Biodegradation of bensulfuron-methyl and its effect on bacterial community in paddy soils

Enhanced efficiency of MS/MS all-ion fragmentation for non-targeted analysis of trace contaminants in surface water using multivariate curve resolution and data fusion

Data-independent acquisition-all-ion fragmentation (DIA-AIF) mode of mass spectrometry can facilitate wide-scope non-target analysis of contaminants in surface water due to comprehensive spectral identification. However, because of the complexity of the resulting MS2 AIF spectra, identifying unknown pollutants remains a significant challenge, with a significant bottleneck in translating non-targeted chemical signatures into environmental impacts. The present study proposes to process fused MS1 and MS2 data sets obtained from LC-HRMS/MS measurements in non-targeted AIF workflows on surface water samples using multivariate curve resolution-alternating least squares (MCR-ALS). This enables straightforward assignment between precursor ions obtained from resolved MS1 spectra and their corresponding MS2 spectra. The method was evaluated for two sets of tap water and surface water contaminated with 14 target chemicals as a proof of concept. The data set of surface water samples consisting of 3506 MS1 and 2170 MS2 AIF mass spectral features was reduced to 81 components via a fused MS1-MS2 MCR model that describes at least 98.8% of the data. Each component summarizes the distinct chromatographic elution of components together with their corresponding MS1 and MS2 spectra. MS2 spectral similarity of more than 82% was obtained for most target chemicals. This highlights the potential of this method for unraveling the composition of MS/MS complex data in a water environment. Ultimately, the developed approach was applied to the retrospective non-target analysis of an independent set of surface water samples.

Enhanced adsorption performance of bensulfuron methyl with B doping biochar: Mechanism and density functional theory calculations

It is an urgent task to develop suitable adsorbents for the control of herbicide-bensulfuron methyl (BSM) in the paddy rice fields at cold regions. Herein, B doping biochar was synthesized via one-step method. Results showed that the adsorption capacity for BSM on 1.0BBC was significantly superior to BC at 15 °C. Besides, low temperature resistance, wide pH adaptability, stable adsorption performance and reusability test suggested that 1.0BBC have potential practical application. The mechanisms of BSM removal by 1.0BBC were mainly attributed to pore filling and π-π electron donor-acceptor (EDA) interaction. Theoretical calculations revealed that BCO₂ could enhance the adsorption capacity by π-π EDA between BSM and adsorbent. Meanwhile, hydroponic experiment demonstrated that the toxicity to soybean after adsorption of BSM by 1.0BBC was within the safe range. This study proves that 1.0BBC is an easy-to-prepare adsorbent with promising application in BSM removal in the rice paddy fields at lower temperature.

Comprehensive characterization of stress tolerant bacteria with plant growth-promoting potential isolated from glyphosate-treated environment

The application of plant growth-promoting bacteria in agricultural systems is an efficient and environment-friendly strategy to improve crop yields and maintain soil quality. However, as different soils have diverse and specific ecological characteristics and may represent adverse abiotic conditions, in vivo application requires the careful selection of the desired beneficial microorganisms. In this study we report Ensifer adhaerens SZMC 25856 and Pseudomonas resinovorans SZMC 25875 isolates recovered from glyphosate-treated soil to possess yet undiscovered plant growth-enhancing potential. The strains were found to promote the growth of tomato seedlings significantly, to have the ability of synthesizing indole-3-acetic acid and siderophores, to tolerate pH in the range of 6.59-7.96, salinity up to 12.5 g L-1 NaCl and drought up to 125 g L-1 polyethylene glycol 6000, as well as to survive in the presence of various pesticides including glyphosate, diuron, chlorotoluron, carbendazim and thiabendazole, and heavy metals such as Al, Fe, Mn, Zn, Pb and Cu. The plant growth-promoting traits of the examined E. adhaerens and P. resinovorans isolates and their tolerance to numerous abiotic stress factors make them promising candidates for application in different agricultural environments, including soils polluted with glyphosate.

Genetically Engineered Methanotroph as a Platform for Bioaugmentation of Chemical Pesticide Contaminated Soil

Bioaugmentation is a promising alternative in soil remediation. One challenge of bioaugmentation is that exogenous pollutant-degrading microbes added to soil cannot establish enough biomass to eliminate pollutants. Considering that methanotrophs have a growth advantage in the presence of methane, we hypothesize that genetically engineered methanotrophs could degrade contaminants efficiently in soil with methane. Here, methanotroph Methylomonas sp. LW13, herbicide bensulfuron-methyl (BSM), and two kinds of soil were chosen to confirm this hypothesis. The unmarked gene knock-in method was first developed for strain LW13. Then, BSM hydrolase encoding gene sulE was inserted into the chromosome of strain LW13, conferring it BSM-degrading ability. After inoculation, the cell amount of strain LW13-sulE in soil raised considerably (over 100 fold in 9 days) with methane provision; meanwhile, >90% of BSM in soil was degraded. This study provides a proof of the concept that genetically engineered methanotroph is a potential platform for soil remediation.

Application of Methylopila sp. DKT for Bensulfuron-methyl Degradation and Peanut Growth Promotion

Bensulfuron-methyl is an herbicide widely used for weed control although its residues cause damage to other crops during crop rotations. In this study, the biodegrading activity of bensulfuron-methyl by a plant growth-promoting bacterial strain was carried out. Methylopila sp. DKT isolated from soil was determined for bensulfuron-methyl degradation and phosphate solubilization in the liquid media and soil. Moreover, the effects of the herbicide on peanut development and the role of Methylopila sp. DKT on the growth promotion of peanut were investigated. The results showed that the isolate effectively utilized the compound as a sole carbon source and solubilized low soluble inorganic phosphates. Methylopila sp. DKT also utilized 2-amino-4,6-dimethoxypyrimidine, a metabolite of bensulfuron-methyl degradation, as a sole carbon and energy source, and released ammonium and nitrate. The supplementation with Methylopila sp. DKT in soil increased the peanut biomass and the phosphorus content in the plant. In addition, the inoculation with Methylopila sp. DKT in soil and peanut cultivation increased the bensulfuron-methyl degradation by 57.7% for 1 month, which suggests that both plants and the bacterial isolate play a key role in herbicide degradation. These results indicate that the studied strain has a high potential for soil remediation and peanut growth promotion.

Environmental fate of bensulfuron-methyl and MCPA in aerobic and anaerobic rice-cropping systems

Bensulfuron-methyl (BM) and 4-chloro-2-methylphenoxyacetic acid (MCPA) are herbicides widely used in rice agroecosystems, and are commonly found in their environments, especially in water resources. The objective of this study was to evaluate the sorption-desorption, leaching, and dissipation of BM and MCPA under aerobic and anaerobic rice cropping conditions. For this purpose, a three-year field experiment was conducted in SW Spain using four management systems: aerobic with sprinkler irrigation and tillage (ST), sprinkler irrigation and no-tillage (SNT), long-term sprinkler irrigation and no-tillage (SNT^LT), and anaerobic with flooding and tillage (FT). At the end of the experiment, the partition coefficients (K_d-values) in ST were (2.7, 3.1, and 3.9) and (1.2, 1.5, and 1.9) times significantly lower than the values in {SNT, SNT^LT, and FT} for BM and MCPA, respectively. Greater sorption was related to lower values of soil pH for both herbicides and to higher contents in humic acids for BM and fulvic acids for MCPA. The persistence was much longer for BM (t_1/2 = 26.9-52.1 days) than for MCPA (t_1/2 = 1.54-21.1 days) in all management systems, and both herbicides' dissipation rates were generally greater under aerobic than under anaerobic conditions. The mobility of MCPA was much greater than that of BM. Compared with SNT and SNT^LT, leaching losses of the applied BM were greater by 51% for ST, and of the applied MCPA by 55% and 99% for ST and FT, respectively. Therefore, only aerobic rice production with no-tillage in the short- or long-terms could be considered as alternative management strategies with which to reduce water contamination by BM and MCPA in rice-growing environments.

Effects of bensulfuron-methyl residue on photosynthesis and chlorophyll fluorescence in leaves of cucumber seedlings

A potted soil experiment was conducted to investigate the effects of bensulfuron-methyl (BSM) residue on the growth and photosynthesis of seedlings of a local cucumber variety (Xia Feng No.1). When the residue of bensulfuron-methyl in soil exceeded 50μg kg^-1, it significantly inhibited the growth of cucumber, chlorophyll content and photosynthetic capacity of cucumber. BSM treatment caused significant decreases in the biomass, chlorophyll content, net photosynthesis rate, stomatal conductance, and transpiration rate, photosystem II (PSII) maximum quantum yield, actual quantum yield, photochemical quenching coefficient, and electron transport rate in cucumber seedlings, but increased the minimal fluorescence yield and dark respiration rate. Moreover, comparisons of the patterns of absorbed light energy partitioning revealed that the fractions of excess and thermally dissipated energy increased with rising concentrations of the BSM residue, but the fraction of PSII photochemistry declined. The BSM residues caused reversible destruction in the PSII reaction centers and decreased the proportion of available excitation energy used in PSII photochemistry. The results suggested that rice or wheat fields sprayed with BSM will not be suitable for planting cucumbers in succession or rotation.

Bensulfuron-Methyl Treatment of Soil Affects the Infestation of Whitefly, Aphid, and Tobacco Mosaic Virus on Nicotiana tabacum

Bensulfuron-methyl (BSM) is widely used in paddy soil for weed control. BSM residue in the soil has been known to inhibit the growth of sensitive crop plants. However, it is unknown whether BSM residue can affect the agrosystem in general. In this study, we have found significant effects of BSM on the infestation of Bemisia tabaci, Myzus persicae, and Tobacco mosaic virus (TMV) in Nicotiana tabacum. The soil was treated with BSM before the pest inoculation. The herbicide-treated tobaccos showed resistance to B. tabaci, but this resistance could not be detected until 15-day post-infestation when smaller number of adults B. tabaci appeared. In M. persicae assay, the longevity of all development stages of insects, and the fecundity of insects were not significantly affected when feeding on BSM-treated plants. In TMV assay, the BSM treatment also reduced virus-induced lesions in early infection time. However, the titer of TMV in BSM treated plants increased greatly over time and was over 40-fold higher than the mock-infected control plants after 20 days. Further studies showed that BSM treatment increased both jasmonic acid (JA) and salicylic acid (SA) levels in tobacco, as well as the expression of target genes in the JA and SA signaling pathways, such as NtWIPK, NtPR1a, and NtPAL. NtPR1a and NtPAL were initially suppressed after virus-inoculation, while NtRDR1 and NtRDR6, which play a key role in fighting virus infection, only showed up- or were down-regulated 20 days post virus-inoculation. Taken together, our results suggested that BSM residue in the soil may affect the metabolism of important phytohormones such as JA and SA in sensitive plants and consequently affect the plant immune response against infections such as whitefly, aphids, and viruses.

Structural changes in soil communities after triclopyr application in soils invaded by Acacia dealbata Link

Triclopyr is a commonly used herbicide in the control of woody plants and can exhibit toxic effects to soil microorganisms. However, the impact on soils invaded by plant exotics has not yet been addressed. Here, we present the results of an 18-month field study conducted to evaluate the impact of triclopyr on the structure of fungal and bacterial communities in soils invaded by Acacia dealbata Link, through the use of denature gradient gel electrophoresis. After triclopyr application, analyses of bacterial fingerprints suggested a change in the structure of the soil bacterial community, whereas the structure of the soil fungal community remained unaltered. Bacterial density and F:B ratio values changed across the year but were not altered due to herbicide spraying. On the contrary, fungal diversity was increased in plots sprayed with triclopyr 5 months after the first application. Richness and diversity (H') of both bacteria and fungi were not modified after triclopyr application.

Effects of a sulfonylurea herbicide on the soil bacterial community

Sulfonylurea herbicides are widely used on a wide range of crops to control weeds. Chevalier® OnePass herbicide is a sulfonylurea herbicide intensively used on cereal crops in Algeria. No information is yet available about the biodegradation of this herbicide or about its effect on the bacterial community of the soil. In this study, we collected an untreated soil sample, and another sample was collected 1 month after treatment with the herbicide. Using a high-resolution melting DNA technique, we have shown that treatment with Chevalier® OnePass herbicide only slightly changed the composition of the whole bacterial community. Two hundred fifty-nine macroscopically different clones were isolated from the untreated and treated soil under both aerobic and microaerobic conditions. The strains were identified by sequencing a conserved fragment of the 16S rRNA gene. The phylogenetic trees constructed using the sequencing results confirmed that the bacterial populations were similar in the two soil samples. Species belonging to the Lysinibacillus, Bacillus, Pseudomonas, and Paenibacillus genera were the most abundant species found. Surprisingly, we found that among ten strains isolated from the treated soil, only six were resistant to the herbicide. Furthermore, bacterial overlay experiments showed that only one resistant strain (related to Stenotrophomonas maltophilia) allowed all the sensitive strains tested to grow in the presence of the herbicide. The other resistant strains allowed only certain sensitive strains to grow. On the basis of these results, we propose that there must be several biodegradation pathways for this sulfonylurea herbicide.