Influence of humic acid, iron and copper on microbial degradation of fungicide Carbendazim

Cooperation Between Rhodococcus qinshengii and Rhodococcus erythropolis for Carbendazim Degradation

Carbendazim (CBZ) is a fungicide widely used on different crops, including soybeans, cereals, cotton, tobacco, peanuts, and sugar beet. Excessive use of this xenobiotic causes environmental deterioration and affects human health. Microbial metabolism is one of the most efficient ways of carbendazim elimination. In this work, Rhodococcus qingshengii RC1 and Rhodococcus erythropolis RC9 were isolated from a bacterial community growing in a biofilm reactor acclimated with microbiota from carbendazim-contaminated soil. Sequencing analysis of genomes of both strains revealed the presence of cbmA, the gene coding for the enzyme that hydrolyses carbendazim to produce 2-aminobenzimidazole (2-AB). The alternative gene for the first catabolic step (mheI) was detected by PCR in strain RC9 but not in RC1. Metabolomic analysis by HPLC and LC-MS showed that both strains have the ability to metabolize carbendazim. R. qingshengii RC1 converts carbendazim to 2-AB, the first degradation intermediary, while R. erythropolis RC9 metabolizes the fungicide to its mineralization, probably because R. qingshengii RC1 lacks the hdx gene coding for 2-AB hydroxylase. HRESIMS-MS/MS results indicate that R. erythropolis RC9 metabolizes carbendazim by cleavage of the benzene ring and subsequent formation of 5-formyl-2-hydroxy-4,5-dihydro-1H-imidazole-4-carboxylic acid (X2 C5H6N2O4). The presence of carbendazim metabolites in culture supernatants of strains RC9 and RC1 suggests that both strains contribute to the efficient degradation of carbendazim in nature.

Microbes as carbendazim degraders: opportunity and challenge

Carbendazim (methyl benzimidazol-2-ylcarbamate, CBZ) is a systemic benzimidazole carbamate fungicide and can be used to control a wide range of fungal diseases caused by Ascomycetes, Basidiomycetes and Deuteromycetes. It is widely used in horticulture, forestry, agriculture, preservation and gardening due to its broad spectrum and leads to its accumulation in soil and water environmental systems, which may eventually pose a potential threat to non-target organisms through the ecological chain. Therefore, the removal of carbendazim residues from the environment is an urgent problem. Currently, a number of physical and chemical treatments are effective in degrading carbendazim. As a green and efficient strategy, microbial technology has the potential to degrade carbendazim into non-toxic and environmentally acceptable metabolites, which in turn can dissipate carbendazim from the contaminated environment. To date, a number of carbendazim-degrading microbes have been isolated and reported, including, but not limited to, Bacillus, Pseudomonas, Rhodococcus, Sphingomonas, and Aeromonas. Notably, the common degradation property shared by all strains was their ability to hydrolyze carbendazim to 2-aminobenzimidazole (2-AB). The complete mineralization of the degradation products is mainly dependent on the cleavage of the imidazole and benzene rings. Additionally, the currently reported genes for carbendazim degradation are MheI and CbmA, which are responsible for breaking the ester and amide bonds, respectively. This paper reviews the toxicity, microbial degradation of carbendazim, and bioremediation techniques for carbendazim-contaminated environments. This not only summarizes and enriches the theoretical basis of microbial degradation of carbendazim, but also provides practical guidance for bioremediation of carbendazim-contaminated residues in the environment.

Carbendazim: Ecological risks, toxicities, degradation pathways and potential risks to human health

Carbendazim is a highly effective benzimidazole fungicide and is widely used throughout the world. The effects of carbendazim contamination on the biology and environment should be paid more attention. We reviewed the published papers to evaluate the biological and environmental risks of carbendazim residues. The carbendazim has been frequently detected in the soil, water, air, and food samples and disrupted the soil and water ecosystem balances and functions. The carbendazim could induce embryonic, reproductive, developmental and hematological toxicities to different model animals. The carbendazim contamination can be remediated by photodegradation and chemical and microbial degradation. The carbendazim could enter into human body through food, drinking water and skin contact. Most of the existing studies were completed in the laboratory, and further studies should be conducted to reveal the effects of successive carbendazim applications in the field.

Rapid method for detection, quantification and measuring microbial degradation of pesticide-thiram using high performance thin layer chromatography (HPTLC)

Thiram (tetramethylthiuramdisulfide) or thiram sulphide is a dithiocarbamate group of non-systemic group of fungicide which are applied for seed treatment, control of the crop pests, to repel animals, etc. Moreover, thiram has also been responsible to cause moderate skin sensitivity and eye irritation. Higher exposure to thiram might also lead to developmental damages to newborn and neurotoxic effects to non-target organisms. Advancing to prevent such toxic effects and prevention of soil fertility from thiram and thiram-like chemicals is indispensable. The analytical High-Performance Thin-Layer Chromatography (HPTLC) is a simple, quick and a reliable method was proposed and validated for the detection and quantification of various small molecules for many years. This manuscript represents the solution to use microbes to degrade the thiram present in the soil and for that, HPTLC based method to study thiram degradation by Pseudomonas has been designed. Herein, a HPTLC protocol formalised to reveal the detection and quantification of thiram within the range of 100 to 700 ng/spot on TLC plate. The same concentration was then used for calculating percent microbial degradation of thiram from the culture broth. To perform the microbial degradation of thiram, Pseudomonas otitidis strain TD-8 and Pseudomonas stutzeri strain TD-18 were taken as thiram degrader microbial strain. The efficacy of TD-8 to degrade thiram was identified to be 81 and 99% when grown in presence of thiram for 4 days and 8 days, respectively, while TD-18 strain's efficacy to degrade thiram was found to be 57% and 99% when grown in presence of thiram for 4 days and 8 days, respectively.

Biodegradation of phorate by bacterial strains in the presence of humic acid and metal ions

Phorate is a systemic insecticide used to eradicate mites, insects, and nematodes. Extensive use of this organophosphate has engendered severe environmental concerns. The current research aimed to explore the kinetic pathways of phorate biodegradation in aqueous solutions. Two novel bacterial strains Pseudomonas aeruginosa strain PR1 (KP268772.1) and Pseudomonas sp. PR_02 (KP268773.1) were isolated, screened, and developed given their potential to degrade phorate. Mineralization of phorate was assayed with and without the addition of metal ions [Fe (II) and Cu (II)] and humic acid (HA). In 14 days, experiment both strains have consumed about 69%-94.5% (half-life from 3.58 to 6.02 days) of phorate. The observed biodegradation rate of phorate with Cu (II) in the system was 73% and 87%, with a half-life of 4.86 and 4.07 days for PR1 and PR2, respectively. The biodegradation of phorate using Fe(II) was 69% and 82%, with half-life periods 5.68 and 4.49 days. Meanwhile, incorporating HA, the phorate biodegradation was inhibited significantly, showing 71% and 85% degradation, with half-life periods of 6.02 and 5.02 days. The results indicated that both bacterial strains were able to mineralize phorate with PR2 > PR1. Summarizing, the inhibition in phorate biodegradation order under different conditions was as HA > Fe (II) > Cu (II). UV-visible measurements and gas chromatography-mass spectrometric assays indicated that the possible degradation pathway of phorate included ethoxy-phosphonothio-methanethiol S-mercaptomethyl-O,O-dihydrogen phosphorodithioate, diethyl-methylphosphonate, methane dithiol, ethanethiol, and phosphate, as the main metabolites identified. Therefore, it was concluded that the newly isolated Pseudomonas strains could be a potential candidates for biodegradation of phorate in a cost-effective, safe, and environmentally friendly alternative.

Characterization of a novel carbendazim-degrading strain Rhodococcus sp. CX-1 revealed by genome and transcriptome analyses

The persistence and ecotoxicity of carbendazim residues pose a potential risk to environmental ecology and human health. Here, a novel and highly efficient carbendazim-degrading bacterium Rhodococcus sp. CX-1, capable of utilizing carbendazim as its sole source of carbon and energy, was isolated from contaminated soil. The biodegradation characteristics and metabolic pathways were studied by mass spectrometry, genomic annotation, and transcriptome analysis. The degradation rate of carbendazim by strain CX-1 was 3.98-9.90 mg/L/h under different conditions, and the optimum degradation conditions were 40 °C and pH 7.0. The addition of carbon sources (glucose, fructose, and sucrose, 100 mg/L) could accelerate carbendazim degradation. HPLC-MS/MS identification suggested that carbendazim is first hydrolyzed into 2-aminobenzimidazole and then to 2-hydroxybenzimidazole, and is ultimately mineralized to carbon dioxide. The genome of strain CX-1 contained 6,511,628 bp nucleotides, 2 linear plasmids, 2 circular plasmids, and 6437 protein coding genes. Genome annotation and transcriptome analysis indicated that carbendazim degradation may be regulated by the degradation genes harbored in the chromosome and in plasmid 2, and two different degradation pathways of carbendazim by imidazole ring cleavage or benzene ring cleavage were predicted. This study provided new insight to reveal the biodegradation mechanism of carbendazim; furthermore, strain CX-1 is a promising bioresource for carbendazim bioremediation.

COVID-19: Environment concern and impact of Indian medicinal system

The COVID-19 outbreak has came in existence in late December 2019 at Wuhan, China. It is declared as an epidemic by WHO. The rationale of this study is to provide the details regarding prevention, environment concern, social economic consequences, and medicines for COVID-19. Social distancing, screening, lockdown, use of mask and application of sanitizer or soap at regular time interval is the best prevention against COVID-19. The "oral-feces" transmission of COVID-19 is threat to environment. Improper disposal of medical/biomedical and human waste may harm the total environment. Nitrifying-enriched activated sludge i.e. NAS approach can play important role to clean the environment compartments like sludge and waste. COVID-19 has shown impact on social and economic life, but there is no alternate until the drug discovery. In medicine or treatment of COVID-19 point of views, an integrated approach between modern and traditional medicine system may ensure an early prevention of further viral spread. Based on the symptoms of COVID-19, list of herbs and drugs of Indian Medicine System has been searched and reported. To develop the potential drug against COVID-19, the detailed experimentation and clinical trials to be performed for future prospective.

Study of the interaction Cu(II) - Carbendazim in natural waters by electrochemical techniques

In order to obtain higher agricultural yields, the use of chemical substances has been increased to prevent the proliferation of pests, as well as ensuring durability in the storage of the food produced. Such substances are known as pesticides that may well present risks to human health and the environment. In the presence of metal ions, these substances can interact forming new species with different characteristics. Carbendazim (MBC) is an example of a harmful pesticide, which has atoms of nitrogen and oxygen in its structure that can form complexes with metal ions. Thus, in this work has studied the interaction between the copper (II) metal ion and carbendazim and its formation in natural water. The Cu-MBC complex showed a reduction peak of 0.007 V and an oxidation peak of 0.500 V, with characteristics of a quasi-reversible process under a glassy carbon electrode. By anodic stripping voltammetry, a different behavior was observed in the interaction of copper and carbendazim in ultrapure water and Billings dam water; however, it was possible to observe the complex in both samples. Carbendazim in the presence of the metal shows lower oxidation potential value, indicating the influence of the metal on the electrochemical response of the pesticide.

Accelerated Biodegradation of the Agrochemical Ametoctradin by Soil-Derived Microbial Consortia

Pesticide-resistant plant pathogens are an increasing threat to the global food supply and have generated a need for novel, efficacious agrochemicals. The current regulatory process for approving new agrochemicals is a tedious but necessary process. One way to accelerate the safety evaluation process is to utilize in vitro systems to demonstrate pesticide degradation by soil microbes prior to ex vivo soil evaluations. This approach may have the capability to generate metabolic profiles free of inhibitory substances, such as humic acids, commonly present in ex vivo soil systems. In this study, we used a packed-bed microbial bioreactor to assess the role of the natural soil microbial community during biodegradation of the triazolopyrimidine fungicide, ametoctradin. Metabolite profiles produced during in vitro ametoctradin degradation were similar to the metabolite profiles obtained during environmental fate studies and demonstrated the degradation of 81% of the parent compound in 72 h compared to a half-life of 2 weeks when ametoctradin was left in the soil. The microbial communities of four different soil locations and the bioreactor microbiome were compared using high throughput sequencing. It was found that biodegradation of ametoctradin in both ex vivo soils and in vitro in the bioreactor correlated with an increase in the relative abundance of Burkholderiales, well characterized microbial degraders of xenobiotic compounds.

Biodegradation of carbendazim by a potent novel Chryseobacterium sp. JAS14 and plant growth promoting Aeromonas caviae JAS15 with subsequent toxicity analysis

In the present study, carbendazim (MBC) degrading bacterial strains were isolated and identified as Chryseobacterium sp. JAS14 and Aeromonas caviae JAS15. Both the strains completely degraded 200 mg l^-1 of MBC in the aqueous medium and soil within 4-9 days of incubation. In an aqueous medium, the degradation process was characterized by a rate constant of 53.16 day^-1 and 42.60 day^-1, following zero order model and DT₅₀ was 1.8 days and 2.34 days for Chryseobacterium sp. JAS14 and A. caviae JAS15, respectively. A Chryseobacterium sp. JAS14 and A. caviae JAS15 inoculated into the soil without the addition of nutrients showed the degradation rate constant of 27.30 day^-1 and 23.87 day^-1, and DT₅₀ was 3.66 days and 4.18 days, respectively. The metabolites during MBC biodegradation by Chryseobacterium sp. JAS14 and A. caviae JAS15 were identified as 2-aminobenzimidazole, 2-hydroxybenzimidazole, 1, 2 diaminobenzene and catechol. To our knowledge, this is the first study of the detailed biodegradation pathway of MBC by Chryseobacterium sp. JAS14 was proposed. Phytotoxicity and cytogenotoxicity assays showed that the toxicity of the MBC reduced after biodegradation by Chryseobacterium sp. JAS14 and A. caviae JAS15. In addition, A. caviae JAS15 possess important plant growth promoting traits under normal and MBC stress condition. These results suggest the Chryseobacterium sp. JAS14 and A. caviae JAS15 could be used as a bioresource for the reclamation of MBC contaminated soil.

An analysis of the versatility and effectiveness of composts for sequestering heavy metal ions, dyes and xenobiotics from soils and aqueous milieus

The persistence and bioaccumulation of environmental pollutants in water bodies, soils and living tissues remain alarmingly related to environmental protection and ecosystem restoration. Adsorption-based techniques appear highly competent in sequestering several environmental pollutants. In this review, the recent research findings reported on the assessments of composts and compost-amended soils as adsorbents of heavy metal ions, dye molecules and xenobiotics have been appraised. This review demonstrates clearly the high adsorption capacities of composts for umpteen environmental pollutants at the lab-scale. The main inferences from this review are that utilization of composts for the removal of heavy metal ions, dye molecules and xenobiotics from aqueous environments and soils is particularly worthwhile and efficient at the laboratory scale, and the adsorption behaviors and effectiveness of compost-type adsorbents for agrochemicals (e.g. herbicides and insecticides) vary considerably because of variabilities in structure, topology, bond connectivity, distribution of functional groups and interactions of xenobiotics with the active humic substances in composts. Compost-based field-scale remediation of environmental pollutants is still sparse and arguably much challenging to implement if, furthermore, real-world soil and water contamination issues are to be addressed effectively. Hence, significant research and process development efforts should be promptly geared and intensified in this direction by extrapolating the lab-scale findings in a cost-effective manner.

Kinetic Study of the Biodegradation of Acephate by Indigenous Soil Bacterial Isolates in the Presence of Humic Acid and Metal Ions

Many bacteria have the potential to use specific pesticides as a source of carbon, phosphorous, nitrogen and sulphur. Acephate degradation by microbes is considered to be a safe and effective method. The overall aim of the present study was to identify acephate biodegrading microorganisms and to investigate the degradation rates of acephate under the stress of humic acid and most common metal ions Fe(III) and copper Cu(II). Pseudomonas azotoformanss strain ACP1, Pseudomonas aeruginosa strain ACP2, and Pseudomonas putida ACP3 were isolated from acephate contaminated soils. Acephate of concentration 100 ppm was incubated with separate strain inoculums and periodic samples were drawn for UV-visible, FTIR (Fourier-transform infrared spectroscopy) and MS (Mass Spectrometry) analysis. Methamidophos, S-methyl O-hydrogen phosphorothioamidate, phosphenothioic S-acid, and phosphenamide were the major metabolites formed during the degradation of acephate. The rate of degradation was applied using pseudo-first-order kinetics to calculate the half-life (t1/2) values, which were 14.33-16.72 d-1 (strain(s) + acephate), 18.81-21.50 d-1 (strain(s) + acephate + Cu(II)), 20.06 -23.15 d-1 (strain(s) + acephate + Fe(II)), and 15.05-17.70 d-1 (strains + acephate + HA). The biodegradation efficiency of the three bacterial strains can be ordered as P. aeruginosa > P. putida > P. azotoformans. The present study illustrated the decomposition mechanism of acephate under different conditions, and the same may be applied to the removal of other xenobiotic compounds.