Cometabolic biodegradation of quizalofop-p-ethyl by Methylobacterium populi YC-XJ1 and identification of QPEH1 esterase

QpmH esterase from cotton rhizosphere bacteria: A novel approach for degrading quizalofop-p-ethyl herbicide

Within the rhizosphere, a rich population of biocontrol bacteria serves as a valuable resource for the biodegradation of environmental herbicides. This study aimed to evaluate rhizospheric microorganisms for their potential to degrade Quizalofop-p-ethyl, a widely used herbicide to control annual and perennial weeds in a variety of crops. A bacterial strain, MJ-8, isolated from cotton rhizosphere soil, demonstrated significant degradation activity. Based on morphological characteristics and 16S rRNA sequencing, the strain was identified as Priestia megaterium. Strain MJ-8 achieved a degradation rate of 90.65 % for Quizalofop-p-ethyl. Genomic analysis and amino acid sequence alignment revealed a key gene, designated QpmH, encoding a 30 kDa protein with strong biodegradation activity. Heterologous expression of the QpmH gene confirmed its role in Quizalofop-p-ethyl degradation. Molecular docking studies and structural modeling further elucidated the enzymatic mechanisms, supported by the analysis of their degradation products. Additionally, when QpmH gene was introduced into rice plants through Agrobacterium-mediated transformation, the resultant transformant conferred resistance to Quizalofop-p-ethyl at the recommended application dose. These findings highlight Priestia megaterium strain MJ-8 as a promising biological agent for sustainable herbicide management and position the QpmH gene as a potential new target for developing herbicide-resistant crops.

Determination of quizalofop-p-ethyl in onion: residual dissipation pattern, weed control efficiency, and food safety assessment under field conditions

Monitoring pesticide residue levels becomes crucial to maintain quality and guarantee food safety as the consumption of onion green leaves and immature and mature bulbs (either raw or processed) rises. A field experiment was conducted for two consecutive seasons with quizalofop-p-ethyl (5% EC) at 50 and 100 g a.i. ha-1 to evaluate weed control efficiency and to determine terminal residues. Post-emergence application of fop herbicide at 100 g a.i. ha-1 kept the weed density and dry weight reasonably at a lower level and enhanced the productivity of onion with higher economic returns. A rapid, sensitive, and analytical method was developed using high-performance liquid chromatography (HPLC) with excellent linearity (r2 > 0.99). The limit of quantification for quizalofop-p-ethyl was established at 0.04 mg kg-1 with signal to noise (S/N) ratio ≥ 10. The method was successfully applied and initial quantified residues were in the range of 2.5-4.4 mg kg-1 irrespective of seasons and doses. Finally, the presence of targeted herbicide residues in harvested samples was confirmed by liquid chromatography tandem mass spectrometry (LC-MS/MS) under optimized operating conditions. Dietary risk assessment assured harvested onions were safe for consumption at the recommended dose. It also can be concluded that quizalofop ethyl did not adversely influence soil micro-organisms at standard rates of application.

Quizalofop-P-ethyl induced developmental toxicity and cardiotoxicity in early life stage of zebrafish (Danio rerio)

Quizalofop-P-ethyl (QpE), a highly efficient selective herbicide, has good control effect on annual and perennial weeds. However, its excessive use will pose a threat to the ecological environment. QpE has been proven harmful to aquatic organisms, but there is little evidence on the adverse effects of QpE in the early life of aquatic organisms. In this work, zebrafish (Danio rerio) embryos were treated with 0.10, 0.20, 0.30, 0.40, and 0.50 mg/L of QpE for 120 h. The findings revealed that the LC₅₀ value of QpE to zebrafish embryos was 0.23 mg/L at 96 hpf. QpE exposure significantly increased the mortality rate, decreased the hatching rate and caused morphological defects during zebrafish embryonic development, with a concentration dependent manner. QpE also caused severe morphological changes in the cardiovascular system, as well as resulted in a dysfunction in cardiovascular performance. Meanwhile, both histopathological examination and neutrophil observations showed inflammatory response occurred in the heart. Furthermore, several genes associated with heart development and inflammation were significantly altered following QpE exposure. A protein-protein interaction (PPI) network analysis proved that there was a connection between the changed heart development-relevant and inflammation-related genes. Taken together, our findings suggest that QpE causes cardiotoxicity in zebrafish embryos by altering the expression of genes in the regulatory network of cardiac development, which might be aggravated by inflammatory reactions, thereby affecting embryo development. These findings generated here are useful for in-depth assessment of the effects of QpE on early development of aquatic organisms and providing theoretical foundation for risk management measures.

Type II Photosynthetic Reaction Center Genes of Avocado (Persea americana Mill.) Bark Microbial Communities are Dominated by Aerobic Anoxygenic Alphaproteobacteria

The tree bark environment is an important microbial habitat distributed worldwide on thrillions of trees. However, the microbial communities of tree bark are largely unknown, with most studies on plant aerial surfaces focused on the leaves. Recently, we presented a metagenomic study of bark microbial communities from avocado. In these communities, oxygenic and anoxygenic photosynthesis genes were very abundant, especially when compared to rhizospheric soil from the same trees. In this work, Evolutionary Placement Algorithm analysis was performed on metagenomic reads orthologous to the PufLM gene cluster, encoding for the bacterial type II photosynthetic reaction center. These photosynthetic genes were found affiliated to different groups of bacteria, mostly aerobic anoxygenic photosynthetic Alphaproteobacteria, including Sphingomonas, Methylobacterium and several Rhodospirillales. These results suggest that anoxygenic photosynthesis in avocado bark microbial communities functions primarily as additional energy source for heterotrophic growth. Together with our previous results, showing a large abundance of cyanobacteria in these communities, a picture emerges of the tree holobiont, where light penetrating the tree canopies and reaching the inner stems, including the trunk, is probably utilized by cyanobacteria for oxygenic photosynthesis, and the far-red light aids the growth of aerobic anoxygenic photosynthetic bacteria.