Role of zearalenone lactonase in protection of Gliocladium roseum from fungitoxic effects of the mycotoxin zearalenone

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.

qPCR quantification of Sphaerodes mycoparasitica biotrophic mycoparasite interaction with Fusarium graminearum: in vitro and in planta assays

Sphaerodes mycoparasitica, a biotrophic mycoparasite of Fusarium species, improved wheat seed germination and seedling growth in vitro compared to Trichoderma harzianum, a necrotrophic mycoparasite. However, under phytotron conditions, both S. mycoparasitica and T. harzianum had positive impact on wheat seedlings growth in the presence of F. graminearum. Once exposed to the mycoparasites, the DNA quantity of F. graminearum in wheat root decreased. Observed shifts in DNA quantity using qPCR, a set of newly designed Sphaerodes-specific SmyITS primers, as well as Trichoderma-TGP4 and Fusarium-Fg16 N primers, demonstrated the mycoparasite's biocontrol effectiveness in planta. In the presence of F. graminearum, the concentration of S. mycoparasitica DNA remained stable in the root, whereas the amount of T. harzianum DNA decreased. The toxicity assays indicated that S. mycoparasitica's mycelia withstand higher concentrations of deoxynivalenol, 3-acetyldeoxynivalenol, and zearalenone mycotoxins than T. harzianum mycelia. This study compares the ability of two fungi to improve the wheat growth, decrease the root colonization of Fusarium, and withstand mycotoxins.

Adsorption and degradation of zearalenone by bacillus strains

Two Bacillus strains; Bacillus subtilis 168 and Bacillus natto CICC 24640 separately adsorbed and degraded zearalenone in liquid media, in vitro. Viable, autoclaved (121°C, 20 min) and acid-treated cells of both strains separately bound more than 55% of zearalenone (ZEN, 20 μg/L) after 30 min and 1-h incubation at 37°C under aerobic conditions, and the amount of ZEN adsorbed was dependent on initial cell volume. In addition, ZEN was degraded by the culture extract of both strains. Degradation by B. subtilis 168 and B. natto CICC 24640 culture extract after 24-h aerobic incubation at 30°C was 81% and 100%, respectively. B. natto CICC 24640 culture extract comprehensively degraded ZEN and, for both strains, no oestrogenic ZEN analogues were present. ZEN degradation was accompanied by carbondioxide emission indicating a decarboxylation reaction. ZEN degradation by the salient B. natto CICC 24640 culture extract varied with initial ZEN concentration, incubation time, temperature and pH. Degradation was enhanced by Mn(2+), Zn(2+), Ca(2+) and Mg(2+) but impeded by Hg(2+), Cu(2+), Pb(2+), ethylenediaminetetraacetic acid and 1,10-phenanthroline. The degradation reaction is associated with a metalloproteinase of molar mass in the range 31-43 kDa. Overall, the two generally recognised as safe Bacillus strains can, potentially, be utilised for detoxification of zearalenone in food.

Sphaerodes mycoparasitica biotrophic mycoparasite of 3-acetyldeoxynivalenol- and 15-acetyldeoxynivalenol-producing toxigenic Fusarium graminearum chemotypes

Fusarium spp. are economically important crop pathogens and causal agents of Fusarium head blight (FHB) of cereals worldwide. Of the FHB pathogens, Fusarium graminearum 3-acetyldeoxynivalenol (3-ADON) and 15-acetyldeoxynivalenol (15-ADON) are the most aggressive mycotoxigenic chemotypes, threatening food and feed quality as well as animal and human health. The objective of the study was to evaluate host specificity and fungal-fungal interactions of Sphaerodes mycoparasitica- a recently described mycoparasite - with F. graminearum 3- and 15-ADON strains by employing in vitro, microscopic and PCR techniques. Results obtained in this study show that the germination of mycoparasite ascospore in the presence of F. graminearum 3- and 15-ADON filtrates was greatly improved compared with Fusarium proliferatum and Fusarium sporotrichioides filtrates, suggesting a compatible interaction. Using quantitative real-time PCR with Fusarium-specific (Fg16N) and trichothecene Tri5 (Tox5-1/2)-specific primer sets, S. mycoparasitica was found to reduce the amount of F. graminearum 3-ADON and 15-ADON DNAs under separate coinoculation assays. Sphaerodes mycoparasitica was not only able to germinate in the presence of F. graminearum filtrates, but also established biotrophic mycoparasitic relations with two F. graminearum chemotypes and suppressed Fusarium growth.

Transformation of zearalenone to zearalenone-sulfate by Aspergillus spp

The primary goal of this research was to assess the biotransformation of zearalenone (ZEA), an oestrogenic mycotoxin, into ZEA-sulfate by some Aspergillus section Nigri isolates. A. niger isolates were shown to be able to convert ZEA after 72 h of incubation at different ZEA concentrations (5 to 150 µg/ml). The product formula corresponding to ZEA-sulfate was determined by accurate mass measurement. This conjugate was shown to be less oestrogenic than ZEA using a MCF-7 proliferation assay. This study demonstrated that A. niger has the ability to transform ZEA over a broad range of ZEA concentrations (5 to 150 µg/ml) and that sulfonation could lead to a less toxic compound. These results are significant as little is known about the ability of fungi, and especially A. niger, to detoxify ZEA by sulfonation. This study could lead to a way of detoxifying feed naturally contaminated with mycotoxins.

Secondary metabolites from anti-insect extracts of endophytic fungi isolated from Picea rubens

The extracts of a selection of 150 foliar fungal endophytes isolated from Picea rubens (red spruce) needles were screened by LC-MS and assayed for toxicity. Three of these strains that were toxic to the forest pest Choristoneura fumiferana (eastern spruce budworm) in dietary bioassays were selected for further study. Their culture extracts were analyzed by LC-NMR spectroscopy, and the major metabolites were isolated by LC-MS-SPE or PTLC/column chromatography and characterized. The structures were elucidated by spectroscopic analyses including 2D NMR, HRMS and by comparison to literature data. Compounds 1 and 5-7 are hitherto unknown whereas compounds 2 and 3 are natural products described for the first time. Compound 4 is reported for the first time as a fungal metabolite and 8-9 were identified as known fungal metabolites in genera.

Preventive and therapeutic methods against the toxic effects of mycotoxins - a review

Ingredients used in animal feeds and their contamination with undesirable substances, such as mycotoxins, are fundamentally important both in terms of the quality of animal products and the potential human health impacts associated with the animal-based food production chain. Feed ingredients contaminated with mycotoxins may have a wide range of toxicological effects on animals. Therefore, mycotoxin contamination of feed ingredients constituting complete feed products represents an important potential hazard in farm animal production. This review summarises the potential effects of some preventive methods used during the storage of cereal grains as well as of nutritive (e.g. antioxidants, amino acids, fats) or non-nutritive compounds (e.g. pharmacological substances, carbon- or silica-based polymers) and detoxifying enzymes recommended for use against the toxic effects of different mycotoxins.

Solid substrate bioassay to evaluate the effect of Trichoderma and Clonostachys on the production of zearalenone by Fusarium species

Fusarium head blight and maize ear rot are destructive diseases in various cereal production regions, leading to significant yield losses and to the contamination of cereal grain with Fusarium mycotoxins. The mycotoxin zearalenone belongs to the three most important mycotoxins produced by Fusarium species worldwide; moreover, its hormonal oestrogenic activity is higher than its toxicity. The compound also exhibits fungitoxic activity. Toxigenic Fusarium species sporulate on cereal crop residues and produce inoculum to infect the next crop. Reduction of mycotoxin production and pathogen sporulation may be influenced by saprophytic fungal antagonists. Selected Trichoderma and Clonostachys isolates in dual culture bioassays on rice reduced zearalenone, α-zearalenol and zearalenone sulphate production by two isolates of Fusarium graminearum Schwabe and two isolates of F. culmorum (W.G. Smith) Saccardo belonging to three different chemotypes, by over 97%. Two Trichoderma isolates reduced the amount of zearalenone produced by the same four Fusarium isolates by 5-83% in solid substrate bioassays, whereas several Clonostachys isolates reduced the amount of zearalenone by over 96%. Examination of the dynamics of zearalenone reduction showed that the reduction occurred at the fastest rate during the first four days of incubation. Selected non-toxigenic Trichoderma and Clonostachys isolates are candidates for biocontrol agents against toxigenic Fusarium pathogens of cereals and may be useful for decomposition of zearalenone in contaminated cereal grain and cereal products.

Localization of zearalenone detoxification gene(s) in pZEA-1 plasmid of Pseudomonas putida ZEA-1 and expressed in Escherichia coli

The gene(s) encoding enzyme(s) involved in the initial reaction during degradation of zearalenone (ZEA) was characterized from the zearalenone utilizer Pseudomonas putida strain ZEA-1, where ZEA was transformed into product with less or no toxicity. A 5.5 kilobase-pair (kbp) Pst1-Kpn1 fragment containing gene(s) encoding for zearalenone degradation was cloned. The cloned gene(s) was actively expressed in Escherichia coli. ZEA degradation by recombinant E. coli was relatively rapid and effective, leaving no detectable ZEA after 24h. In further experiments, cell-free extract of E. coli has been used in the same way, both to confirm these observations and the enzymatic nature of the degradation activity.