Biodegradation of monocrotophos by Brucella intermedia Msd2 isolated from cotton plant.

Widespread and inadequate use of Monocrotophos has led to several environmental issues. Biodegradation is an ecofriendly method used for detoxification of toxic monocrotophos. In the present study, Msd2 bacterial strain was isolated from the cotton plant growing in contaminated sites of Sahiwal, Pakistan. Msd2 is capable of utilizing the monocrotophos (MCP) organophosphate pesticide as its sole carbon source for growth. Msd2 was identified as Brucella intermedia on the basis of morphology, biochemical characterization and 16S rRNA sequencing. B. intermedia showed tolerance of MCP up to 100 ppm. The presence of opd candidate gene for pesticide degradation, gives credence to B. intermedia as an effective bacterium to degrade MCP. Screening of the B. intermedia strain Msd2 for plant growth promoting activities revealed its ability to produce ammonia, exopolysaccharides, catalase, amylase and ACC-deaminase, and phosphorus, zinc and potassium solubilization. The optimization of the growth parameters (temperatures, shaking rpm, and pH level) of the MCP-degrading isolate was carried out in minimal salt broth supplemented with MCP. The optimal pH, temperature, and rpm for Msd2 growth were observed as pH 6, 35 °C, and 120 rpm, respectively. Based on optimization results, batch degradation experiment was performed. Biodegradation of MCP by B. intermedia was monitored using HPLC and recorded 78% degradation of MCP at 100 ppm concentration within 7 days of incubation. Degradation of MCP by Msd2 followed the first order reaction kinetics. Plant growth promoting and multi-stress tolerance ability of Msd2 was confirmed by molecular analysis. It is concluded that Brucella intermedia strain Msd2 could be beneficial as potential biological agent for an effective bioremediation for polluted environments.

Neuroprotective Effect of N-acetylcysteine Against Monocrotophos-Induced Oxidative Stress in Different Brain Regions of Rats.

Monocrotophos (MCP) is systemic organophosphate insecticide used against crop pests. It is reported to cause mammalian toxicity through both acute and chronic exposure. In the present study, we have shown the protective role of N-acetylcysteine (NAC) against MCP-induced oxidative stress in frontal cortex, corpus striatum and hippocampus brain regions of rats. Male Albino Wistar rats were divided into control, NAC-treated, MCP and NAC + MCP-treated groups. An oral dose of MCP (0.9 mg/kg b.wt) and NAC (200 mg/kg b.wt) was administered for 28 days. Results showed an increase in lipid peroxidation (LPO) and protein oxidation followed by decreased antioxidant enzymes after 28 days of MCP exposure. Histopathological analysis showed that monocrotophos exposure caused neurodegenerative changes as evident by neurons with dystrophic changes in the form of shrunken hyperchromatic nuclei in all the regions of the rat brain. N-acetylcysteine supplementation to MCP-treated rats showed a reduction in oxidative stress and ameliorated cellular alterations in all of the three regions. The results of the study indicate that N-acetylcysteine offers neuroprotection by improving antioxidant response and decreasing oxidative stress in different regions of the rat brain.

N-acetylcysteine ameliorates monocrotophos exposure-induced mitochondrial dysfunctions in rat liver.

Background: Monocrotophos (MCP) is an organophosphate pesticide with well-known toxicity in mammals. Exposure of MCP is associated with altered molecular physiology at sub-cellular levels. This study investigated the efficacy of N-acetylcysteine (NAC) against MCP exposure mediated mitochondrial dysfunctions in hepatic tissue of rats.Methods: Male Wistar rats were given NAC (200 mg/kg b.wt), MCP (0.9 mg/kg b.wt) and NAC together with MCP, intragastrically for 28 consecutive days. Mitochondrial complexes activities were evaluated using biochemical analysis. mRNA expression of mitochondrial complexes subunits, PGC-1α and its downstream regulators were analyzed using polymerase chain reaction.Results: Exposure of MCP (0.9 mg/kg b.wt, intragastrically, 28 d) decreased mitochondrial complexes activities and gene expression of complexes subunits. The expression of PGC-1α, NRF-1, NRF-2, and Tfam was also reduced significantly. The administration of NAC (200 mg/kg b.wt, intragastrically, 28 d) significantly increased mitochondrial complexes activities and gene expression of complexes subunits. Additionally, NAC also maintained mitochondrial functions, and enhanced the gene expression of PGC-1α and its downstream regulators.Conclusion: The results of this study indicate that NAC prevents hepatic mitochondrial dysfunctions and maintains PGC-1α signaling. In conclusion, NAC might be speculated as a therapeutic agent for mitochondrial dysfunctions following toxic exposures.

Biodegradation of insecticide monocrotophos by Bacillus subtilis KPA-1, isolated from agriculture soils.

Twenty bacterial strains, which are capable of degrading monocrotophos, were isolated from five soil samples collected from agriculture soils in India. The ability of the strains to mineralize monocrotophos was investigated under different culture conditions. A potential strain degrading monocrotophos was selected and named KPA-1. The strain was identified as a Bacillus subtilis on the basis of the results of its cellular morphology, physiological and chemotaxonomic characteristics, and phylogenetic conclusion of 16S ribosomal DNA (rDNA) gene sequences. Organophosphate hydrolase (opdA gene) involved in the initial biodegradation of monocrotophos in KPA-1 was quantitatively expressed, which was a constitutively expressed cytosolic enzyme. RT-qPCR data revealed that KPA-1 harboring opdA gene in an early stage was significantly downregulated from opdA gene in a degradation stage (1.5 fold more) with a p value of 0.0375 (p < 0.05). We have optimized culture conditions for the efficient degradation (94.2 %) of monocrotophos under aerobic conditions. Growth and degradation kinetic studies proved that KPA-1 was able to grow in minimal salt medium containing 1000 ppm monocrotophos as the only carbon source. Hence, KPA-1 culture has a great potential utility for the bioremediation of agriculture soils contaminated with organophosphorus pesticides, particularly monocrotophos.

Effect of an organophosphate pesticide, monocrotophos, on phosphate-solubilizing efficiency of soil fungal isolates.

Soil is a sink of pesticide residues as well as microorganisms. Fungi are well known for solubilization of inorganic phosphates, and this activity of fungal isolates may be affected by the presence of pesticide residues in the soil. In the present study, five generically different fungal isolates, viz. Aspergillus niger JQ660373, Aspergillus flavus, Penicillium aculeatum JQ660374, Fusarium pallidoroseum and Macrophomina sp., were tested and compared for their phosphate-solubilizing ability in the absence and presence of monocrotophos (500 mg L(-1)). After 168 h of incubation, four times high amount of tricalcium phosphate was solubilized by isolates in the growth medium containing monocrotophos in comparison to control (without monocrotophos). Concurrently, 78 % of the applied monocrotophos was degraded by these fungal isolates. Kinetics of phosphate solubilization shifted from logarithmic to power model in the presence of monocrotophos. Similarly, the phosphatase activity was also found significantly high in the presence of monocrotophos. The combined order of phosphate solubilization as well as monocrotophos degradation was found to be A. niger JQ660373 > P. aculeatum JQ660374 > A. flavus > F. pallidoroseum > Macrophomina sp. On the contrary, phosphate solubilization negatively correlated with the pH of the growth medium. Hence, it could be concluded that these fungal species efficiently solubilize inorganic phosphates and monocrotophos poses a positive effect on their ability and in turn degraded by them. To the best of our knowledge, this is the first report on P solubilization by Macrophomina sp. and F. pallidoroseum.

Monocrotophos induces the expression and activity of xenobiotic metabolizing enzymes in pre-sensitized cultured human brain cells.

The expression and metabolic profile of cytochrome P450s (CYPs) is largely missing in human brain due to non-availability of brain tissue. We attempted to address the issue by using human brain neuronal (SH-SY5Y) and glial (U373-MG) cells. The expression and activity of CYP1A1, 2B6 and 2E1 were carried out in the cells exposed to CYP inducers viz., 3-methylcholanthrene (3-MC), cyclophosphamide (CPA), ethanol and known neurotoxicant- monocrotophos (MCP), a widely used organophosphorous pesticide. Both the cells show significant induction in the expression and CYP-specific activity against classical inducers and MCP. The induction level of CYPs was comparatively lower in MCP exposed cells than cells exposed to classical inducers. Pre-exposure (12 h) of cells to classical inducers significantly added the MCP induced CYPs expression and activity. The findings were concurrent with protein ligand docking studies, which show a significant modulatory capacity of MCP by strong interaction with CYP regulators-CAR, PXR and AHR. Similarly, the known CYP inducers- 3-MC, CPA and ethanol have also shown significantly high docking scores with all the three studied CYP regulators. The expression of CYPs in neuronal and glial cells has suggested their possible association with the endogenous physiology of the brain. The findings also suggest the xenobiotic metabolizing capabilities of these cells against MCP, if received a pre-sensitization to trigger the xenobiotic metabolizing machinery. MCP induced CYP-specific activity in neuronal cells could help in explaining its effect on neurotransmission, as these CYPs are known to involve in the synthesis/transport of the neurotransmitters. The induction of CYPs in glial cells is also of significance as these cells are thought to be involved in protecting the neurons from environmental insults and safeguard them from toxicity. The data provide better understanding of the metabolizing capability of the human brain cells against xenobiotics.

In vitro comparative analysis of monocrotophos degrading potential of Aspergillus flavus, Fusarium pallidoroseum and Macrophomina sp.

Fungal degradation is emerging as a new powerful tool for the removal of potent neurotoxin pesticide, monocrotophos. Therefore, the present study is aimed at comparative characterization of monocrotophos degrading ability of three different fungal strains. Fungal strains were isolated from local agricultural soil by enrichment culture method, screened by gradient culture and identified as Aspergillus flavus, Fusarium pallidoroseum and Macrophomina sp. Growth kinetics revealed a direct positive influence of monocrotophos on the viability of fungal isolates. Fungal degradation was studied in phosphorus free liquid culture medium supplemented with 150 mg L(-1) concentration of monocrotophos for a period of 15 days under optimized culture conditions. Degradation of MCP followed first order kinetics with kdeg of 0.007, 0.002 and 0.005 day(-1) and half life (t1/2) of 4.21, 12.64 and 6.32 days for A. flavus, F. pallidoroseum and Macrophomina sp. respectively. To the best of our knowledge, it is the first report signifying the potential of monocrotophos degradation by Fusarium and Macrophomina sp. The results were further confirmed by HPTLC and FTIR which indicates disappearance of monocrotophos by hydrolytic cleavage of vinyl phosphate bond. Degradation of monocrotophos by fungal isolates was accompanied by the release of extracellular alkaline phosphatases, inorganic phosphates and ammonia. The overall comparative analysis followed the order of A. flavus > Macrophomina sp. > F. pallidoroseum. Therefore, it could be concluded from the study that these three different fungal strains could be effectively used as a potential candidate for the removal of monocrotophos from contaminated sites.

Enzymatic degradation of monocrotophos by extracellular fungal OP hydrolases.

The present study explores the potential of extracellular fungal organophosphate (OP) hydrolase for the degradation of monocrotophos. Extracellular OP hydrolases were isolated and purified from five different fungal isolates viz. Aspergillus niger (M1), Aspergillus flavus (M2), Penicillium aculeatum (M3), Fusarium pallidoroseum (M4), and Macrophomina sp. (M5) by AmSO4 precipitation, dialysis, and G-100 chromatography. M3 showed highest percentage yield of 68.81 followed by 55.41 % for M1. Each of the purified enzyme fraction constituted of two different subunits of 33- and 67-kDa molecular weight. Optimum enzyme fraction (150 µg ml(-1)) rapidly degraded monocrotophos within 120 h in phosphorus-free liquid culture medium (CZM) with K deg of 0.0368, 0.0138, 0.048, 0.016, 0.0138, and 0.048 day(-1) and half-life of 0.79, 2.11, 0.6, 1.8, and 2.11 days for M1, M2, M3, M4, and M5, respectively. The results were further confirmed by high performance thin layer chromatography and Fourier transform infrared which indicate the disappearance of monocrotophos by hydrolytic cleavage of vinyl phosphate bond. The overall order of enzymatic degradation was found to be P. aculeatum > A. niger > F. pallidoroseum > A. flavus = Macrophomina sp. Hence, the study concludes that extracellular OP hydrolases efficiently degraded monocrotophos and could be used as a potential candidate for the detoxification of this neurotoxin pesticide.

Comparative purification and characterization of two distinct extracellular monocrotophos hydrolases secreted by Penicillium aculeatum and Fusarium pallidoroseum isolated from agricultural fields.

The present study aimed at a comparative characterization of two distinct extracellular monocrotophos hydrolases, from Penicillium aculeatum ITCC 7980.10 (M3) and Fusarium pallidoroseum ITCC 7785.10 (M4), isolated from agricultural fields. The MCP hydrolases were purified by Sephadex G-100 column and DEAE-Sepharose CL-6B ion-exchange column followed by SDS-PAGE analysis, which showed the presence of two hydrolases, of 33 and 67 kDa respectively. Both enzymes were most active at alkaline pH and were stable over a wide range of temperatures (60-70 °C). Between the strains, the MCP hydrolases from M3 were 2-fold more active than that from M4. Enzyme kinetic studies showed lowest Km (33.52 mM) and highest Vmax (5.18 U/mg protein) for OPH67 of M3 in comparison to the Km and Vmax of the other hydrolases purified from M3 and M4, suggesting that M3 OPH67 was the most efficient MCP hydrolase. To the best of our knowledge, this is the first report of the purification of two distinct extracellular thermostable MCP hydrolases from fungal strains Penicillium aculeatum ITCC 7980.10 and Fusarium pallidoroseum ITCC 7785.10. Owing to its potential MCP hydrolyzing activity, M3 OPH67 can perhaps used directly or in the encapsulated form for remediation of MCP contaminated sites.

Pesticide tolerant and phosphorus solubilizing Pseudomonas sp. strain SGRAJ09 isolated from pesticides treated Achillea clavennae rhizosphere soil.

In this study, an attempt was made to identify an effective phosphate solubilizing bacteria from pesticide polluted field soil. Based on the formation of solubilization halo on Pikovskaya's agar, six isolates were selected and screened for pesticide tolerance and phosphate (P) solubilization ability through liquid assay. The results showed that only one strain (SGRAJ09) obtained from Achillea clavennae was found to tolerate maximum level of the pesticides tested and it was phylogenetically identified as Pseudomonas sp. It possessed a wide range of pesticide tolerance, ranging from 117 µg mL(-1) for alphamethrin to 2,600 µg mL(-1) for endosulfan. The available P concentrations increased with the maximum and double the maximum dose of monocrotophos and imidacloprid, respectively. On subjected to FT-IR and HPLC analysis, the presence of organic acids functional group in the culture broth and the production of gluconic acid as dominant acid aiding the P solubilization were identified. On comparison with control broth, monocrotophos and imidacloprid added culture broth showed quantitatively high organic acids production. In addition to gluconic acid production, citric and acetic acids were also observed in the pesticide amended broth. Furthermore, the Pseudomonas sp. strain SGRAJ09 possessed all the plant growth promoting traits tested. In presence of monocrotophos and imidacloprid, its plant growth promoting activities were lower than that of the pesticides unamended treatment.

Assessment of dermal exposure to pesticide residues during re-entry.

Currently, the determination of health risks to pesticide applicators from dermal exposure to these chemicals is assessed using either a concentrate of the compound or a relevant aqueous dilution. Neither of these conditions reflects a normal exposure of an individual when re-entering an area after pesticide application, that is, contact with dried residue of the diluted product on foliage. Methodology has therefore been developed to determine a relevant estimate of this potential dermal re-entry exposure from pesticide residues. Potential delivery platforms have been characterized for the transfer of pesticide residue to skin. Spin coating has been used to deposit uniform pesticide layers on to each platform. Five pesticides have been chosen to encompass a wide range of physicochemical properties: atrazine, 2,4-dichlorophenoxyacetic acid (2,4-D), chlorpyrifos, monocrotophos, and acetochlor. In vitro (Franz diffusion cell) experiments have been performed to monitor the transfer of these pesticides from the delivery platforms onto and through excised porcine skin. Parallel experiments were also conducted with aqueous pesticide dilutions for comparison, and a final in vivo measurement using ibuprofen (as a model compound) complemented the in vitro data. The results demonstrate that transfer of chemical residue onto and subsequently through the skin is dependent on the physical attributes of the residue formed. Thus, assessing dermal exposure to pesticides based on skin contact with either the chemical concentrate or a relevant aqueous dilution may incorrectly estimate the risk for re-entry scenarios.

Acetylcholinesterase biosensor based on gold nanoparticles and cysteamine self assembled monolayer for determination of monocrotophos.

In this paper, a simple method for immobilization of acetylcholinesterase (AChE) on cysteamine assembled glassy carbon electrode coupled with gold nanoparticles (GNPs) was proposed and thus a sensitive, fast and stable amperometric biosensor for quantitative determination of monocrotophos was developed. The fabrication procedure was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and contact angles. The presence of GNPs not only led to an increased effective surface to provide a sufficient amount of sites for binding enzyme, but also promoted electron transfer reactions and catalyzed the electro-oxidation of thiocholine, thus amplifying the detection sensitivity. Due to the notable decrease in voltammetric signal of the immobilized AChE, a simple method for determination of monocrotophos was established. The inhibition of monocrotophos was proportional to its concentration in two ranges, from 0.5 to 10 ng mL(-1) and from 10 to 600 ng mL(-1), with a detection limit lower than 0.3 ng mL(-1). The constructed biosensor processing prominent characteristics and performance such as good precision and reproducibility, acceptable stability and accuracy, fast response and low detection limit has potential application in detection of toxic compounds.

Influence of endosulfan and monocrotophos exposure on the activity of NADPH cytochrome C reductase (NCCR) of Labeo rohita (Ham).

The response of NADPH cytochrome C reductase (NCCR) activity in liver of Labeo rohita fish exposed to the pesticides, 0.25 microgl(-1) endosulfan and 2 mg/l monocrotophos was studied. In terms of specific enzyme activity (mU/mg protein) a significant level of NCCR was observed in the liver tissues of Labeo rohita exposed to the pesticides, when compared to the control fish (2.460 mU/mg protein). Increase of NCCR activity was more in the liver of the fish exposed to monocrotophos (4.595 mU/mg protein) than those exposed to endosulfan (2.850 mU/mg protein). The results demonstrate that the pesticides, endosulfan and monocrotophos, interfere with NADPH dependent monoxygenase mechanism and are effective inducers of NADPH cytochrome C reductase. The activity of NCCR in the liver tissue of Labeo rohita may serve as a useful tool for monitoring aquatic pollution.

Impact of repeated pesticide applications on the binding and release of methyl 14C-monocrotophos and U-ring labelled 14C-carbaryl to soil matrices under field conditions.

The dissipation of (O-methyl-14C) monocrotophos and U-ring labelled 14C-carbaryl was monitored for over two years in absence and presence of other insecticides using in situ soil columns. The dissipation of 14C-monocrotophos from soil treated with methomyl and carbaryl showed a faster rate of downward movement than in a control column tagged with the labelled insecticide alone. The same trend was observed in experiments with 14C-carbaryl that dissipated more readily in soil treated with non-labelled monocrotophos and methomyl. In the presence of other insecticides the percentage of bound residues was generally lower than in control experiments. The bound residues at the top of the column are released at a low rate under conditions prevailing in the field. The overall time required for dissipation of 50% of monocrotophos and carbaryl (t50) as estimated from control experiment was approximately 20 and 24 weeks, respectively. The data indicate that repeated applications of pesticides might enhance the release of 14C-bound residues.

[Isolation of a monocrotophos-degrading bacterial strain and characterization of enzymatic degradation].

A monocrotophos [dimethyl (E)-1-2-methylcarbamoylvinylphosphate or MCP] -degrading strain named as M-1 was isolated from sludge collected from the wastewater treatment pool of a pesticide factory and identified as Paracoccus sp. according to its morphology and biochemical properties and 16S rDNA sequence analysis. Using MCP as a sole carbon source, M-1 was able to degrade MCP(100 mg x L(-1)) by 92.47% in 24 h. The key enzyme(s) involved in the initial biodegradation of monocrotophos in M-1 was shown to be constitutively expressed cytosolic proteins and showed the greatest activity at pH 8.0 and 25 degrees C, with its Michaelis-Mentn's constant (K(m)) and maximum degradation rate (V(max)) of 0.29 micromol x mL(-1) and 682.12 micromol (min x mg)(-1) respectively. This degrading enzyme(s) was sensitive to high temperature, but kept high activity under alkaline conditions.

Isolation and characterization of a denitrifying monocrotophos-degrading Paracoccus sp. M-1.

A bacterium strain, which is capable of degrading monocrotophos, was isolated from sludge collected from the bottom of a wastewater treatment system of a chemical factory, and named M-1. On the basis of the results of the cellular morphology, physiological and chemotaxonomic characteristics and phylogenetic similarity of 16S rDNA gene sequences, the strain was identified as a Paracoccus sp. The ability of the strain to mineralize monocrotophos was investigated under different culture conditions. Other organophosphorus insecticides and amide herbicides were also degraded by M-1. The key enzyme (s) involved in the initial biodegradation of monocrotophos in M-1 was shown to be a constitutively expressed cytosolic protein. The addition of M-1 (10(6) CFU g(-1)) to fluvo-aquic soil and a high-sand soil containing monocrotophos (50 mg kg(-1)) resulted in a higher degradation rate than that obtained from noninoculated soil. This microbial culture has great potential utility for the bioremediation of wastewater or soil contaminated with organophosphorus pesticides and amide herbicides.

Purification and characterization of phosphotriesterases from Pseudomonas aeruginosa F10B and Clavibacter michiganense subsp. insidiosum SBL11.

A microbial biodegradation of monocrotophos was studied in the present investigation. The monocrotophos-degrading enzyme was purified and characterized from two soil bacterial strains. The cells were disrupted and the membrane-bound fractions were studied for purification and characterization. Solubilization of the membrane-bound fractions released nearly 80% of the bound protein. Phase separation further enriched the enzyme fraction 34-41 times. The enzyme phosphotriesterase (PTE) from both the strains was purified to more than 1000-fold with 13%-16% yield. Purified PTE from Clavibacter michiganense subsp. insidiosum SBL11 is a monomeric enzyme with a molecular mass of 43.5 kDa (pI of 7.5), while PTE from Pseudomonas aeruginosa F10B is a heterodimeric enzyme with a molecular mass of 43 and 41 kDa (pI of 7.9 and 7.35). Both purified enzymes are stable enzymes with peak activity at pH 9.0. The enzyme from strain F10B was more thermostable (half-life=7.3 h) than that from SBL11 (half-life=6.4 h at 50 degrees C), while both showed the same temperature optimum of 37 degrees C. Inhibitors like dithiothreitol and EDTA inhibited the purified enzyme, while p-chloromercuribenzoic acid and indoleacetic acid had a very little effect.

Hydrolysis of organophosphorus compounds by an esterase isozyme from insecticide resistant pest Helicoverpa armigera.

Esterase activity of resistant and susceptible H. armigera were compared in gels with different substrate such as naphthyl acetate, naphthyl phosphate, paraoxon and monocrotophos. Whole body extract of resistant H. armigera hydrolyzed paraoxon, monocrotophos and naphthyl phosphate in gels. Resistant H. armigera showed high esterase, phosphatase and paraoxon hydrolase activity compared to susceptible ones.

Identification of factors responsible for insecticide resistance in Helicoverpa armigera.

Moth larvae (Helicoverpa armigera Hübner) collected from field crops were tested for resistance to cypermethrin, fenvalerate, endosulfan, monocrotophos and quinolphos. Larvae were treated with a dose of the pesticide that would kill 99% of the susceptible insects. The percent survival of the resistant strains was determined. Highest seasonal average percentage survival was recorded by fenvalerate (65.0%) followed by cypermethrin (62.4%). Acetylcholinesterase of resistant larvae was less sensitive to monocrotophos and methyl paraoxon. Resistant larvae showed higher activities of esterases, phosphatases and methyl paraoxon hydrolase compared with susceptible larvae. The presence of high activity of esterases was attributed to appearance of extra bands of esterases in native PAGE. The presence of P-glycoprotein expression was detected in resistant larvae using P-gp antibodies; this was not detected in the susceptible larvae. Our results indicate that the high level of resistance detected in the field pests could be because of a combined effect of decreased sensitivity to AChE, higher levels of esterases, phosphatases and the expression of P-gp.

Esterase-mediated tolerance to a formulation of the organophosphate insecticide monocrotophos in the entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuill: a promising biopesticide.

The use of biopesticides compatible with chemical pesticides is recommended in pest management as an effective and ecologically sound strategy. The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuill, which is used as a biopesticide, was found to exhibit and lose tolerance to two organophosphorus insecticides widely used in Indian fields. The pattern of response is similar to the esterase-mediated organophosphate tolerance in aphids achieved through esterase gene duplication. Therefore the role of esterase in the tolerance exhibited by isolates of B. bassiana to the organophosphate, monocrotophos, was studied. Both the total soluble protein content and esterase activity were found to increase significantly in B. bassiana cultures that were able to grow in the presence of monocrotophos. With the hitherto established linkage between esterase overproduction and organophosphate tolerance in insects and the observed similarity in response of the insects and B. bassiana to the chemical, it is concluded that tolerance to monocrotophos in B. bassiana may be due to a mechanism similar to that operating in insects. Habituation of the fungus to monocrotophos to initiate expression of esterase gene may help in achieving compatibility between the two.