Production of fumonisin analogs by Fusarium species

Effect of fumonisin-containing diet on the myenteric plexus of the jejunum in rats

Fumonisins are mycotoxins that naturally occur as contaminants in grains that are destined for animal and human consumption. These mycotoxins cause hepatotoxic, nephrotoxic, carcinogenic, teratogenic, immunotoxic, and neurotoxic effects in different intensities based on dose, time of exposure, and animal species. In the present study, male Wistar rats were fed between postnatal days 21 and 63 with diets that contained fumonisins B1+B2 at concentrations of 1 and 3mg/kg. The objective of the present study was to evaluate the effects of fumonisins on food intake, growth, weight gain, serum activity of the alanine aminotransferase and aspartate aminotransferase enzymes, and quantitative and morphometric parameters of myenteric neurons in the jejunum that are immunoreactive to HuC/D protein and neuronal nitric oxide synthase enzyme (nNOS). Diets that contained fumonisins did not significantly alter food intake or body and blood parameters. We did not observe significant differences in the neuronal density and proportion of nitrergic neurons but found a significant reduction of cell body areas in both neuronal populations. This study is the first to report the effects of fumonisins in the enteric nervous system. The possible mechanisms by which fumonisins impair neuronal development and the use of the enteric nervous system as a tool for the study of the neurotoxic effects of fumonisins are discussed. In conclusion, fumonisin-containing food negatively affected the growth of myenteric neurons.

Development of a single-chain variable fragment antibody-based enzyme-linked immunosorbent assay for determination of fumonisin B₁ in corn samples

BACKGROUND

Fumonisin B1 (FB1 ) is a cancer-promoting mycotoxin produced by Fusarium species and one of the major food-borne toxins in corn and corn products. The objective of this study was to produce a single-chain variable fragment (scFv) antibody for determination of FB1 in corn samples.

RESULTS

Anti-FB1 monoclonal antibodies were obtained via the hybridoma technique. Specific heavy- and light-chain variable fragments were amplified with degenerate primers and constructed into scFv antibody fragments by splice overlap extension polymerase chain reaction with linker sequences. The resulting scFv DNA fragments were cloned into the phagemid pHEN1for selection and identification of functional scFv fragment by phage display. Prokaryotic expression vector pET22b-scFv was constructed to prepare anti-FB1 scFv antibody for establishment of indirect competitive ELISA. The detection capability (CCβ) of the scFv-based ELISA was 15.00 µg kg(-1), and the limit of detection was 8.32 µg kg(-1). The recoveries and coefficients of variation were 86.74-107.34% and 9.72-14.03%, respectively. In addition, the determined results of 30 naturally contaminated corn samples by the scFv-based ELISA are in agreement with the findings of high-performance liquid chromatography (R(2) = 0.97).

CONCLUSION

This scFv-based ELISA could be used as an efficient screening method for routine monitoring the residues FB1 in corn samples.

Antifungal activity and inhibition of fumonisin production by Rosmarinus officinalis L. essential oil in Fusarium verticillioides (Sacc.) Nirenberg

The chemical composition of Rosmarinus officinalis L. essential oil (REO) was analysed by gas chromatography-mass spectrometry and nuclear magnetic resonance spectroscopy. The main compounds of the REO were 1.8 cineole (52.2%), camphor (15.2%) and α-pinene (12.4%). The mycelial growth of Fusarium verticillioides (Sacc.) Nirenberg was reduced significantly by 150 μg/mL of REO. Significant microscopic morphological changes were visualised, such as the rupture of the cell wall and the leakage of cytoplasm at 300 μg/mL of REO. At lower concentrations of REO, the effects on the production of ergosterol and the biomass of mycelium varied, as did the effects on the production of fumonisins, but at ≥300 μg/mL of REO, these processes were significantly inhibited, showing the effectiveness of the REO as an antifungal agent. The results suggested that the REO acts against F. verticillioides by disrupting the cell wall and causing the loss of cellular components, subsequently inhibiting the production of fumonisins and ergosterol.

The HAP complex in Fusarium verticillioides is a key regulator of growth, morphogenesis, secondary metabolism, and pathogenesis

Among eukaryotic organisms, the HAP complex is a conserved, multimeric transcription factor that regulates gene expression by binding to the consensus sequence CCAAT. In filamentous fungi, the HAP complex has been linked to primary and secondary metabolism, but its role in pathogenesis has not been investigated extensively. The overarching goal of this study was to elucidate the role of the HAP complex in Fusariumverticillioides, a ubiquitous and damaging pathogen of maize. To this end, orthologs of core HAP complex genes (FvHAP2, FvHAP3, and FvHAP5) were identified and deleted in F. verticillioides via a reverse genetics approach. Deletion of FvHAP2, FvHAP3, or FvHAP5 resulted in an indistinguishable phenotype among the deletion strains, including reduced radial growth and conidiation, altered colony morphology, and derepression of pigmentation. Additionally, disruption of the HAP complex impaired infection and colonization of maize stalks. Deletion strains were hypersensitive to osmotic and oxidative stress, which suggests the HAP complex of F. verticillioides may mediate responses to environmental stress during pathogenesis. This study directly implicates the HAP complex in primary and secondary metabolism in F. verticillioides and provides one of the first links between the HAP complex and virulence in a plant pathogenic fungus.

Natural occurrence of mycotoxins in medicinal plants: a review

Medicinal plants are widely used as home remedies and raw materials for the pharmaceutical industries. Herbal remedies are used in the prevention, treatment and cure of disorders and diseases since ancient times. However, use of medicinal herbs may not meet the requirements of quality, safety and efficacy. During harvesting, handling, storage and distribution, medicinal plants are subjected to contamination by various fungi, which may be responsible for spoilage and production of mycotoxins. The increasing consumption of medicinal plants has made their use a public health problem due to the lack of effective surveillance of the use, efficacy, toxicity and quality of these natural products. The increase in use of medicinal plants may lead to an increase in the intake of mycotoxins therefore contamination of medicinal plants with mycotoxins can contribute to adverse human health problems and therefore represents a special hazard. Numerous natural occurrences of mycotoxins in medicinal plants and traditional herbal medicines have been reported from various countries including Spain, China, Germany, India, Turkey and from Middle East as well. This review discusses the important mycotoxins and their natural occurrences in medicinal plants and their products.

Tricarballylic ester formation during biosynthesis of fumonisin mycotoxins in Fusarium verticillioides

Fumonisins are agriculturally important mycotoxins produced by the maize pathogen Fusarium verticillioides. The chemical structure of fumonisins contains two tricarballylic esters, which are rare structural moieties and important for toxicity. The mechanism for the tricarballylic ester formation is not well understood. FUM7 gene of F. verticillioides was predicted to encode a dehydrogenase/reductase, and when it was deleted, the mutant produced tetradehydro fumonisins (DH₄–FB). MS and NMR analysis of DH₄–FB₁ indicated that the esters consist of aconitate with a 3′-alkene function, rather than a 2′-alkene function. Interestingly, the purified DH₄–FB₁ eventually yielded three chromatographic peaks in HPLC. However, MS revealed that the metabolites of the three peaks all had the same mass as the initial single-peak DH₄–FB₁. The results suggest that DH₄–FB₁ can undergo spontaneous isomerization, probably including both cis–trans stereoisomerization and 3′- to 2′-ene regioisomerization. In addition, when FUM7 was expressed in Escherichia coli and the resulting enzyme, Fum7p, was incubated with DH₄–FB, no fumonisin with typical tricarballylic esters was formed. Instead, new fumonisin analogs that probably contained isocitrate and/or oxalosuccinate esters were formed, which reveals new insight into fumonisin biosynthesis. Together, the data provided both genetic and biochemical evidence for the mechanism of tricarballylic ester formation in fumonisin biosynthesis.

UBL1 of Fusarium verticillioides links the N-end rule pathway to extracellular sensing and plant pathogenesis

Fusarium verticillioides produces fumonisin mycotoxins during colonization of maize. Currently, molecular mechanisms underlying responsiveness of F.verticillioides to extracellular cues during pathogenesis are poorly understood. In this study, insertional mutants were created and screened to identify genes involved in responses to extracellular starch. In one mutant, the restriction enzyme-mediated integration cassette disrupted a gene (UBL1) encoding a UBR-Box/RING domain E3 ubiquitin ligase involved in the N-end rule pathway. Disruption of UBL1 in F.verticillioides (Δubl1) influenced conidiation, hyphal morphology, pigmentation and amylolysis. Disruption of UBL1 also impaired kernel colonization, but the ratio of fumonisin B1 per unit growth was not significantly reduced. The inability of a Δubl1 mutant to recognize an N-end rule degron confirmed involvement of UBL1 in the N-end rule pathway. Additionally, Ubl1 physically interacted with two G protein α subunits of F.verticillioides, thus implicating UBL1 in G protein-mediated sensing of the external environment. Furthermore, deletion of the UBL1 orthologue in F.graminearum reduced virulence on wheat and maize, thus indicating that UBL1 has a broader role in virulence among Fusarium species. This study provides the first linkage between the N-end rule pathway and fungal pathogenesis, and illustrates a new mechanism through which fungi respond to the external environment.

Effect of Zingiber officinale essential oil on Fusarium verticillioides and fumonisin production

The antifungal activity of ginger essential oil (GEO; Zingiber officinale Roscoe) was evaluated against Fusarium verticillioides (Saccardo) Nirenberg. The minimum inhibitory concentration (MIC) of GEO was determined by micro-broth dilution. The effects of GEO on fumonisin and ergosterol production were evaluated at concentrations of 500-5000 μg/mL in liquid medium with a 5mm diameter mycelial disc of F. verticillioides. Gas chromatography-mass spectrometry showed that the predominant components of GEO were α-zingiberene (23.9%) and citral (21.7%). GEO exhibited inhibitory activity, with a MIC of 2500 μg/mL, and 4000 and 5000 μg/mL reduced ergosterol biosynthesis by 57% and 100%, respectively. The inhibitory effect on fumonisin B1 (FB1) and fumonisin B2 (FB2) production was significant at GEO concentrations of 4000 and 2000 μg/mL, respectively. Thus, the inhibition of fungal biomass and fumonisin production was dependent on the concentration of GEO. These results suggest that GEO was able to control the growth of F. verticillioides and subsequent fumonisin production.

Fumonisin measurement from maize samples by high-performance liquid chromatography coupled with corona charged aerosol detector

Fumonisins are a class of mycotoxins produced mainly by Fusarium species, which is primary fungal contaminant of the maize and maize-derived products around the world. The B-series fumonisins (FB1, FB2 and FB3) are the most abundant and toxic constituent; thus, their levels are regulated generally worldwide. In this study, we developed a reliable method for the measurement of fumonisin FB1, FB2 and FB3 mycotoxins from maize samples without the time-consuming derivatization step using a high-performance liquid chromatograph coupled with corona charged aerosol detector. The detection and quantitation limit of the whole method were 0.02 and 0.04 mg/kg for each fumonisins, respectively. The detection linearity was tested in the calibration range of 2 orders of magnitude and the recoveries from the spiked samples were determined. The developed method proved to be sufficient to measure the maximum residue levels of fumonisins, which are specified in European Union and United States in maize and maize-based products.

The N-terminus region of the putative C2H2 transcription factor Ada1 harbors a species-specific activation motif that regulates asexual reproduction in Fusarium verticillioides

Fusarium verticillioides is an important plant pathogenic fungus causing maize ear and stalk rots. In addition, the fungus is directly associated with fumonisin contamination of food and feeds. Here, we report the functional characterization of Ada1, a putative Cys2-His2 zinc finger transcription factor with a high level of similarity to Aspergillus nidulans FlbC, which is required for the activation of the key regulator of conidiation brlA. ADA1 is predicted to encode a protein with two DNA binding motifs at the C terminus and a putative activator domain at the N terminus region. Deletion of the flbC gene in A. nidulans results in "fluffy" cotton-like colonies, with a defect in transition from vegetative growth to asexual development. In this study we show that Ada1 plays a key role in asexual development in F. verticillioides. Conidia production was significantly reduced in the knockout mutant (Δada1), in which aberrant conidia and conidiophores were also observed. We identified genes that are predicted to be downstream of ADA1, based on A. nidulans conidiation signaling pathway. Among them, the deletion of stuA homologue, FvSTUA, resulted in near absence of conidia production. To further investigate the functional conservation of this transcription factor, we complemented the Δada1 strain with A. nidulans flbC, F. verticillioides ADA1, and chimeric constructs. A. nidulans flbC failed to restore conidia production similar to the wild-type level. However, the Ada1N-terminal domain, which contains a putative activator, fused to A. nidulans FlbC C-terminal motif successfully complemented the Δada1 mutant. Taken together, Ada1 is an important transcriptional regulator of asexual development in F. verticillioides and that the N-terminus domain is critical for proper function of this transcription factor.

Birth, death and horizontal transfer of the fumonisin biosynthetic gene cluster during the evolutionary diversification of Fusarium

Fumonisins are a family of carcinogenic secondary metabolites produced by members of the Fusarium fujikuroi species complex (FFSC) and rare strains of Fusarium oxysporum. In Fusarium, fumonisin biosynthetic genes (FUM) are clustered, and the cluster is uniform in gene organization. Here, sequence analyses indicated that the cluster exists in five different genomic contexts, defining five cluster types. In FUM gene genealogies, evolutionary relationships between fusaria with different cluster types were largely incongruent with species relationships inferred from primary-metabolism (PM) gene genealogies, and FUM cluster types are not trans-specific. In addition, synonymous site divergence analyses indicated that three FUM cluster types predate diversification of FFSC. The data are not consistent with balancing selection or interspecific hybridization, but they are consistent with two competing hypotheses: (i) multiple horizontal transfers of the cluster from unknown donors to FFSC recipients and (ii) cluster duplication and loss (birth and death). Furthermore, low levels of FUM gene divergence in F. bulbicola, an FFSC species, and F. oxysporum provide evidence for horizontal transfer of the cluster from the former, or a closely related species, to the latter. Thus, uniform gene organization within the FUM cluster belies a complex evolutionary history that has not always paralleled the evolution of Fusarium.

Stable isotope dilution analysis of small molecules with carboxylic acid functions using 18O labeling for HPLC-ESI-MS/MS: analysis of fumonisin B1

(18)O labeling is a well-known method for the stable isotope labeling of proteins and peptides. This study describes a modified procedure for using (18)O labeling on small molecules. Fumonisin B1, a worldwide occurring mycotoxin, which is routinely analyzed by HPLC-MS/MS, was chosen as model compound. (18)O labeling was achieved by acid-catalyzed oxygen exchange from H2(18)O. A mixture of different isotopologues was obtained from the exchange, which, however, could be used as an internal standard for HPLC-MS/MS analysis. The identity of the (18)O-labeled fumonisin B1 was confirmed by NMR and HRMS measurements. The applicability as internal standard has been verified by comparison of results obtained from the method described in this paper to results obtained by reference methods. The presented method is of special interest as the (18)O labeling can be generally applied to a large group of small molecules containing carboxylic groups.

Development of a nucleic acid lateral flow strip for detection of hepatitis C virus (HCV) core antigen

The object of this study was to develop a simple, rapid, specific, and highly sensitive method to detect HCV core antigen. A nucleic acid aptamer was designed with the high specificity and sensitivity in a nucleic acid lateral flow strip to compete with HCV core antigen and DNA probes. The lower detection limit of the test strip was calculated to be 10 pg/mL with the scanner and 100 pg/mL with naked eyes. Results showed that there were no cross-interactions with other proteins such as HCV NS3, E1/E2 antigens, HIV p24 antigens, or BSA proteins (HCV unrelated protein). When the viral load exceeded 10(4) copies/mL, the positive coincidence rates of ELISA and strip detection, when compared with the HCV RNA assay, were 98.44% and 97.28%, respectively. The results indicated that the ELISA detection and strip assay were in good agreement with the measured value. The results indicated that a nucleic acid lateral flow strip was a simple, rapid, specific, highly sensitive, and cost-effective field-based method for detecting HCV core antigen. The strip assay is an acceptable alternative to diagnose HCV core antigen and to investigate its epidemiology in clinical laboratories lacking specialized equipment and skills.

Fusarium verticillioides and maize interaction in vitro: relationship between oxylipin cross-talk and fumonisin synthesis

Fusarium verticillioides is one of the most important fungal pathogens causing ear and stalk rot in maize. Even if frequently asymptomatic, it can produce a harmful series of compounds named fumonisins. Plant and fungal oxylipins play a crucial role in determining the outcome of the interaction between the pathogen and its host. Moreover, oxylipins are factors able to modulate the secondary metabolism in fungi. To uncover the existence of the relationship between oxylipin production and fumonisin synthesis in F. verticillioides, we analysed some molecular and physiological parameters, such as the expression of genes whose products are related to oxylipin synthesis (i.e. lipoxygenase, diol synthases and fatty acid oxidase), the oxylipin profile of both cracked maize and the pathogen by using a lipidomic approach (i.e. combining LC-TOF and LC-MS/MS approaches with a robust statistical analysis) and the synthesis of fumonisin B1. The results suggested a close relationship between the modification of the pathogen oxylipin profile with the fumonisin synthesis. Notably, a modification of the oxylipin profile of the pathogen during its growth on cracked maize can be demonstrated. The switch in oxylipin synthesis could indicate that the ‘presence’ of maize determinants (e.g. plant cell wall fragments and/or lipids) was able to promote the modification of the pathogen lifestyle, also by adapting the secondary metabolism, notably fumonisin synthesis.

ESI-MS and MS/MS identification of the first ceramide analogues of fumonisin B₁ mycotoxin from a Fusarium verticillioides culture following RP-HPLC separation

Following the earlier detection of six new esterified fumonisin B₁ (EFB₁) isomers containing three acyl groups in a Fusarium verticillioides-inoculated rice culture, it was assumed that linoleic, palmitic or oleic acid esterifies one of the free OH groups on the fumonisin backbone. On the basis of the results of our recent investigations we now propose that these EFB₁ isomers are actually 3-O- and 5-O-acyl derivatives of FB₁ (3-O-linoleoyl-FB₁, 5-O-linoleoyl-FB₁, 3-O-palmitoyl-FB₁, 5-O-palmitoyl-FB₁, 3-O-oleoyl-FB₁ and 5-O-oleoyl-FB₁). A F. verticillioides strain was identified that produced not only O-acyl-FB₁ isomers, but also low amounts of three N-acyl derivatives (N-linoleoyl-FB₁, N-palmitoyl-FB₁ and N-oleoyl-FB₁), which eluted from the HPLC column after the six O-acyl compounds and in the same sequence as for the O-acyl compounds. The characteristic positive and negative ESI-MS/MS spectra obtained after solid-phase extraction of the culture extract facilitated identification of these N-acyl-FB₁ derivatives. The biosynthesis of N-palmitoyl-FB₁ by F. verticillioides was verified by spiking the culture extract with synthetic N-palmitoyl-FB₁. This is the first report of the separation and mass spectrometric identification of the six O-acyl- and three N-acyl-FB₁ derivatives extracted from a F. verticillioides culture.

Molecular biodiversity of mycotoxigenic fungi that threaten food safety

Fungal biodiversity is one of the most important contributors to the occurrence and severity of mycotoxin contamination of crop plants. Phenotypic and metabolic plasticity has enabled mycotoxigenic fungi to colonize a broad range of agriculturally important crops and to adapt to a range of environmental conditions. New mycotoxin-commodity combinations provide evidence for the ability of fungi to adapt to changing conditions and the emergence of genotypes that confer enhanced aggressiveness toward plants and/or altered mycotoxin production profiles. Perhaps the most important contributor to qualitative differences in mycotoxin production among fungi is variation in mycotoxin biosynthetic genes. Molecular genetic and biochemical analyses of toxigenic fungi have elucidated specific differences in biosynthetic genes that are responsible for intra- and inter-specific differences in mycotoxin production. For Aspergillus and Fusarium, the mycotoxigenic genera of greatest concern, variation in biosynthetic genes responsible for production of individual families of mycotoxins appears to be the result of evolutionary adaptation. Examples of such variation have been reported for: a) aflatoxin biosynthetic genes in Aspergillus flavus and Aspergillus parasiticus; b) trichothecene biosynthetic genes within and among Fusarium species; and c) fumonisin biosynthetic genes in Aspergillus and Fusarium species. Understanding the variation in these biosynthetic genes and the basis for variation in mycotoxin production is important for accurate assessment of the risks that fungi pose to food safety and for prevention of mycotoxin contamination of crops in the field and in storage.

Mycotoxins in corn and wheat silage in Israel

Silage is an important feed source for intensive dairy herds worldwide. Fungal growth and mycotoxin production before and during silage storage is a well-known phenomenon, resulting in reduced nutritional value and a possible risk factor for animal health. With this in mind, a survey was conducted to determine for the first time the occurrence of mycotoxins in corn and wheat silage in Israel. A total of 30 corn and wheat silage samples were collected from many sources and analysed using a multi-mycotoxin method based on LC-MS/MS. Most mycotoxins recorded in the present study have not been reported before in Israel. Overall, 23 mycotoxins were found in corn silage; while wheat silage showed a similar pattern of mycotoxin occurrence comprising 20 mycotoxins. The most common post-harvest mycotoxins produced by the Penicillium roqueforti complex were not found in any tested samples, indicative of high-quality preparation and use of silage. Moreover, none of the European Union-regulated mycotoxins--aflatoxin B1, ochratoxin, T-2 toxin, diacetoxyscirpenol and deoxynivalenol--were found above their limits of detection (LODs). The Alternaria mycotoxins--macrosporin, tentoxin and alternariol methyl ether--were highly prevalent in both corn and wheat silage (>80%), but at low concentrations. The most prominent (>80%) Fusarium mycotoxins in corn silage were fusaric acid, fumonisins, beauvericin, monilifomin, equisetin, zearalenone and enniatins, whereas in wheat silage only beauvericin, zearalenone and enniatins occurred in more than 80% of the samples. The high prevalence and concentration of fusaric acid (mean = 765 µg kg⁻¹) in Israeli corn silage indicates that this may be the toxin of highest potential concern to dairy cow performance. However, more data from different harvest years and seasons are needed in order to establish a more precise evaluation of the mycotoxin burden in Israeli silage.

Cornmeal and starch influence the dynamic of fumonisin B, A and C production and masking in Fusarium verticillioides and F. proliferatum

Fusarium verticillioides and F. proliferatum can infect maize ears and produce fumonisins. The fumonisin B (FB) series is the most prolifically produced, followed by fumonisin C (FC), A (FA) and P (FP); moreover hidden forms of fumonisins have been detected in maize and derivatives. There is a lack of information about which maize component may affect fumonisin pattern production. Therefore, in this work we studied the role of cornmeal and corn starch, as the sole source of nutrition, in the production dynamic of all fumonisin series, hidden forms included, in different strains of F. verticillioides and F. proliferatum incubated at 25°C for 7-45days. Both Fusarium species produced high amounts of FB, following the chemotype FB1>FB2>FB3; FC and FA were produced in lesser amounts, showing the chemotypes: FA2+FA3>FA1 and FC1>FC2+FC3>FC4, respectively; while no FP were detected. F. verticillioides was more prolific than F. proliferatum in fumonisin production (ten times more on average) in all the tested conditions. Fumonisin production was higher in cornmeal than in starch based medium in both Fusarium species; FA and FC were detected only in the former medium. An important role of amylopectin as an inducing factor for fumonisin biosynthesis was suggested, as were acid pH conditions. Fumonisin hidden forms may occur in cornmeal medium, whereas they were never found at significant levels in corn starch medium.

Practical aspects of fumonisin production under laboratory conditions

Studies were performed to develop an efficient method for fumonisin toxin production in sufficient quantities for animal toxicological experiments, on the basis of three earlier published fumonisin toxin production methods.Three absolutely necessary factors were taken into account and tested in a serial experiment. TheFusarium verticillioides strain MRC 826 was directly inoculated onto soaked, autoclaved, whole maize kernels (50 g/1.71 jar). The inoculation was performed by standard spore suspension (l×l0(6)/ml), a 5/2 surface/volume culture was prepared and incubated at 25 °C for 5 weeks. To maintain the optimal aw of approximately 1.00, the evaporated water was re-filled weekly. A final concentration of 4454±1060.9 ppm fumonisin B1 was reached, with good repeatability. In the laboratory practice, consistent production of constant amounts of FB1 can be obtained by applying the above settings.

Determination of fumonisins B₁ and B₂ in Chinese rice wine by HPLC using AQC precolumn derivatisation

BACKGROUND

Fumonisins are a group of naturally occurring mycotoxins produced by various Fusarium species that commonly infect maize and other cereals, including sorghum and rice. In this study a sensitive and selective method was developed for the determination of fumonisins B₁ and B₂ (FB₁ and FB₂) in Chinese rice wine. The method is based on high-performance liquid chromatography and fluorescence detection following precolumn derivatisation with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC).

RESULTS

FB₁ and FB₂ in Chinese rice wine were extracted and purified using strong anion exchange cartridges and derivatised with AQC at room temperature. The AQC derivatives were stable for 5 days. Optimal fluorescence was obtained at an excitation wavelength of 246 nm and an emission wavelength of 390 nm. Chromatography was performed using a C18 column and gradient elution at 1 mL min⁻¹ with methanol and 0.05 mol L⁻¹ phosphate buffer at pH 4. The limit of detection was 6 µg L⁻¹ for both FB₁ and FB₂. The method was successfully applied to the determination of FB₁ and FB₂ in Chinese rice wine, with recoveries of 87.5-94.5% being obtained.

CONCLUSION

The established method was stable and sensitive for the determination of FB₁ and FB₂ in Chinese rice wine.

Environmental factors related to fungal infection and fumonisin accumulation during the development and drying of white maize kernels

In Southern Europe where whole maize kernels are ground and used for making bread and other food products, infection of the kernels by Fusarium verticillioides and subsequent fumonisin contamination pose a serious safety issue. The influence of environmental factors on this fungal infection and mycotoxin accumulation as the kernel develops has not been fully determined, especially in such food grade maize. The objectives of the present study were to determine which environmental factors may contribute to kernel invasion by F. verticillioides and fumonisin accumulation as kernels develop and dry in naturally infected white maize. Three maize hybrids were planted at two different sowing dates and kernel samples were collected 20, 40, 60, 80 and 100 days after silking. The percentage of kernels infected, and ergosterol and fumonisin contents were recorded for each sampling. F. verticillioides was the most prevalent species identified as the kernels developed. Temperature and moisture conditions during the first 80 days after silking favored natural kernel infection by F. verticillioides rather than by Aspergillus or Penicillium species. Fumonisin was found in kernels as early as 20 days after silking however significant fumonisin accumulation above levels acceptable in the EU did not occur until after physiological maturity of the kernel indicating that kernel drying in the field poses a high risk. Our results suggest that this could be due to increasing kernel damage by insects that favor fungal development, such as the damage by the moth Sitotroga cerealella, and to the occurrence of stress conditions for F. verticillioides growth that could trigger fumonisin biosynthesis, such as exposure to suboptimal temperatures for growth simultaneously with low water activity.

Diversity of pea-associated F. proliferatum and F. verticillioides populations revealed by FUM1 sequence analysis and fumonisin biosynthesis

Fusarium proliferatum and F. verticillioides are considered as minor pathogens of pea (Pisum sativum L.). Both species can survive in seed material without visible disease symptoms, but still contaminating it with fumonisins. Two populations of pea-derived F. proliferatum and F. verticillioides strains were subjected to FUM1 sequence divergence analysis, forming a distinct group when compared to the collection strains originating from different host species. Furthermore, the mycotoxigenic abilities of those strains were evaluated on the basis of in planta and in vitro fumonisin biosynthesis. No differences were observed in fumonisin B (FB) levels measured in pea seeds (maximum level reached 1.5 μg g(-1)); however, in rice cultures, the majority of F. proliferatum genotypes produced higher amounts of FB1-FB3 than F. verticillioides strains.

Analysis of potential fumonisin-producing Fusarium species in corn products from three main maize-producing areas in eastern China

BACKGROUND

Fusarium species are common fungal contaminants of maize and a number of them can produce mycotoxin fumonisins. China is one of the largest maize producers in the world. This study investigated the contamination of maize samples from three areas in eastern China by Fusarium and fumonisin-producing fungi as well as their fumonisin-producing potential.

RESULTS

A total of 22 Fusarium strains were isolated, 19 of which were able to produce fumonisin. Among the 19 strains, 16 belonged to F. verticillioides, two to F. subglutinans and one to F. proliferatum. The majority (17/19) of the fumonisin-forming strains were high FB(1) producers, which is a potential health risk for the population in these areas. Fusarium contamination in samples from the mideastern area was the most serious (11 Fusarium strains, with nine producing fumonisin, isolated from 24 samples), followed by the northeastern area (nine Fusarium strains, with all nine producing fumonisin, isolated from 21 samples) and the southeastern area (two Fusarium strains, with one producing fumonisin, isolated from 19 samples).

CONCLUSION

Although the overall levels of FBs and contamination by fumonisin-producing fungi in corn samples were not serious, the contaminating Fusarium strains possessed fairly strong toxicogenic ability and potential risk for food safety.

[Determination of fumonisins B1 and B2 in corn by high performance liquid chromatography with post-column derivatization method]

A high performance liquid chromatography-fluorescence detection with post-column derivatization method was developed to detect fumonisin B1 (FB1) and fumonisin B2 (FB2) in corn. Several factors, such as the pH of derivatization buffer, concentration and flow rate of derivatization reagents, excitation wavelength, emission wavelength, which affected the detection of fumonisins were optimized. The separation was performed on a ZORBAX SB C18 column operated at 40 degrees C with the gradient elution by two mobile phases of 0.1 mol/L sodium dihydrogen phosphate solution (pH 3.3) and methanol at a flow rate of 0.8 mL/min. The derivatization was performed at ambient temperature. The o-phthalaldehyde (OPA) flow rate was 0.4 mL/min. The results showed that the optimum conditions were pH 10.5 of the derivatization reagent, OPA concentration at 2 g/L, and excitation wavelength of 335 nm, emission wavelength of 440 nm. The linear plots of FB1 and FB2 were obtained between 0.2 to 20 mg/L, with the correlation coefficients above 0.999 for both FB1 and FB2. The limits of detection of fumonisins B1 and B2 were 0.02 mg/kg. The mean recoveries at the three spiked levels of 0.1 - 4.0 mg/kg were 82.5% - 89.8%. This method is accurate, simple, rapid and suitable for the determination of fumonisins B1 and B2 in corn.

Identification of a cis-acting factor modulating the transcription of FUM1, a key fumonisin-biosynthetic gene in the fungal maize pathogen Fusarium verticillioides

Fumonisins, toxic secondary metabolites produced by some Fusarium spp. and Aspergillus niger, have strong agro-economic and health impacts. The genes needed for their biosynthesis, named FUM, are clustered and co-expressed in fumonisin producers. In eukaryotes, coordination of transcription can be attained through shared transcription factors, whose specificity relies on the recognition of cis-regulatory elements on target promoters. A bioinformatic analysis on FUM promoters in the maize pathogens Fusarium verticillioides and Aspergillus niger identified a degenerated, over-represented motif potentially involved in the cis-regulation of FUM genes, and of fumonisin biosynthesis. The same motif was not found in various FUM homologues of fungi that do not produce fumonisins. Comparison of the transcriptional strength of the intact FUM1 promoter with a synthetic version, where the motif had been mutated, was carried out in vivo and in planta for F. verticillioides. The results showed that the motif is important for efficient transcription of the FUM1 gene.

Alkaline cooking (nixtamalisation) and the reduction in the in vivo toxicity of fumonisin-contaminated corn in a rat feeding bioassay

Nixtamalisation is a widely used food processing method in which whole kernel corn is cooked and steeped in alkaline water. It reduces the amount of fumonisin B1 (FB1) that can be detected after cooking. However, the fate of FB1 during nixtamalisation is not fully understood and potentially toxic reaction products, including matrix-associated "masked" FB1 forms that are not detected by routine analytical methods might remain in nixtamalised corn. To assess how nixtamalisation of whole kernel corn affects fumonisin toxicity, male rats were fed diets containing low, mid or high levels of uncooked (LU, MU, HU) or alkaline cooked (LC, MC, HC) FB1-contaminated corn for 3 weeks. The control diet contained uncontaminated corn only. Apoptotic kidney lesions of the type caused by FB1 were not found in the LC or MC groups. Lesions in the group fed HC were minimal and less severe than those found in the rats fed LU, MU or HU. Furthermore, significantly increased sphinganine and sphingosine concentrations indicative of FB1 exposure were found in the kidneys of the rats given LU, MU or HU. Concentrations were also elevated, but to a lesser extent, in rats fed HC, whereas sphinganine and sphingosine concentrations in rats given LC or MC did not differ from the control group. FB1 concentrations in the LC (0.08 mg kg(-1)), MC (0.13 mg kg(-1)) and HC (0.37 mg kg(-1)) diets were markedly reduced compared with their LU (1.8 mg kg(-1)), MU (3.5 mg kg(-1)) and HU (4.2 mg kg(-1)) counterparts as determined by HPLC (n =  1 analysis/diet). Taken together, the findings show that nixtamalisation is an effective cooking method for reducing the potential toxicity of FB1 contaminated corn.

Fumonisins B, A and C profile and masking in Fusarium verticillioides strains on fumonisin-inducing and maize-based media

The production of fumonisin B, A and C and hidden and partially hydrolysed fumonisin occurrence was investigated in 3 strains of Fusarium verticillioides isolated from maize, cultured for 21-45days on malt extract medium at 25°C and 0.955-0.990 water activity (a(w)). Fumonisin A-B and C series were produced by all the strains in all conditions studied, with B-fumonisin≫C-fumonisin>A-fumonisin following a similar trend. The dynamic of fumonisin production was significantly influenced by factors considered and their interaction, with a(w)=0.990 as favourable condition in ITEM 10026 and ITEM 10027. All fumonisins were maximised at 30days incubation in ITEM 10027 and ITEM 1744 and at 45days incubation in ITEM 10026. Partially hydrolysed fumonisins were detected only for the B-group. Hidden fumonisins were never observed in Fusarium cultures grown on malt extract medium but were detected in the additional trial on maize-based medium, suggesting that the masking phenomenon can occur only in a complex matrix.

The kinetics of urinary fumonisin B1 excretion in humans consuming maize-based diets

SCOPE

Fumonisins (FB) are mycotoxins found in maize. The purpose of this study was to (i) determine the relationship between FB(1) , FB(2) , and FB(3) intake and urinary excretion in humans, (ii) validate a method to isolate urinary FB on C(18) -SPE cartridges for international shipment, and (iii) test the method using samples from Guatemala.

METHODS AND RESULTS

Volunteers (n = 10) consumed 206 grams/day of tortillas and biscuits prepared from masa flour and a product containing maize flour. Volunteers estimated their daily urine output and samples were analyzed for FB(1) , FB(2) , and FB(3) and hydrolyzed FB(1) . Only FB(1) was detected in urine suggesting lower absorption of FB(2) and FB(3) . Excretion was highly variable peaking soon after consumption began and decreasing rapidly after consumption stopped. Within 5 days after consumption ended, FB(1) was not detected in urine. In a study with eight volunteers, the average total urinary FB(1) was 0.5% of the intake. FB(1) was detected in 61% (107/177) of the samples collected in Guatemala.

CONCLUSION

The results support the use of urinary FB(1) to assess ongoing exposure in population-based studies. However, relating the FB(1) concentration in urine to dietary intake of FB by individual subjects will be complicated due to interindividual variability and the rapidity of clearance.