Sulfonylurea Bridge Research Articles

Synergistic adsorption and degradation of sulfonylurea herbicides by biochar-supported nano zero-valent iron composites in in-situ soil remediation

The extensive and continuous application of sulfonylurea herbicide is crucial for weed management but has resulted in widespread non-point source pollution. In this study, nano zero-valent iron/biochar (nZVI/BC) was synthesized by using FeCl3-impregnated corn stalks under anoxic pyrolysis conditions, which was applied in the in-situ remediation of bensulfuron methyl (BSFM) and sulfometuron methyl (SMTM) polluted soil. The results show that nZVI/BC with a 2.7 ratio of Fe/C had the highest efficiency in removing sulfonylurea herbicides. The removal efficiencies of BSFM and SMTM by nZVI/BC were negatively correlated to initial concentrations of sulfonylurea herbicides and positively correlated to nZVI/BC addition amount in the soil. Moreover, nZVI/BC could remove 53 % of BSFM and 72 % of SMTM at the concentration of 5 mg/kg after 21 d, which was much higher than that of BC. Notably, the removal efficiency of BSFM by nZVI/BC reached 36 % within 7 d, while the removal efficiency of SMTM by nZVI/BC was up to 68 % even within 3 d. The adsorption of herbicides by nZVI/BC was mainly driven by chemical processes involving multilayer adsorption. Furthermore, the removal mechanisms of BMTM and SMTM by nZVI/BC also involved C = O and C–O groups and oxidation of nZVI to FeO and Fe3O4 along with the cleavage of the sulfonylurea bridge. This study provides a promising application of nZVI/BC in in-situ remediating sulfonylurea herbicide- polluted soil.

Biochemical insights into the biodegradation mechanism of typical sulfonylureas herbicides and association with active enzymes and physiological response of fungal microbes: A multi-omics approach

The extensive use of sulfonylurea herbicides has raised major concerns regarding their long-term soil residues and agroecological risks despite their role in agricultural protection. Microbial degradation is an important approach to remove sulfonylureas, whereas understanding the associated biodegradation mechanisms, enzymes, and physiological responses remains incomplete. Based on the rapid biodegradation of nicosulfuron by typical fungal isolate Talaromyces flavus LZM1, the dependency on cellular accumulation and environmental conditions, e.g. pH and nutrient supplies, was shown in the study. The biodegradation of nicosulfuron occurred intracellularly and followed the cascade of reactions including hydrolysis, Smile contraction rearrangement, hydroxylation, and opening of the pyrimidine ring. Besides 2-amino-4,6-dimethoxypyrimidine (ADMP) and 2-aminosulfonyl-N,N-dimethylnicotinamide (ASDM), numerous products and intermediates were newly identified and the structural forms of methoxypyrimidine and sulfonylurea bridge contraction rearrangement are predicted to be more toxic than nicosulfuron. The biodegradation should be enzymatically regulated by glycosylphosphatidylinositol transaminase (GPI-T) and P450s, which were manifested with the significant upregulation in proteomics. It is the first time that the hydrolysis of nicosulfuron into ADMP and ASDM have been associated with GPI-T. The integrated pathways of biodegradation were further elucidated through the involvement of various active enzymes. Except for the enzymatic catalysis, the physiological responses verified by metabolo-proteomics were critical not only to regulate material synthesis, uptake, utilization, and energy transfer but also to maintain antioxidant homeostasis, biodegradability, and tolerance of nicosulfuron by the differentially expressed metabolites, such as acetolactate synthase and 3-isopropylmalate dehydratase. The obtained results would help understand the biodegradation mechanism of sulfonylurea from chemicobiology and enzymology and promote the use of fungal biodegradation in pollution rehabilitation.

Current insights into the microbial degradation of nicosulfuron: Strains, metabolic pathways, and molecular mechanisms

Nicosulfuron is among the sulfonylurea herbicides that are widely used to control annual and perennial grass weeds in cornfields. However, nicosulfuron residues in the environment are likely to cause long-lasting harmful environmental and biological effects. Nicosulfuron degrades via photo-degradation, chemical hydrolysis, and microbial degradation. The latter is crucial for pesticide degradation and has become an essential strategy to remove nicosulfuron residues from the environment. Most previous studies have focused on the screening, degradation characteristics, and degradation pathways of biodegrader microorganisms. The isolated nicosulfuron-degrading strains include Bacillus, Pseudomonas, Klebsiella, Alcaligenes, Rhodopseudomonas, Ochrobactrum, Micrococcus, Serratia, Penicillium, Aspergillus, among others, all of which have good degradation efficiency. Two main intermediates, 2-amino-4,6-dimethoxypyrimidine (ADMP) and 2-aminosulfonyl-N,N-dimethylnicotinamide (ASDM), are produced during microbial degradation and are derived from the C–N, C–S, and S–N bond breaks on the sulfonylurea bridge, covering almost every bacterial degradation pathway. In addition, enzymes related to the degradation of nicosulfuron have been identified successively, including the manganese ABC transporter (hydrolase), Flavin-containing monooxygenase (oxidase), and E3 (esterase). Further in-depth studies based on molecular biology and genetics are needed to elaborate on their role in the evolution of novel catabolic pathways and the microbial degradation of nicosulfuron. To date, few reviews have focused on the microbial degradation and degradation mechanisms of nicosulfuron. This review summarizes recent advances in nicosulfuron degradation and comprehensively discusses the potential of nicosulfuron-degrading microorganisms for bioremediating contaminated environments, providing a reference for further research development on nicosulfuron biodegradation in the future.

Characterization of a new chlorimuron-ethyl-degrading strain Cedecea sp. LAM2020 and biodegradation pathway revealed by multiomics analysis.

The widespread use of the herbicide chlorimuron-methyl is hazard to rotational crops and causes soil degradation problems. Biodegradation is considered a promising way for removing herbicide residues from the environment. Here, a new isolated strain, Cedecea sp. LAM2020, enabled complete degradation of 100mg/L chlorimuron-methyl within five days. Transcriptome analysis revealed that ABC transporters, atrazine degradation and purine metabolism were enriched in the KEGG pathway. Integrating GO and KEGG classification with related reports, we predict that carboxylesterases are involved in the biodegradation of chlorimuron-methyl by LAM2020. Heterologous expression of the carboxylesterase gene carH showed 26.67% degradation of 50mg/L chlorimuron-methyl within 6h. The intracellular potential biological response and extracellular degradation process of chlorimuron-ethyl were analyzed by the nontarget metabolomic and mass spectrometry respectively, and the biodegradation characteristics and complete mineralization pathway was revealed. The cleavage of the sulfonylurea bridge and the ester bond achieved the first step in the degradation of chlorimuron-methyl. Together, these results reveal the presence of acidolysis and enzymatic degradation of chlorimuron-methyl by strain LAM2020. Hydroponic corn experiment showed that the addition of strain LAM2020 alleviated the toxic effects of chlorimuron-ethyl on the plants. Collectively, strain LAM2020 may be a promising microbial agent for plants chlorimuron-ethyl detoxification and soil biofertilizer.

<em>Mucor </em>assisted degradation of sulfosulfuron in irrigation water

Sulfosulfuron is a widely used wheat herbicide, which has two major environmental issues, viz. carryover effect to succeeding crops, and groundwater and surface water contamination. The safer aquatic environment requires the degradation of the herbicide. In this present investigation, we have attempted to isolate an efficient fungus naturally abundant in water, which can degrade sulfosulfuron in aqueous phase. Mucor sp., a fungus isolated from irrigation water was characterized as a sulfosulfuron-degrading microorganism. It survived in the minimal broth having sulfosulfuron at a level of 2000 mgL-1. It was able to degrade entire amount of sufosulfuron applied to water within 27 days. Two major routes of degradation were established. One route involved the cleavage of sulfonylurea bridge resulting in the formation of a couple of major metabolites, viz. 2-amino-4,6-dimethoxypyrimidine (I) and 2-ethylsulfonylimidazo{1,2-a}pyridine-3-sulfonamide (II). The other route was the cleavage of sulfonylamide linkage, which formed the metabolite N-(4,6-dimethoxypyrimidin-2-yl)urea (III). Three other metabolites, N-(4,6-dimethoxypyrimidin-2-yl)-N'-hydroxyurea (IV), N,N'-bis(4,6-dimethoxypyrimidin-2- yl)urea (V) and N-(4,6-dimethoxypyrimidin)-N-(4-hydroxy-6-methoxy pyrimidin-2-yl)urea (VI) were also identified. The survival of Mucor sp. at a very high concentration of sulfosulfuron and its ability to degrade the herbicide through various biochemical mechanisms showed its potential in the bioremediation process of sulfosulfuron contaminated water.

Whole-Genome Sequencing of a Chlorimuron-Ethyl-Degrading Strain: Chenggangzhangella methanolivorans CHL1 and Its Degrading Enzymes.

ABSTRACTChlorimuron-ethyl is a commonly used sulfonylurea herbicide, and its long-term residues cause serious environmental problems. Biodegradation of chlorimuron-ethyl is effective and feasible, and many degrading strains have been obtained, but still, the genes and enzymes involved in this degradation are often unclear. In this study, whole-genome sequencing was performed on chlorimuron-ethyl-degrading strain, Chenggangzhangella methanolivorans CHL1. The complete genome of strain CHL1 contains one circular chromosome of 5,542,510 bp and a G+C content of 68.17 mol%. Three genes, sulE, pnbA, and gst, were predicted to be involved in the degradation of chlorimuron-ethyl, and this was confirmed by gene knockout and gene complementation experiments. The three genes were cloned and expressed in Escherichia coli BL21 (DE3) to allow for the evaluation of the catalytic activities of the respective enzymes. The glutathione-S-transferase (GST) catalyzes the cleavage of the sulfonylurea bridge of chlorimuron-ethyl, and the esterases, PnbA and SulE, both de-esterify it. This study identifies three key functional genes of strain CHL1 that are involved in the degradation of chlorimuron-ethyl and also provides new approaches by which to construct engineered bacteria for the bioremediation of environments polluted with sulfonylurea herbicides.IMPORTANCE Chlorimuron-ethyl is a commonly used sulfonylurea herbicide, worldwide. However, its residues in soil and water have a potent toxicity toward sensitive crops and other organisms, such as microbes and aquatic algae, and this causes serious problems for the environment. Microbial degradation has been demonstrated to be a feasible and promising strategy by which to eliminate xenobiotics from the environment. Many chlorimuron-ethyl-degrading microorganisms have been reported, but few studies have investigated the genes and enzymes that are involved in the degradation. In this work, two esterase-encoding genes (sulE, pnbA) and a glutathione-S-transferase-encoding gene (gst) responsible for the detoxification of chlorimuron-ethyl by strain Chenggangzhangella methanolivorans CHL1 were identified, then cloned and expressed in Escherichia coli BL21 (DE3). These key chlorimuron-ethyl-degrading enzymes are candidates for the construction of engineered bacteria to degrade this pesticide and enrich the resources for bioremediating environments polluted with sulfonylurea herbicides.

Persistence and transformation of flucetosulfuron herbicide in soil as affected by biotic and abiotic factors

Effect of biotic and abiotic factors of soil on persistence and transformation of flucetosulfuron was studied in three soils from paddy growing zones of India. Herbicide residues in three soils dissipated with half-life ranging from 1.41 to 8.38 and 0.58 to 1.14 days under sterile and non-sterile conditions, respectively. Acidic pH and soil microbial activity contributed more toward the degradation of flucetosulfuron in soil. Under flooded soils, dissipation was bit slower than under field capacity moisture level. Five transformation products were identified with LC-MS/MS analysis. Ester hydrolysis and sulfonyl urea bridge cleavage seems to be the major transformation pathways for flucetosulfuron in soil.

Dicationic Herbicidal Ionic Liquids Comprising Two Active Ingredients Exhibiting Different Modes of Action.

In the framework of this study, dicationic herbicidal ionic liquids (HILs) containing tetramethylene-1,4-bis(decyldimethylammonium) and dodecylmethylene-1,12-bis(decyldimethylammonium), including two different herbicidal anions exhibiting different modes of action, were synthesized and characterized. One herbicide incorporated into the HILs was a tribenuron-methyl belonging to ALS inhibitors, while the second herbicidal anion was a synthetic auxin that acts as a growth regulator, namely 2,4-dichlorophenoxyacetate (2,4-D), 2-(2,4-dichlorophenoxy)propionate, (2,4-DP), 2,4,5-trichlorophenoxyacetate (2,4,5-T), 4-chloro-2-methylphenoxyacetiate (MCPA), 2-(4-chloro-2-methylphenoxy)propionate (MCPP), and 4-chlorophenoxyacetate (4-CPA). The obtained products were found to be unstable and decomposed, which can be attributed to the presence of an additional methyl group within the sulfonylurea bridge of the tribenuron-methyl. The synthesized HILs exhibited good affinity with polar and semipolar solvents, with ethyl acetate and hexane as the only solvents that did not dissolve the HILs. Greenhouse tests demonstrated that most of the obtained HILs were more effective than the reference herbicide containing tribenuron-methyl. The length of the alkyl chain in the cation also influenced the effectiveness of the HILs. Better effects were observed for dodecylmethylene-1,12-bis(decyldimethylammonium) cations compared to tetramethylene-1,4-bis(decyldimethylammonium). Therefore, the novel dicatonic HILs showed to integrate the advent of the combination of the different herbicides into a single molecule, enhance herbicidal efficacy, and reduce the risk of weed resistance due to the various modes of action of the applied treatment.

Rapid degradation of the sulfonylurea herbicide–chlorimuron-ethyl by three novel strains of fungi

Chlorimuron-ethyl is a sulfonylurea herbicide with broad-spectrum weed control characteristics, low utilization rate, relatively high persistence in the soil. Chlorimuron-ethyl has been widely used world-over, and strategies for its removal have attracted increasing attention. Microbial degradation is considered the most acceptable dissipation method. We obtained the best biodegradation conditions using response surface methodology. Through the cleavage of the sulfonylurea bridge, we proposed a metabolic route for chlorimuron-ethyl degradation. Under these conditions (pH 6, 30 °C), Irpex lacteus could degrade 72.40% of the initially supplemented 40 mg L−1 chlorimuron-ethyl within 7 days. The half-life of chlorimuron-ethyl after inoculation was fairly short (4.696 days). The biodegradation rate of chlorimuron-ethyl by Irpex lacteus was 56.1%, which was higher than that of Phlebia sp. (50.8%) and Funalia trogii (25.4%). The pH value has an impact on the free state of the substrate molecule and the dissociation state of the enzyme molecule. The biodegradation rate was the highest (58.5%) at a pH value of 6. When the temperature was 30 °C, 56.3% of chlorimuron-ethyl was eliminated. As the temperature increased, the biodegradation rate of chlorimuron-ethyl by white-rot fungi decreased. Based on the results of LC–MS analysis, a metabolic route for chlorimuron-ethyl biodegradation was proposed. The fragment at m/z 161 (2-amino-4-chloro-6-methoxypyrimidine) originates from the cleavage of the C-N bond of the sulfonylurea bridge, while generating ethyl 2-sulfamoyl benzoate. The fragment at m/z 202 (2-sulfamoyl benzoic acid) corresponds to the ethyl group lost from ethyl 2-sulfamoyl benzoate. Due to the different secreted enzymes, there was a gap between the three strains in the degradation efficiency of chlorimuron-ethyl. The degradation rate of the herbicide by Phlebia sp. was the highest (61.7%), while by Irpex lacteus was the lowest (42.7%). Three white-rot fungi could degrade chlorimuron-ethyl in malt extract. LC–MS analysis indicated that the cleavage of sulfonylurea bridge through Irpex lacteus mediated the degradation of chlorimuron-ethyl. And, inoculation with white-rot fungi enhanced chlorimuron-ethyl degradation in aseptic soil samples. This is the principal report revealing that white-rot fungi can evacuate sulfonylurea herbicides, demonstrating that white-rot fungi will give novel ideas into the biodegradation of herbicides.

Synthesis, herbicidal activity study and molecular docking of novel pyrimidine thiourea

According to the pharmacophore binding strategy and principle of bioelectronic isobaric, used the sulfonylurea bridge as the parent structure, a series of novel thiourea compounds containing aromatic-substituted pyrimidines were designed and synthesized. The preliminary herbicidal activity tests showed that some compounds had good herbicidal activity against Digitaria adscendens, Amaranthus retroflexus, especially for compound 4d and 4f. The results showed that compound 4d had an inhibition rate of 81.5% on the root growth of Brassica napus L. at the concentration of 100 mg L−1, and compound 4f had an inhibition rate of 81% on the root growth of Digitaria adscendens at the concentration of 100 mg L−1. Compounds 4d and 4f had higher comparative activity on Echinochloa crus-galli than the commercial herbicide bensulfuron-methyl. The preliminary structure-activity relationship (SAR) was also summarized. We also tested the in vivo AHAS enzyme activity inhibition experiment of 14 compounds at 100 mg L−1, and the results showed that they all have inhibitory activity on the enzyme, with the highest inhibition rate reaching 44.4% (compound 4d). Based on the results of molecular docking to yeast acetohydroxyacid synthase (AHAS), the possible herbicidal activity mechanism of these compounds was evaluated.

Aspergillus niger-mediated degradation of orthosulfamuron in rice soil.

Orthosulfamuron, a rice herbicide of the family pyrimidinyl sulfonylurea, causes ground water contamination for its moderate persistence and high water solubility. It may cause phytotoxicity and, thereby, affect the growth of succeeding crops. Keeping in view of the environmental safety, the interaction between orthosulfamuron and soil fungi was investigated. Ten different fungal species were found to survive in the soil containing orthosulfamuron at the level of 50mgkg-1. However, based on the previous research reports, Aspergillus niger was selected for the degradation study on orthosulfamuron in the sterilized soil. It exhibited concentration-depended degradation rate for orthosulfamuron, where the rate decreased with the increasing concentration of the herbicide. The degradation pattern of the herbicide followed the first-order rate kinetics for each applied concentration. The structural elucidation of the five degradation products by liquid chromatography-mass spectroscopic analysis indicated that the fungal strain could degrade the herbicide through various biochemical processes. The major degradation of the herbicide took place through the hydrolytic cleavage of sulfonylurea bridge and cleavage of N (urea bridge)-C (pyrimidinyl ring) bond. The rate and degradation pattern of orthosulfamuron found in the present study strongly imply the presence of a recognition mechanism for the substrate and a consequent metabolic response system in the A. niger strain isolated from the agricultural soil.

Study on the characteristics and mechanisms of nicosulfuron biodegradation by Bacillus velezensis CF57.

Nicosulfuron is one of the main sulfonylurea herbicides that have been widely used to protect maize crops. A total of 10 nicosulfuron-degrading strains were isolated from the intestine tract of earthworm Eisenia foetida. Among them, Bacillus velezensis CF57 with the highest degradation efficiency was selected and studied in detail. The degradation characteristics of CF57 showed that it was able to effectively degrade nicosulfuron in a wide range of temperature, pH, and a low inoculation amount, and the response surface analysis revealed that the optimum degradation conditions were 30.8°C, pH 6.31, and inoculation amount 3.04%. Meanwhile, CF57 could degrade high-concentration nicosulfuron efficiently and posed a broad degradation spectrum of other sulfonylurea herbicides. Furthermore, the localization of degradation enzyme indicated that the nicosulfuron-degrading enzyme was an extracellular fraction. By analyzing the metabolites of nicosulfuron, it could be further determined that the degradation of nicosulfuron by strain CF57 was mainly through the extracellular enzyme, and its possible degradation pathway was mainly derived from the cleavage of the C-N bond of the sulfonylurea bridge. These results may provide new insights into bioremediation of nicosulfuron-contaminated environments and enrich the resources of degrading bacteria of sulfonylurea herbicides.

Toward an Understanding of the Formation and Desolvation of Methanol Solvate, and Structure of Methanolysis Product: A Case Study of Nicosulfuron

Nicosulfuron (NS) is a widely used sulfonylurea herbicide because of its high selectivity, broad spectrum of herbicide activity, and excellent performance. In this work, nicosulfuron methanol solvate (NS-MeOH) and [[3-[(Dimethylamino)carbonyl]-2-pyridinyl]sulfonyl]carbamic acid methyl ester (PCM) as a product of methanolysis of NS were obtained. Both of their structures were determined by a single crystal X-ray diffraction. A broad range of analytical techniques was applied to characterize the NS-MeOH, such as Powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and hot stage microscopy (HSM). Combined with the analysis of the Independent gradient model (IGM), Atom-in-molecules (AIM), and Hirshfeld surface (HS), direct insights into the role of solvent played in the formation of NS-MeOH and the mechanism of solid-to-solid phase transformation of NS-MeOH could be obtained. In addition, the aqueous solubility of NS was improved through the formation of NS-MeOH. A systematic investigation of herbicidal activity of NS and PCM was carried out. It was found that NS and NS-MeOH had similar herbicidal activities at the experimental concentrations while PCM exhibited significantly lower activity. It was suggested that methanolysis of the sulfonylurea bridge in the NS molecule exerted a great influence on the herbicidal activity.

Insight into the Characteristics and New Mechanism of Nicosulfuron Biodegradation by a Pseudomonas sp. LAM1902.

A total of five strains of nicosulfuron-degrading bacteria were isolated from a continuously cultivated microbial consortium using culturomics. Among them, a novel Pseudomonas strain, LAM1902, with the highest degradation efficiency was investigated in detail. The characteristics of nicosulfuron-degradation by LAM1902 were investigated and optimized by response surface analysis. Furthermore, non-targeted metabolomic analysis of extracellular and intracellular biodegradation of nicosulfuron by LAM1902 was carried out by liquid chromatography/mass spectroscopy (LC-MS) and gas chromatography-time-of-flight/mass spectroscopy (GC-TOF/MS). It was found that nicosulfuron was degraded by LAM1902 mainly via breaking the sulfonylurea bridge, and this degradation might be attributed to oxalate accumulation. The results of GC-TOF/MS also showed that the intracellular degradation of nicosulfuron did not occur. However, nicosulfuron exerted a significant influence on the metabolism of inositol phosphate, pyrimidine, arginine/proline, glyoxylate, and dicarboxylate metabolism and streptomycin biosynthesis. The changes of myo-inositol, trehalose, and 3-aminoisobutanoic acid were proposed as a mechanism of self-protection against nicosulfuron stress.

Simulated solar driven photolytic ozonation for the oxidation of aqueous recalcitrant-to-ozone tritosulfuron. Transformation products and toxicity

This work reports the combination of ozone and solar radiation as an advanced oxidation process to remove the herbicide tritosufuron (TSF) in water. Firstly, the recalcitrance of TSF has been assessed, obtaining an ozonation second order rate constant of 5–154 M−1 min−1 in the range of pH from 5 to 8; while the rate constant with HO was found to be (1.8–3.1)·109 M−1 s−1. Secondly, the simultaneous application of simulated solar radiation in between 300 and 800 nm and ozone resulted positive in the oxidation rate of TSF. Mineralization extent was also higher. Less effective oxidation was achieved after limiting the radiation to the range 360–800 nm or 390–800 nm; also completely inappropriate for mineralization. Thirdly, the detected transformation products (TPs) demonstrated the vulnerability of TSF molecule to be attacked by HO in the sulfonylurea bridge. The combination of ozone and radiation of 300–800 nm led to the most effective removal of the TPs. Finally, after the photolytic ozonation treatment toxicity was also evaluated in terms of phytotoxicity towards the germination and root elongation of Lactuca Sativa seeds, and toxicity by immobilization tests of Daphnia Magna.

Nicosulfuron Degradation by an Ascomycete Fungus Isolated From Submerged Alnus Leaf Litter.

Nicosulfuron is a selective herbicide belonging to the sulfonylurea family, commonly applied on maize crops. Its worldwide use results in widespread presence as a contaminant in surface streams and ground-waters. In this study, we isolated, for the first time, the Plectosphaerella cucumerina AR1 nicosulfuron-degrading fungal strain, a new record from Alnus leaf litter submerged in freshwater. The degradation of nicosulfuron by P. cucumerina AR1 was achieved by a co-metabolism process and followed a first-order model dissipation. Biodegradation kinetics analysis indicated that, in planktonic lifestyle, nicosulfuron degradation by this strain was glucose concentration dependent, with a maximum specific degradation rate of 1 g/L in glucose. When grown on natural substrata (leaf or wood) as the sole carbon sources, the Plectosphaerella cucumerina AR1 developed as a well-established biofilm in 10 days. After addition of nicosulfuron in the medium, the biofilms became thicker, with rising mycelium, after 10 days for leaves and 21 days for wood. Similar biofilm development was observed in the absence of herbicide. These fungal biofilms still conserve the nicosulfuron degradation capacity, using the same pathway as that observed with planktonic lifestyle as evidenced by LC-MS analyses. This pathway involved first the hydrolysis of the nicosulfuron sulfonylurea bridge, leading to the production of two major metabolites: 2-amino-4,6-dimethoxypyrimidine (ADMP) and 2-(aminosulfonyl)-N,N-dimethyl-3-pyridinecarboxamide (ASDM). One minor metabolite, identified as 2-(1-(4,6-dimethoxy-pyrimidin-2-yl)-ureido)-N,N-dimethyl-nicotinamide (N3), derived from the cleavage of the C-S bond of the sulfonylurea bridge and contraction by elimination of sulfur dioxide. A last metabolite (N4), detected in trace amount, was assigned to 2-(4,6-dimethoxy-pyrimidin-2-yl)-N,N-dimethyl-nicotinamide (N4), resulting from the hydrolysis of the N3 urea function. Although fungal growth was unaffected by nicosulfuron, its laccase activity was significantly impaired regardless of lifestyle. Leaf and wood surfaces being good substrata for biofilm development in rivers, P. cucumerina AR1 strain could thus have potential as an efficient candidate for the development of methods aiming to reduce contamination by nicosulfuron in aquatic environments.

Expression and functional analysis of three nicosulfuron-degrading enzymes from Bacillus subtilis YB1

ABSTRACTTo investigate the degradation activity of the manganese ABC transporter, vegetative catalase 1 and acetoin dehydrogenase E1 from Bacillus subtilis YB1, the proteins were prokaryotically expressed and purified. Assay results showed that the three enzymes were able to degrade nicosulfuron (2- (4,6-dimethoxypyrimidine-2-pyrimidinylcarbamoylaminosulfonyl) -N,N-dimethylnicotinamide), with vegetative catalase 1 exhibiting the highest activity. To further examine the degradation pathway, the degradation products of the three enzymes and the YB1 strain were detected by liquid chromatography-mass spectrometry(LC-MS). The nicosulfuron degradation products of the three enzymes were consistent with those of the YB1 strain, indicating the presence of two pathways: one due to cleavage of sulfonylurea bridges and ring-opening of 1-(4,6-dimethoxy-pyrimidin-2-yl)-3-(2-methyliminomethanesulfonyl-acetyl)-ureaas the pyrimidine ring, yielding the product; and the another due to cleavage of a sulfonylurea bridge, yielding 4,6-dihydroxy pyrimidine (111 m/z), 2-ylamine −4,6-dimethoxy pyrimidine and ((4-(dimethycarbamoyl)pyridine-2-yl)sulfonyl)carbamic acid as products, which were further degraded to 4,6-dihydroxy pyrimidine and N,N-dimethyl-2-sulfamoyl-isonicotinamide. The above results reveal a major contribution of extracellular enzymes to the degradation of nicosulfuron by the YB1 strain. Our data help in elucidation of the mechanism of nicosulfuron bio-degradation and may facilitate the construction of engineered strains.

Hydrolysis, adsorption, and biodegradation of bensulfuron methyl under methanogenic conditions

Bensulfuron methyl (BSM), one of the most widely used herbicides in paddy soils, is frequently detected in natural and artificial aquatic systems. However, BSM transformation under methanogenic conditions has not been given sufficient attention. In this study, BSM elimination and transformation by anaerobic enrichment cultures were investigated. The results showed that BSM can be mineralized to methane through hydrolysis, adsorption, and biodegradation under a methanogenic environment. The adsorption led to protein static quenching in the extracellular polymeric substances (EPSs) of the enrichment cultures. Specifically, BSM mainly reacted with the amine, amide, amino acid, and amino sugar functional groups in proteins. BSM hydrolysis and biodegradation occurred through the breakage of the sulfonylurea bridge and sulfonyl amide linkage. The cleavage of the sulfonylurea bridge occurred in both hydrolysis and biodegradation, while the cleavage of the sulfonyl amide linkage only occurred in hydrolysis. These results elucidated the complex transformation of BSM under methanogenic conditions, which will advance the studies on sulfonylurea herbicide biotransformation and hazard assessment in the environment.

Biodegradation and detoxification of chlorimuron-ethyl by Enterobacter ludwigii sp. CE-1

The application of the herbicide chlorimuron-ethyl has a lasting toxic effect on some succession crops. Here, a bacterium capable of utilizing chlorimuron-ethyl as the sole source of nitrogen was isolated from the contaminated soil and was identified as Enterobacter ludwigii sp. CE-1, and its detoxification and degradation of the herbicide were then examined. The biodegradation of chlorimuron-ethyl by the isolate CE-1 was significantly accelerated with increasing concentration (1–10mg/l) and temperature (20–40°C). The optimal pH for the degradation of chlorimuron-ethyl by the isolate CE-1 was pH 7.0. A pathway for the biodegradation of chlorimuron-ethyl by the isolate CE-1 was proposed, in which it could be first converted into 2-amino-4-chloro-6-methoxypyrimidine and an intermediate product by the cleavage of the sulfonylurea bridge and then transformed into saccharin via hydrolysis and amidation. The plant height and fresh weight of corn that had been incubated in nutrient solution containing 0.2mg/l of chlorimuron-ethyl significantly recovered to 83.9% and 83.1% compared with those in the uninoculated control, although the root growth inhibition of chlorimuron-ethyl could not be alleviated after inoculation for 14 d. The results indicate that the isolate CE-1 is a promising bacterial resource for the biodegradation and detoxification of chlorimuron-ethyl.

Degradation of nicosulfuron by a novel isolated bacterial strain Klebsiella sp. Y1: condition optimization, kinetics and degradation pathway.

A novel bacterial strain Klebsiella sp. Y1 was isolated from the soil of a constructed wetland, and it was identified based on the 16S rDNA sequence analysis. The co-metabolic degradation of nicosulfuron with glucose by Klebsiella sp. Y1 was investigated. The response surface methodology analysis indicated that the optimal pH and temperature were 7.0 and 35 °C, respectively, for the degradation of nicosulfuron. Under the optimal conditions, the degradation of nicosulfuron fitted Haldane kinetics model well. The removal of nicosulfuron was triggered by the acidification of glucose, which accelerated the hydrolysis of nicosulfuron. Then, the C-N bond of the sulfonylurea bridge was attacked and cleaved. Finally, the detected intermediate 2-amino-4,6-dimethoxypyrimidine was further biodegraded.