Application of a yeast estrogen reporter system for screening zearalenone degrading microbes

Zearalenone degradation by peptide-based enzyme mimics attached membrane reactor: Performance and mechanism

Zearalenone (ZEN) is a nonsteroidal estrogenic mycotoxin with widespread contamination. Inspired by lactone hydrolases, a peptide-based enzyme mimetic material for degrading ZEN was developed by combining serine, histidine and glutamate (S/H/E) catalytic triad with pro-hydrophobic self-assembling sequences and oxyanion hole site. Chitosan hybrid membranes were prepared, followed by immobilizing enzyme mimic on the membrane surface to fabricate biocatalytic membrane reactor. The membrane reactor, with good thermal stability and high catalytic activity after repeated use, can be applied to the degradation of ZEN in food. Computer simulation studies of the degradation mechanism indicated that the carbon atom on the lactone bond within ZEN molecule was susceptible to catalytic triplex attack, leading to lactone bond broken, followed by spontaneous decarboxylation to produce dihydroxyphenyl derivatives with greatly reduced binding capacity to the estrogen receptors. This kind of peptide-based enzyme mimetic material would be very promising in degrading mycotoxins in food safety field.

Actinobacteria as Promising Biocontrol Agents for In Vitro and In Planta Degradation and Detoxification of Zearalenone

Zearalenone (ZEN) is a prevalent mycotoxin found in grains and grain-derived products, inducing adverse health effects in both animals and humans. The in-field application of microorganisms to degrade and detoxify ZEN is a promising strategy to enhance the safety of food and feed. In this study, we investigated the potential of three actinobacterial strains to degrade and detoxify ZEN in vitro and in planta on wheat ears. The residual ZEN concentration and toxicity in the samples were analysed with UHPLC-MS/MS and a bioluminescence BLYES assay, respectively. Streptomyces rimosus subsp. rimosus LMG19352 could completely degrade and detoxify 5 mg/L ZEN in LB broth within 24 h, along with significant reductions in ZEN concentration both in a minimal medium (MM) and on wheat ears. Additionally, it was the only strain that showed a significant colonisation of these ears. Rhodococcus sp. R25614 exhibited partial but significant degradation in LB broth and MM, whereas Streptomyces sp. LMG16995 degraded and detoxified ZEN in LB broth after 72 h by 39% and 33%, respectively. Although all three actinobacterial strains demonstrated the metabolic capability to degrade and detoxify ZEN in vitro, only S. rimosus subsp. rimosus LMG19352 showed promising potential to mitigate ZEN in planta. This distinction underscores the importance of incorporating in planta screening assays for assessing the potential of mycotoxin-biotransforming microorganisms as biocontrol agents.

Bacterial Lactonases ZenA with Noncanonical Structural Features Hydrolyze the Mycotoxin Zearalenone

Zearalenone (ZEN) is a mycoestrogenic polyketide produced by Fusarium graminearum and other phytopathogenic members of the genus Fusarium. Contamination of cereals with ZEN is frequent, and hydrolytic detoxification with fungal lactonases has been explored. Here, we report the isolation of a bacterial strain, Rhodococcus erythropolis PFA D8-1, with ZEN hydrolyzing activity, cloning of the gene encoding α/β hydrolase ZenA encoded on the linear megaplasmid pSFRL1, and biochemical characterization of nine homologues. Furthermore, we report site-directed mutagenesis as well as structural analysis of the dimeric ZenARe of R. erythropolis and the more thermostable, tetrameric ZenAScfl of Streptomyces coelicoflavus with and without bound ligands. The X-ray crystal structures not only revealed canonical features of α/β hydrolases with a cap domain including a Ser-His-Asp catalytic triad but also unusual features including an uncommon oxyanion hole motif and a peripheral, short antiparallel β-sheet involved in tetramer interactions. Presteady-state kinetic analyses for ZenARe and ZenAScfl identified balanced rate-limiting steps of the reaction cycle, which can change depending on temperature. Some new bacterial ZEN lactonases have lower KM and higher kcat than the known fungal ZEN lactonases and may lend themselves to enzyme technology development for the degradation of ZEN in feed or food.

A Probiotic Bacillus amyloliquefaciens D-1 Strain Is Responsible for Zearalenone Detoxifying in Coix Semen

Zearalenone (ZEN) is a mycotoxin produced by Fusarium spp., which commonly and severely contaminate food/feed. ZEN severely affects food/feed safety and reduces economic losses owing to its carcinogenicity, genotoxicity, reproductive toxicity, endocrine effects, and immunotoxicity. To explore efficient methods to detoxify ZEN, we identified and characterized an efficient ZEN-detoxifying microbiota from the culturable microbiome of Pseudostellaria heterophylla rhizosphere soil, designated Bacillus amyloliquefaciens D-1. Its highest ZEN degradation rate reached 96.13% under the optimal condition. And, D-1 can almost completely remove ZEN (90 μg·g-1) from coix semen in 24 h. Then, the D-1 strain can detoxify ZEN to ZEM, which is a new structural metabolite, through hydrolyzation and decarboxylation at the ester group in the lactone ring and amino acid esterification at C2 and C4 hydroxy. Notably, ZEM has reduced the impact on viability, and the damage of cell membrane and nucleus DNA and can significantly decrease the cell apoptosis in the HepG2 cell and TM4 cell. In addition, it was found that the D-1 strain has no adverse effect on the HepG2 and TM4 cells. Our findings can provide an efficient microbial resource and a reliable reference strategy for the biological detoxification of ZEN.

Microbial and enzymatic battle with food contaminant zearalenone (ZEN)

Zearalenone (ZEN) contamination of various foods and feeds is an important global problem. In some animals and humans, ZEN causes significant health issues in addition to massive economic losses, annually. Therefore, removal or degradation of the ZEN in foods and feeds is required to be done. The conventional physical and chemical methods have some serious issues including poor efficiency, decrease in nutritional value, palatability of feed, and use of costly equipment. Research examined microbes from diverse media for their ability to degrade zearalenone and other toxins, and the findings of several investigations revealed that enzymes produced from microbes play a significant role in the degradation of mycotoxins. In established bacterial hosts, genetically engineered technique was used to enhance heterologously produced degrading enzymes. Then, the bio-degradation of ZEN by the use of micro-organisms or their enzymes is much more advantageous and is close to nature and ecofriendly. Furthermore, an effort is made to put forward the work done by different scientists on the biodegradation of ZEN by the use of fungi, yeast, bacteria, and/or their enzymes to degrade the ZEN to non-toxic products. KEY POINTS: •Evolved microbial strains degraded ZEA more quickly •Different degrading properties were studied.

High-Throughput Analysis of Endocrine-Disrupting Compounds Using BLYES and BLYAS Bioluminescent Yeast Bioassays

Bioluminescent yeast assays BLYES and BLYAS are whole-cell bioassays that utilize genetically modified Saccharomyces cerevisiae bioreporters to detect estrogenic and androgenic activities, respectively. The bioreporter strains chromosomally express human estrogen receptor alpha (BLYES) or androgen receptor (BLYAS) and contain a reporter plasmid expressing the complete bacterial luciferase gene cassette (luxCDABE) under the control of an estrogen- or androgen-responsive promoter. Exposure to endocrine-disrupting compounds activates the receptor which subsequently turns on the expression of the reporter genes, resulting in dose-dependent bioluminescence (i.e., light) emission. These yeast whole-cell bioassays provide rapid, cost-effective, and high-throughput detection of endocrine-disrupting activities in environmental samples. This protocol will provide a detailed description of the standard assay procedures as well as a framework for data analysis.

Degradation of Aflatoxin B1 and Zearalenone by Bacterial and Fungal Laccases in Presence of Structurally Defined Chemicals and Complex Natural Mediators

Aflatoxin B₁ (AFB₁) and zearalenone (ZEN) exert deleterious effects to human and animal health. In this study, the ability of a CotA laccase from Bacillus subtilis (BsCotA) to degrade these two mycotoxins was first investigated. Among the nine structurally defined chemical compounds, methyl syringate was the most efficient mediator assisting BsCotA to degrade AFB₁ (98.0%) and ZEN (100.0%). BsCotA could also use plant extracts, including the Epimedium brevicornu, Cucumis sativus L., Lavandula angustifolia, and Schizonepeta tenuifolia extracts to degrade AFB₁ and ZEN. Using hydra and BLYES as indicators, it was demonstrated that the degraded products of AFB₁ and ZEN using the laccase/mediator systems were detoxified. Finally, a laccase of fungal origin was also able to degrade AFB₁ and ZEN in the presence of the discovered mediators. The findings shed light on the possibility of using laccases and a mediator, particularly a natural plant-derived complex mediator, to simultaneously degrade AFB₁ and ZEN contaminants in food and feed.

Degradation of Four Major Mycotoxins by Eight Manganese Peroxidases in Presence of a Dicarboxylic Acid

Enzymatic treatment is an attractive method for mycotoxin detoxification, which ideally prefers the use of one or a few enzymes. However, this is challenged by the diverse structures and co-contamination of multiple mycotoxins in food and feed. Lignin-degrading fungi have been discovered to detoxify organics including mycotoxins. Manganese peroxidase (MnP) is a major enzyme responsible for lignin oxidative depolymerization in such fungi. Here, we demonstrate that eight MnPs from different lignocellulose-degrading fungi (five from Irpex lacteus, one from Phanerochaete chrysosporium, one from Ceriporiopsis subvermispora, and another from Nematoloma frowardii) could all degrade four major mycotoxins (aflatoxin B1, AFB1; zearalenone, ZEN; deoxynivalenol, DON; fumonisin B1, FB1) only in the presence of a dicarboxylic acid malonate, in which free radicals play an important role. The I. lacteus and C. subvermispora MnPs behaved similarly in mycotoxins transformation, outperforming the P. chrysosporium and N. frowardii MnPs. The large evolutionary diversity of these MnPs suggests that mycotoxin degradation tends to be a common feature shared by MnPs. MnP can, therefore, serve as a candidate enzyme for the degradation of multiple mycotoxins in food and feed if careful surveillance of the residual toxicity of degradation products is properly carried out.

Detoxification Strategies for Zearalenone Using Microorganisms: A Review

Zearalenone (ZEA) is a mycotoxin produced by Fusarium fungi that is commonly found in cereal crops. ZEA has an estrogen-like effect which affects the reproductive function of animals. It also damages the liver and kidneys and reduces immune function which leads to cytotoxicity and immunotoxicity. At present, the detoxification of mycotoxins is mainly accomplished using biological methods. Microbial-based methods involve zearalenone conversion or adsorption, but not all transformation products are nontoxic. In this paper, the non-pathogenic microorganisms which have been found to detoxify ZEA in recent years are summarized. Then, two mechanisms by which ZEA can be detoxified (adsorption and biotransformation) are discussed in more detail. The compounds produced by the subsequent degradation of ZEA and the heterogeneous expression of ZEA-degrading enzymes are also analyzed. The development trends in the use of probiotics as a ZEA detoxification strategy are also evaluated. The overall purpose of this paper is to provide a reliable reference strategy for the biological detoxification of ZEA.

The Protective Role of Bacillus velezensis A2 on the Biochemical and Hepatic Toxicity of Zearalenone in Mice

Zearalenone (ZEN) is an estrogen-like mycotoxin produced by Fusarium that seriously compromises the safety of animal and human health. In this study, our aim was to evaluate the protective effect of Bacillus velezensis A2 against biochemical and pathological changes induced by zearalenone in mice. Kunming mice (n = 40; 25 ± 2 g) were allotted to four treatment groups: a control group (basic feed); a ZEN group (basic feed with a ZEN dose of 60 mg/kg); an A2 strain fermented feed group (150 g of feed mixed with 150 mL of sterile distilled water and inoculated with 5 mL of phosphate buffer salt (PBS) resuspended A2 strain); and an A2 strain fermented ZEN-contaminated feed group. (A2 strain group 150 mL pure bacterial distilled water system mixed with 150 g ZEN-contaminated feed.) Our results showed that the Bacillus velezensis A2 strain can completely degrade the ZEN-contaminated feed within 5 days. (The concentration of ZEN in fermentation was 60 μg/mL.) After the mice fed for 28 days, compared with the control group, the activities of AST and ALT were increased, the activities of glutathione peroxidase (GSH-PX) and total superoxide dismutase (T-SOD) were decreased, and the amount of creatinine (CRE), blood urea nitrogen (BUN), uric acid (UA), and malondialdehyde (MDA) in the ZEN group were increased in the mice serum (p < 0.05; p < 0.01). However, compared with the ZEN group, these biochemical levels were reversed in the A2 strain fermented feed group and in the A2 strain fermented ZEN-contaminated feed group (p < 0.05; p < 0.01). Furthermore, histopathological analysis only showed pathological changes of the mice liver in the ZEN group. The results showed that Bacillus velezensis A2 as additive could effectively remove ZEN contamination in the feed and protect the mice against the toxic damage of ZEN. In conclusion, Bacillus velezensis A2 has great potential use as a microbial feed additive to detoxify the toxicity of zearalenone in production practice.

Bacillus velezensis A2 fermentation exerts a protective effect on renal injury induced by Zearalenone in mice

Zearalenone (ZEN) is an estrogen-like mycotoxin occurring in food and feeds, and it can cause oxidative damage and apoptosis in the testis, liver, and kidney. A current concern for researchers is how to reduce the harm it causes to humans and animals. In this study, our aim was to isolate and identify a novel and efficient ZEN-detoxifying strain of bacteria, and we aimed to assess the protective effect of the isolated strain on kidney damage caused by ZEN in mice. Our results indicated that a strain of Bacillus velezensis (B. velezensis), named A2, could completely degrade ZEN (7.45 μg/mL) after three days of incubation at 37 °C in the Luria-Bertani (LB) medium. This fermentation broth of the B. velezensis A2 strain was given to mice. The histopathological analysis indicated that the fermentation broth from the B. velezensis A2 strain reduced the degree of renal injury that is induced by ZEN. Furthermore, it greatly reduced the increase in serum levels of creatinine (CRE), uric acid (UA), and urea nitrogen (BUN) caused by ZEN. In addition, B. velezensis A2 strain also significantly inhibited the increase of malonaldehyde (MDA) content, and reversed the decreases of total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-Px) activities caused by ZEN. Studies have shown that ZEN is involved in the regulation of mRNA and protein levels of genes involved in the ER stress-induced apoptotic pathway, such as heavy chain binding protein (BIP), C-/-EBP homologous protein (CHOP), cysteine Aspartate-specific protease-12 (Caspase-12), c-Jun N-terminal kinase (JNK), and BCL2-related X protein (Bcl-2 and Bax). However, when mice were administered the fermentation broth of the B. velezensis A2 strain, it significantly reversed the expressions of these genes in their kidney tissue. In conclusion, our results indicate that the newly identified strain of B. velezensis A2, has a protective effect from renal injury induced by ZEN in mice. This strain has a potential application in the detoxification of ZEN in feed and protects animals from ZEN poisoning.

Development of a combined method to assess the complex effect of atrazine on sex steroid synthesis in H295R cells

The aim of the study was to develop a rapid, cost-effective combined testing method to assess the indirect effect of compounds interfering with sex steroid synthesis and to determine complex effects of atrazine on estrogen and androgen synthesis in vitro on H295R human cell line. Steroidogenic assay was performed on H295R human adrenocortical carcinoma cell line. Instead of standard analytical methods, bioluminescence bioreporter assays (Saccharomyces cerevisiae BLYES and BLYAS) were used to measure estrogenic and androgenic effects of sex steroid hormones released by human cells in response to atrazine. Atrazine resulted in elevated estrogen production presumably due to its well documented inductive effect on aromatase on H295R cell line, detected by BLYES. Interestingly, results of BLYAS test showed concentration-dependent increase of androgen production in H295R cells. That indicates that atrazine can not only increase estrogen level via aromatase induction, but may interfere in androgen synthesis as well. The combined method allows us to assess the androgenic and estrogenic effect of sex steroids produced by human cells in increased or decreased quantity as a result of the different chemicals, without determining specific analytical measurement endpoints, by using the yeast based bioluminescent bioreporter test.

Biodegradation of Mycotoxins: Tales from Known and Unexplored Worlds

Exposure to mycotoxins, secondary metabolites produced by fungi, may infer serious risks for animal and human health and lead to economic losses. Several approaches to reduce these mycotoxins have been investigated such as chemical removal, physical binding, or microbial degradation. This review focuses on the microbial degradation or transformation of mycotoxins, with specific attention to the actual detoxification mechanisms of the mother compound. Furthermore, based on the similarities in chemical structure between groups of mycotoxins and environmentally recalcitrant compounds, known biodegradation pathways and degrading organisms which hold promise for the degradation of mycotoxins are presented.

Standardized application of yeast bioluminescent reporters as endocrine disruptor screen for comparative analysis of wastewater effluents from membrane bioreactor and traditional activated sludge

A standardized protocol is demonstrated for bioluminescent strains Saccharomyces cerevisiae BLYES, BLYAS and BLYR as high-throughput screening tools to monitor the estrogenic, androgenic and toxic potencies in wastewater. The sensitivity and reproducibility of the assay in wastewater monitoring was evaluated for 7 day semi-continuous batch reactor using activated sludge with hormones spiked raw sewage. Yeast bioluminescent assay successfully captured the rapid removal of estrogenic and androgenic activities in the bioreactors, and demonstrated rapid response (≤4 h) with good reproducibility. This standardized protocol was then applied in a 12 months monitoring of the effluent of a WWTP located at Powell, TN, USA featuring parallel-operated full-scale membrane bioreactor (MBR) and traditional activated sludge (TAS) treatment. Monitoring results showed that estrogenic activity was persistent in all TAS and most MBR effluent samples, while residual androgenic activity was non-detectable throughout the monitored period. The estrogenic equivalents (EEQ) in TAS effluent ranged from 21.61 ng/L to 0.04 pg/L and averaged 3.25 ng/L. The EEQ in MBR effluent ranged from 2.88 ng/L to 0.0134 pg/L and averaged ~10 fold less (0.32 ng/L) than TAS. Despite the large temporal variation, MBR effluent EEQ was consistently lower than TAS on any given sampling date. Most MBR effluent samples also exhibited less cytotoxicity than TAS. Further analysis did not demonstrate significant correlation between effluent EEQ level and WWTP operational parameters including MLSS, SRT, HRT and BOD.