Kinetics of carbendazim degradation in a horizontal tubular biofilm reactor

Dynamic and structural response of a multispecies biofilm to environmental perturbations induced by the continuous increase of benzimidazole fungicides in a permeable reactive biobarrier

Purpose

This work explores the dynamics of spatiotemporal changes in the taxonomic structure of biofilms and the degradation kinetics of three imidazole group compounds: carbendazim (CBZ), methyl thiophanate (MT), and benomyl (BN) by a multispecies microbial community attached to a fixed bed horizontal tubular reactor (HTR). This bioreactor mimics a permeable reactive biobarrier, which helps prevent the contamination of water bodies by pesticides in agricultural wastewater.

Methods

To rapidly quantify the microbial response to crescent loading rates of benzimidazole compounds, a gradient system was used to transiently raise the fungicide volumetric loading rates, measuring the structural and functional dynamics response of a microbial community in terms of the volumetric removal rates of the HTR entering pollutants.

Results

The loading rate gradient of benzimidazole compounds severely impacts the spatiotemporal taxonomic structure of the HTR biofilm-forming microbial community. Notable differences with the original structure in HTR stable conditions can be noted after three historical contingencies (CBZ, MT, and BN gradient loading rates). It was evidenced that the microbial community did not return to the composition prior to environmental disturbances; however, the functional similarity of microbial communities after steady state reestablishment was observed.

Conclusions

The usefulness of the method of gradual delivery of potentially toxic agents for a microbial community immobilized in a tubular biofilm reactor was shown since its functional and structural dynamics were quickly evaluated in response to fungicide composition and concentration changes. The rapid adjustment of the contaminants' removal rates indicates that even with changes in the taxonomic structure of a microbial community, its functional redundancy favors its adjustment to gradual environmental disturbances.

Construction of a portable immunosensor for the sensitive detection of carbendazim in agricultural products using a personal glucose meter

Portable and sensitive detection of carbendazim (CBD) is highly desirable for food safety and environmental protection. Herein, a portable immunosensor for the sensitive detection of CBD is proposed based on alkaline phosphatase (ALP)-labeled and secondary antibody-modified gold nanoparticles (AuNPs). The quantification is based on ALP catalyzing the dephosphorylation of glucose-1-phosphate disodium salt to generate glucose, thus converting the concentration of CBD into glucose, thereby realizing the portable detection of CBD by personal glucose meter. Benefiting from signal amplification strategy that integrates the large specific surface area of AuNPs, the enzymatic reactions of terminal deoxynucleotidyl transferase and ALP, a low detection limit of 0.37 ng/mL for CBD is achieved. When this portable method is used to analyze citrus fruit, canned citrus, and cabbage, good-consistency results are obtained with the UPLC-MS/MS method. The good performance demonstrates the great potential of this portable method for CBD monitoring in resource-poor settings.

The Use of PGPB to Promote Plant Hydroponic Growth

Improvements to the world's food supply chain are needed to ensure sufficient food is produced to meet increasing population demands. Growing food in soilless hydroponic systems constitutes a promising strategy, as this method utilizes significantly less water than conventional agriculture, can be situated in urban areas, and can be stacked vertically to increase yields per acre. However, further research is needed to optimize crop yields in these systems. One method to increase hydroponic plant yields involves adding plant growth-promoting bacteria (PGPB) into these systems. PGPB are organisms that can significantly increase crop yields via a wide range of mechanisms, including stress reduction, increases in nutrient uptake, plant hormone modulation, and biocontrol. The aim of this review is to provide critical information for researchers on the current state of the use of PGPB in hydroponics so that meaningful advances can be made. An overview of the history and types of hydroponic systems is provided, followed by an overview of known PGPB mechanisms. Finally, examples of PGPB research that has been conducted in hydroponic systems are described. Amalgamating the current state of knowledge should ensure that future experiments can be designed to effectively transition results from the lab to the farm/producer, and the consumer.

Biofilm-mediated bioremediation is a powerful tool for the removal of environmental pollutants

Biofilm-mediated bioremediation is an attractive approach for the elimination of environmental pollutants, because of its wide adaptability, biomass, and excellent capacity to absorb, immobilize, or degrade contaminants. Biofilms are assemblages of individual or mixed microbial cells adhering to a living or non-living surface in an aqueous environment. Biofilm-forming microorganisms have excellent survival under exposure to harsh environmental stressors, can compete for nutrients, exhibit greater tolerance to pollutants compared to free-floating planktonic cells, and provide a protective environment for cells. Biofilm communities are thus capable of sorption and metabolization of organic pollutants and heavy metals through a well-controlled expression pattern of genes governed by quorum sensing. The involvement of quorum sensing and chemotaxis in biofilms can enhance the bioremediation kinetics with the help of signaling molecules, the transfer of genetic material, and metabolites. This review provides in-depth knowledge of the process of biofilm formation in microorganisms, their regulatory mechanisms of interaction, and their importance and application as powerful bioremediation agents in the biodegradation of environmental pollutants, including hydrocarbons, pesticides, and heavy metals.

A multicolor enzyme-linked immunoassay method for visual readout of carbendazim

Enzyme-linked immunosorbent assay (ELISA) with high specificity and sensitivity is one of the most popular techniques for detecting carbendazim (CBD), a commonly used benzimidazole fungicide in agriculture. However, the traditional ELISA based on the horseradish peroxidase (HRP)-3,3',5,5'-tetramethylbenzidine (TMB) system for CBD only displays the yellow color of TMB²⁺ from deep to light, making it difficult for the naked eye to judge whether CBD in fruits and vegetables exceeds the maximum residue limit. In this article, we intend to improve the traditional ELISA method to establish a multicolor signal output ELISA to achieve visual semiquantitative detection of CBD. This method is based on the optical properties of gold nanorods (AuNRs). After introducing AuNRs into TMB²⁺ solution, which was produced by the HRP-TMB system of traditional ELISA, AuNRs were quickly etched by TMB²⁺. Consequently, the longitudinal localized surface plasmon resonance peak of AuNRs shows a clear blue shift and a vivid color change. Different concentrations of CBD generate different amounts of TMB²⁺, which in turn leads to different etching degrees of AuNRs, and ultimately results in a rainbow-like color change. As a result, CBD from 0.08 to 100 ng mL^-1 can be easily distinguished by the naked eye, which does not require any large instruments. Moreover, the colors displayed by 0.49 ng mL^-1 (purple) and 0 ng mL^-1 (pink) are significantly different from each other. It should be noted that 0.49 ng mL^-1 is far below the most stringent maximum residue limit of CBD in the world. Additionally, the quantitative determination of CBD spiked in canned citrus, citrus fruits, chives, and cabbage samples showed satisfactory recoveries. The good performance of the AuNR-based ELISA makes it have a wide range of application prospects in food safety and international trade.

Advances in the Microbiology of Stenotrophomonas maltophilia

Stenotrophomonas maltophilia is an opportunistic pathogen of significant concern to susceptible patient populations. This pathogen can cause nosocomial and community-acquired respiratory and bloodstream infections and various other infections in humans. Sources include water, plant rhizospheres, animals, and foods. Studies of the genetic heterogeneity of S. maltophilia strains have identified several new genogroups and suggested adaptation of this pathogen to its habitats. The mechanisms used by S. maltophilia during pathogenesis continue to be uncovered and explored. S. maltophilia virulence factors include use of motility, biofilm formation, iron acquisition mechanisms, outer membrane components, protein secretion systems, extracellular enzymes, and antimicrobial resistance mechanisms. S. maltophilia is intrinsically drug resistant to an array of different antibiotics and uses a broad arsenal to protect itself against antimicrobials. Surveillance studies have recorded increases in drug resistance for S. maltophilia, prompting new strategies to be developed against this opportunist. The interactions of this environmental bacterium with other microorganisms are being elucidated. S. maltophilia and its products have applications in biotechnology, including agriculture, biocontrol, and bioremediation.

Biotreatment and bacterial succession in an upflow immobilized cell bioreactor fed with fludioxonil wastewater

The large quantities and the persistent nature of fungicide wastewaters have increased the efforts towards a sustainable technological solution. In this context, fludioxonil-contaminated wastewater was treated in an upflow immobilized cell bioreactor, resulting in chemical oxygen demand (COD) removal efficiency even higher than 80%, whereas the electrical conductivity (EC) of the effluent was gradually increased. Organic-F was mineralized by 94.0 ± 5.2%, which was in accordance with the high fludioxonil removal efficiency (95.4 ± 4.0%). In addition, effluent total Kjeldahl nitrogen (TKN) concentration reduced significantly during bioprocessing. A strong relationship among COD removal, TKN/total nitrogen removal, and effluent EC increase (p < 0.01) was identified. Despite the adequate aeration provided, effluent nitrite and nitrate concentrations were negligible. Illumina sequencing revealed a reduction in the relative abundances of Betaproteobacteria, Chloroflexi, Planctomycetes, and Firmicutes and an increase in the proportion of Alphaproteobacteria and Actinobacteria. A shift in bacterial communities occurred during fludioxonil treatment, resulting in the significant increase of the relative abundances of Empedobacter, Sphingopyxis, and Rhodopseudomonas (from 0.67 ± 0.13% at the start-up to 34.34 ± 1.60% at the end of biotreatment). In conclusion, the immobilized cell bioreactor permitted the proliferation of specialized activated sludge microbiota with an active role in the depuration of postharvest fungicides.

Degradation kinetics of carbendazim by Klebsiella oxytoca, Flavobacterium johnsoniae, and Stenotrophomonas maltophilia strains

The fungicide carbendazim is an ecotoxic pollutant frequently found in water reservoirs. The ability of microorganisms to remove pollutants found in diverse environments, soil, water, or air is well documented. Although microbial communities have many advantages in bioremediation processes, in many cases, those with the desired capabilities may be slow-growing or have low pollutant degradation rates. In these cases, the manipulation of the microbial community through enrichment with specialized microbial strains showing high specific growth rates and high rates and efficiencies of pollutant degradation is desirable. In this work, bacteria of the genera Klebsiella, Flavobacterium, and Stenotrophomonas, isolated from the biofilm attached to the packed zones of a biofilm reactor, were able to grow individually in selective medium containing carbendazim. In the three bacteria studied, the mheI gene encoding the first enzyme involved in the degradation of the fungicide carbendazim was found. Studying the dynamics of growth and carbendazim degradation of the three bacteria, the effect of co-formulants was also evaluated. The pure compound and a commercial formulation of carbendazim were used as substrates. Finally, the study made it possible to define the biokinetic advantages of these strains for amendment of microbial communities.