Abstract
Overuse of pesticides in agriculture may harm environmental and agricultural yields. Sustainable maintenance of soil fertility and management of the environment have become a concern due to the persistence of pesticides in the soil. Microbes have various mechanisms for the bioremediation of persistent organic pollutants from the environment. A bacterium that degrades clothianidin was isolated from the pesticide and applied to agricultural soil by the enrichment technique. The identity of the bacterium was determined by studying morphological, cultural, and biochemical characteristics and 16S rRNA gene sequences. The ability to metabolize clothianidin was confirmed using UV-visible spectrophotometric, chromatographic, and spectroscopic analyses. A Gram-negative bacterium, designated smk, isolated from clothianidin-contaminated soil was confirmed to be a member of Pseudomonas stutzeri. The biodegradation of clothianidin was studied using P. stutzeri smk. Approximately 62% degradation of clothianidin was achieved within two weeks when grown at 30°C and pH 7. The effects of various physicochemical parameters, including pH, temperature, and clothianidin concentrations, on catabolic rates were studied. The biodegradation studies using UV-Vis spectrophotometry, HPLC, FTIR, and LC-MS indicated the production of the following metabolites: 2-chloro-5-methyl thiazole (CMT), methyl nitroguanidine (MNG), methyl 3-[thiazole-yl], and methyl guanidine (TMG). Identification of specific degradation metabolites indicates that bioremediation of toxic neonicotinoid insecticides may be achieved by application of P. stutzeri smk.
Highlights
Pests cause significant agronomic damage; damage is controlled with integrated pest management, which involves the use of different insecticides and pesticides [1]
After 14 days of incubation, the flask contents were centrifuged at 10000 ×g for 10 min, and the culture supernatants were extracted using ethyl acetate in 1 :1 (v/v) proportion. e supernatants were air-dried, were resuspended in 1 ml of HPLC grade methanol, and were used in highpressure liquid chromatography (HPLC), Fourier-transform infrared (FTIR) spectroscopy, and liquid chromatography mass spectrometry (LC-MS) analyses. e concentrations of clothianidin were measured (250 nm) in samples obtained from the flask that was inoculated with P. stutzeri smk and incubated for a period of 14 days. e intrinsic loss of clothianidin was determined in samples obtained from a flask that was not inoculated with P. stutzeri smk
After 14 days of incubation, cultures were centrifuged at 10000 ×g for 10 min, and culture supernatant containing intermediate and terminal metabolites generated by bacterial degradation of clothianidin was extracted using ethyl acetate in a 1 : 1 (v/v) proportion. e extracted components were concentrated using a rotary evaporator and were air-dried. e airdried residual mass was resuspended in 1 ml of HPLC grade methanol and was further used in HPLC, FTIR, and LC-MS analyses
Summary
Pests cause significant agronomic damage; damage is controlled with integrated pest management, which involves the use of different insecticides and pesticides [1]. Ese products are important to agriculture because of their activity against sucking insect pests and some Heteroptera, Coleoptera, and Lepidoptera [3, 4]. Due to their broad spectrum and pesticide potential, neonicotinoid insecticides are one of the most important classes of commercial insecticides used worldwide. Clothianidin, ([E]-1-[2chloro-1,3-thiazol-5-yl-methyl]-3-methyl-2nitroguanidine), has been used broadly for the long-term control of a wide variety of insect pests, including Hemiptera, ysanoptera, Coleoptera, Lepidoptera, and Diptera, with excellent systemic action, using a variety of application methods [11]. E extensive application of neonicotinoids has led to the introduction of extremely toxic effects on nontarget economically important insects such as honeybees and silkworms. Mulligan et al [26] reported aerobic degradation of clothianidin. us, we sought to isolate a clothianidindegrading bacterium and to elucidate its degradation pathway
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