Co-metabolic degradation of dimethoate by Raoultella sp. X1

Microbiology and Biochemistry of Pesticides Biodegradation

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

Dimethoate residues in Pakistan and mitigation strategies through microbial degradation: a review

Organophosphate pesticides (OPs) are used extensively for crop protection worldwide due to their high water solubility and relatively low persistence in the environment compared to other pesticides, such as organochlorines. Dimethoate is a broad-spectrum insecticide that belongs to the thio-organophosphate group of OPs. It is applied to cash crops, animal farms, and houses. It has been used in Pakistan since the 1960s, either alone or in a mixture with other OPs or pyrethroids. However, the uncontrolled use of this pesticide has resulted in residual accumulation in water, soil, and tissues of plants via the food chain, causing toxic effects. This review article has compiled and analyzed data reported in the literature between 1998 and 2021 regarding dimethoate residues and their microbial bioremediation. Different microorganisms such as bacteria, fungi, and algae have shown potential for bioremediation. However, an extensive role of bacteria has been observed compared to other microorganisms. Twenty bacterial, three fungal, and one algal genus with potential for the remediation of dimethoate have been assessed. Active bacterial biodegraders belong to four classes (i) alpha-proteobacteria, (ii) gamma-proteobacteria, (iii) beta-proteobacteria, and (iv) actinobacteria and flavobacteria. Microorganisms, especially bacterial species, are a sustainable technology for dimethoate bioremediation from environmental samples. Yet, new microbial species or consortia should be explored.

Biotransformation of dimethoate into novel metabolites by bacterial isolate Pseudomonas kilonensis MB490

Bacterial strain (Pseudomonas kilonensis MB490) isolated from agricultural fields of Mianwali, was selected to check its potential to degrade Organophosphate insecticide dimethoate (DM). Strain MB490 was able to degrade dimethoate equally well at given pH range (6.0, 7.0 and 8.0), thus showing its pH independence for dimethoate degradation. Optimum temperature for dimethoate degradation varied from 25-30 °C. There was more dimethoate degradation under shaking conditions with optimum growth. Strain MB490 showed 90% dimethoate degradation in M-9 broth and 90.6% in soil slurry, while exhibited 81.5% dimethoate degradation in soil microcosm within 9 days, based on HPLC analysis of bacterial samples supplemented with 200 mg/L dimethoate. The average half-life (t _1/2) of dimethoate after bacterial degradation ranged from 1.95 days in 1st phase to 5 days in 2nd phase in M-9 broth, soil slurry and soil microcosm, while in control media without bacteria, it ranged from 30 to 64.3 days. GCMS investigation revealed the transformation of dimethoate into 5 metabolic products namely Methyl diethanol amine, Aspartylglycine ethyl ester, Phosphonothioic acid propyl-O, S-dimethyl ester, O, O, O-Trimethyl thiophosphate and omethoate which were ultimately mineralized by the strain MB490, providing energy for its growth.

Isolation and characterization of a novel benzophenone-3-degrading bacterium Methylophilus sp. strain FP-6

Benzophenone-3 (BP-3) is extensively applied in sunscreens and some other related cosmetic products. It is necessary to efficiently and safely remove BP-3 from environments by application of various treatment technologies. However, to the authors' knowledge, BP-3 biodegradation by a single bacterial strain has not been reported before. In this study, a Gram-negative aerobic bacterium capable of degrading BP-3 as a sole carbon source was isolated from a municipal wastewater treatment plant and classified as Methylophilus sp. FP-6 according to BIOLOG GEN III and 16S rDNA analysis. Methanol was chosen for further experiments as a co-metabolic carbon source to enhance the microbial degradation efficiency of BP-3. Orthogonal and one-way experiments were all performed to investigate the optimal culture conditions for degradation of BP-3 by Methylophilus sp. FP-6. The degradation rate of BP-3 reached about 65% after 8 days of incubation with strain FP-6 under optimal culture conditions. The half-life (t_1/2) of BP-3 biodegradation by strain FP-6 was estimated as 2.95 days according to the BP-3 degradation curve. The metabolite intermediates generated during the BP-3 degradation process were analyzed by LC-MS/MS and three metabolite products were identified. According to the analysis of metabolic intermediates, three pathways for degradation of BP-3 by strain FP-6 were proposed. The results from this study gave first insights into the potential of BP-3 biodegradation by a single bacterial strain.

Co-metabolic degradation of iomeprol by a Pseudomonas sp. and its application in biological aerated filter systems

The non-ionic water-soluble X-ray contrast agent iomeprol (IOM) enters the water supply through sewage treatment plants, which can cause considerable environmental harm. In this study, Pseudomonas sp. I-24 (I-24) was tested for its ability to remove IOM from water via co-metabolic pathways. The optimum removal rate of IOM by I-24 was 38.43% ± 3.70% when starch served as the source of external carbon, and its co-metabolism of IOM conformed to the first-order kinetics. The highest activity of intracellular enzyme (degrading enzyme) extracted from I-24 was 0.143 ± 0.005 mU in starch condition. The Michaelis constant of the degrading enzyme was found to be 91.08 μmol L^-1. However, glucose and maltose showed the best promotive effects on the growth and electron transport activity of I-24, indicating that overgrowth may result in competitive inhibition and a reduced degradation rate of IOM. Adding I-24 and degrading enzymes to biological aerated filters increased IOM removal rates without affecting COD_Mn removal.

Environmental Fate and Toxicology of Dimethoate

The insecticide dimethoate, an organophosphate, was first introduced in 1962 for broad spectrum control of a wide range of insects including mites, flies, aphids, and plant hoppers. It inhibits AChE activity, resulting in nerve damage, which may lead to death. It is considered highly toxic to insects although dimethoate resistance has been observed. Dimethoate has both a low vapor pressure (0.247 mPa) and Henry's law constant (l.42x10(-6) Pa m3/mol), thus volatilization is not a major route of dissipation from either water or moist soils. Photolysis is considered a minor dissipation pathway. However, studies have shown that in the presence of a catalyst, the rate of photolysis does increase. The insecticide has high water solubility (39,800 mg/L) and under alkaline conditions, hydrolysis predominates representing a major degradation pathway. It has a low soil sorption capacity (Koc=20) which varies by soil type and organic matter content. Dimethoate is degraded by microbes under anaerobic conditions and bacterial species have been identified that are capable of using dimethoate as a carbon source. Although many intermediate by-products have been identified by abiotic and biotic processes, the major degradation product is omethoate. Dimethoate has been found to adversely impact many organisms. In plants, photosynthesis and growth are highly impacted, whereas birds exhibit inhibition in brain enzyme activity, thus sublethal effects are apparent. Furthermore, aquatic organisms are expected to be highly impacted via direct exposure, often displaying changes in swimming behavior. Toxicity results include inhibition in growth and more importantly, inhibition of acetylcholinesterase activity.

Isolation, identification and cyfluthrin-degrading potential of a novel Lysinibacillus sphaericus strain, FLQ-11-1

Strain FLQ-11-1, isolated from sewage sludge, was able to degrade cyfluthrin and was identified as Lysinibacillus sphaericus based on its morphology, 16S rRNA sequence and fatty acid methyl ester (FAME) analyses. This strain could use cyfluthrin as its carbon or nitrogen source. Response surface methodology (RSM) analysis showed that the optimum conditions for degradation were at pH 7.0 and 35 °C, using an inoculum amount with an OD600nm value of 1.6. Under these conditions, approximately 80.4% of cyfluthrin (50 mgl(-1)) was degraded within five days (d) of incubation. Four metabolic compounds were detected during cyfluthrin degradation and identified as methyl-3-(2,2-dichlorovinyl)-2,2-dimethyl-(1-cyclopropane)-carboxylate, 4-fluoro-3-phenoxy-benzoic acid methyl ester, methyl-3-phenoxybenzoate, 3-phenoxy-benzaldehyde by gas chromatography-mass spectrometry (GC-MS) and tandem mass spectrum (MS/MS) analysis and no cyfluthrin was detected after seven days of incubation. A possible degradation pathway was proposed, and our data showed that cyfluthrin could be efficiently degraded by FLQ-11-1, indicating that this strain could potentially be used to eliminate the contamination of pyrethroid herbicides.

Metabonomics analysis of urine and plasma from rats given long-term and low-dose dimethoate by ultra-performance liquid chromatography-mass spectrometry

This study assessed the effects of long-term, low-dose dimethoate administration to rats by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Dimethoate (0.04, 0.12, and 0.36 mg/kg body weight/day) was administered daily to male Wistar rats through their drinking water for 24 weeks. Significant changes in serum clinical chemistry were observed in the middle- and high-dose groups. UPLC-MS revealed evident separate clustering among the different dose groups using global metabolic profiling by supervised partial least squares-discriminant analysis. Metabonomic analysis showed alterations in a number of metabolites (12 from urine and 13 from plasma), such as L-tyrosine, dimethylthiophosphate (DMTP), dimethyldithiophosphate (DMDTP), citric acid, uric acid, suberic acid, glycylproline, allantoin, isovalerylglutamic acid and kinds of lipids. The results suggest that long-term, low-dose exposure to dimethoate can cause disturbances in liver function, antioxidant and nervous systems, as well as the metabolisms of lipids, glucose, fatty acids, amino acids, and collagen in rats. DMTP and DMDTP, which had the most significant changes among all other studied biomarkers, were considered as early, sensitive biomarkers of exposure to dimethoate. The other aforementioned proposed toxicity biomarkers in metabonomic analysis may be useful in the risk assessment of the toxic effects of dimethoate. Metabonomics as a systems toxicology approach was able to provide comprehensive information on the dynamic process of dimethoate induced toxicity. In addition, the results indicate that metabonomic approach could detect systemic toxic effects at an earlier stage compared to clinical chemistry. The combination of metabonomics and clinical chemistry made the toxicity of dimethoate on rats more comprehensive.

Cometabolic biotransformation of fenpropathrin by Clostridium species strain ZP3

A novel bacterial strain capable of degrading the pyrethroid pesticide fenpropathrin was isolated from mixed wastewater and sludge samples. Phylogenetic analysis of the 16S rDNA sequence revealed that the organism belongs to the genus Clostridium. The organism can co-metabolically transform fenpropathrin at 100 mg l(-1) at 35°C and pH 7.5 in 12 days. Metabolic products of fenpropathrin from strain ZP3 were examined by gas chromatography/mass spectrometry, and the results showed that the organism degraded fenpropathrin with an oxidization process to yield benzyl alcohol, benzenemethanol, 3,5-dimethylamphetamine. Analyses of cell-free extracts from this strain showed that the optimal degrading conditions for degrading fenpropathrin were 35°C and pH 7.5, and degradation efficiency was 20.0 mg l(-1) day(-1), and it might be potential using for rapid treating fenpropathrin, for example, on the surface of fruits and vegetables.