Molecular docking studies and in vitro degradation of four aflatoxins (AFB1 , AFB2 , AFG1 , and AFG2 ) by a recombinant laccase from Saccharomyces cerevisiae

Biodegradation Characteristics and Mechanism of Aflatoxin B1 by Bacillus amyloliquefaciens from Enzymatic and Multiomics Perspectives

Aflatoxin B1 (AFB1), a mycotoxin and natural carcinogen, commonly contaminates cereals and animal feeds, posing serious health risks to human and animal. In this study, Bacillus amyloliquefaciens ZG08 isolated from kimchi could effectively remove 80.93% of AFB1 within 72 h at 37 °C and pH 7.0. Metabolome and transcriptome analysis showed that metabolic processes including glycerophospholipid metabolism and amino acid metabolism were most affected in B. amyloliquefaciens ZG08 exposed to AFB1. The adaptation mechanism likely involved activation of the thioredoxin system to restore intracellular redox equilibrium. The key genes, tpx and gldA, overexpressed in Escherichia coli BL21, achieved degradation rates of 60.15% and 47.16% for 100 μg/kg AFB1 under optimal conditions of 37 °C and pH 8.0 and 45 °C and pH 7.0, respectively. The degradation products, identified as AFD1, were less cytotoxic than AFB1 in HepG2 cells. These findings suggest potential strategies for utilizing probiotics and engineered enzymes in AFB1 detoxification.

One stone two birds: Recycling of an agri-waste to synthesize laccase-immobilized hierarchically porous magnetic biochar for efficient degradation of aflatoxin B1 in aqueous solutions and corn oil

Aflatoxin B1 (AFB1) contamination of oils is a serious concern for the safety of edible oil consumers. Enzyme-assisted detoxification of AFB1 is an efficient and safe method for decontaminating oils, but pristine enzymes are unstable in oils and require modifications before use. Therefore, we designed a novel and magnetically separable laccase-carrying biocatalyst containing spent-mushroom-substrate (SMS)-derived biochar (BF). Laccase was immobilized on NH2-activated magnetic biochar (BF-NH2) through covalent crosslinking, which provided physicochemical stability to the immobilized enzyme. After 30 days of storage at 4 °C, the immobilized laccase (product named "BF-NH2-Lac") retained ~95 % of its initial activity, while after five repeated cycles of ABTS oxidation, ~85 % activity retention was observed. BF-NH2-Lac was investigated for the oxidative degradation of AFB1, which exhibited superior performance compared to free laccase. Among many tested natural compounds as mediators, p-coumaric acid proved the most efficient in activating laccase for AFB1 degradation. BF-NH2-Lac demonstrated >90 % removal of AFB1 within 5.0 h, while the observed degradation efficiency in corn oil and buffer was comparable. An insight into the adsorptive and degradative removal of AFB1 revealed that AFB1 removal was governed mainly by degradation. The coexistence of multi-mycotoxins did not significantly affect the AFB1 degradation capability of BF-NH2-Lac. Investigation of the degradation products revealed the transformation of AFB1 into non-toxic AFQ1, while corn oil quality remained unaffected after BF-NH2-Lac treatment. Hence, this study holds practical importance for the research, knowledge-base and industrial application of newly proposed immobilized enzyme products.

Phytochemicals analysis and aflatoxin B1 detoxification potential of leaves extract of Moringa oleifera and Calotropis procera

The present study aimed to identify the presence of certain classes of phytochemicals in the leaf extract of medicinal herbs viz. Moringa oleifera and Calotropis procera, using qualitative detection tests and explored the potential of aqueous and ethanolic extract to inhibit aflatoxin production by thin layer chromatography at 25 °C and pH (7) of different incubation times i.e. 0-, 1-, 3-, 6- and 24-h. Qualitative phytochemical analysis reported that the aqueous leave extracts of M. oleifera and C. procera contained tannins, phlobatannins, quinones, steroids, sugar, betacyanins, fatty acids, phenols, and volatile oils. Aflatoxin analysis reported that the ethanolic extract of M. oleifera was found more effective than detoxifying 100% of AFB1 after 24 h of incubation. In the case of C. procera, the aqueous extract reduced 96.5% of AFB1 and ethanolic extract reduced 96% of AFB1 after 24-h of incubation. The results revealed that natural plant products have a high potential to reduce AFB1 and could contribute to mitigation plans for AFB1. There is a need for further characterisation using techniques such as GC-MS, LC-MS, or NMR which would provide valuable information on the chemical composition of the extracts.

Food-Grade Expression of Two Laccases in Pichia pastoris and Study on Their Enzymatic Degradation Characteristics for Mycotoxins

Mycotoxin contamination poses substantial health risks to humans and animals. In this study, the two laccases PpLac1 and AoLac2 from Pleurotus pulmonarius and Aspergillus oryzae were selected and heterologously expressed in Pichia pastoris in a food-grade manner to detoxify aflatoxin B1 (AFB1), zearalenone (ZEN), and deoxynivalenol (DON). Both laccases exhibited degradation activity toward these three mycotoxins, while the efficiency of these for DON was relatively low. Therefore, molecular docking between these laccases and DON was conducted to analyze their potential interaction mechanisms. Furthermore, the degradation conditions of AFB1 and ZEN by the two laccases were optimized, and the optimal degradation rates for AFB1 and ZEN by PpLac1 reached 78.51 and 78.90%, while those for AFB1 and ZEN by AoLac2 reached 72.27 and 80.60%, respectively. The laccases PpLac1 and AoLac2 successfully transformed AFB1 and ZEN into the compounds AFQ1 and 15-OH-ZEN, which were 90 and 98% less toxic than the original compounds, respectively. Moreover, the culture supernatants demonstrated effective mycotoxin degradation results for AFB1 and ZEN in contaminated feed samples. The residual levels of AFB1 and ZEN in all samples ranged from 6.61 to 8.72 μg/kg and 3.44 to 98.15 μg/kg, respectively, and these levels were below the limit set by the European Union standards. All of the results in this study indicated that the two laccases have excellent application potential in the feed industry.

Microbial Composition of Water Kefir Grains and Their Application for the Detoxification of Aflatoxin B1

Water kefir grains (WKGs), the starter used to develop a traditional beverage named water kefir, consist of a symbiotic mixture of probiotics with diverse bioactivities, but little is known about their abilities to remove mycotoxins that have serious adverse effects on humans and animals. This study investigated the ability of WKGs to remove aflatoxin B1 (AFB1), one of the most toxic mycotoxins, under different settings, and determined the mechanism of absorption mediated by WKGs and the effect of WKGs on the toxicity induced by AFB1 and the reduction in AFB1 in cow milk and tea soups. The results showed the WKGs used herein were dominated by Lactobacillus, Acetobacter, Phenylobacterium, Sediminibacterium, Saccharomyces, Issatchenkia, and Kodamaea. HPLC analysis demonstrated that the WKGs effectively removed AFB1 at concentrations ranging from 1 to 5 µg/mL, pH values ranging from 3 to 9, and temperatures ranging from 4 to 45 °C. Additionally, the removal of AFB1 mainly depended on absorption, which was consistent with the Freundlich and pseudo-second-order kinetic models. Moreover, only 49.63% of AFB1 was released from the AFB1-WKG complex after four washes when the release of AFB1 was non-detectable. Furthermore, WKG treatment caused a dramatic reduction in the mutagenicity induced by AFB1 according to an Ames test and reduced more than 54% of AFB1 in cow milk and three tea soups. These results suggested that WKGs can act as a potential bio-absorbent with a high binding ability to detoxify AFB1 in food and feed via a chemical action step and multi-binding sites of AFB1 absorption in a wide range of scenarios.

New insights into searching patulin degrading enzymes in Saccharomyces cerevisiae through proteomic and molecular docking analysis

Global warming has increased the contamination of mycotoxins. Patulin (PAT) is a harmful contaminant that poses a serious threat to food safety and human health. Saccharomyces cerevisiae biodegrades PAT by its enzymes during fermentation, which is a safe and efficient method of detoxification. However, the key degradation enzymes remain unclear. In this study, the proteomic differences of Saccharomyces cerevisiae under PAT stress were investigated. The results showed that the proteins involved in redox reactions and defense mechanisms were significantly up-regulated to resist PAT stress. Subsequently, molecular docking was used to virtual screen for degrading enzymes. Among 18 proteins, YKL069W showed the highest binding affinity to PAT and was then expressed in Escherichia coli, where the purified YKL069W completely degraded 10 μg/mL PAT at 48 h. YKL069W was demonstrated to be able to degrade PAT into E-ascladiol. Molecular dynamics simulations confirmed that YKL069W was stable in catalyzing PAT degradation with a binding free energy of - 7.5 kcal/mol. Furthermore, it was hypothesized that CYS125 and CYS101 were the key amino acid residues for degradation. This study offers new insights for the rapid screening and development of PAT degrading enzymes and provides a theoretical basis for the detoxification of mycotoxins.

Optimizing the degradation of aflatoxin B1 in corn by Trametes versicolor and improving the nutritional composition of corn

BACKGROUND

Corn, being an important grain, is prone to contamination by aflatoxin B1 (AFB1 ), and AFB1 -contaminated corn severely endangers the health of humans and livestock. Trametes versicolor, a fungus that can grow in corn, possesses the ability to directly degrade AFB1 through its laccase. This study aimed to optimize the fermentation conditions for T. versicolor to degrade AFB1 in corn and investigate the effect of T. versicolor fermentation on the nutritional composition of corn. AFB1 -contaminated corn was used as the culture substrate for T. versicolor. A combination of single-factor experiments and response surface methodology was employed to identify the optimal conditions of AFB1 degradation.

RESULTS

The optimal conditions of AFB1 degradation were as follows: 9 days of fermentation, a fermentation temperature of 26.7 °C, a moisture content of 70.5% and an inoculation amount of 4.9 mL (containing 51.99 mg of T. versicolor mycelia). With the optimal conditions, the degradation rate of AFB1 in corn could reach 93.01%, and the dry basis content of protein and dietary fiber in the fermented corn was significantly increased. More importantly, the lysine content in the fermented corn was also significantly increased.

CONCLUSION

This is the first report that direct fermentation of AFB1 -contaminated corn by T. versicolor not only efficiently degrades AFB1 but also improves the nutritional composition of corn. These findings suggest that the fermentation of corn by T. versicolor is a promising, environmentally friendly and efficient approach to degrade AFB1 and improve the nutritional value of corn. © 2023 Society of Chemical Industry.

Aflatoxin Decontamination in Maize Steep Liquor Obtained from Bioethanol Production Using Laccases from Species within the Basidiomycota Phylum

Maize (Zea mays L.) is an important crop in Argentina. Aspergillus section Flavi can infect this crop at the pre-harvest stage, and the harvested grains can be contaminated with aflatoxins (AFs). During the production of bioethanol from maize, AF levels can increase up to three times in the final co-products, known as, dry and wet distiller's grain with solubles (DDGS and WDGS), intended for animal feed. Fungal enzymes like laccases can be a useful tool for reducing AF contamination in the co-products obtained from this process. The aim of the present study was to evaluate the ability of laccase enzymes included in enzymatic extracts (EE) produced by different species in the Basidiomycota phylum to reduce AF (AFB1 and AFB2) accumulation under the conditions of in vitro assays. Four laccase activities (5, 10, 15, and 20 U/mL) exerted by nine isolates were evaluated in the absence and presence of vanillic acid (VA), serving as a laccase redox mediator for the degradation of total AFs. The enzymatic stability in maize steep liquor (MSL) was confirmed after a 60 h incubation period. The most effective EE in terms of reducing AF content in the buffer was selected for an additional assay carried out under the same conditions using maize steep liquor obtained after the saccharification stage during the bioethanol production process. The highest degradation percentages were observed at 20 U/mL of laccase enzymatic activity and 1 mM of VA, corresponding to 26% for AFB1 and 26.6% for AFB2. The present study provides valuable data for the development of an efficient tool based on fungal laccases for preventing AF accumulation in the co-products of bioethanol produced from maize used for animal feed.

Mechanisms by which microbial enzymes degrade four mycotoxins and application in animal production: A review

Mycotoxins are toxic compounds that pose a serious threat to animal health and food safety. Therefore, there is an urgent need for safe and efficient methods of detoxifying mycotoxins. As biotechnology has continued to develop, methods involving biological enzymes have shown great promise. Biological enzymatic methods, which can fundamentally destroy the structures of mycotoxins and produce degradation products whose toxicity is greatly reduced, are generally more specific, efficient, and environmentally friendly. Mycotoxin-degrading enzymes can thus facilitate the safe and effective detoxification of mycotoxins which gives them a huge advantage over other methods. This article summarizes the newly discovered degrading enzymes that can degrade four common mycotoxins (aflatoxins, zearalenone, deoxynivalenol, and ochratoxin A) in the past five years, and reveals the degradation mechanism of degrading enzymes on four mycotoxins, as well as their positive effects on animal production. This review will provide a theoretical basis for the safe treatment of mycotoxins by using biological enzyme technology.

Recombinant Oxidase from Armillaria tabescens as a Potential Tool for Aflatoxin B1 Degradation in Contaminated Cereal Grain

Forage grain contamination with aflatoxin B1 (AFB1) is a global problem, so its detoxification with the aim of providing feed safety and cost-efficiency is still a relevant issue. AFB1 degradation by microbial enzymes is considered to be a promising detoxification approach. In this study, we modified an previously developed Pichia pastoris GS115 expression system using a chimeric signal peptide to obtain a new recombinant producer of extracellular AFB1 oxidase (AFO) from Armillaria tabescens (the yield of 0.3 g/L), purified AFO, and selected optimal conditions for AFO-induced AFB1 removal from model solutions. After a 72 h exposure of the AFB1 solution to AFO at pH 6.0 and 30 °C, 80% of the AFB1 was degraded. Treatments with AFO also significantly reduced the AFB1 content in wheat and corn grain inoculated with Aspergillus flavus. In grain samples contaminated with several dozen micrograms of AFB1 per kg, a 48 h exposure to AFO resulted in at least double the reduction in grain contamination compared to the control, while the same treatment of more significantly (~mg/kg) AFB1-polluted samples reduced their contamination by ~40%. These findings prove the potential of the tested AFO for cereal grain decontamination and suggest that additional studies to stabilize AFO and improve its AFB1-degrading efficacy are required.

Edible fungi efficiently degrade aflatoxin B1 in cereals and improve their nutritional composition by solid-state fermentation

Aflatoxin B₁ (AFB₁) is extremely harmful to human and livestock. Laccase, a green catalyst, has been shown to effectively degrade AFB₁ and can be obtained from edible fungi. The objective of this study was to screen edible fungi with high laccase activity and determine their effects on the degradation of AFB₁ in cereals and the nutritional composition of the cereals through solid-state fermentation. Results from plate assays confirmed that 51 of the 55 tested edible fungi could secrete laccase. Submerged fermentation results showed that 17 of the 51 edible fungi had maximum laccase activity exceeding 100 U/L. The growth of different edible fungi varied significantly in corn, rice and wheat. More importantly, 6 edible fungi with high laccase activity and good growth could efficiently degrade AFB₁ in cereals. We found for the first time that Ganoderma sinense could not only secrete highly active laccase and efficiently degrade AFB₁ in corn by 92.91%, but also improve the nutritional quality of corn. These findings reveal that solid-state fermentation of cereals with edible fungi is an environmentally friendly and efficient approach for degrading AFB₁ in cereals and improving the nutritional composition of cereals.

Three recombinant peroxidases as a degradation agent of aflatoxin M1 applied in milk and beer

The aim of this work was to estimate the effects of three recombinant peroxidases (rPODs) on the degradation of aflatoxin M₁ (AFM₁) in a model solution and were applied in milk and beer to study the AFM₁ degradation. Besides, the contents of AFM₁ in model solution, milk and beer were evaluated, and the kinetic parameters of rPODs were determined (Michaelis-Menten constant - K_m and maximal velocity - V_max). The optimized reaction conditions (The degradation was over 60 %) for these three rPODs in the model solution were, respectively as follows: pH were 9, 9, and 10; hydrogen peroxide concentrations were 60, 50, and 60 mmol/L; at an ionic strength of 75 mmol/L and reaction temperature of 30 °C with 1 mmol/L K⁺ or 1 mmol/L Na⁺. These three rPODs (1 U /mL) presented the maximum activity for degradation of AFM₁ of 22.4 %, 25.6 %, and 24.3 % in milk, while 14.5 %, 16.9 %, and 18.2 % in beer, respectively. Meanwhile, the survival rate of Hep-G2 cells raised about 1.4 times after treated with peroxidase-generated AFM₁ degradation products. Therefore, POD may be a promising alternative to reduce the pollution of AFM₁ in model solution, milk, beer, and minimize their impact on the environment in humans.

In-Vitro and In-Silico Investigation for the Spent-Coffee Bioactive Phenolics as a Promising Aflatoxins Production Inhibitor

Aflatoxin, is a naturally occurring polyketide generated by Aspergillus flavus via biosynthetic pathways, including polyketide synthase (PKS) and non-ribosomal enzymes. The in vitro analysis supported by molecular dynamics (MD) techniques was used to examine the antifungal and anti-aflatoxigenic activity of spent coffee grounds (SCGs) methanol extract. The High-Performance Liquid Chromatography results revealed the presence of 15 phenolic acids and five flavonoids. (R)-(+)-Rosmarinic acid (176.43 ± 2.41 µg/g) was the predominant of the detected acids, followed by gallic acid (34.83 ± 1.05 µg/g). At the same time, apigenin-7-glucoside is the dominant flavonoid in the SCGs extract by 1717.05 ± 5.76 µg/g, and naringin (97.27 ± 1.97 µg/g) comes next. The antifungal and anti-aflatoxigenic activity of the SCGs extracts was 380 µL/mL and 460 µL/mL, respectively. The SGGs’ effect of inhibiting five Aspergillus strains’ growth on the agar media ranged between 12.81 ± 1.71 to 15.64 ± 1.08 mm by two diffusion assays. Molecular docking results confirmed the inhibitory action of different phenolics and flavonoids on the PKS and NPS key enzymes of the aflatoxin biosynthetic mechanism. The SCGs extract components with the highest free binding energy, naringin (−9.1 kcal/mL) and apigenin 7-glucoside (−9.1 kcal/mol), were subjected to an MD simulation study. The computational results infer the stabilizing effects on the enzymes upon ligand binding led to the impairment in its functionality. The current study represents a novel attempt to assess the anti aflatoxins mechanism of phenolics and flavonoids targeting PKS and NPS via computational approaches compared to in-vitro assays.

Computational Studies of Aflatoxin B1 (AFB1): A Review

Aflatoxin B₁ (AFB₁) exhibits the most potent mutagenic and carcinogenic activity among aflatoxins. For this reason, AFB₁ is recognized as a human group 1 carcinogen by the International Agency of Research on Cancer. Consequently, it is essential to determine its properties and behavior in different chemical systems. The chemical properties of AFB₁ can be explored using computational chemistry, which has been employed complementarily to experimental investigations. The present review includes in silico studies (semiempirical, Hartree-Fock, DFT, molecular docking, and molecular dynamics) conducted from the first computational study in 1974 to the present (2022). This work was performed, considering the following groups: (a) molecular properties of AFB₁ (structural, energy, solvent effects, ground and the excited state, atomic charges, among others); (b) theoretical investigations of AFB₁ (degradation, quantification, reactivity, among others); (c) molecular interactions with inorganic compounds (Ag⁺, Zn²⁺, and Mg²⁺); (d) molecular interactions with environmentally compounds (clays); and (e) molecular interactions with biological compounds (DNA, enzymes, cyclodextrins, glucans, among others). Accordingly, in this work, we provide to the stakeholder the knowledge of toxicity of types of AFB₁-derivatives, the structure-activity relationships manifested by the bonds between AFB₁ and DNA or proteins, and the types of strategies that have been employed to quantify, detect, and eliminate the AFB₁ molecule.

Experimental-theoretical study of laccase as a detoxifier of aflatoxins

We investigate laccase-mediated detoxification of aflatoxins, fungal carcinogenic food contaminants. Our experimental comparison between two aflatoxins with similar structures (AFB₁ and AFG₂) shows significant differences in laccase-mediated detoxification. A multi-scale modeling approach (Docking, Molecular Dynamics, and Density Functional Theory) identifies the highly substrate-specific changes required to improve laccase detoxifying performance. We employ a large-scale density functional theory-based approach, involving more than 7000 atoms, to identify the amino acid residues that determine the affinity of laccase for aflatoxins. From this study we conclude: (1) AFB₁ is more challenging to degrade, to the point of complete degradation stalling; (2) AFG₂ is easier to degrade by laccase due to its lack of side products and favorable binding dynamics; and (3) ample opportunities to optimize laccase for aflatoxin degradation exist, especially via mutations leading to π-π stacking. This study identifies a way to optimize laccase for aflatoxin bioremediation and, more generally, contributes to the research efforts aimed at rational enzyme optimization.

Microbial Enzymes Involved in the Biotransformation of Major Mycotoxins

Mycotoxins, the most researched biological toxins, can contaminate food and feed, resulting in severe health implications for humans and animals. Physical, chemical, and biological techniques are used to mitigate mycotoxin contamination. The biotransformation method using whole microbial cells or isolated enzymes is the best choice to mitigate mycotoxins. Using specific enzymes may avoid the disadvantages of utilizing a full microbe, such as accidental harm to the product's organoleptic characteristics and hazardous safety features. Moreover, the degradation rates of the isolated enzymes are higher than those of the whole-cell reactions, and they are substrate-specific. Their specificity is comprehensive and is shown at the positional and/or chiral center in many circumstances. Currently, only a few enzymes of microbial origin are commercially available. Therefore, there is a need to identify more novel enzymes of microbial origin that can mitigate mycotoxins. In this review, we conducted an in-depth summary of the microbial enzymes involved in the biotransformation of mycotoxins.

Degradation of Aflatoxin B1 by recombinant laccase extracellular produced from Escherichia coli

Bioenzymatic degradation of aflatoxin B1 (AFB1) is a safe, efficient and environmentally friendly detoxification technology. In this work, AFB1 was successfully degraded by recombinant laccase (fmb-rL103) in the absence of a mediator. The laccase gene was cloned from Bacillus vallismortis fmb-103, and was expressed in heterologous host Escherichia coli after codon optimization. The extracellular production of fmb-rL103 could be induced by adding methanol (6 %, v/v), and the maximum yield was 1545.6 U/L. In the 10 L bioreactor, the extracellular yield increased to 50,950.6 U/L after 20 h of induction, accounting for three quarters of the total yield. The mechanism of methanol-induced extracellular secretion was further studied by measuring acetate content, lac103 gene expression and cell membrane permeability. Furthermore, we explored the biochemical properties of fmb-rL103 and its degradation conditions on AFB1. The degradation efficiency increased constantly with increase in incubation pH and temperature, and exceeded 60 % at pH 7.0 and 37 °C. This work provides new insight into developing the large-scale production of laccase and its application to degrade AFB1.

Effects of Compound Mycotoxin Detoxifier on Alleviating Aflatoxin B1-Induced Inflammatory Responses in Intestine, Liver and Kidney of Broilers

In order to alleviate the toxic effects of aflatoxins B1 (AFB1) on inflammatory responses in the intestine, liver, and kidney of broilers, the aflatoxin B1-degrading enzyme, montmorillonite, and compound probiotics were selected and combined to make a triple-action compound mycotoxin detoxifier (CMD). The feeding experiment was divided into two stages. In the early feeding stage (1−21 day), a total of 200 one-day-old Ross broilers were randomly divided into four groups; in the later feeding stage (22−42 day), 160 broilers aged at 22 days were assigned to four groups: Group A: basal diet (4.31 μg/kg AFB1); Group B: basal diet with 40 μg/kg AFB1; Group C: Group A plus 1.5 g/kg CMD; Group D: Group B plus 1.5 g/kg CMD. After the feeding experiment, the intestine, liver, and kidney tissues of the broilers were selected to investigate the molecular mechanism for CMD to alleviate the tissue damages. Analyses of mRNA abundances and western blotting (WB) of inflammatory factors, as well as immunohistochemical (IHC) staining of intestine, liver, and kidney tissues showed that AFB1 aggravated the inflammatory responses through NF-κB and TN-α signaling pathways via TLR pattern receptors, while the addition of CMD significantly inhibited the inflammatory responses. Phylogenetic investigation showed that AFB1 significantly increased interleukin-1 receptor-associated kinase (IRAK-1) and mitogen-activated protein kinase (MAPK) activities (p < 0.05), which were restored to normal levels by CMD addition, indicating that CMD could alleviate cell inflammatory damages induced by AFB1.

Tyrosinase-functionalized polyhydroxyalkanoate bio-beads as a novel biocatalyst for degradation of bisphenol analogues

Bisphenol compounds are emerging contaminants of high concerns with known endocrine-disrupting effects. Biocatalysis provides a green chemistry alternative for advanced treatment in water reclamation. This study createda novel biocatalyst through genetically immobilizing the Bacillus megaterium tyrosinase enzyme (BmTyr) on the surface ofself-assembled polyhydroxyalkanoate (PHA) biopolymer beads (termed PHA-BmTyr) by using synthetic biology techniques and demonstrated one-pot in vivo production of the biocatalyst for effective degradation and detoxification of various bisphenol analogues for the first time. The degradation pathway of bisphenols was determined to be mediated by the monophenolase and diphenolase activity of BmTyr. Notably, biocatalytic bisphenol degradation by PHA-BmTyr could substantially reduce or eliminate estrogenic activity of the contaminants, and the degradation products had remarkably lower acute and chronic toxicity than their parent compounds. Furthermore, the PHA-BmTyr biocatalyst had high reusability for multiple bisphenol degradation reaction cycles and showed excellent stability that retained 100% and 86.6% of the initial activity when stored at 4 °C and room temperature, respectively for 30 days. Also, the PHA-BmTyr biocatalyst could efficiently degrade bisphenol analogues in real wastewater effluent matrix. This study provides a promising approach to develop innovative biocatalysis technologies for sustainable water reclamation.

In silico analytical toolset for predictive degradation and toxicity of hazardous pollutants in water sources

Different phenolic compounds, including multimeric lignin derivatives in the β-O-4 form, are among the most prevalent compounds in wastewater, often generated from paper industries. Relatively small concentrations of lignin are hazardous to aquatic organisms and can trigger severe environmental hazards. Herein, we present a predictive toolset to insight the induced toxic hazards prediction, and their Lignin peroxidase (LiP)-assisted degradation mechanism of selected multimeric lignin model compounds. T.E.ST and Toxtree toolset were deployed for toxic hazards estimation in different endpoints. To minimize the concerning hazards, we screened multimeric compounds for binding affinity with LiP. The binding affinity was found to be significantly lower than the reference compound. An Extra precision (XP) Glide score of -6.796 kcal/mol was found for dimer (guaiacyl 4-O-5 guaiacyl) complex as lowest compared to reference compound (-4.007 kcal/mol). The active site residues ASP-153, HIP-226, VAL-227, ARG-244, GLU-215, 239, PHE-261 were identified as site-specific key binding AA residues actively involved with corresponding ligands, forming Hydrophobic, H-Bond, π-Stacking, π-π type interactions. The DESMOND-assisted molecular dynamics simulation's (MDS) trajectories of protein-ligand revealed the considerable binding behavior and attained stability and system equilibrium state. Such theoretical and predictive conclusions indicted the feasibility of LiP assisted sustainable mitigation of lignin-based compounds, and such could be used to protect the environment from the potential hazards posed by recognized similar pollutants.

Considerations regarding affinity determinants for aflatoxin B1 in binding cavity of fungal laccase based on in silico mutational and in vitro verification studies

Laccase, a multicopper oxidase, is well known for its industrial potentials to remove environmental pollutants due to its low substrate specificity to oxidize phenols and thus catalytic versatility. Many efforts focused on the metabolic mechanism, yet to decipher the structural determinants responsible for the differentiation between substrates. Aflatoxin B1 (AFB1), a new substrate for laccase, is a mycotoxin with a formidable environmental threat to public health and food safety. In the present study, we combined biochemical, in silico mutational and molecular-docking data to gain an insight to the function of key residues in the active cavity close to the T1 copper site in a characterized recombinant laccase from Cerrena unicolor (rCuL). Kinetic data for computer-assisted virtual mutants established the binding affinity of hydrogen bonds and residues (Asn336, Asp207, Val391, and Thr165) in rCuL to AFB1. The augmented binding affinity to AFB1 may be related to the conformational rearrangements of the laccase and its ability to hydrogen-bond with the substrate. Furthermore, the optimal pH and temperature for rCuL and variants mediated AFB1 degradation may depend on their pH stability and thermostability. Our findings reinforce the importance of the structure-function relationship of fungal laccases in degrading AFB1, providing mechanistic guidance for future biocatalyst and bioengineering applications.

Isolation, Purification, and Characterization of a Laccase-Degrading Aflatoxin B1 from Bacillus amyloliquefaciens B10

Aflatoxins, widely found in feed and foodstuffs, are potentially harmful to human and animal health because of their high toxicity. In this study, a strain of Bacillus amyloliquefaciens B10 with a strong ability to degrade aflatoxin B1 (AFB1) was screened; it could degrade 2.5 μg/mL of AFB1 within 96 h. The active substances of Bacillus amyloliquefaciens B10 for the degradation of AFB1 mainly existed in the culture supernatant. A new laccase with AFB1-degrading activity was separated by ammonium sulfate precipitation, diethylaminoethyl (DEAE) and gel filtration chromatography. The results of molecular docking showed that B10 laccase and aflatoxin had a high docking score. The coding sequence of the laccase was successfully amplified from cDNA by PCR and cloned into E. coli. The purified laccase could degrade 79.3% of AFB1 within 36 h. The optimum temperature for AFB1 degradation was 40 °C, and the optimum pH was 6.0–8.0. Notably, Mg²⁺ and dimethyl sulfoxide (DMSO) could enhance the AFB1-degrading activity of B10 laccase. Mutation of the three key metal combined sites of B10 laccase resulted in the loss of AFB1-degrading activity, indicating that these three metal combined sites of B10 laccase play an essential role in the catalytic degradation of AFB1.

Recent technological advances in mechanism, toxicity, and food perspectives of enzyme-mediated aflatoxin degradation

Aflatoxins are carcinogenic secondary metabolites produced by Aspergillus section Flavi that contaminates a wide variety of food and feed products and is responsible for serious health and economic consequences. Fermented foods are prepared with a wide variety of substrates over a long fermentation time and are thus vulnerable to contamination by aflatoxin-producing fungi, leading to the production of aflatoxin B1. The mitigation and control of aflatoxin is currently a prime focus for developing safe aflatoxin-free food. This review summarizes the role of major aflatoxin-degrading enzymes such as laccase, peroxidase, and lactonase, and microorganisms in the context of their application in food. A putative mechanism of enzyme-mediated aflatoxin degradation and toxicity evaluation of the degraded products are also extensively discussed to evaluate the safety of degradation processes for food applications. The review also describes aflatoxin-degrading microorganisms isolated from fermented products and investigates their applicability in food as aflatoxin preventing agents. Furthermore, a summary of recent technological advancements in protein engineering, nanozymes, in silico and statistical optimization approaches are explored to improve the industrial applicability of aflatoxin-degrading enzymes.

Identification of Two Myrosinases from a Leclercia adecarboxylata Strain and Investigation of Its Tolerance Mechanism to Glucosinolate Hydrolysate

Glucosinolates (GSLs), secondary metabolites synthesized by cruciferous plants, can be hydrolyzed by myrosinase into compounds, such as isothiocyanates (ITCs), with various bioactivities. Thus, myrosinase plays an important role in the utilization of GSLs. We isolated a bacterial strain, which was identified as Leclercia adecarboxylata, from the rhizosphere soil of rape seedlings and identified two myrosinase genes and an ITC hydrolase gene. Both myrosinases are intracellular and have 658 amino acid residues. Via molecular docking and chemical modification assays investigating the active sites of the myrosinases, arginine was found to be essential for their catalytic activity. Transcriptomic analysis of the response to sinigrin revealed significant up-regulation of some genes involved in allyl-ITC detoxification, with metallo-β-lactamase 3836 having the highest fold change. Thus, we discovered two myrosinases from L. adecarboxylata and demonstrated that the mechanism of tolerance of the bacterium to allyl-ITC likely involved metallo-β-lactamase activity.

Detoxification of aflatoxin B1 in broiler chickens by a triple-action feed additive

The aim of this study was to evaluate the detoxification of aflatoxin B₁ (AFB₁) in vitro and in broiler chickens using a triple-action compound mycotoxin detoxifier (CMD). Response surface methodology (RSM) was used to evaluate AFB1 detoxification in artificial gastrointestinal fluid (AGIF) in vitro. The AFB₁-degradation rate was 41.5% (P < .05) when using a compound probiotic (CP) in which the visible counts of Bacillus subtilis, Lactobacillus casein, Enterococcus faecalis and Candida utilis were 1.0 × 10⁵, 1.0 × 10⁵, 1.0 × 10⁷ and 1.0 × 10⁵ CFU/mL, respectively. When CP was combined with 0.1% AFB₁-degrading enzyme to give CPADE, the AFB₁-degradation rate was increased to 55.28% (P < .05). The AFB₁-removal rate was further increased to above 90% when CPADE was combined with 0.03% montmorillonite to make CMD. In vivo, a total of 150 one-day-old Ross broilers were allotted to 3 groups, 5 replications for each group, 10 broilers in each replication. Group A: basal diet, Group B: basal diet with 40 μg/kg AFB₁, Group C: basal diet with 40 μg/kg AFB₁ plus CMD. The feeding experiment period was 21 d. The results showed that broiler growth was increased, and AFB₁ residues in serum, excreta and liver were decreased by CMD addition in broiler diet (P < .05). In conclusion, CMD was able to remove AFB₁ efficiently in vitro and to increase broiler production performance and reduce AFB₁ residues in the chickens.

Co-Cultivation of Two Bacillus Strains for Improved Cell Growth and Enzyme Production to Enhance the Degradation of Aflatoxin B1

Bacillus sp. H16v8 and Bacillus sp. HGD9229 were identified as Aflatoxin B₁ (AFB₁) degrader in nutrient broth after a 12 h incubation at 37 °C. The degradation efficiency of the two-strain supernatant on 100 μg/L AFB₁ was higher than the bacterial cells and cell lysate. Moreover, degradations of AFB₁ were strongly affected by the metal ions in which Cu²⁺ stimulated the degradation and Zn²⁺ inhibited the degradation. The extracellular detoxifying enzymes produced by co-cultivation of two strains were isolated and purified by ultrafiltration. The molecular weight range of the detoxifying enzymes was 20-25 kDa by SDS-PAGE. The co-culture of two strains improved the total cell growth with the enhancement of the total protein content and detoxifying enzyme production. The degradation efficiency of the supernatant from mixed cultures increased by 87.7% and 55.3% compared to Bacillus sp. H16v8 and HGD9229, individually. Moreover, after the degradation of AFB₁, the four products of the lower toxicity were identified by LC-Triple TOF-MS with the two proposed hypothetical degradation pathways.

Degradation of aflatoxin B1 by a recombinant laccase from Trametes sp. C30 expressed in Saccharomyces cerevisiae: A mechanism assessment study in vitro and in vivo

Aflatoxin B₁ (AFB₁) is the most harmful mycotoxin and presents risks to human health. Utilization of enzyme to degrade AFB1 is a promising strategy to overcome this problem. In this study, we evaluated the effect of recombinant laccase expressed in Saccharomyces cerevisiae on the degradation of AFB₁. It was found that AFB₁ could be degraded effectively by laccase up to 91%.The results of ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS) showed that there were four main degradation products of AFB₁ including C₁₆H₂₂O₄, C₁₄H₁₆N₂O₂, C₇H₁₂N₆O and C₂₄H₃₀O₆. Two possible degradation pathways were proposed: 1) AFB₁ lost -CO continuously, and then double bonds of furan ring were broken after reactions with H₂O, H⁺, and -NH₂; 2) AFB₁ occurred decarbonylation reaction after losing -CO and double bonds were broken by additional reaction with H⁺. Two toxicological activity sites in AFB₁, including a double bond of furo-furan ring and lactone ring in the coumarin in moiety, were destroyed. The toxicity of AFB₁ degradation products was evaluated on HepG2 cells and in vivo tests, and the results indicated a decrease in hepatocytes apoptosis, liver and kidney histopathological lesions, oxidative stress, and inflammation as compared to non-laccase degraded AFB_1. Moreover, the AFB₁ degradation products significantly decreased the cytotoxicity and hepatotoxicity. This investigation provides innovative evidence on the effectiveness of laccase expressed in Saccharomyces cerevisiae in detoxifying AFB₁.

Aflatoxin Detoxification Using Microorganisms and Enzymes

Mycotoxin contamination causes significant economic loss to food and feed industries and seriously threatens human health. Aflatoxins (AFs) are one of the most harmful mycotoxins, which are produced by Aspergillus flavus, Aspergillus parasiticus, and other fungi that are commonly found in the production and preservation of grain and feed. AFs can cause harm to animal and human health due to their toxic (carcinogenic, teratogenic, and mutagenic) effects. How to remove AF has become a major problem: biological methods cause no contamination, have high specificity, and work at high temperature, affording environmental protection. In the present research, microorganisms with detoxification effects researched in recent years are reviewed, the detoxification mechanism of microbes on AFs, the safety of degrading enzymes and reaction products formed in the degradation process, and the application of microorganisms as detoxification strategies for AFs were investigated. One of the main aims of the work is to provide a reliable reference strategy for biological detoxification of AFs.

A New Laccase of Lac 2 from the White Rot Fungus Cerrena unicolor 6884 and Lac 2-Mediated Degradation of Aflatoxin B1

Aflatoxin B₁ (AFB₁) is a known toxic human carcinogen and can be detoxified by laccases, which are multicopper oxidases that convert several environmental pollutants and toxins. In this study, a new laccase that could catalyze AFB₁ degradation was purified and identified from the white-rot fungus Cerrena unicolor 6884. The laccase was purified using (NH₄)₂SO₄ precipitation and anion exchange chromatography, and then identified as Lac 2 through zymogram and UHPLC-MS/MS based on the Illumina transcriptome analysis of C. unicolor 6884. Six putative laccase protein sequences were obtained via functional annotation. The lac 2 cDNA encoding a full-length protein of 512 amino acids was cloned and sequenced to expand the fungus laccase gene library for AFB₁ detoxification. AFB₁ degradation by Lac 2 was conducted in vitro at pH 7.0 and 45 °C for 24 h. The half-life of AFB₁ degradation catalyzed by Lac 2 was 5.16 h. Acetosyringone (AS), Syrinagaldehyde (SA) and [2,2' -azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid)] (ABTS) at 1 mM concentration seemed to be similar mediators for strongly enhancing AFB₁ degradation by Lac 2. The product of AFB₁ degradation catalyzed by Lac 2 was traced and identified to be Aflatoxin Q₁ (AFQ₁) based on mass spectrometry data. These findings are promising for a possible application of Lac 2 as a new aflatoxin oxidase in degrading AFB₁ present in food and feeds.