Preparation and characterization of the deepoxy trichothecenes: deepoxy HT-2, deepoxy T-2 triol, deepoxy T-2 tetraol, deepoxy 15-monoacetoxyscirpenol, and deepoxy scirpentriol

Microbial detoxification of mycotoxins in food

Mycotoxins are toxic secondary metabolites produced by certain genera of fungi including but not limited to Fusarium, Aspergillus, and Penicillium. Their persistence in agricultural commodities poses a significant food safety issue owing to their carcinogenic, teratogenic, and immunosuppressive effects. Due to their inherent stability, mycotoxin levels in contaminated food often exceed the prescribed regulatory thresholds posing a risk to both humans and livestock. Although physical and chemical methods have been applied to remove mycotoxins, these approaches may reduce the nutrient quality and organoleptic properties of food. Microbial transformation of mycotoxins is a promising alternative for mycotoxin detoxification as it is more specific and environmentally friendly compared to physical/chemical methods. Here we review the biological detoxification of the major mycotoxins with a focus on microbial enzymes.

Isolation and Characterization of Two New Deoxynivalenol-Degrading Strains, Bacillus sp. HN117 and Bacillus sp. N22

Deoxynivalenol (DON), produced by Fusarium species, is one of the most common trichothecenes detected in cereals pre- and post-harvest, which poses a great threat to the health of livestock and human beings due to its strong toxicity. In this study, we isolated and characterized two DON-degrading bacterial strains, Bacillus sp. HN117 and Bacillus sp. N22. Both strains could degrade DON efficiently in a wide range of temperatures (from 25 °C to 42 °C) and concentrations (from 10 mg/L to 500 mg/L). After optimization of the degradation conditions, 29.0% DON was eliminated by HN117 in 72 h when it was incubated with 1000 mg/L DON; meanwhile, the DON degradation rate of N22 was boosted notably from 7.41% to 21.21% within 120 h at 500 mg/L DON. Degradation products analysis indicated HN117 was able to transform DON into a new isomer M-DOM, the possible structure of which was deduced based on LC-MS and NMR analysis, and N22 could convert DON into potential low-toxic derivatives norDON E and 9-hydroxymethyl DON lactone. These two strains have the potential to be developed as new biodegrading agents to control DON contamination in food and feed industries.

In Vitro Assay of Translation Inhibition by Trichothecenes Using a Commercially Available System

Trichothecenes are a family of major secondary metabolites produced by some common filamentous fungi, including plant pathogenic and entomopathogenic fungi. It may be considered difficult to conduct a comparison between the toxicities of trichothecenes with consideration of different conditions and cell lines. In the current study, we developed an in vitro assay based on a commercially available system to estimate the translation inhibition, that is, the main toxicity, of trichothecenes. The assay was applied to estimate the inhibition of protein synthesis by trichothecenes. Initially, we examined the assay using trichothecene dissolved in water followed by an assessment of trichothecene solutions dissolved in acetonitrile. The obtained data showed that the assay tolerated the small amount of acetonitrile. The assay examined in this study has the advantages of a short operation time (one day), ease of use, and data stability, as it is a non-cell-based assay whose components are commercially available. It is expected that this assay will contribute to the evaluation of the toxicity of a vast number of trichothecenes.

Mechanisms of deoxynivalenol (DON) degradation during different treatments: a review

Deoxynivalenol (DON) is one of the main trichothecenes, that causes health-related issues in humans and animals and imposes considerable financial loss to the food industry each year. Numerous treatments have been reported in the literature on the degradation of DON in food products. These treatments include thermal, chemical, biological/enzymatic, irradiation, light, ultrasound, ozone, and atmospheric cold plasma treatments. Each of these methods has different degradation efficacy and degrades DON by a distinct mechanism, which leads to various degradation byproducts with different toxicity. This manuscript focuses to review the degradation of DON by the aforementioned treatments, the chemical structure and toxicity of the byproducts, and the degradation pathway of DON. Based on the type of treatment, DON can be degraded to norDONs A-F, DON lactones, and ozonolysis products or transformed into de-epoxy deoxynivalenol, DON-3-glucoside, 3-acetyl-DON, 7-acetyl-DON, 15-acetyl-DON, 3-keto-DON, or 3-epi-DON. DON is a major problem for the grain industry and the studies focusing on DON degradation mechanisms could be helpful to select the best method and overcome the DON contamination in grains.

Novel Soil Bacterium Strain Desulfitobacterium sp. PGC-3-9 Detoxifies Trichothecene Mycotoxins in Wheat via De-Epoxidation under Aerobic and Anaerobic Conditions

Trichothecenes are the most common mycotoxins contaminating small grain cereals worldwide. The C12,13 epoxide group in the trichothecenes was identified as a toxic group posing harm to humans, farm animals, and plants. Aerobic biological de-epoxidation is considered the ideal method of controlling these types of mycotoxins. In this study, we isolated a novel trichothecene mycotoxin-de-epoxidating bacterium, Desulfitobacterium sp. PGC-3-9, from a consortium obtained from the soil of a wheat field known for the occurrence of frequent Fusarium head blight epidemics under aerobic conditions. Along with MMYPF media, a combination of two antibiotics (sulfadiazine and trimethoprim) substantially increased the relative abundance of Desulfitobacterium species from 1.55% (aerobic) to 29.11% (aerobic) and 28.63% (anaerobic). A single colony purified strain, PGC-3-9, was isolated and a 16S rRNA sequencing analysis determined that it was Desulfitobacterium. The PGC-3-9 strain completely de-epoxidated HT-2, deoxynivalenol (DON), nivalenol and 15-acetyl deoxynivalenol, and efficiently eliminated DON in wheat grains under aerobic and anaerobic conditions. The strain PGC-3-9 exhibited high DON de-epoxidation activity at a wide range of pH (6–10) and temperature (15–50 °C) values under both conditions. This strain may be used for the development of detoxification agents in the agriculture and feed industries and the isolation of de-epoxidation enzymes.

Risk to human and animal health related to the presence of 4,15-diacetoxyscirpenol in food and feed

4,15‐Diacetoxyscirpenol (DAS) is a mycotoxin primarily produced by Fusarium fungi and occurring predominantly in cereal grains. As requested by the European Commission, the EFSA Panel on Contaminants in the Food Chain (CONTAM) assessed the risk of DAS to human and animal health related to its presence in food and feed. Very limited information was available on toxicity and on toxicokinetics in experimental and farm animals. Due to the limitations in the available data set, human acute and chronic health‐based guidance values (HBGV) were established based on data obtained in clinical trials of DAS as an anticancer agent (anguidine) after intravenous administration to cancer patients. The CONTAM Panel considered these data as informative for the hazard characterisation of DAS after oral exposure. The main adverse effects after acute and repeated exposure were emesis, with a no‐observed‐adverse‐effect level (NOAEL) of 32 μg DAS/kg body weight (bw), and haematotoxicity, with a NOAEL of 65 μg DAS/kg bw, respectively. An acute reference dose (ARfD) of 3.2 μg DAS/kg bw and a tolerable daily intake (TDI) of 0.65 μg DAS/kg bw were established. Based on over 15,000 occurrence data, the highest acute and chronic dietary exposures were estimated to be 0.8 and 0.49 μg DAS/kg bw per day, respectively, and were not of health concern for humans. The limited information for poultry, pigs and dogs indicated a low risk for these animals at the estimated DAS exposure levels under current feeding practices, with the possible exception of fattening chicken. Assuming similar or lower sensitivity than for poultry, the risk was considered overall low for other farm and companion animal species for which no toxicity data were available. In consideration of the similarities of several trichothecenes and the likelihood of co‐exposure via food and feed, it could be appropriate to perform a cumulative risk assessment for this group of substances.

Appropriateness to set a group health based guidance value for T2 and HT2 toxin and its modified forms

The EFSA Panel on Contaminants in the Food Chain (CONTAM) established a tolerable daily intake (TDI) for T2 and HT2 of 0.02 μg/kg body weight (bw) per day based on a new in vivo subchronic toxicity study in rats that confirmed that immune- and haematotoxicity are the critical effects of T2 and using a reduction in total leucocyte count as the critical endpoint. An acute reference dose (ARfD) of 0.3 μg for T2 and HT2/kg bw was established based on acute emetic events in mink. Modified forms of T2 and HT2 identified are phase I metabolites mainly formed through hydrolytic cleavage of one or more of the three ester groups of T2. Less prominent hydroxylation reactions occur predominantly at the side chain. Phase II metabolism involves conjugation with glucose, modified glucose, sulfate, feruloyl and acetyl groups. The few data on occurrence of modified forms indicate that grain products are their main source. The CONTAM Panel found it appropriate to establish a group TDI and a group ARfD for T2 and HT2 and its modified forms. Potency factors relative to T2 for the modified forms were used to account for differences in acute and chronic toxic potencies. It was assumed that conjugates (phase II metabolites of T2, HT2 and their phase I metabolites), which are not toxic per se, would be cleaved releasing their aglycones. These metabolites were assigned the relative potency factors (RPFs) of their respective aglycones. The RPFs assigned to the modified forms were all either 1 or less than 1. The uncertainties associated with the present assessment are considered as high. Using the established group, ARfD and TDI would overestimate any risk of modified T2 and HT2.

Aerobic De-Epoxydation of Trichothecene Mycotoxins by a Soil Bacterial Consortium Isolated Using In Situ Soil Enrichment

Globally, the trichothecene mycotoxins deoxynivalenol (DON) and nivalenol (NIV) are among the most widely distributed mycotoxins that contaminate small grain cereals. In this study, a bacterial consortium, PGC-3, with de-epoxydation activity was isolated from soil by an in situ soil enrichment method. Screening of 14 soil samples that were sprayed with DON revealed that 4 samples were able to biotransform DON into de-epoxydized DON (dE-DON). Among these, the PGC-3 consortium showed the highest and most stable activity to biotransform DON into dE-DON and NIV into dE-NIV. PGC-3 exhibited de-epoxydation activity at a wide range of pH (5–10) and temperatures (20–37 °C) values under aerobic conditions. Sequential subculturing with a continued exposure to DON substantially reduced the microbial population diversity of this consortium. Analyses of the 16S rDNA sequences indicated that PGC-3 comprised 10 bacterial genera. Among these, one species, Desulfitobacterium, showed a steady increase in relative abundance, from 0.03% to 1.55% (a 52-fold increase), as higher concentrations of DON were used in the subculture media, from 0 to 500 μg/mL. This study establishes the foundation to further develop bioactive agents that can detoxify trichothecene mycotoxins in cereals and enables for the characterization of detoxifying genes and their regulation.

Microbial biotransformation of DON: molecular basis for reduced toxicity

Bacteria are able to de-epoxidize or epimerize deoxynivalenol (DON), a mycotoxin, to deepoxy-deoxynivalenol (deepoxy-DON or DOM-1) or 3-epi-deoxynivalenol (3-epi-DON), respectively. Using different approaches, the intestinal toxicity of 3 molecules was compared and the molecular basis for the reduced toxicity investigated. In human intestinal epithelial cells, deepoxy-DON and 3-epi-DON were not cytotoxic, did not change the oxygen consumption or impair the barrier function. In intestinal explants, exposure for 4 hours to 10 μM DON induced intestinal lesions not seen in explants treated with deepoxy-DON and 3-epi-DON. A pan-genomic transcriptomic analysis was performed on intestinal explants. 747 probes, representing 323 genes, were differentially expressed, between DON-treated and control explants. By contrast, no differentially expressed genes were observed between control, deepoxy-DON and 3-epi-DON treated explants. Both DON and its biotransformation products were able to fit into the pockets of the A-site of the ribosome peptidyl transferase center. DON forms three hydrogen bonds with the A site and activates MAPKinases (mitogen-activated protein kinases). By contrast deepoxy-DON and 3-epi-DON only form two hydrogen bonds and do not activate MAPKinases. Our data demonstrate that bacterial de-epoxidation or epimerization of DON altered their interaction with the ribosome, leading to an absence of MAPKinase activation and a reduced toxicity.

Multifaceted impact of trichothecene metabolites on plant-microbe interactions and human health

Fungi present in rhizosphere produce trichothecene metabolites which are small in size and amphipathic in nature and some of them may cross cell membranes passively. Hypocreaceae family of rhizosphere fungi produce trichothecene molecules, however it is not a mandatory characteristic of all genera. Some of these molecules are also reported as growth adjuvant, while others are reported as deleterious for the plant growth. In this review, we are exploring the roles of these compounds during plant-microbe interactions. The three-way interaction among the plants, symbiotic microbial agents (fungi and bacteria), and the pathogenic microbes (bacteria, fungi) or multicellular pathogens like nematodes involving these compounds may only help us to understand better the complex processes happening in the microcosm of rhizosphere. These metabolites may further modulate the activity of different proteins involved in the cell signalling events of defence-related response in plants. That may induce the defence system against pathogens and growth promoting gene expression in plants, while in animal cells, these molecules have reported biochemical and pharmacological effects such as inducing oxidative stress, cell-cycle arrest and apoptosis, and may be involved in maintenance of membrane integrity. The biochemistry, chemical structures and specific functional group-mediated activity of these compounds have not been studied in details yet. Few of these molecules are also recently reported as novel anti-cancer agent against human chondrosarcoma cells.

Barcoded pyrosequencing-based metagenomic analysis of the faecal microbiome of three purebred pig lines after cohabitation

The microbial communities in the pig gut perform a variety of beneficial functions. Along with host genetics and diet, farm management practices are an important aspect of agricultural animal production that could influence gut microbial diversity. In this study, we used barcoded pyrosequencing of the V1-V3 regions of the 16S ribosomal RNA (rRNA) genes to characterise the faecal microbiome of three common commercial purebred pig lines (Duroc, Landrace and Yorkshire) before and after cohabitation. The diversity of faecal microbiota was characterised by employing phylogenetic, distance-based and multivariate-clustering approaches. Bacterial diversity tended to become more uniform after mixing of the litters. Age-related shifts were also observed at various taxonomic levels, with an increase in the proportion of the phylum Firmicutes and a decrease in Bacteroidetes over time, regardless of the purebred group. Cohabitation had a detectable effect on the microbial shift among purebred pigs. We identified the bacterial genus Parasutterella as having utility in discriminating pigs according to time. Similarly, Dialister and Bacteroides can be used to differentiate the purebred lines used. The microbial communities of the three purebred pigs became more similar after cohabitation, but retained a certain degree of breed specificity, with the microbiota of Landrace and Yorkshire remaining distinct from that of their distant relative, Duroc.

Exposure assessment for Italian population groups to deoxynivalenol deriving from pasta consumption

Four hundred and seventy-two pasta samples were collected from long retail distribution chain sales points located in North, Central and South Italy. Representative criteria in the sample collection were followed in terms of number of samples collected, market share, and types of pasta. Samples were analysed by an accredited HPLC-UV method of analysis. The mean contamination level (64.8 μg/kg) of deoxynivalenol (DON) was  in the 95th percentile (239 μg/kg) and 99th percentile (337 μg/kg), far below the legal limit (750 μg/kg) set by Regulation EC/1126/2007, accounting for about one tenth, one third and half the legal limit, respectively. Ninety-nine percent of samples fell below half the legal limit. On the basis of the obtained occurrence levels and considering the consumption rates reported by the Italian official database, no health concern was assessed for all consumer groups, being that exposure was far below the Tolerable Daily Intake (TDI) of 1000 ng/kg b.w/day. Nevertheless, despite this, particular attention should be devoted to the exposure to DON by high consumers, such as children aged 3-5 years, who could reach the TDI even with very low levels of DON contamination.

Microbial detoxification of mycotoxins

Mycotoxins are fungal natural products that are toxic to vertebrate animals including humans. Microbes have been identified that enzymatically convert aflatoxin, zearalenone, ochratoxin, patulin, fumonisin, deoxynivalenol, and T-2 toxin to less toxic products. Mycotoxin-degrading fungi and bacteria have been isolated from agricultural soil, infested plant material, and animal digestive tracts. Biotransformation reactions include acetylation, glucosylation, ring cleavage, hydrolysis, deamination, and decarboxylation. Microbial mycotoxin degrading enzymes can be used as feed additives or to decontaminate agricultural commodities. Some detoxification genes have been expressed in plants to limit the pre-harvest mycotoxin production and to protect crop plants from the phytotoxic effects of mycotoxins. Toxin-deficient mutants may be useful in assessing the role of mycotoxins in the ecology of the microorganisms.

Glucosylation and other biotransformations of T-2 toxin by yeasts of the trichomonascus clade

Trichothecenes are sesquiterpenoid toxins produced by Fusarium species. Since these mycotoxins are very stable, there is interest in microbial transformations that can remove toxins from contaminated grain or cereal products. Twenty-three yeast species assigned to the Trichomonascus clade (Saccharomycotina, Ascomycota), including four Trichomonascus species and 19 anamorphic species presently classified in Blastobotrys, were tested for their ability to convert the trichothecene T-2 toxin to less-toxic products. These species gave three types of biotransformations: acetylation to 3-acetyl T-2 toxin, glycosylation to T-2 toxin 3-glucoside, and removal of the isovaleryl group to form neosolaniol. Some species gave more than one type of biotransformation. Three Blastobotrys species converted T-2 toxin into T-2 toxin 3-glucoside, a compound that has been identified as a masked mycotoxin in Fusarium-infected grain. This is the first report of a microbial whole-cell method for producing trichothecene glycosides, and the potential large-scale availability of T-2 toxin 3-glucoside will facilitate toxicity testing and development of methods for detection of this compound in agricultural and other products.

Biological detoxification of the mycotoxin deoxynivalenol and its use in genetically engineered crops and feed additives

Deoxynivalenol (DON) is the major mycotoxin produced by Fusarium fungi in grains. Food and feed contaminated with DON pose a health risk to humans and livestock. The risk can be reduced by enzymatic detoxification. Complete mineralization of DON by microbial cultures has rarely been observed and the activities turned out to be unstable. The detoxification of DON by reactions targeting its epoxide group or hydroxyl on carbon 3 is more feasible. Microbial strains that de-epoxidize DON under anaerobic conditions have been isolated from animal digestive system. Feed additives claimed to de-epoxidize trichothecenes enzymatically are on the market but their efficacy has been disputed. A new detoxification pathway leading to 3-oxo-DON and 3-epi-DON was discovered in taxonomically unrelated soil bacteria from three continents; the enzymes involved remain to be identified. Arabidopsis, tobacco, wheat, barley, and rice were engineered to acetylate DON on carbon 3. In wheat expressing DON acetylation activity, the increase in resistance against Fusarium head blight was only moderate. The Tri101 gene from Fusarium sporotrichioides was used; Fusarium graminearum enzyme which possesses higher activity towards DON would presumably be a better choice. Glycosylation of trichothecenes occurs in plants, contributing to the resistance of wheat to F. graminearum infection. Marker-assisted selection based on the trichothecene-3-O-glucosyltransferase gene can be used in breeding for resistance. Fungal acetyltransferases and plant glucosyltransferases targeting carbon 3 of trichothecenes remain promising candidates for engineering resistance against Fusarium head blight. Bacterial enzymes catalyzing oxidation, epimerization, and less likely de-epoxidation of DON may extend this list in future.

Aerobic and anaerobic de-epoxydation of mycotoxin deoxynivalenol by bacteria originating from agricultural soil

One hundred and fifty soil samples collected from different crop fields in southern Ontario, Canada were screened to obtain microorganisms capable of transforming deoxynivalenol (DON) to de-epoxy DON (dE-DON). Microbial DON to dE-DON transformation (i.e. de-epoxydation) was monitored by using liquid chromatography-ultraviolet-mass spectrometry (LC-UV-MS). The effects of growth substrates, temperature, pH, incubation time and aerobic versus anaerobic conditions on the ability of the microbes to de-epoxydize DON were evaluated. A mixed microbial culture from one composite soil sample showed 100% DON to dE-DON biotransformation in mineral salts broth (MSB) after 144 h of incubation. Treatments of the culture with selective antibiotics followed an elevated temperature (50°C) for 1.5 h considerably reduced the microbial diversity. Partial 16S-rRNA gene sequence analysis of the bacteria in the enriched culture indicated the presence of at least six bacterial genera, namely Serratia, Clostridium, Citrobacter, Enterococcus, Stenotrophomonas and Streptomyces. The enriched culture completely de-epoxydized DON after 60 h of incubation. Bacterial de-epoxydation of DON occurred at pH 6.0-7.5, and a wide array of temperatures (12-40°C). The culture showed rapid de-epoxydation activity under aerobic conditions compared to anaerobic conditions. This is the first report on microbial DON to dE-DON transformation under aerobic conditions and moderate temperatures. The culture could be used to detoxify DON contaminated feed and might be a potential source for gene(s) for DON de-epoxydation.

T-2 toxin, a trichothecene mycotoxin: review of toxicity, metabolism, and analytical methods

This review focuses on the toxicity and metabolism of T-2 toxin and analytical methods used for the determination of T-2 toxin. Among the naturally occurring trichothecenes in food and feed, T-2 toxin is a cytotoxic fungal secondary metabolite produced by various species of Fusarium. Following ingestion, T-2 toxin causes acute and chronic toxicity and induces apoptosis in the immune system and fetal tissues. T-2 toxin is usually metabolized and eliminated after ingestion, yielding more than 20 metabolites. Consequently, there is a possibility of human consumption of animal products contaminated with T-2 toxin and its metabolites. Several methods for the determination of T-2 toxin based on traditional chromatographic, immunoassay, or mass spectroscopy techniques are described. This review will contribute to a better understanding of T-2 toxin exposure in animals and humans and T-2 toxin metabolism, toxicity, and analytical methods, which may be useful in risk assessment and control of T-2 toxin exposure.

Decontamination and detoxification strategies for the Fusarium mycotoxin deoxynivalenol in animal feed and the effectiveness of microbial biodegradation

Trichothecenes are a group of mycotoxins mainly produced by fungi of the Fusarium genus. Deoxynivalenol (DON) is one of the most abundant and important trichothecenes in food and feed, and is a significant contaminants due to its frequent occurrence in toxicologically relevant concentrations worldwide. Since toxin production depends strongly on environmental conditions, such as temperature and humidity, Fusarium toxin contamination can not be avoided completely. Therefore, exposure to this toxin is a permanent health risk for both humans and farm animals. As cereal crops are commonly contaminated with DON and animal diets consist mainly of cereals, it can be assumed that animals are frequently exposed to DON-contaminated feeds. Many strategies can be undertaken to reduce the toxic effect of DON. In addition to the general necessity for minimizing all risk factors that might influence the contamination of cereals with DON, such as the so-called field toxins before harvest, several post-harvest strategies can be applied to counteract possible deleterious effects of this mycotoxin in farm animals. Another approach for decontamination in feedstuffs is the use of adsorbent materials. Adsorbent materials may bind mycotoxins in the gastrointestinal tract and reduce absorption and systemic toxicity. It has been shown that some adsorbents are suitable to alleviate the toxic effects of specific mycotoxins, but its efficacy against trichothecenes is practically zero. Therefore, alternative strategies to reduce animal and human health risk are needed. The use of microbial additives is a method which uses microorganisms having the capability to detoxify mycotoxins by metabolism or degradation prior to their resorption in the gastrointestinal tract. DON has been reported to be completely transformed to de-epoxy-DON by ruminal and intestinal microflora. Eubacterium BBSH 797 was capable of DON degradation and counteracted the toxic effects of DON in animals. This review focuses on the efficacy of microbial feed additives in ameliorating the toxic effects of DON. According to the results of experiments to date, it appears that microorganisms are the main living organisms suitable for this mycotoxin biodegradation. However, the use of this approach depends on its effectiveness from both a practical and economic perspective.

Structural elucidation of T-2 toxin thermal degradation products and investigations toward their occurrence in retail food

The stability of T-2 toxin under the conditions of baking or cooking was investigated using heating experiments with the model substances alpha-d-glucose, alpha-d-methyl-glucopyranosid, N-alpha-acetyl-l-lysine methyl ester, and N-alpha-acetyl-cysteine methyl ester. The reaction residue was screened for degradation products using gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography with evaporative light-scattering detection (HPLC-ELSD). Although T-2 toxin was degraded under all conditions, only heating of T-2 toxin with alpha-d-glucose produced a mixture of three degradation products, which were isolated and identified by MS and nuclear magnetic resonance (NMR) experiments. The reaction mechanism for the formation of the T-2 degradation products was elucidated by quantum chemical calculations. The relevance of these degradation products was investigated by baking experiments as well as the analysis of retail food samples. In cell-culture studies using immortalized human kidney epithelial (IHKE) cells, the T-2 degradation products were less cytotoxic (formazan dye cytotoxicity assay) compared to T-2 toxin.

Microbial transformation of trichothecene mycotoxins

Trichothecene mycotoxins produced by the Fusarium genus are highly toxic to humans and animals. They are commonly found in cereals worldwide, which is not only a concern for food safety, but also highly relevant to the livestock industry. Controlling trichothecenes in food and feed has been a challenge since the toxins are markedly stable under different environmental conditions. Thermal processing is usually ineffective, and chemical treatments generally are expensive and often result in side effects. Previous studies on innovative biological approaches, such as the use of microorganisms and enzymes, to convert the toxins into non or less toxic compounds have shown promise. This review will briefly describe the chemical structures and toxicity of trichothecenes, and examine the microorganisms, including both bacteria and fungi, from various natural sources that are able to detoxify the toxins as either mixed cultures or a pure culture of single isolates. Finally, challenges and innovative strategies in the development of technology to detoxify trichothecenes by microorganisms are described.

Degradation of trichothecene mycotoxins by chicken intestinal microbes

The degradation of 12 trichothecene mycotoxins by chicken intestinal microbes was monitored by liquid chromatography-ultraviolet-mass spectrometry under positive ion atmospheric pressure chemical ionization. Two pathways were observed: deacylation and deepoxidation. Essentially complete conversions to the deepoxy metabolites were observed for the non-acylated trichothecenes 4-deoxynivalenol, nivalenol, and verrucarol. However, deacetylation was the predominant pathway for the monoacetyl trichothecenes 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol (15ADON), and fusarenon X. Small amounts of the deepoxy metabolites were observed from 15ADON and large amounts from 15-monoacetoxyscirpenol where steric hindrance protected the C-15 acetyl groups from enzymatic attack. Diacetylated trichothecenes diacetoxyscirpenol and neosolaniol exhibited only deacetylation. The larger isovaleryl functionality was resistant to removal and deepoxidation was the prevalent reaction in HT-2 toxin and T-2 triol, whereas T2 toxin showed only deacetylation.

Thermal degradation of the Fusarium mycotoxin deoxynivalenol

Deoxynivalenol (DON) is a toxic secondary metabolite produced by molds of the Fusarium genus, which are able to infect cereal crops in the field. Concerning its rate of occurrence and mean concentration, DON is one of the most important mycotoxins in cereal commodities. Its toxic effects range from causing diarrhea, vomiting, and gastro-intestinal inflammation to noncompetitive inhibition of the biosynthesis of proteins in eukaryotic cells. To study the stability of DON under food-processing conditions such as cooking or baking, we performed model heating experiments and screened the residue for degradation products. Heating of DON and 3-acetyldeoxynivalenol (3-AcDON), especially under alkaline conditions, gave a mixture of compounds, which were isolated and structurally elucidated by NMR and MS experiments. Three of these compounds were already known (norDON A, norDON B, and norDON C), while four were new and named 9-hydroxymethyl DON lactone, norDON D, norDON E, and norDON F. The significance of the DON degradation products was checked by analyzing commercially available food samples. norDON A, B, and C were detected in 29-66% of the samples in mean concentrations ranging from 3 to 15 microg/kg. Furthermore, cell culture experiments using IHKE cells showed that the compounds that were detected in food samples are less cytotoxic in the formazan dye cytotoxicity assay compared to DON. Whereas DON revealed a median effective concentration (EC50) at 1.1 micromol/L, all other compounds did not show any significant effect up to 100 micromol/L. These findings indicate that the degradation of DON under thermal treatment might reduce the toxicity of DON contaminated food.

Structural elucidation and analysis of thermal degradation products of theFusarium mycotoxin nivalenol

The major class of mycotoxins produced by Fusarium moulds are trichothecenes, a large group of sesquiterpenes sharing the same basic chemical structure, a 12,13-epoxytrichothec-9-ene ring system. Their toxic effects range from causing diarrhoea, vomiting and gastro-intestinal inflammation to noncompetitive inhibition of the biosynthesis of proteins in eukaryotic cells. Trichothecenes in general are relatively stable compounds, their degradation is observed only at high temperatures and prolonged heating time. In order to investigate the stability of the trichothecene nivalenol (NIV) under food processing conditions such as cooking or baking, we performed model heating experiments and screened the residue for degradation products using gas chromatography-mass spectrometry (GC-MS). Heating of nivalenol, especially under mild alkaline conditions, gave a mixture of four compounds (norNIV A, norNIV B, norNIV C, and NIV lactone), which where isolated and identified by nuclear magnetic resonance (NMR) and MS experiments. Although their formation was also demonstrated in heating experiments with spiked flour samples, only norNIV B was detectable in a screening of several commercially available samples, possibly due to the very low contamination with nivalenol. Furthermore, cell culture experiments using immortalized human kidney epithelial (IHKE) cells showed that the four compounds are less cytotoxic (formazan dye cytotoxicity assay) compared to nivalenol. Whereas nivalenol revealed an EC50 at 0.9 micromol, all other compounds did not show any significant effect up to 100 micromol.

Comparative cytotoxicity of deoxynivalenol, nivalenol, their acetylated derivatives and de-epoxy metabolites

The cytotoxicity of the de-epoxy metabolites of trichothecenes nivalenol (NIV) and deoxynivalenol (DON) was determined and compared with the cytotoxicity of the respective toxin with an intact epoxy group and their acetylated derivatives. The cytotoxic effects was determined by using the 5-bromo-2'-deoxyuridine (BrdU) incorporation assay assessing DNA-synthesis. The toxicity of NIV and DON expressed as the concentration inhibiting 50% of the DNA synthesis (IC(50)), was occurring at similar micromolar concentrations (1.19+/-0.06 and 1.50+/-0.34 microM). The toxicity of fusarenon X (4-acetyl NIV) in the assay was similar to the toxicity of NIV, and the toxicity of 15-AcDON was equal to the toxicity of DON. 3-AcDON was less toxic than DON and 15-AcDON. The IC(50) value for de-epoxy DON was 54 times higher in the assay than the IC(50) for DON, while the IC(50) of de-epoxy NIV was 55 times higher than the IC(50) for NIV. The results verify previous findings that the de-epoxidation is a detoxification reaction.

Lack of de-epoxidation of type B trichothecenes in incubates with human faeces

The ability of human gastrointestinal organisms to transform the trichothecenes 3-acetyldeoxynivalenol and nivalenol was investigated. Samples of human faeces were incubated under anaerobic conditions for 48 h with the toxins. They were then extracted and analysed for trichothecenes and metabolites. 3-acetyldeoxynivalenol was metabolized to deoxynivalenol during the incubation period. In contrast to what has been reported for other species such as rats, mice and pigs, no de-epoxidated metabolites were detected in the faecal incubates. The toxicological significance of the difference in the intestinal ability to transform trichothecenes between species is unknown.

Structural characterization of metabolites after the microbial degradation of type A trichothecenes by the bacterial strain BBSH 797

Contamination of feed with trichothecenes, a group of Fusarium mycotoxins, leads to losses in performance due to their immunosupressive effects and the negative effect on the gastrointestinal system in animal production. A possible way of detoxification is microbial degradation, which was the focus of this study. A bacterial strain--BBSH 797--which can degrade some mycotoxins of the trichothecene group, has already been isolated. It transforms deoxynivalenol (DON) into its metabolite DOM-1, the non-toxic deepoxide of DON. Analogous to the microbial degradation of DON, the transformation of six different type A trichothecenes was observed. The metabolites appearing were characterized by GC-MS after derivatization with TRI-SIL TBT. Two metabolites were additionally, identified by liquid chromatography-mass spectrometry with particle beam interface (LC-PB-MS) with electron impact (EI)-ionization mode. The major finding was that scirpentriol was completely transformed into its non-toxic metabolite deepoxy scirpentriol, while the mycotoxin T-2 triol underwent a more complicated metabolism. According to the study, T-2-triol was degraded into its non-toxic deepoxy form and into T-2 tetraol, which was then further metabolized to deepoxy T-2 tetraol. GC-MS after derivatization with TRI-SIL TBT was suitable for the structural characterization of trichothecenes and their degradation products. Besides the mass spectra of already known degradation products, spectra of new metabolites could be recorded by LC-PB-MS.

Influence of level of deoxynivalenol in the diet of dairy cows on feed intake, milk production, and its composition

Eighteen primiparous Holstein cows were used in a 10-wk lactation study, preceded by a 2-wk covariate period, to determine the effect of concentration of deoxynivalenol in the diet on cow performance and transfer of deoxynivalenol and its metabolite, deepoxydeoxynivalenol, to milk. Diets were formulated to contain deoxynivalenol at 0, 6, and 12 mg/kg of concentrate DM, and daily intake of deoxynivalenol was .59, 42, and 104 mg, respectively. Increasing deoxynivalenol in the diet did not affect intake of concentrate or forage. Total milk output was not affected; however, milk fat responded quadratically; cows given deoxynivalenol at 6 mg/kg of concentrate DM had the lowest milk fat content and fat output. Overall energetic efficiency was not influenced because reduced energy output in milk was compensated by increased BW gains. No transfer of deoxynivalenol or deepoxydeoxynivalenol to milk was observed; concentrations were below detectable limits (1 microgram/ml) using HPLC-mass spectroscopy. We concluded that diets containing deoxynivalenol up to 6 mg/kg of dietary DM did not reduce feed intake of cows in this study and that deoxynivalenol or deepoxydeoxynivalenol was not transferred to milk. Further studies are required to confirm the apparent lack of effect of deoxynivalenol on milk production.

Structure-activity relationships among mycotoxins

Relationships between structural features and biological effects of mycotoxins are reviewed. Structure-activity relationships are characterized at the molecular, subcellular, cellular, or supracellular level. Major chemical and physicochemical factors responsible for bioactivity of mycotoxins are stressed. A variety of chemical families of mycotoxins are then discussed from the point of view of structure-activity relationships. The structurally related families comprise small lactones, macrocyclic lactones, isocoumarin derivatives, aflatoxins and related compounds trichothecenes, anthraquinones, indole-derived tremorgens and selected amino acid-derived mycotoxins such as sporidesmins and cyclosporines. Biological effects of mycotoxins include acute and chronic toxicity, antimicrobial activity, mutagenicity and genotoxicity, carcinogenicity and biochemical modes of action.

The role of intestinal microflora in the metabolism of trichothecene mycotoxins

The role of faecal and intestinal microflora on the metabolism of trichothecene mycotoxins was examined in this study. Suspensions of microflora obtained from the faeces of horses, cattle, dogs, rats, swine and chickens were incubated anaerobically with the trichothecene mycotoxin, diacetoxyscirpenol (DAS). Micro-organisms from rats, cattle and swine completely biotransformed DAS, primarily to the deacylated deepoxidation products, deepoxy monoacetoxyscirpenol (DE MAS) and deepoxy scirpentriol (DE SCP). By contrast, faecal microflora from chickens, horses and dogs failed to reduce the epoxide group in DAS and yielded only the deacylation products, monoacetoxyscirpenol (MAS) and scirpentriol (SCP), in addition to unmetabolized parent compound. Intestinal microflora obtained from rats completely biotransformed DAS to DE MAS, DE SCP and SCP; and T-2 toxin to the deepoxy products, deepoxy HT-2 (DE HT-2) and deepoxy T-2 triol (DE TRIOL). Rat intestinal microflora also biotransformed the polar trichothecenes, T-2 tetraol and scirpentriol, to their corresponding deepoxy analogues. Deepoxy T-2 toxin (DE T-2) was synthesized from T-2 toxin and demonstrated to be 400 times less toxic than T-2 toxin in the rat skin irritation bioassay and non-toxic to mice given 60 mg/kg ip, demonstrating that epoxide reduction is a significant single step detoxification reaction for trichothecene mycotoxins.