Activity, biomass and composition of microbial communities and their degradation pathways in exposed propazine soil

Investigation of the Persistence, Toxicological Effects, and Ecological Issues of S-Triazine Herbicides and Their Biodegradation Using Emerging Technologies: A Review

S-triazines are a group of herbicides that are extensively applied to control broadleaf weeds and grasses in agricultural production. They are mainly taken up through plant roots and are transformed by xylem tissues throughout the plant system. They are highly persistent and have a long half-life in the environment. Due to imprudent use, their toxic residues have enormously increased in the last few years and are frequently detected in food commodities, which causes chronic diseases in humans and mammals. However, for the safety of the environment and the diversity of living organisms, the removal of s-triazine herbicides has received widespread attention. In this review, the degradation of s-triazine herbicides and their intermediates by indigenous microbial species, genes, enzymes, plants, and nanoparticles are systematically investigated. The hydrolytic degradation of substituents on the s-triazine ring is catalyzed by enzymes from the amidohydrolase superfamily and yields cyanuric acid as an intermediate. Cyanuric acid is further metabolized into ammonia and carbon dioxide. Microbial-free cells efficiently degrade s-triazine herbicides in laboratory as well as field trials. Additionally, the combinatorial approach of nanomaterials with indigenous microbes has vast potential and considered sustainable for removing toxic residues in the agroecosystem. Due to their smaller size and unique properties, they are equally distributed in sediments, soil, water bodies, and even small crevices. Finally, this paper highlights the implementation of bioinformatics and molecular tools, which provide a myriad of new methods to monitor the biodegradation of s-triazine herbicides and help to identify the diverse number of microbial communities that actively participate in the biodegradation process.

Integrated microbiology and metabolomics analysis reveal responses of cotton rhizosphere microbiome and metabolite spectrum to conventional seed coating agents

Fludioxonil (FL) and metalaxyl-M·fludioxonil·azoxystrobin (MFA) are conventional seed coating agents for controlling cotton seedling diseases. However, their effects on seed endophytic and rhizosphere microecology are still poorly understood. This study aimed to assess the effects of FL and MFA on cotton seed endophytes, rhizosphere soil enzymatic activities, microbiome and metabolites. Both seed coating agents significantly changed seed endophytic bacterial and fungal communities. Growing coated seeds in the soils originating from the Alar (AL) and Shihezi (SH) region inhibited soil catalase activity and decreased both bacterial and fungal biomass. Seed coating agents increased rhizosphere bacterial alpha diversity for the first 21 days but decreased fungal alpha diversity after day 21 in the AL soil. Seed coating reduced the abundance of a number of beneficial microorganisms but enriched some potential pollutant-degrading microorganisms. Seed coating agents may have affected the complexity of the co-occurrence network of the microbiome in the AL soil, reducing connectivity, opposite to what was observed in the SH soil. MFA had more pronounced effects on soil metabolic activities than FL. Furthermore, there were strong links between soil microbial communities, metabolites and enzymatic activities. These findings provide valuable information for future research and development on application of seed coatings for disease management.

In vitro interactions of two pesticides, propazine and quinoxyfen with bovine serum albumin: Spectrofluorometric and molecular docking investigations

Binding mechanisms of two selected pesticides, propazine (PRO) and quinoxyfen (QUI) with bovine serum albumin (BSA) was examined using fluorescence, absorption and molecular docking methods. Intrinsic fluorescence of BSA was quenched in the presence of both PRO and QUI. The quenching was ascertained to be conversely linked to temperature, which suggested the contribution of static quenching process in the PRO-BSA and QUI-BSA complex formations. This results were validated by the enhancement in absorption spectrum of BSA upon binding with PRO and QUI. Binding constant values (K_f = 9.55-0.60 × 10^-3 M^-1 for PRO-BSA system; K_f = 7.08-5.01 × 10² M^-1 for QUI-BSA system) and number of binding site (n) values for the PRO-BSA and QUI-BSA systems at different temperatures affirmed a weak binding strength with a set of equivalent binding sites on BSA. Thermodynamic data obtained for both the PRO-BSA and QUI-BSA interactions predicted that the association process was spontaneous and non-covalent contacts such as hydrophobic interactions, van der Waals forces and hydrogen bonds participated in the binding reactions. This result was further supported by the molecular docking assessments. Three-dimensional spectral results revealed the microenvironmental alterations near tryptophan (Trp) and tyrosine (Tyr) residues in BSA by the addition of PRO and QUI. The docking analysis demonstrated the binding pattern for the PRO-BSA and QUI-BSA systems and disclosed the preferred binding site of both PRO and QUI as site I (subdomain IIA) of BSA.

DNA-SIP and repeated isolation corroborate Variovorax as a key organism in maintaining the genetic memory for linuron biodegradation in an agricultural soil

The frequent exposure of agricultural soils to pesticides can lead to microbial adaptation, including the development of dedicated microbial populations that utilize the pesticide compound as a carbon and energy source. Soil from an agricultural field in Halen (Belgium) with a history of linuron exposure has been studied for its linuron-degrading bacterial populations at two time points over the past decade and Variovorax was appointed as a key linuron degrader. Like most studies on pesticide degradation, these studies relied on isolates that were retrieved through bias-prone enrichment procedures and therefore might not represent the in situ active pesticide-degrading populations. In this study, we revisited the Halen field and applied, in addition to enrichment-based isolation, DNA stable isotope probing (DNA-SIP), to identify in situ linuron-degrading bacteria in linuron-exposed soil microcosms. Linuron dissipation was unambiguously linked to Variovorax and its linuron catabolic genes and might involve the synergistic cooperation between two species. Additionally, two novel linuron-mineralizing Variovorax isolates were obtained with high 16S rRNA gene sequence similarity to strains isolated from the same field a decade earlier. The results confirm Variovorax as a prime in situ degrader of linuron in the studied agricultural field soil and corroborate the genus as key for maintaining the genetic memory of linuron degradation functionality in that field.

Environmental disappearance of acetochlor and its bioavailability to weed: A general prototype for reduced herbicide application instruction

The consecutive application of herbicide acetochlor has resulted in the widespread drug resistance of weeds and the high risks to environment and human health. To assess environmental behaviors and minimal dosage of acetochlor application in the realistic soil, we systematically investigated the acetochlor adsorption/desorption, mobility, leaching, degradation, weed bioavailability and lethal dosage of acetochlor in three soil types including Nanjing (NJ), Yancheng (YC) and Yingtan (YT). Under the same conditions (60% moisture and darkness), acetochlor had a half-life of disappearance 3 days in NJ, 4.9 days in YC and 25.7 days in YT soils. The HRLC-Q-TOF-MS/MS analyses identified ten metabolites and eight conjugates generated through dealkylation, hydroxylation, thiol conjugation and glycosylation pathways. The acetochlor adsorption to soils ranked in the order of YT > YC > NJ and was committed to the Freundlich model. By examining the effects of soil moisture, microbial activity, illumination/darkness, etc. on acetochlor degradation in soils, we showed that the chemical metabolisms could undergo multiple processes through soil microbial degradation, hydrolysis or photolysis-mediated mechanisms. The longitudinal migration assay revealed that acetochlor leaching ability in the three soils was YT > YC > NJ, which was negatively associated with the order of adsorption behavior. Four kinds of weed were grown in the acetochlor-contaminated NJ soil. The lethal concentrations for the weed plantlets were 0.16-0.3 mg/kg, much lower than the dosage of realistic field application. Overall, our work provided novel insights into the mechanism for acetochlor behaviors in soils, the natural degradation process in the environment, and the lethal concentration to the tested weed plants.

Emerging nanobiotechnology in agriculture for the management of pesticide residues

Utilization of pesticides is often necessary for meeting commercial requirements for crop quality and yield. However, incessant global pesticide use poses potential risks to human and ecosystem health. This situation increases the urgency of developing nano-biotechnology-assisted pesticide formulations that have high efficacy and low risk of side effects. The risks associated with both conventional and nanopesticides are summarized in this review. Moreover, the management of residual pesticides is still a global challenge. The contamination of soil and water resources with pesticides has adverse impact over agricultural productivity and food security; ultimately posing threats to living organisms. Pesticide residues in the eco-system may be treated via several biological and physicochemical processes, such as microbe-based degradation and advanced oxidation processes. With these issues in mind, we present a review that explores both existing and emerging techniques for management of pesticide residues and environmental risks. These techniques can offer a sustainable solution to revitalize the tarnished water/soil resources. Further, state-of-the-art research approaches to investigate biotechnological alternatives to conventional pesticides are discussed along with future prospects and mitigation techniques are recommended.

Physiochemical assessment of environmental behaviors of herbicide atrazine in soils associated with its degradation and bioavailability to weeds

Atrazine residue in soil is one of the serious environmental problems and continues to risk ecosystem and human health. To address the environmental behaviors and dissipation of atrazine and better manage the application of atrazine in reality, we comprehensively investigated the adsorption and desorption, migration ability, and vanishing of atrazine in three distinct soils in China including Jiangxi (JX, pH 5.45, TOC 0.54%), Nanjing (NJ, pH 6.15, TOC 2.13%), and Yancheng (YC, pH 8.60, TOC 0.58%) soils. The atrazine adsorptive capacity to the soils was arranged in the order of NJ > YC > JX. The leaching assay with profiles of the soils showed strong migration, suggesting it had a high bioavailability to weeds and potential for underground water contamination. We further investigated the effects of environmental factors such as soil moisture, microbial activity and photolysis on atrazine degradation and showed that the degradation of atrazine in the soil mainly underwent the abiotic process, most likely through hydrolysis and photolysis-mediated mechanisms, and to less extend through soil microbial catabolism. Using HRLC-Q-TOF-MS/MS and by comparing the measured and theoretical m/z values and fragmentation data, ten metabolites comprising eight degraded products and two conjugates were characterized. Atrazine existing in the soils and sprayed coordinately blocked the growth of three common weeds, which prompted us to use the minimal atrazine in practice to control the waste of the pesticide and its impact on the environment. Overall, our work provided an insight into the mechanisms for the degradation of atrazine residues in the soils and contributed to the environmental risk assessment of the pesticide and management in its application control in the crop rotation and safe production.

Identification of a novel function of a component in the jasmonate signaling pathway for intensive pesticide degradation in rice and environment through an epigenetic mechanism

Developing a biotechnical system with rapid degradation of pesticide is critical for reducing environmental, food security and health risks. Here, we investigated a novel epigenetic mechanism responsible for the degradation of the pesticide atrazine (ATZ) in rice crops mediated by the key component CORONATINE INSENSITIVE 1a (OsCOI1a) in the jasmonate-signaling pathway. OsCOI1a protein was localized to the nucleus and strongly induced by ATZ exposure. Overexpression of OsCOI1a (OE) significantly conferred resistance to ATZ toxicity, leading to the improved growth and reduced ATZ accumulation (particularly in grains) in rice crops. HPLC/Q-TOF-MS/MS analysis revealed increased ATZ-degraded products in the OE plants, suggesting the occurrence of vigorous ATZ catabolism. Bisulfite-sequencing and chromatin immunoprecipitation assays showed that ATZ exposure drastically reduced DNA methylation at CpG context and histone H3K9me2 marks in the upstream of OsCOI1a. The causal relationships between the DNA demethylation (hypomethylatioin), OsCOI1a expression and subsequent detoxification and degradation of ATZ in rice and environment were well established by several lines of biological, genetic and chemical evidence. Our work uncovered a novel regulatory mechanism implicated in the defense linked to the epigenetic modification and jasmonate signaling pathway. It also provided a modus operandi that can be used for metabolic engineering of rice to minimize amounts of ATZ in the crop and environment.

Identification of intermediates, acute toxicity removal, and kinetics investigation to the Ametryn treatment by direct photolysis (UV254), UV254/H2O2, Fenton, and photo-Fenton processes

This paper reports the degradation of 10 mg L^-1 Ametryn solution with different advanced oxidation processes and by ultraviolet (UV₂₅₄) irradiation alone with the main objective of reducing acute toxicity and increase biodegradability. The investigated factors included Fe²⁺ and H₂O₂ concentrations. The effectiveness of the UV₂₅₄ and UV₂₅₄/H₂O₂ processes were investigated using a low-pressure mercury UV lamp (254 nm). Photo-Fenton process was explored using a blacklight blue lamp (BLB, λ = 365 nm). The UV₂₅₄ irradiation process achieved complete degradation of Ametryn solution after 60 min. The degradation time of Ametryn was greatly improved by the addition of H₂O₂. It is worth pointing out that a high rate of Ametryn removal was attained even at low concentrations of H₂O₂. The kinetic constant of the reaction between Ametryn and HO^● for UV₂₅₄/H₂O₂ was 3.53 × 10⁸ L mol^-1 s^-1. The complete Ametryn degradation by the Fenton and photo-Fenton processes was observed following 10 min of reaction for various combinations of Fe²⁺ and H₂O₂ under investigation. Working with the highest concentration (150 mg L^-1 H₂O₂ and 10 mg L^-1 Fe²⁺), around 30 and 70% of TOC removal were reached within 120 min of treatment by Fenton and photo-Fenton processes, respectively. Although it did not obtain complete mineralization, the intermediates formed in the degradation processes were hydroxylated and did not promote acute toxicity of Vibrio fischeri. Furthermore, a substantial improvement of biodegradability was obtained for all studied processes.

Isoproturon-Induced Salicylic Acid Confers Arabidopsis Resistance to Isoproturon Phytotoxicity and Degradation in Plants

This study identified the effect of salicylic acid on degradation of isoproturon in Arabidopsis. Three T-DNA insertion mutant lines pal1- 1, pal1- 2, and eps1- 1 defective in salicylic acid synthesis were tested, which showed higher isoproturon accumulation and a toxic symptom in the mutants. When treated with 5 mg/L salicylic acid, these lines displayed a lower level of isoproturon and showed an attenuated toxic symptom. An RNA-sequencing study identified 2651 (1421 up and 1230 down) differentially expressed genes (DEGs) in eps1- 1 and 2211 (1556 up and 655 down) in pal1- 2 mutant plants (>2.0 fold change, p < 0.05). Some of the DEGs covered Phase I-III reaction components, like glycosyltransferases (GTs) and ATP-binding cassette transporters (ABCs). Using ultra performance liquid chromatography-time-of-flight-tandem-mass spectrometer/mass spectrometer (UPLC/Q-TOF-MS/MS), 13 Phase I and four Phase II metabolites were characterized. Of these, two metabolites 1-OH-isopropyl-benzene-O-glucoside and 4-isopropylphenol-S-2-methylbutanoyl-serine, have been identified and reported for the first time.

Reduced phytotoxicity of propazine on wheat, maize and rapeseed by salicylic acid

Propazine belongs to the triazine herbicide family and widely used in the farmland for crop production. Recent studies have shown that the residue of propazine in environment is accumulative. This inevitably results in accumulation of propazine in crops. Therefore, reduction of propazine toxicity and accumulation in crops is critically important. In this study, the growth of wheat, maize and rapeseed was significantly inhibited by 2, 8 and 0.4 mg kg^-1 propazine in soils. The chlorophyll content of the three crops also showed significant decrease, while the electrolyte permeability, a biomarker of cellular damage, increased in the plant cells. However, when plants were sprayed with 5 mg L^-1 of salicylic acid (SA), the propazine phytotoxicity of the crops was relieved, with increased chlorophyll content and reduced electrolyte permeability of all crops. Meanwhile, the activities of peroxidase (POD) and glutathione transferase (GST) remained lower. The propazine accumulation in the crops and the residues in the soil were determined by high performance liquid chromatography. The concentration of propazine in plants and soils treated by SA was less than that of the untreated control. Six propazine degraded products (derivatives) in rhizosphere of wheat were characterized using ultraperformance liquid chromatography with a quadrupole-time-of-flight tandem mass spectrometer. Our work indicates that the improved growth of crops was possibly due to the acceleration of propazine degradation by salicylic acid.