Rapid Onset of the Accelerated Degradation of Dicarboximide Fungicides in a UK Soil with a Long History of Agrochemical Exclusion

Metabolism of a fungicide propiconazole by Cunninghamella elegans ATCC36112

The metabolic breakdown of propiconazole by fungi was examined, and it was found that the microbial model (Cunninghamella elegans ATCC36112) efficiently degrades the triazole fungicide propiconazole through the action of cytochrome P450. This enzyme primarily facilitates the oxidation and hydrolysis processes involved in phase I metabolism. We observed major metabolites indicating hydroxylation/oxidation of propyl groups of propiconazole. Around 98% of propiconazole underwent degradation within a span of 3 days post-treatment, leading to the accumulation of five metabolites (M1-M5). The experiments started with a preliminary identification of propiconazole and its metabolites using GC-MS. The identified metabolites were then separated and identified by in-depth analysis using preparative UHPLC and MS/MS. The metabolites of propiconazole are M1 (CGA-118245), M2(CGA-118244), M3(CGA-136735), M4(GB-XLIII-42-1), and M5(SYN-542636). To further investigate the role of key enzymes in potential fungi, we treated the culture medium with piperonyl butoxide (PB) and methimazole (MZ), and then examined the kinetic responses of propiconazole and its metabolites. The results indicated a significant reduction in the metabolism rate of propiconazole in the medium treated with PB, while methimazole showed weaker inhibitory effects on the metabolism of propiconazole in the fungus C. elegans.

The response of soil and phyllosphere microbial communities to repeated application of the fungicide iprodione: accelerated biodegradation or toxicity?

Pesticides interact with microorganisms in various ways with the outcome being negative or positive for the soil microbiota. Pesticides' effects on soil microorganisms have been studied extensively in soil but not in other pesticides-exposed microbial habitats like the phyllosphere. We tested the hypothesis that soil and phyllosphere support distinct microbial communities, but exhibit a similar response (accelerated biodegradation or toxicity) to repeated exposure to the fungicide iprodione. Pepper plants received four repeated foliage or soil applications of iprodione, which accelerated its degradation in soil (DT50_1st = 1.23 and DT50_4th = 0.48 days) and on plant leaves (DT50_1st > 365 and DT50_4th = 5.95 days). The composition of the epiphytic and soil bacterial and fungal communities, determined by amplicon sequencing, was significantly altered by iprodione. The archaeal epiphytic and soil communities responded differently; the former showed no response to iprodione. Three iprodione-degrading Paenarthrobacter strains were isolated from soil and phyllosphere. They hydrolyzed iprodione to 3,5-dichloraniline via the formation of 3,5-dichlorophenyl-carboxiamide and 3,5-dichlorophenylurea-acetate, a pathway shared by other soil-derived arthrobacters implying a phylogenetic specialization in iprodione biotransformation. Our results suggest that iprodione-repeated application could affect soil and epiphytic microbial communities with implications for the homeostasis of the plant-soil system and agricultural production.

The dissipation of fipronil, chlorpyrifos, fosthiazate and ethoprophos in soils from potato monoculture areas: first evidence for the enhanced biodegradation of fosthiazate

BACKGROUND

A limited number of pesticides are available for the control of soil pests in potato. This, together with the monoculture nature of potato cultivation, does not favour chemical rotation, increasing the risk of reduced biological efficacy due to microbial adaptation. The dissipation of three major organophosphates (chlorpyrifos, ethoprophos and fosthiazate) was studied in comparison with fipronil, an insecticide recently introduced in potato cultivation, in 17 soils from potato monoculture areas in Greece to explore the extent of enhanced biodegradation development.

RESULTS

The dissipation time of the four pesticides varied in the different soils, with DT50 values of 1.7-30.8 days, 2.7-56 days, 7.0-31.0 days and 24.5-116.5 days for fosthiazate, chlorpyrifos, ethoprophos and fipronil, respectively. A rapid dissipation of ethoprophos and fosthiazate in two soils with previous exposure to these nematicides provided first evidence for the development of enhanced biodegradation. Sterilisation of the given soils inhibited the dissipation of fosthiazate. Additionally, fosthiazate dissipation in the soils increased upon repeated applications.

CONCLUSION

The development of enhanced biodegradation of fosthiazate in soils from potato monoculture regions was verified. This is the first report of enhanced biodegradation for this chemical. Further studies will focus on the isolation of microorganisms responsible for the dissipation of fosthiazate.

Polycyclic aromatic hydrocarbon-degrading bacteria from aviation fuel spill site at Ibeno, Nigeria

Polycyclic aromatic hydrocarbon (PAH)-degrading bacteria were isolated from aviation fuel contaminated soil at Inua Eyet Ikot in Ibeno, Nigeria. PAH-degrading bacteria in the contaminated soil were isolated by enrichment culture technique. Isolates with high PAH degrading potential characterized by their extensive growth on PAH-supplemented minimal salt medium were screened for their naphthalene, phenanthrene and chrysene degradability. The screening medium which contained selected PAHs as the sole source of carbon and energy showed that Micrococcus varians AFS-2, Pseudomonas putida AFS-3 and Alcaligenes faecalis AFS-5 exhibited a concentration-dependent growth in all the PAH-compounds tested. There were visible changes in the color of growth medium suggesting the production of different metabolites. Their acclimation to different PAH substrates was also evident as A. faecalis AFS-5 isolated from chrysene grew well on other less complex aromatic compounds. The isolate exhibited best growth (0.44 OD(600)) when exposed to 10 ppm of chrysene for 5 days and could utilize up to 90 ppm of chrysene. This isolate and others with strong PAH-degrading potentials are recommended for bioremediation of PAHs in aviation fuel-contaminated sites in the tropics.

Effects of repeated applications of fungicide carbendazim on its persistence and microbial community in soil

Carbendazim, a systemic benzimidazole fungicide, is applied repeatedly to control plant diseases including soilborne diseases, over a growing season. Studies were carried out under laboratory conditions to assess the effects of repeated carbendazim applications on its persistence and microbial community in soil. The results indicate that dissipation of carbendazim in soil was accelerated with its application frequency. The degradation rate constant of carbendazim was increased significantly from 0.074 d(-1) to 0.79 d(-1). The corresponding half-life was shorten markedly from 9.3 d to 0.9 d after four repeated applications. No significant inhibitory effect of carbendazim on soil microbial utilization of the carbon sources was observed after first treatment, but a slight increase in average well color development (AWCD) was shown after second, third, and fourth applications. It suggested that soil microorganisms become adapted to carbendazim after repeated application. Simpson and Shannon indexes of soil microbial community from carbendazim treated soil were also similar to those from the control soil, indicating that the richness and dominant character of soil microorganisms remain unchangeable after repeated application. However, after first, second, and third addition of carbendazim, McIntosh indexes on day 21 were significantly higher compared with the control, suggesting that balance of soil microorganisms was altered due to the enrichment of the specific carbendazim-adapting strains in soil.

Responses of soil microorganisms and enzymes to repeated applications of chlorothalonil

Introduction of anthropogenic chemicals into soil may have lasting effects on soil microbial activities and thus soil health. This study was conducted with chlorothalonil to evaluate its effects on soil bacterial, fungal, and actinomycete populations and soil enzymes (acid phosphatase, alkaline phosphatase, urease, catalase, and invertase) after repeated applications. After the first addition of chlorothalonil, the soil bacterial and actinomycete populations were significantly reduced, whereas the population of soil fungi was unchanged. The most marked inhibition on soil microorganisms was observed after the second pesticide addition. However, after initial variations, soil bacteria, fungi, and actinomycetes adapted gradually to chlorothalonil, and the negative effects became transient and weaker following the third and fourth treatments. The inhibitory effect of repeated chlorothalonil applications on soil enzymes followed a similar trend to that on soil microorganisms. Repeated chlorothalonil applications did not result in significant changes in its persistence. Three bacterial strains capable of utilizing chlorothalonil as a sole source of carbon and energy for growth were isolated 21 days after the fourth treatment with chlorothalonil, which indicated that the capability of soil microorganisms for degrading chlorothalonil was formed during the experiment.

Microbial degradation of organophosphorus compounds

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.

Biotransformation of vinclozolin by the fungus Cunninghamella elegans

This study investigated the biotransformation of the dicarboximide fungicide vinclozolin [3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-1,3-oxazolidine-2,4-dione] by the fungus Cunninghamella elegans. Experiments with phenyl-[U-ring-14C]vinclozolin showed that after 96 h incubation, 93% had been transformed to four major metabolites. Metabolites were separated by HPLC and characterized by mass and NMR spectroscopy. Biotransformation occurred predominantly on the oxazolidine-2,4-dione portion of vinclozolin. The metabolites were identified as the 3R- and 3S- isomers of 3',5'-dichloro-2,3,4-trihydroxy-2-methylbutyranilide, N-(2-hydroxy-2-methyl-1-oxobuten-3-yl)-3,5-dichlorophenyl-1-carbamic acid, and 3',5'-dichloro-2-hydroxy-2-methylbut-3-enanilide. The enanilide compound has been reported previously as a plant and mammalian metabolite and is implicated to contain antiandrogenic activity. The 3R- and 3S- isomers of 3',5'-dichloro-2,3,4-trihydroxy-2-methylbutyranilide are novel metabolites.