Oxidative biodegradation of phosphorothiolates by fungal laccase (original) (raw)
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Activation and Detoxication of S-Alkyl Phosphorothiolate Insecticides
Journal of Pesticide Science, 1984
Prothiophos oxon (S-propyl form) and its S-methyl, ethyl and butyl homologs were poor in vitro inhibitors of acetylcholinesterase (AChE), but the S-propyl and butyl oxons were highly insecticidal to houseflies, and inhibited ACNE in vivo. Evidence indicates that such 5alkyl oxons are converted to unstable intermediates by mixed function oxidase system, which have been oxidized on the sulfur and are more reactive with AChE in the case of the S-propyl and butyl oxons, when more hydrolyzable in the case of the S-methyl and ethyl oxons.
Chemosphere, 2007
Four organophosphorus compounds: azinphos-methyl, chlorpyrifos, malathion and malaoxon in aqueous solution were degraded by using a 125 W xenon parabolic lamp. Gas chromatography-mass spectrometry (GC-MS) was used to monitor the disappearance of starting compounds and formation of degradation products as a function of time. AChE-thermal lens spectrometric bioassay was employed to assess the toxicity of photoproducts. The photodegradation kinetics can be described by a first-order degradation curve C = C 0 e Àkt , resulting in the following half lives: 2.5 min for azinphos-methyl, 11.6 min for malathion, 13.3 min for chlorpyrifos and 45.5 min for malaoxon, under given experimental conditions. During the photoprocess several intermediates were identified by GC-MS suggesting the pathway of OP degradation. The oxidation of chlorpyrifos results in the formation of chlorpyrifos-oxon as the main identified photoproduct. In case of malathion and azinphos-methyl the corresponding oxon analogues were not detected. The formation of diethyl (dimethoxy-phosphoryl) succinate in traces was observed during photodegradation of malaoxon and malathion. Several other photoproducts including trimethyl phosphate esters, which are known to be AChE inhibitors and 1,2,3-benzotriazin-4(3H)-one as a member of triazine compounds were identified in photodegraded samples of malathion, malaoxon, and azinphos-methyl. Based on this, two main degradation pathways can be proposed, both result of the (P-S-C) bond cleavage taking place at the side of leaving group. The enhanced inhibition of AChE observed with the TLS bioassay during the initial 30 min of photodegradation in case of all four OPs, confirmed the formation of toxic intermediates. With the continuation of irradiation, the AChE inhibition decreased, indicating that the formed toxic compounds were further degraded to AChE non-inhibiting products. The presented results demonstrate the importance of toxicity monitoring during the degradation of OPs in processes of waste water remediation, before releasing it into the environment.
Microbial degradation of organophosphorus compounds
Fems Microbiology Reviews, 2006
Synthetic organophosphorus compounds are used as pesticides, plasticizers, air fuel ingredients and chemical warfare agents. Organophosphorus compounds are the most widely used insecticides, accounting for an estimated 34% of world-wide insecticide sales. Contamination of soil from pesticides as a result of their bulk handling at the farmyard or following application in the field or accidental release may lead occasionally to contamination of surface and ground water. Several reports suggest that a wide range of water and terrestrial ecosystems may be contaminated with organophosphorus compounds. These compounds possess high mammalian toxicity and it is therefore essential to remove them from the environments. In addition, about 200 000 metric tons of nerve (chemical warfare) agents have to be destroyed world-wide under Chemical Weapons Convention (1993). Bioremediation can offer an efficient and cheap option for decontamination of polluted ecosystems and destruction of nerve agents. The first micro-organism that could degrade organophosphorus compounds was isolated in 1973 and identified as Flavobacterium sp. Since then several bacterial and a few fungal species have been isolated which can degrade a wide range of organophosphorus compounds in liquid cultures and soil systems. The biochemistry of organophosphorus compound degradation by most of the bacteria seems to be identical, in which a structurally similar enzyme called organophosphate hydrolase or phosphotriesterase catalyzes the first step of the degradation. organophosphate hydrolase encoding gene opd (organophosphate degrading) gene has been isolated from geographically different regions and taxonomically different species. This gene has been sequenced, cloned in different organisms, and altered for better activity and stability. Recently, genes with similar function but different sequences have also been isolated and characterized. Engineered microorganisms have been tested for their ability to degrade different organophosphorus pollutants, including nerve agents. In this article, we review and propose pathways for degradation of some organophosphorus compounds by microorganisms. Isolation, characterization, utilization and manipulation of the major detoxifying enzymes and the molecular basis of degradation are discussed. The major achievements and technological advancements towards bioremediation of organophosphorus compounds, limitations of available technologies and future challenge are also discussed.
A theoretical approach to the mechanism of biological oxidation of organophosphorus pesticides
Toxicology, 2000
Organophosphorus pesticides are the most common classes involved in poisonings related to pesticides. We used enzymatic activity of chloroperoxidase on the metabolism of some phosphorothioate pesticides published previously and molecular mechanics methods to perform a theoretical approach of the mechanism of biological oxidation of this class of pesticides. The molecular structure of eight pesticides were optimized by molecular mechanics methods using the CAChe program package for biomolecules, ver. 3.11 (Oxford Molecular Ltd., Campbell, CA). Total energy resulted from the structure optimization process and the partial charges of both phosphorus and sulfur were computed for every pesticide. Phosphorus partial charge and enzymatic activity were significantly related by linear regression analysis (r=0.82, P B0.05). Analyzing our results and using previously reported enzymatic activity of chloroperoxidase on these pesticides, we deduced chemical events involved in activation of the active site of chloroperoxidase and proposed a novel mechanism of oxidation for this class of pesticides. This mechanism will also help to understand the oxidation process of pesticides by cytochrome P450, and production of toxic metabolites.
Chloroperoxidase-Mediated Oxidation of Organophosphorus Pesticides
Pesticide Biochemistry and Physiology, 1998
Chloroperoxidase from Caldariomyces fumago was tested for the oxidation of 10 organophosphorus pesticides. Organophosphorus pesticides containing the phosphorothioate group, azinphos-methyl, chlorpyrifos, dichlorofenthion, dimethoate, parathion, phosmet, and terbufos were oxidized by chloroperoxidase in the presence of hydrogen peroxide and chloride ions. The products were identified as oxon derivatives (phosphates), where the sulfur atom from the thioate group is substituted by an oxygen atom. No hydrolysis products were detected after enzymatic oxidation of these pesticides, and no halogenation of substrates was detected. Chloroperoxidase oxidation of relatively toxic organophosphorus pesticides produces metabolites similar to those formed by cytochrome P450 during the metabolic activation of pesticides in vivo. However, the major difference between these biocatalysts is that further cleavage of oxons, which is typical of the P450-catalyzed reaction, was not observed with chloroperoxidase.
Microbial Degradation of Organophosphorus Pesticides
Bioremediation and Phytoremediation Technologies in Sustainable Soil Management
Pesticide application increases crop yield by controlling, repelling, or destroying pests; but their excessive use cause harmful effects to various life forms including humans. When applied in large amounts, the agricultural pesticides move longer distances and can reach the water table at observable concentration. Consequently, pesticides can contaminate the areas which are far away from the sites where they were used actually. Among different groups of pesticides, organophosphorus pesticides (OPs) are applied globally and constitute the crucial and most commonly applied group which accounts for almost 36% of the entire world market. Methyl parathion (MP) is one of the most commonly used OPs. It has been recorded across the world that excessive use of OPs leads to the contamination of soil and water bodies and exposure to OPs causes disastrous effects to human health, various life forms and ecosystems. Thus, decontaminating pesticide contaminated area is a costly affair. Microorganisms play an important role in biodegradation of pesticides due to their adaptive nature to the environment that is contaminated. Mostly, organophosphorus compounds (OPCs) are completely mineralized by the microorganisms. Microorganisms degrade most of the OPCs as carbon or phosphorus source. From microbes, different enzymes have been isolated for studying and understanding the pathways involved in the biodegradation of OPs. 6.1 INTRODUCTION Pesticides are toxic chemical substances which are applied to control, repel, destroy, prevent, or mitigate any pest, i.e., insects, nematodes, mites, weeds, Apple Academic Press Author Copy Non Commercial Use 160 Bioremediation and Phytoremediation Technologies in Sustainable Soil Management, Volume 4 rats, etc.; hence beneficial for agricultural productivity [102]. On an average, 35% of potential crop productivity is destroyed all over the world to pre harvest pests [118]. Besides these, losses of food chain are also comparatively huge [68]. The world population is projected to rise in 2050 by 30% to nearly 9.2 billion. Therefore, agriculture has to meet an increasing demand for biofuel, food, fiber, feed, and other bio-based commodities [102]. Depletion of yield because of pests, weeds, and pathogens are main challenges to agricultural production worldwide [119]. Among crops, the potential damage caused by the pests ranges from almost 50% in wheat yield to over 80% in production of cotton at global level. Studies found 26-29% loss for cotton, soybean, and wheat and 40%, 37% and 31% for potatoes, rice, and maize, respectively [76]. In United States only, around 9.2 billion USD (United State Dollar) are invested on pesticides annually for improving crop production [102]. The 15-20 fold rises in the quantity of globally applied pesticides significantly improved the crop protection [118]. However, their excessive use results in the contamination of environment [15]. The pesticides are classed into four main groups namely organochlorine (OC), organophosphate (OP), carbamate, and pyrethroid pesticides. One of the important groups of pesticides which are used broadly are OPs viz. methyl parathion (MP), diazonin, malathion, chlorpyrifos (CPS), dimethoate, endosulfan, profenofos, monocrotophos [151], fenithrothion, fenamiphos (FEN) [154], dicrotophos, and coumaphos (Table 6.1). The OPs are primarily used to protect crops from pests, but their unused portion along with their derivatives remain as contaminants in soils, which in turn leads to acidification of soil, fertility loss, improved weed species resistance, nitrate leaching and biodiversity loss [111, 165, 170]. OPs are neurotoxicants which act on acetylcholinesterase (AChE) and inactivate AChE in both central and peripheral nervous system, as a result of which acetate and choline are formed [45]. Additionally, nerves are considerably over stimulated and blocked in mammals and insects. This suppression results in convulsion, paralysis, and finally death [154]. OPs also possess the proficiency for causing genotoxic and carcinogenic effect [82]. TABLE 6.1 Some Important OPs Along with Their Chemical Name Example Type Soil Half-Life (Days) Methyl parathion Insecticide 3-30
Molecules, 2019
Organophosphorus compounds (OP) are chemicals widely used as pesticides in different applications such as agriculture and public health (vector control), and some of the highly toxic forms have been used as chemical weapons. After application of OPs in an environment, they persist for a period, suffering a degradation process where the biotic factors are considered the most relevant forms. However, to date, the biodegradation of OP compounds is not well understood. There are a plenty of structure-based biodegradation estimation methods, but none of them consider enzymatic interaction in predicting and better comprehending the differences in the fate of OPs in the environment. It is well known that enzymatic processes are the most relevant processes in biodegradation, and that hydrolysis is the main pathway in the natural elimination of OPs in soil samples. Due to this, we carried out theoretical studies in order to investigate the interactions of these OPs with a chosen enzyme—the phosphotriesterase. This one is characteristic of some soils’ microorganisms, and has been identified as a key player in many biodegradation processes, thanks to its capability for fast hydrolyzing of different OPs. In parallel, we conducted an experiment using native soil in two conditions, sterilized and not sterilized, spiked with specific amounts of two OPs with similar structure—paraoxon-ethyl (PXN) and O-(4-nitrophenyl) O-ethyl methylphosphonate (NEMP). The amount of OP present in the samples and the appearance of characteristic hydrolysis products were periodically monitored for 40 days using analytical techniques. Moreover, the number of microorganisms present was obtained with plate cell count. Our theoretical results were similar to what was achieved in experimental analysis. Parameters calculated by enzymatic hydrolysis were better for PXN than for NEMP. In soil, PXN suffered a faster hydrolysis than NEMP, and the cell count for PXN was higher than for NEMP, highlighting the higher microbiological toxicity of the latter. All these results pointed out that theoretical study can offer a better comprehension of the possible mechanisms involved in real biodegradation processes, showing potential in exploring how biodegradation of OPs relates with enzymatic interactions.
A Convenient Method for Oxidation of Organophosphorus Pesticides in Organic Solvents
Environmental Research, 2000
Since organophosphorus pesticides can be oxidized to oxons in vivo and in the environment and their determination based on inhibition of cholinesterases can be more sensitive after their oxidation to oxons, development of an efAcient method for their in vitro oxidation is important for their toxicological and analytical studies. This study demonstrated that treatment of organophosphorus pesticides with 10 molar excess bromine in acetonitrile is a rapid and efAcient method for their oxidation. For the nine organophosphorus pesticides tested, the reaction was complete within a few seconds. All reactions gave the respective oxons as single major product, except that of fenthion, which gave two major products, the respective oxon and another product from further oxidation of the oxon. The yields of the oxons were 82+100%. The inhibitory power of the pesticides on acetylcholinesterase before and after oxidation was measured and, for all pesticides tested, the power after oxidation was much higher than that before oxidation. Inhibition calibration curves for both unoxidized and oxidized forms of fenitrothion and parathion were obtained. The sensitivity of the detection of these pesticides was much higher after oxidation.