F2=F3>F4>F5.

Purification and characterization of a novel chlorpyrifos hydrolase from Cladosporium cladosporioides Hu-01

Chlorpyrifos is of great environmental concern due to its widespread use in the past several decades and its potential toxic effects on human health. Thus, the degradation study of chlorpyrifos has become increasing important in recent years. A fungus capable of using chlorpyrifos as the sole carbon source was isolated from organophosphate-contaminated soil and characterized as Cladosporium cladosporioides Hu-01 (collection number: CCTCC M 20711). A novel chlorpyrifos hydrolase from cell extract was purified 35.6-fold to apparent homogeneity with 38.5% overall recovery by ammoniumsulfate precipitation, gel filtration chromatography and anion-exchange chromatography. It is a monomeric structure with a molecular mass of 38.3 kDa. The pI value was estimated to be 5.2. The optimal pH and temperature of the purified enzyme were 6.5 and 40°C, respectively. No cofactors were required for the chlorpyrifos-hydrolysis activity. The enzyme was strongly inhibited by Hg²⁺, Fe³⁺, DTT, β-mercaptoethanol and SDS, whereas slight inhibitory effects (5–10% inhibition) were observed in the presence of Mn²⁺, Zn²⁺, Cu²⁺, Mg²⁺, and EDTA. The purified enzyme hydrolyzed various organophosphorus insecticides with P-O and P-S bond. Chlorpyrifos was the preferred substrate. The Km and Vmax values of the enzyme for chlorpyrifos were 6.7974 μM and 2.6473 μmol·min⁻¹, respectively. Both NH2-terminal sequencing and matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometer (MALDI-TOF-MS) identified an amino acid sequence MEPDGELSALTQGANS, which shared no similarity with any reported organophosphate-hydrolyzing enzymes. These results suggested that the purified enzyme was a novel hydrolase and might conceivably be developed to fulfill the practical requirements to enable its use in situ for detoxification of chlorpyrifos. Finally, this is the first described chlorpyrifos hydrolase from fungus.

Phytoremediation of chlorpyrifos by Populus and Salix

Chlorpyrifos is one of the commonly used organophosphorus insecticides that are implicated in serious environmental and human health problems. To evaluate plant potential for uptake of chlorpyrifos, several plant species of poplar (Populus sp.) and willow (Salix sp.) were investigated. Chlorpyrifos was taken up from nutrient solution by all seven plant species. Significant amounts of chlorpyrifos accumulated in plant tissues, and roots accumulated higher concentrations of chlorpyrifos than did shoots. Chlorpyrifos did not persist in the plant tissues, suggesting further metabolism of chlorpyrifos in plant tissue. To our knowledge, this work represents the first report for phytoremediation of chlorpyrifos using poplar and willow plants.

Adsorption and degradation of triazophos, chlorpyrifos and their main hydrolytic metabolites in paddy soil from Chaohu Lake, China

Triazophos and chlorpyrifos are organophosphorus pesticides (OPs), and their primary hydrolytic metabolites are 1-phenyl-3-hydroxy-1,2,4-triazole (BZC) and 3,5,6-trichloro-2-pyridinol (TCP). In this study, the adsorption and degradation of triazophos, chlorpyrifos, BZC and TCP were investigated in paddy soil from Chaohu Lake, China. Adsorption tests demonstrated that the adsorption of these compounds to soils could be described by the Freundlich equation. Moreover, chlorpyrifos displayed the highest affinity for adsorption, followed by triazophos, BZC and TCP. Degradation of these compounds in non-sterile soil followed first-order exponential decay kinetics, and the half-life (t(1/2)) of these contaminants ranged from 8.40 to 44.34 d. Sterilization of soil decreased the degradation rate, indicating that microorganisms played a significant role in the degradation of these compounds. The values of t(1/2) and K(oc) were fitted to obtain models that could predict the leaching potential of the contaminants from soil. Compared to their parent compounds, BZC and TCP showed high potential for leaching into groundwater. The inoculation of OPs-degrading bacterium (Diaphorobacter sp. GS-1) removed 95.38%, 100% and 100% of triazophos, chlorpyrifos and BZC in paddy soil after 21 d, respectively. The pollution risk of triazophos, chlorpyrifos and BZC could be greatly decreased by inoculating soil with Diaphorobacter sp. GS-1, which decreases the t(1/2) of the contaminants.

Chlorpyrifos degradation by the cyanobacterium Synechocystis sp. strain PUPCCC 64

BACKGROUND, AIM, AND SCOPE

Indiscriminate use of insecticides leads to environmental problems and poses a great threat to beneficial microorganisms. The aim of the present work was to study chlorpyrifos degradation by a rice field cyanobacterium Synechocystis sp. strain PUPCCC 64 so that the organism is able to reduce insecticide pollution in situ.

MATERIAL AND METHODS

The unicellular cyanobacterium isolated and purified from a rice field was identified by partial 16S rRNA gene sequence as Synechocystis sp. strain PUPCCC 64. Tolerance limit of the organism was determined by studying its growth in graded concentrations (2.5-20 mg/L) of chlorpyrifos. Chlorpyrifos removal was studied by its depletion from the insecticide supplemented growth medium, and its biodegradation products were identified in the cell extract, biomass wash, and growth medium.

RESULTS AND DISCUSSION

The organism tolerated chlorpyrifos up to 15 mg/L. Major fraction of chlorpyrifos was removed by the organism during the first day followed by slow uptake. Biomass, pH, and temperature influenced the insecticide removal and the organism exhibited maximum chlorpyrifos removal at 100 mg protein/L biomass, pH 7.0, and 30°C. The cyanobacterium metabolized chlorpyrifos producing a number of degradation products as evidenced by GC-MS chromatogram. One of the degradation products was identified as 3,5,6-trichloro-2-pyridinol.

CONCLUSION AND RECOMMENDATIONS

Present study reports the biodegradation of chlorpyrifos by Synechocystis sp. Biodegradation of the insecticide by the cyanobacterium is significant as it can be biologically removed from the environment. The cyanobacterium may be used for bioremediation of chlorpyrifos-contaminated soils.

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.

Simultaneous degradation of mixed insecticides by mixed fungal culture isolated from sewage sludge

The degradation of mixed (DDT and chlorpyrifos) insecticides by mixed insecticide enriched cultures was investigated. The mixed fungal population was isolated from mixed insecticide acclimatized sewage sludge over a period of 90 days. Gas chromatography was used to detect the concentration of mixed insecticides and calculate the degradation efficiency. The results showed that the degradation capability of the mixed microbial culture was higher in low concentrations than in high concentrations of the mixed insecticides. After 12 weeks of incubation, mixed pesticide enriched cultures were able to degrade 79.5-94.4% of DDT and 73.6-85.9% of chlorpyrifos in facultative cometabolic conditions. The fungal strains isolated from the mixed microbial consortium were identified as Fusarium sp. isolates GFSM-4 (ITCC 6841) and GFSM-5 (ITCC 6842). The fungal culture GFSM-4 could not utilize mixed insecticides as source of carbon and nitrogen, probably due to high combined toxicity of the mixed insecticides. Liquid media deficient in carbon (1% mannitol) and nitrogen (0.1% sodium nitrate) source increased the degradation efficiency of DDT and chlorpyrifos to 69 and 45%, respectively. The media with normal carbon and deficient nitrogen (0.1% sodium nitrate) sources extensively increased the degradation efficiencies of DDT (94%) and chlorpyrifos (69.2%). Traces of p,p'-dichlorobenzophenone and desdiethylchlorpyrifos were observed in the liquid medium, which did not accumulate probably due to further rapid degradation. This fungal isolate (GFSM-4) was able to degrade simultaneously DDT (26.94%) and chlorpyrifos (24.94%) in sterile contaminated (50 mg of each insecticide kg(-1)) soil in aerobic conditions.

Organophosphorus hydrolase (OpdB) of Lactobacillus brevis WCP902 from kimchi is able to degrade organophosphorus pesticides

Lactobacillus brevis WCP902 that is capable of biodegrading chlorpyrifos was isolated from kimchi. The opdB gene cloned from this strain revealed 825 bp, encoding 274 aa, and an enzyme molecular weight of about 27 kDa. OpdB contains the same Gly-X-Ser-X-Gly motif found in most bacterial and eukaryotic esterase, lipase, and serine hydrolases, yet it is a novel member of the GDSVG family of esterolytic enzymes. Its conserved serine residue, Ser82, is significantly involved with enzyme activity that may have application for removing some pesticides. Optimum organophosphorus hydrolase (OpdB) activity appeared at pH 6.0 and 35 degrees C and during degradation of chlorpyrifos, coumaphos, diazinon, methylparathion, and parathion.

Effects of drain-fill cycling on chlorpyrifos mineralization in wetland sediment-water microcosms

Constructed treatment wetlands are efficient at retaining a range of pesticides, however the ultimate fate of many of these compound is not well understood. This study evaluated the effect of drain-fill cycling on the mineralization of chlorpyrifos, a commonly used organophosphate insecticide, in wetland sediment-water microcosms. Monitoring of the fate of (14)C ring-labeled chlorpyrifos showed that drain-fill cycling resulted in significantly lower mineralization rates relative to permanently flooded conditions. The reduction in mineralization was linked to enhanced partitioning of the pesticide to the sediment phase, which could potentially inhibit chlorpyrifos hydrolysis and mineralization. Over the nearly two-month experiment, less than 2.5% of the added compound was mineralized. While rates of mineralization in this experiment were higher than those reported for other soils and sediments, their low magnitude underscores how persistent chlorpyrifos and its metabolites are in aquatic environments, and suggests that management strategies and ecological risk assessment should focus more on ultimate mineralization rather than the simple disappearance of the parent compound.

Comparative toxicity of chlorpyrifos and its oxon derivatives to soil microbial activity by combined methods

The inhibitory effects of the pesticide Chlorpyrifos (CPF) and its oxon derivative (CPO) on soil microbial activity were evaluated through the measurement of metabolic parameters and the microbial urease enzyme. The thermodynamic parameters related to microbial activity were measured and recorded as power-time curves. Microbial growth rate constant k, total heat evolution Q(T), metabolic enthalpy DeltaH(met), mass specific heat rate J(Q/S), microbial biomass C and inhibitory ratio I were calculated. They showed the linear relationship with doses of CPF and CPO. Thereinto, the linear correlations, k versus biomass C and DeltaH(met) versus biomass C, elucidated that k and DeltaH(met) were growth yield dependent. In this work, 20% inhibitory ratio IC(20) was obtained with 9.8 microg g(-1) for CPF and 0.37 microg g(-1) CPO, meaning that the acute toxicity of CPO was 26 times that of CPF, since the CPO had more potent toxicity to living organism due to its active functional group. Comparing the change tendency of DeltaH(met) and other parameter, the values almost kept constant when exposure to CPF (<5.0 microg g(-1)). It illustrates that individual reacted to stress resulted from environment change by shifting resources from other biological activities (such as reproduction or growth) toward survival to some extent. Urease activity responses in relation to the CPF and CPO exposure were observed and consistent with above thermodynamic parameters.

Immobilization of an enzyme from a Fusarium fungus WZ-I for chlorpyrifos degradation

The free enzyme extracted from WZ-I, which was identified as Fusarium LK. ex Fx, could effectively degrade chlorpyrifos, an organophosphate insecticide. The methods of immobilizing this free enzyme and determined its degradation-related characteristics were investigated. The properties of the immobilized enzyme were compared with those of the free enzyme. The optimal immobilization of the enzyme was achieved in a solution of 30 g/L sodium alginate at 4 degrees C for 4-12 hr. The immobilized enzyme showed the maximal activity at pH 8.0, 45 degrees C. The maximum initial rate and the substrate concentration of the immobilized enzyme were less than that of the free enzyme. The immobilized enzyme, therefore, had a higher capacity to withstand a broader range of temperatures and pH conditions than the free enzyme. With varying pH and temperatures, the immobilized enzyme was more active than the free enzyme in the degradation reaction. In addition, the immobilized enzyme exhibited only a slight loss in its initial activity, even after three repeated uses. The results showed that the immobilized enzyme was more resistant to different environmental conditions, suggesting that it was viable for future practical use.

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.

Biodegradation of chlorpyrifos by lactic acid bacteria during kimchi fermentation

We examined the role of microorganisms in the degradation of the organophosphorus (OP) insecticide chlorpyrifos (CP) during kimchi fermentation. During the fermentation of kimchi, 30 mg L(-1) of CP was added and its stability assayed during fermentation. CP was degraded rapidly until day 3 (83.3%) and degraded completely by day 9. Four CP-degrading lactic acid bacteria (LAB) were isolated from kimchi fermentation in the presence of 200 mg L(-1) CP and were identified as Leuconostoc mesenteroides WCP907, Lactobacillus brevis WCP902, Lactobacillus plantarum WCP931, and Lactobacillus sakei WCP904. CP could be utilized by these four strains as the sole source of carbon and phosphorus. Coumaphos (CM), diazinon (DZ), parathion (PT), and methylparathion (MPT) were also degraded by WCP907, WCP902, WCP931, and WCP904 when provided as sole sources of carbon and phosphorus.

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

A chlorpyrifos-methyl (CM) degrading bacterium (designated strain KR100) was isolated from a Korean rice paddy soil and was further tested for its sensitivity against eight commercial antibiotics. Based on morphological, biochemical, and molecular characteristics, this bacterium showed greatest similarity to members of the order Burkholderiales and was shown to be most closely related to members of the Burkholderia cepacia group. Strain KR100 hydrolyzed CM to 3,5,6-trichloro-2-pyridinol (TCP) and utilized TCP as the sole source of carbon for its growth. The isolate was also able to degrade chlorpyrifos, dimethoate, fenitrothion, malathion, and monocrotophos at 300 microg/ml but diazinon, dicrotophos, parathion, and parathion-methyl at 100 microg/ml. The ability to degrade CM was found to be encoded on a single plasmid of approximately 50 kb, pKR1. Genes encoding resistance to amphotericin B, polymixin B sulfate, and tetracycline were also located on the plasmid. This bacterium merits further study as a potential biological agent for the remediation of soil, water, or crop contaminated with organophosphorus compounds because of its greater biodegradation activity and its broad specificity against a range of organophosphorus insecticides.

Biodegradation of chlorpyrifos in soil by enriched cultures

Three aerobic bacterial consortia, AC, BC, and DC, developed from pesticide-contaminated soils of Punjab were able to degrade chlorpyrifos after 21 days of incubation in basal medium by 54, 46, and 61% and chlorpyrifos (50 mg/L) in soil after 30 days by 50, 56, and 64%. Pseudomonas aeruginosa, Bacillus cereus, Klebsiella sp., and Serratia marscecens obtained from these consortia showed 84, 84, 81, and 80% degradation of chlorpyrifos (50 mg/L) in liquid medium after 20 days and 92, 60, 56, and 37% degradation of chlorpyrifos (50 mg/L) in soil after 30 days. Populations of Bacillus cereus, Klebsiella sp., and Serratia marscecens remained steady in soil experiments except for P. aeruginosa, where the population showed a substantial increase. Formation of 3,5,6-trichloro-2-pyridinol, the major metabolite of chlorpyrifos degradation, was observed during the degradation of chlorpyrifos by P. aeruginosa, which disappeared to negligible amounts.

Cloning of active human manganese superoxide dismutase and its oxidative protection in Escherichia coli

Superoxide radical (O2*-) is a toxic byproduct of oxidative metabolism that extensively damages cellular macromolecules and organelles. Superoxide dismutase (SOD) catalyzes the conversion of superoxide radical to hydrogen peroxide (H2O2) and molecular oxygen (O2) thus providing a biological defense against oxygen toxicity. The structural gene of human manganese superoxide dismutase (hMnSOD) was successfully cloned into the pET46Ek/LIC by using a Ligation Independent Cloning (LIC) technique. The recombinant human MnSOD was expressed in E. coli strain BL21(DE3)pLysS and purified to homogeneity by Ni2+ -NTA. Supplementation of Mn2+ in the bacterial growth media was proven to be crucial for production of enzymatically active hMnSOD. The recombinant enzyme revealed a specific activity up to 2,857 U mg(-1) as measured by inhibition of photoreduction of nitroblue tetrazolium (NBT). The molecular weight of each subunit was estimated to be 22 kDa by SDS-PAGE. More interestingly, E. coli expressing hMnSOD provides resistance against oxidative stress induced by the herbicide paraquat up to 1.2 mM. These findings gain insights into the biochemical characterization and significant roles of oxidative-protection of the hMnSOD in biological systems.

Wheat yield dynamics: a structural econometric analysis

In this study we initially have tried to explore the wheat situation in Turkey, which has a small-open economy and in the member countries of European Union (EU). We have observed that increasing the wheat yield is fundamental to obtain comparative advantage among countries by depressing domestic prices. Also the changing structure of supporting schemes in Turkey makes it necessary to increase its wheat yield level. For this purpose, we have used available data to determine the dynamics of wheat yield by Ordinary Least Square Regression methods. In order to find out whether there is a linear relationship among these series we have checked each series whether they are integrated at the same order or not. Consequently, we have pointed out that fertilizer usage and precipitation level are substantial inputs for producing high wheat yield. Furthermore, in respect for our model, fertilizer usage affects wheat yield more than precipitation level.

Mineralization of chlorpyrifos by co-culture of Serratia and Trichosporon spp

A bacterial strain (Serratia sp.) that could transform chlorpyrifos to 3,5,6-trichloro-2-pyridinol (TCP) and a TCP-mineralizing fungal strain (Trichosporon sp.) were isolated from activated sludge by enrichment culture technique. The fungus could also degrade 50 mg chlorpyrifos l(-1) within 7 days. Co-cultures completely mineralized 50 mg chlorpyrifos l(-1) within 18 h at 30 degrees C and pH 8 using a total inocula of 0.15 g biomass l(-1).

Isolation of a chlorpyrifos-degrading bacterium, Sphingomonas sp. strain Dsp-2, and cloning of the mpd gene

A highly effective chlorpyrifos-degrading bacterium strain Dsp-2 was isolated from the polluted treatment system of a chlorpyrifos manufacturer. This strain was preliminarily identified as Sphingomonas sp. based on its morphological, physiological and biochemical tests as well as 16S rDNA analysis. It utilized chlorpyrifos as its sole source of carbon for growth, by hydrolyzing chlorpyrifos to 3,5,6-trichloro-2-pyridinol (TCP). It could also utilize parathion, parathion-methyl, fenitrothion and profenofos, but not phoxin and triazophos. Bioremediation of chlorpyrifos-contaminated soil was examined using Dsp-2. Dsp-2 addition to soil treated with 100mgkg(-1) chlorpyrifos resulted in a higher degradation rate than control soils without inoculation. The moderate pH, moisture and inoculum density could have promoted degradation. The gene encoding the chlorpyrifos hydrolytic enzyme was cloned by PCR. Although BLAST sequence search results indicated that this gene has 99% similarity to mpd (a gene encoding the parathion-methyl hydrolyzing enzyme in Plesiomonas sp. M6), its hydrolytic efficiency for chlorpyrifos was significantly greater than the wild-type mpd from strain M6.

Microbial degradation of organophosphorus xenobiotics: metabolic pathways and molecular basis

Organophosphorus (OP) xenobiotics are used worldwide as pesticides and petroleum additives. OP compounds share the major portion of the pesticide market globally. Owing to large-scale use of OP compounds, contaminations of soil and water systems have been reported from all parts of the world. OP compounds possess very high mammalian toxicity and therefore early detection and subsequent decontamination and detoxification of the polluted environment is essential. Additionally, about 200,000 tons of extremely toxic OP chemical warfare agents are required to be destroyed by 2007 under Chemical Warfare Convention (1993). Chemical and physical methods of decontamination are not only expensive and time-consuming, but also in most cases they do not provide a complete solution. These approaches convert compounds from toxic into less toxic states, which in some cases can accumulate in the environment and still be toxic to a range of organisms. Bioremediation provides a suitable way to remove contaminants from the environment as, in most of the cases, OP compounds are totally mineralized by the microorganisms. Most OP compounds are degraded by microorganisms in the environment as a source of phosphorus or carbon or both. Several soil bacteria have been isolated and characterized, which can degrade OP compounds in laboratory cultures and in the field. The biochemical and genetic basis of microbial degradation has received considerable attention. Several genes/enzymes, which provide microorganisms with the ability to degrade OP compounds, have been identified and characterized. Some of these genes and enzymes have been engineered for better efficacy. Bacteria capable of complete mineralization are constructed by transferring the complete degradation pathway for specific compounds to one bacterium. In the present article, we review microbial degradation and metabolic pathways for some OP compounds. The biochemical and molecular basis of OP degradation by microbes and the evolution and distribution of genes/enzymes are also reviewed. This article also examines applications and future use of OP-degrading microbes and enzymes for bioremediation, treatment of OP poisoning, and as biosensors.

Cloning of mpd gene from a chlorpyrifos-degrading bacterium and use of this strain in bioremediation of contaminated soil

An effective chlorpyrifos-degrading bacterium (named strain YC-1) was isolated from the sludge of the wastewater treating system of an organophosphorus pesticides manufacturer. Based on the results of phenotypic features, phylogenetic similarity of 16S rRNA gene sequences and BIOLOG test, strain YC-1 was identified as the genus Stenotrophomonas. The isolate utilized chlorpyrifos as the sole source of carbon and phosphorus for its growth and hydrolyzed chlorpyrifos to 3,5,6-trichloro-2-pyridinol. Parathion, methyl parathion, and fenitrothion also could be degraded by strain YC-1 when provided as the sole source of carbon and phosphorus. The gene encoding the organophosphorus hydrolase was cloned using a PCR cloning strategy based on the known methyl parathion degrading (mpd) gene of Plesiomonas sp. M6. Sequence blast result indicated this gene has 99% similar to mpd. The inoculation of strain YC-1 (10(6) cells g(-1)) to soil treated with 100 mg kg(-1) chlorpyrifos resulted in a higher degradation rate than in noninoculated soils. Theses results highlight the potential of this bacterium to be used in the cleanup of contaminated pesticide waste in the environment.