Rapid biodegradation of metsulfuron-methyl by a soil fungus in pure cultures and soil

Cations impact the biodegradation of iodosulfuron-methyl herbicidal ionic liquids by fungi

In the framework of this study, six fungal isolates which demonstrated a high capability for biodegrading iodosulphuron-methyl sodium as well as herbicidal ionic liquids based on this herbicide were isolated from different soil samples. The isolates were identified based on the ITS region, whereas biodegradation residues were determined based on LC-MS/MS. Depending on the isolate, the half-lives values of the biodegraded herbicide or herbicidal ionic liquid ranged significantly from just 1.25 days to more than 40 days. The research findings unveiled that the structure of cations is a central limiting factor affecting fungal growth and herbicide transformation in case of ionic liquids. The length of the alkyl chain has been identified as the primary driver of herbicide toxicity, emphasizing the importance of structural factors in herbicide design. In cases when dodecyl(2-hydroxyethyl)dimethyl cation was used, its biodegradation ranged from 0 to approx. 20% and the biodegradability of the iodosulfuron-methyl was notably limited for the majority of the studied isolates. This knowledge provides guidance for development and selection of herbicides with reduced environmental impact. This study highlights the ecological importance of soil fungi, their potential role in herbicide biodegradation, the influence of cations on fungal growth and herbicide transformation, and the structural factors governing herbicide toxicity. Further research in these areas may lead to more efficient and environmentally friendly approaches to herbicide management.

Exposure to three herbicide mixtures influenced maize root-associated microbial community structure, function and the network complexity

Herbicide mixtures are a new and effective agricultural strategy for managing suppress weed resistance and have been widely used in controlling weeding growth in maize fields. However, the potential ecotoxicological impact of these mixtures on the microbial community structure and function within various root-associated niches, remains inadequately understood. Here, the effects of nicosulfuron, mesotrione and atrazine on soil enzyme activity and microbial community structure and function were investigated when applied alone and in combination. The findings indicated that herbicide mixtures exhibit a prolonged half-life compared to single herbicides. Ecological niches are the major factor influencing the structure and functions of the microbial community, with the rhizosphere exhibiting a more intensive response to herbicide stress. Herbicides significantly inhibited the activities of soil functional enzymes, including dehydrogenase, urease and sucrose in the short-term. Single herbicide did not drastically influence the alpha or beta diversity of the soil bacterial community, but herbicide mixtures significantly increased the richness of the fungal community. Meanwhile, the key functional microbial populations, such as Pseudomonas and Enterobacteriaceae, were significantly altered by herbicide stress. Both individual and combined use of the three herbicides reduced the complexity and stability of the bacterial network but increased the interspecific cooperations of fungal community in the rhizosphere. Moreover, by quantification of residual herbicide concentrations in the soil, we showed that the degradation period of the herbicide mixture was longer than that of single herbicides. Herbicide mixtures increased the contents of NO3--N and NH4+-N in the soil in the short-term. Overall, our study provided a comprehensive insight into the response of maize root-associated microbial communities to herbicide mixtures and facilitated the assessment of the ecological risks posed by herbicide mixtures to the agricultural environment from an agricultural sustainability perspective.

Microbial degradation as a powerful weapon in the removal of sulfonylurea herbicides

Sulfonylurea herbicides have been widely used worldwide and play a significant role in modern agricultural production. However, these herbicides have adverse biological effects that can damage the ecosystems and harm human health. As such, rapid and effective techniques that remove sulfonylurea residues from the environment are urgently required. Attempts have been made to remove sulfonylurea residues from environment using various techniques such as incineration, adsorption, photolysis, ozonation, and microbial degradation. Among them, biodegradation is regarded as a practical and environmentally responsible way to eliminate pesticide residues. Microbial strains such as Talaromyces flavus LZM1, Methylopila sp. SD-1, Ochrobactrum sp. ZWS16, Staphylococcus cohnii ZWS13, Enterobacter ludwigii sp. CE-1, Phlebia sp. 606, and Bacillus subtilis LXL-7 can almost completely degrade sulfonylureas. The degradation mechanism of the strains is such that sulfonylureas can be catalyzed by bridge hydrolysis to produce sulfonamides and heterocyclic compounds, which deactivate sulfonylureas. The molecular mechanisms associated with microbial degradation of sulfonylureas are relatively poorly studied, with hydrolase, oxidase, dehydrogenase and esterase currently known to play a pivotal role in the catabolic pathways of sulfonylureas. Till date, there are no reports specifically on the microbial degrading species and biochemical mechanisms of sulfonylureas. Hence, in this article, the degradation strains, metabolic pathways, and biochemical mechanisms of sulfonylurea biodegradation, along with its toxic effects on aquatic and terrestrial animals, are discussed in depth in order to provide new ideas for remediation of soil and sediments polluted by sulfonylurea herbicides.

Changed degradation behavior of pesticides when present in mixtures

Soil microorganisms are indispensable for a healthy soil environment, where the fate of pesticides is contingent on microbial activity. Conversely, soil ecosystems can be distorted by all kinds of variables, such as agrochemicals. These crop protection products have been universally in use for decades in agriculture. In modern crop cultivation, fungicides are increasingly applied because of their high and broad effectivity on plant pathogens. While their use can enhance harvest yields, fungicides, particularly broad-spectrum ones, are responsible for the alteration of the soil microflora. Furthermore, successive and combined application of pesticides is an agronomic routine, which aggravates the concurrent existence of synthetic chemicals in the soil and marine environments. Mutual interactions of such different molecules, or their effects on soil life, can negatively impact the dissipation of biodegradable pesticides from the ecosystems. The direct effects of individual agrochemicals on microbial soil parameters, as well as agronomic efficiency and interactions of mixtures have been thoroughly studied over the past 80 years. The indirect impacts of mixtures on soil and aquatic ecosystems, however, may be overlooked. Moreover, the current regulatory risk assessment of agrochemicals is based on fate investigations of individual substances to derive predicted environmental concentrations, which does not reflect real agricultural scenarios and needs to be updated. In this article, we summarized the results from our own experiments and previous studies, demonstrating that the degradation of pesticides is impacted by the co-existence of fungicides by their effects on microbial and enzymatic activities in soil.

Prokaryotic and microeukaryotic communities in an experimental rice plantation under long-term use of pesticides

Conventional agricultural practices, such as rice plantations, often contaminate the soil and water with xenobiotics. Here we evaluated the microbiota composition in experimental rice planting with a record of prolonged pesticide use, using 16S and 18S rRNA amplicon sequencing. We investigated four components of a complete agricultural system: affluent water (A), rice rhizosphere soil (R), sediment from a storage pond (S), and effluent (E) water (drained from the storage pond). Despite the short spatial distance between our sites, the beta diversity analysis of bacterial communities showed two well-defined clusters, separating the water and sediment/rhizosphere samples; rhizosphere and sediment were richer while the effluent was less diverse. Overall, the site with the highest evenness was the rhizosphere. Unlike the bacterial communities, Shannon diversity of microeukaryotes was significantly different between A and E. The effluent presented the lowest values for all ecological indexes tested and differed significantly from all sampled sites, except on evenness. When mapped the metabolic pathways, genes corresponding to the degradation of aromatic compounds, including genes related to pesticide degradation, were identified. The most abundant genes were related to the degradation of benzoate. Our results indicate that the effluent is a selective environment for fungi. Interestingly, the overall fungal diversity was higher in the affluent, the water that reached the system before pesticide application, and where the prokaryotic diversity was the lowest. The affluent and effluent seem to have the lowest environmental quality, given the presence of bacteria genera previously recorded in environments with high concentrations of pesticide residues. The microbiota, environmental characteristics, and pesticide residues should be further studied and try to elucidate the potential for pesticide degradation by natural consortia. Thus, extensive comparative studies are needed to clarify the microbial composition, diversity, and functioning of rice cultivation environments, and how pesticide use changes may reflect differences in microbial structure.

High bioremediation potential of strain Chenggangzhangella methanolivorans CHL1 for soil polluted with metsulfuron-methyl or tribenuron-methyl in a pot experiment

Soil contamination caused by long-term application of metsulfuron-methyl and tribenuron-methyl has become an issue of increasing concern. In our previous study, strain Chenggangzhangella methanolivorans CHL1, capable of efficiently degrading sulfonylurea herbicides, was isolated. Here, the bioremediation potential of strain CHL1 was assessed for soil polluted with metsulfuron-methyl or tribenuron-methyl in a pot experiment. The growth parameters of waxy maize were measured on day 21 of the pot experiment. Additionally, the residues of metsulfuron-methyl and tribenuron-methyl in soils were analyzed, and the soil microbial community was investigated using a phospholipid fatty acids (PLFAs) method on days 1, 7, 14, and 21. The results indicated that strain CHL1 greatly accelerated the degradation of metsulfuron-methyl and tribenuron-methyl in soils. The degradation rates in the treatments inoculated with strain CHL1were all more than 91% after 7 days, significantly higher than the 25-36% degradation measured in non-inoculated treatments. Furthermore, strain CHL1 reduced the negative effects of tribenuron-methyl and metsulfuron-methyl on waxy maize growth, especially the primary root length. Moreover, inoculation with strain CHL1 also reduced the effects of tribenuron-methyl and metsulfuron-methyl on soil microbial biomass, diversity, and community structure. The present study demonstrates that strain CHL1 has great potential application to remediate soil contaminated with metsulfuron-methyl or tribenuron-methyl.

Perspectives of using fungi as bioresource for bioremediation of pesticides in the environment: a critical review

Pesticides are used for controlling the development of various pests in agricultural crops worldwide. Despite their agricultural benefits, pesticides are often considered a serious threat to the environment because of their persistent nature and the anomalies they create. Hence removal of such pesticides from the environment is a topic of interest for the researchers nowadays. During the recent years, use of biological resources to degrade or remove pesticides has emerged as a powerful tool for their in situ degradation and remediation. Fungi are among such bioresources that have been widely characterized and applied for biodegradation and bioremediation of pesticides. This review article presents the perspectives of using fungi for biodegradation and bioremediation of pesticides in liquid and soil media. This review clearly indicates that fungal isolates are an effective bioresource to degrade different pesticides including lindane, methamidophos, endosulfan, chlorpyrifos, atrazine, cypermethrin, dieldrin, methyl parathion, heptachlor, etc. However, rate of fungal degradation of pesticides depends on soil moisture content, nutrient availability, pH, temperature, oxygen level, etc. Fungal strains were found to harbor different processes including hydroxylation, demethylation, dechlorination, dioxygenation, esterification, dehydrochlorination, oxidation, etc during the biodegradation of different pesticides having varying functional groups. Moreover, the biodegradation of different pesticides was found to be mediated by involvement of different enzymes including laccase, hydrolase, peroxidase, esterase, dehydrogenase, manganese peroxidase, lignin peroxidase, etc. The recent advances in understanding the fungal biodegradation of pesticides focusing on the processes, pathways, genes/enzymes and factors affecting the biodegradation have also been presented in this review article.

Fungal degradation of an acetolactate synthase (ALS) inhibitor pyrazosulfuron-ethyl in soil

Owing to reported phytotoxicity of some sulfonylurea class of herbicides in number of sensitive crops and higher persistence in soil, present study was conducted to isolate and identify pyrazosulfuron-ethyl degrading fungi from soil of rice field. Penicillium chrysogenum and Aspergillus niger, were isolated and identified from rhizospere soil of rice field, as potent pyrazosulfuron-ethyl degrading fungi. Degradation of pyrazosulfuron-ethyl by P. chrysogenum and A. niger, yielded transformation products/metabolites which were identified and characterized by LC/MS/MS. The rate of dissipation of pyrazosulfuron-ethyl was found higher in soil of rice field and soil inoculated with P. chrysogenum. This showed important route of degradation of pyrazosulfuron-ethyl by microbes apart from chemical degradation.

Biodegradation of pyrazosulfuron-ethyl by three strains of bacteria isolated from contaminated soils

Three bacterial strains capable of transforming pyrazosulfuron-ethyl, designated as D61, D66, and D713, were isolated from pyrazosulfuron-ethyl contaminated soils. According to the sequence analysis of the partial 16S rRNA gene, it is found that the strains D61 and D66 belong to Pseudomonas sp., and the strain D713 belongs to Bacillus sp. The effects of pyrazosulfuron-ethyl concentration, pH and temperature on biodegradation were examined. At a concentration of 10.0mgL(-1), pyrazosulfuron-ethyl was completely degraded by Pseudomonas sp. D61 after 2d and by Pseudomonas sp. D66 after 5d. At a concentration of 90.0mgL(-1), pyrazosulfuron-ethyl can be completely degraded by Pseudomonas sp. D66 and D61 after 12d. More than 85.9% degradation rate was observed with Bacillus sp. D713 after 12d. The growth of these three strains was inhibited at low pH buffers. The abiotic degradation occurs much faster at low pH than at neutral and basic pH conditions. The degradation rate of pyrazosulfuron-ethyl at 28 degrees C was faster than those at 20 degrees C and 37 degrees C by these strains, except the highest degradation rate of Bacillus sp. D713 was obtained at 37 degrees C. The pyrazosulfuron-ethyl biodegradation products were identified by liquid chromatography-mass spectroscopy with positive/negative modes and tandem MS-MS techniques. The main degradation product was detected and identified as 5-(N-(4,6-dimethoxypyrimidin-2-ylcarbamoyl)sulfamoyl)-1-methyl-1H-pyrazole-4-carboxylic acid based on mass spectral data and fragmentation patterns.

Isolation and characterization of Sporobolomyces sp. LF1 capable of degrading chlorimuron-ethyl

A yeast strain which was capable of degrading sulfonylurea herbicide chlorimuron-ethyl named as LF1 was isolated from a chlorimuron-ethyl contaminated soil near the warehouse of the factory producing chlorimuron-ethyl in Shenyang City, Northeast China. The strain was identified as Sporobolomyces sp., based on its morphological and physiological characteristics and the phylogenetic analysis of 18S rRNA gene sequence. So far, this is the only yeast strain of Sporobolomyces sp. which is able to degrade chlorimuron-ethyl. Incubation tests showed that when the initial concentration of chlorimuron-ethyl in culture was 5 mg/L, LFI could degrade more than 77% of the herbicide after incubation for 4 d at 30 degrees C. The possible mechanism of chlorimuron-ethyl degradation by LF1 could be the acidic hydrolysis caused by the acids from the metabolism of the yeast strain. Further study should be conducted to examine the pathways of chlorimuron-ethyl degradation by LF1 and to approach the feasibility of using LF1 to degrade the chlorimuron-ethyl in soil system.