Hydrolysis, Photolysis, and Biotoxicity Assessment of a Novel Biopesticide, Guvermectin

Photodegradation of Diquat in water under UV irradiation: Identification of transformation products and elucidation of photodegradation pathway

In aquatic settings, photodegradation is a significant non-biodegradation method of pesticide degradation. In this investigation, the photodegradation of the herbicide Diquat in aqueous solution was examined under distinct conditions and concentrations. The initial concentration of Diquat and the pH value of the water environment significantly affected the half-life of photodegradation of Diquat, and the opposite was true for different types of water. The photodegradation transformation products (PTPs) formed by the photodegradation of Diquat in an aqueous solution under UV-Vis irradiation were separated and identified using ultra-high-performance liquid chromatography coupled with time-of-fight mass spectrometry (UPLC-QTOF-MS). Based on mass spectral information, four main transition products were identified. Calculations of constituent composition, a comparison of structural analogs, and extant literature all contributed to the structure's determination. The main pathways of photodegradation were found to be oxidation, pyridine ring-opening, cleavage of [C-C] on the piperazine ring, Demethylation reaction and Hydroxylation. These results serve as a foundation for further environmental risk assessment and help explain how Diquat behaves in aquatic environments.

First insight into the formation of transformation products of a biopesticide guvermectin in rat and its health risk

Guvermectin is a new chemical isolated from the microbial metabolites and is registered as a novel plant growth regulator. However, the biotransformation behavior and toxicity of guvermectin to mammals remain unclear and have unknown implications for consumers or occupationally exposed persons. Therefore, we investigated the biotransformation of guvermectin in vivo and in vitro, its effects on CYP450s activities, and its oral toxicity in rats. The results showed that guvermectin could be rapidly absorbed when administered orally and eliminated rapidly in the serum, with a half-life of 6.3 h. Four phase І metabolism products of guvermectin in the serum were screened and identified using UPLC-QTOF/MS. Two products, adenine and psicofuramine, were confirmed using reference standards. Hydrolysis and oxidation reactions were the main transformation pathways. Oral toxicity tests in rats showed that guvermectin exhibited light toxicity to rats (LC50 > 5000 mg/kg b.w.). However, an in vitro probe drug experiment revealed that guvermectin could induce CYP2D6 activity, and a lower concentration of guvermectin exhibited a stronger effect on CYP2D6 than higher concentration (1.38-fold). Molecular docking studies implied that guvermectin was an antagonist of CYP1A2, CYP2C9, and CYP3A4. These findings provided a better understanding of the environmental and human health risks associated with guvermectin and promote its rational use. However, the potential risk of endocrine disruption can not be ignored due to the presence of nucleoside-like metabolites.

Degradation of a novel herbicide fluchloraminopyr in soil: Dissipation kinetics, degradation pathways, transformation products identification and ecotoxicity assessment

With the continuous application of new agricultural chemicals in agricultural systems, it is imperative to study the environmental fate and potential transformation products (TPs) of these chemicals to better assess their ecological and health risks, as well as guide scientific application. The dissipation of fluchloraminopyr was firstly evaluated under aerobic/anaerobic condition in four representative soils, with Dissipation Time 50 (DT50) values ranging from 0.107 to 4.76 days. Eight TPs generated by soil degradation were identified via Ultra-High Performance Liquid Chromatography coupled with Quadrupole Time-of-Flight Mass Spectrometry (UHPLC-QTOF/MS) and Density Functional Theory (DFT) calculations. The predominant transformation reactions of fluchloraminopyr in soil include oxidation, dechlorination, hydroxylation, and acetylation. The predictions from toxicological software indicated that the acute and chronic toxicity of TPs to aquatic organisms was significantly lower than that of fluchloraminopyr. Moreover, both M267 and M221 exhibited higher acute oral toxicity to terrestrial organisms compared to the parent compound. Consequently, these findings offer essential ecological risk evaluation data for the judicious application of fluchloraminopyr.

Uptake and Biotransformation of Guvermectin in Three Crops after In Vivo and In Vitro Exposure

Guvermectin, as a novel nucleoside-like biopesticide, could increase the rice yield excellently, but the potential environmental behaviors remain unclear, which pose potential health risks. Therefore, the uptake and biotransformation of guvermectin in three types of crops (rice, lettuce, and carrot) were first evaluated with a hydroponic system. Guvermectin could be rapidly absorbed and reached equilibrium in roots (12-36 h) and shoots (24-60 h) in three plants, and guvermectin was also vulnerable to dissipation in roots (t1/2 1.02-3.65 h) and shoots (t1/2 9.30-17.91 h). In addition, 8 phase I and 2 phase II metabolites, transformed from guvermectin degradation in vivo and in vitro exposure, were identified, and one was confirmed as psicofuranine, which had antibacterial and antitumor properties; other metabolites were nucleoside-like chemicals. Molecular simulation and quantitative polymerase chain reaction further demonstrated that guvermectin was metabolized by the catabolism pathway of an endogenous nucleotide. Guvermectin had similar metabolites in three plants, but the biotransformation ability had a strong species dependence. In addition, all the metabolites exhibit neglectable toxicities (bioconcentration factor <2000 L/kg b.w., LC50,rat > 5000 mg/kg b.w.) by prediction. The study provided valuable evidence for the application of guvermectin and a better understanding of the biological behavior of nucleoside-like pesticides.

Natural product guvermectin inhibits guanosine 5'-monophosphate synthetase and confers broad-spectrum antibacterial activity

Bacterial diseases caused substantial yield losses worldwide, with the rise of antibiotic resistance, there is a critical need for alternative antibacterial compounds. Natural products (NPs) from microorganisms have emerged as promising candidates due to their potential as cost-effective and environmentally friendly bactericides. However, the precise mechanisms underlying the antibacterial activity of many NPs, including Guvermectin (GV), remain poorly understood. Here, we sought to explore how GV interacts with Guanosine 5'-monophosphate synthetase (GMPs), an enzyme crucial in bacterial guanine synthesis. We employed a combination of biochemical and genetic approaches, enzyme activity assays, site-directed mutagenesis, bio-layer interferometry, and molecular docking assays to assess GV's antibacterial activity and its mechanism targeting GMPs. The results showed that GV effectively inhibits GMPs, disrupting bacterial guanine synthesis. This was confirmed through drug-resistant assays and direct enzyme inhibition studies. Bio-layer interferometry assays demonstrated specific binding of GV to GMPs, with dependency on Xanthosine 5'-monophosphate. Site-directed mutagenesis identified key residues crucial for the GV-GMP interaction. This study elucidates the antibacterial mechanism of GV, highlighting its potential as a biocontrol agent in agriculture. These findings contribute to the development of novel antibacterial agents and underscore the importance of exploring natural products for agricultural disease management.

Development and Application of the Novel Plant Growth Regulator Guvermectin: A Perspective

Plant growth regulators (PGRs) play an important role in alleviating the detrimental effects of biotic and abiotic stress and improving crop yield and quality. As a novel PGR from Streptomyces registered in 2021, guvermectin (GV) has the potential to improve plant yield and defense, making its application in agriculture a subject of interest. Here, we describe the discovery process, functional activities, agricultural applications, toxicity, environmental safety, and biosynthetic mechanism of GV. This Perspective provides a guide for the development of novel PGRs from microorganisms.

Design, One-Step Highly Selective Synthesis and Enhancing Insecticidal Activity and Photo-Self-Degradation of Phenylpyrazole Esterified Derivatives as GABA and nACh Receptor Inhibitors

In the pursuit of novel insecticides with high activity and a unique mode of action on the GABA receptor, a series of phenylpyrazole esterified derivatives (PEs) were synthesized using an improved Pinner reaction with high selectivity. Lewis acid catalysis was employed in a one-step solvent-thermal method to convert the cyano group of fipronil into an ester unit. FeCl3 was found to exhibit the highest selectivity for PEs synthesis, yielding PEs at 96.4%, with the byproduct being phenylpyrazole amide (PE0) at 2.1%. Initial biological assays indicated superior insecticidal activity of the target compounds against Plutella xylostella and Mythimna separata compared to fipronil. Particularly, the smaller and shorter ester units, PE3, PE5, and PE8, demonstrated 2-2.5 times higher insecticidal activity against P. xylostella than fipronil. The higher activity of ester units compared to amide and acylhydrazone units can be attributed to the enhanced lipid solubility of PEs. Additionally, it may be due to the impact of PEs on the neurotransmitter nACh or the coordination of calcium and chloride ions with the ester's -C═O and -O- bonds, blocking the chloride ion channel. Hydrophobic parameters were confirmed by reversed-phase high-performance liquid chromatography (HPLC), indicating the enhanced lipophilicity conferred by the ester units of PEs. Molecular docking and CoMFA analysis preliminarily validated the strong interactions and structure-activity relationships between PEs and the GABA receptor and nACh receptor in P. xylostella. Furthermore, under simulated natural sunlight, PEs exhibited photodegradation capabilities, transforming back into fipronil parent fragments and enhancing their insecticidal activity. Moreover, PEs displayed excellent fluorescent properties, enabling self-detection of residues. These research findings provide new insights and directions for the development of efficient pesticides, with potential wide applications in the fields of medicine and biosensors.

Toxicity assessment of a novel biopesticide guvermectin and identification of its transformation products in soils

Guvermectin is a novel biopesticide often used as seed soaking to promote the rice yield. However, its biotoxicity and degradation behavior in soils were still not disclosed, which posed a knowledge gap to guide its rational application. Therefore, the degradation behaviors of guvermectin in four typical soils under aerobic and anaerobic conditions were investigated in the laboratory. The results showed that guvermectin was degraded fast with DT50 ranging from 0.95 to 10.10 d, and the degradation rate was higher in aerobic condition than that in anaerobic condition. Eight transformation products were screened using UPLC-QTOF/MS. The acute toxicities tests of guvermectin to Coturnix coturnix japonica and Apis mellifera were measured by biological laboratory experiments, and the acute and chronic toxicities of transformation products to Danio rerio, Daphnia magna Straus and Green algae were predicted by ECOSAR software. The results showed that guvermectin has low toxic to quail and honeybee (LD50 2000 mg a.i./kg body weight, LD50 ˃ 100 μg a.i./bee), and its transformation products were also low toxic class to Danio rerio, Daphnia magna Straus and Green algae (LC50/EC50 > 100 mg a.i./L). However, the nucleoside-like metabolites may pose a potential risk due to their similarity to genetic material, which should be concerned. The findings provided important environmental risk assessment data for the rational use of guvermectin.