Simple Approach for the Rapid Detection of Alternariol in Pear Fruit by Surface-Enhanced Raman Scattering with Pyridine-Modified Silver Nanoparticles

A simple method based on surface-enhanced Raman scattering (SERS) was developed for the rapid determination of alternariol (AOH) in pear fruits using an easily prepared silver-nanoparticle (AgNP) substrate. The AgNP substrate was modified by pyridine to circumvent the weak affinity of the AOH molecules to the silver surface and to improve the sensitivity of detection. Quantitative analysis was performed in AOH solutions at concentrations ranging from 3.16 to 316.0 μg/L, and the limit of detection was 1.30 μg/L. The novel method was also applied to the detection of AOH residues in pear fruits purchased from the market and in pear fruits that were artificially inoculated with Alternaria alternata. AOH was not found in any of the fresh fruit, whereas it resided in the rotten and inoculated fruits. Finally, the SERS method was cross validated against HPLC. It was revealed that the SERS method has great potential utility in the rapid detection of AOH in pear fruits and other agricultural products.

Occurrence of pathogenic and endophytic fungi and their influence on quality of medicinal plants applied in management of neurological diseases and mental disorders

Due to increasing demand of medicinal plants (MPs), quality and safety more attention to the plant health should be paid. Among herb pathogens, especially fungi cause serious diseases in these plants decreasing yield and quality of herbal raw material. Some species, i.e. Fusarium sp., Alternaria sp., Penicillium sp. are known as mycotoxin producers. Paradoxically, self-treatment with herbal raw material can expose the patient to mycotoxin activity. In tissues of some MPs species, asymptomatically endophytic fungi residue. It is known that they are able to influence a biosynthesis of secondary metabolites in their host plant or produce biologically active compounds. Until recently these microorganisms have been neglected as a component of MPs, the reason why there have unexplored bioactivity and biodiversity. The paper presents an overview of herbal plants that are used in the treatment of nervous system diseases. Pathogenic fungi that infect these plants are described. It focused mainly on species producing harmful mycotoxins. The publication presents a list of these mycotoxins and a brief description of their effects on human health. The second part of this article provides information on the occurrence of endophytic fungi in herbal plants and their effects on human health. Coexistence of fungi and medicinal plants is not fully understood but can be crucial to ensure health and safety of patients with neurological diseases and mental disorders.

Secreted protein extract analyses present the plant pathogen Alternaria alternata as a suitable industrial enzyme toolbox

Lignocellulosic plant biomass is the most abundant carbon source in the planet, which makes it a potential substrate for biorefinery. It consists of polysaccharides and other molecules with applications in pharmaceutical, food and feed, cosmetics, paper and textile industries. The exploitation of these resources requires the hydrolysis of the plant cell wall, which is a complex process. Aiming to discover novel fungal natural isolates with lignocellulolytic capacities, a screening for feruloyl esterase activity was performed in samples taken from different metal surfaces. An extracellular enzyme extract from the most promising candidate, the natural isolate Alternaria alternata PDA1, was analyzed. The feruloyl esterase activity of the enzyme extract was characterized, determining the pH and temperature optima (pH 5.0 and 55-60 °C, respectively), thermal stability and kinetic parameters, among others. Proteomic analyses derived from two-dimensional gels allowed the identification and classification of 97 protein spots from the extracellular proteome. Most of the identified proteins belonged to the carbohydrates metabolism group, particularly plant cell wall degradation. Enzymatic activities of the identified proteins (β-glucosidase, cellobiohydrolase, endoglucanase, β-xylosidase and xylanase) of the extract were also measured. These findings confirm A. alternata PDA1 as a promising lignocellulolytic enzyme producer.

SIGNIFICANCE

Although plant biomass is an abundant material that can be potentially utilized by several industries, the effective hydrolysis of the recalcitrant plant cell wall is not a straightforward process. As this hydrolysis occurs in nature relying almost solely on microbial enzymatic systems, it is reasonable to infer that further studies on lignocellulolytic enzymes will discover new sustainable industrial solutions. The results included in this paper provide a promising fungal candidate for biotechnological processes to obtain added value from plant byproducts and analogous substrates. Moreover, the proteomic analysis of the secretome of a natural isolate of Alternaria sp. grown in the presence of one of the most used vegetal substrates on the biofuels industry (sugar beet pulp) sheds light on the extracellular enzymatic machinery of this fungal plant pathogen, and can be potentially applied to developing new industrial enzymatic tools. This work is, to our knowledge, the first to analyze in depth the secreted enzyme extract of the plant pathogen Alternaria when grown on a lignocellulosic substrate, identifying its proteins by means of MALDI-TOF/TOF mass spectrometry and characterizing its feruloyl esterase, cellulase and xylanolytic activities.

A Review of Current Methods for Analysis of Mycotoxins in Herbal Medicines

The presence of mycotoxins in herbal medicines is an established problem throughout the entire world. The sensitive and accurate analysis of mycotoxin in complicated matrices (e.g., herbs) typically involves challenging sample pretreatment procedures and an efficient detection instrument. However, although numerous reviews have been published regarding the occurrence of mycotoxins in herbal medicines, few of them provided a detailed summary of related analytical methods for mycotoxin determination. This review focuses on analytical techniques including sampling, extraction, cleanup, and detection for mycotoxin determination in herbal medicines established within the past ten years. Dedicated sections of this article address the significant developments in sample preparation, and highlight the importance of this procedure in the analytical technology. This review also summarizes conventional chromatographic techniques for mycotoxin qualification or quantitation, as well as recent studies regarding the development and application of screening assays such as enzyme-linked immunosorbent assays, lateral flow immunoassays, aptamer-based lateral flow assays, and cytometric bead arrays. The present work provides a good insight regarding the advanced research that has been done and closes with an indication of future demand for the emerging technologies.

Determination of Multi-Class Mycotoxins in Tartary Buckwheat by Ultra-Fast Liquid Chromatography Coupled with Triple Quadrupole Mass Spectrometry

Considering crops are susceptible to toxicogenic fungi during plantation, pre-processing and storage, an ultra-fast liquid chromatography coupled with triple quadrupole mass spectrometry (UFLC-QTrap-MS/MS) method was developed and validated for simultaneous determination of the 12 most frequent mycotoxins, including aflatoxin B₁, B₂, G₁, G₂, HT-2, T-2 toxin, ochratoxin A, fumonisin B₁, B₂, zearalanone, zearalenone, and deoxynivalenol, in 14 batches of Tartary buckwheat cultivar, collected from different origins in Sichuan Province, China. Differing from those complicated approaches, a simple and cost-efficient pretreatment method based on dilute-and-shoot was employed. Based on optimized chromatographic and mass spectrometry conditions, these 12 mycotoxins could be analyzed with high correlation coefficients (all over 0.995), high precision (RSD 0.47–9.26%), stability (RSD 0.72–11.36%), and recovery (79.52% to 108.92%, RSD 4.35–14.27%). Furthermore, this analysis method exhibited good determination performance with little disturbance of the matrix effect. Finally, this proposed method was applied for 14 batches of Tartary buckwheat seeds, in which aflatoxin B₁ (AFB₁) was detected in one moldy cultivar, Meigu No. 2, with its concentration exceeding the maximum residue limits set by EU regulations. The method thus established, which has significant advantages, could provide a preferred determination approach candidate for measurement of multiple mycotoxins measurement in Tartary buckwheat, even other kinds of foodstuffs.

An integrated in silico/in vitro approach to assess the xenoestrogenic potential of Alternaria mycotoxins and metabolites

Xenoestrogenic mycotoxins may contaminate food and feed posing a public health issue. Besides the zearalenone group, the Alternaria toxin alternariol (AOH) has been described as a potential mycoestrogen. However, the estrogenicity of Alternaria toxins is still largely overlooked and further data are needed to better describe the group toxicity. In the frame of risk assessment, mixed in silico/in vitro approaches already proved to be effective first-line analytical tools. An integrated in silico/in vitro approach was used to investigate the effects of metabolic and chemical modifications on the estrogenicity of AOH. Among the considered modifications, methylation was found critical for enhancing estrogenicity (as seen for alternariol monomethyl ether (AME)) while hydroxylation and glucuronidation had the opposite effect (as seen for 4-hydroxy AOH and 4-hydroxy AME). The structure-activity relationship analysis provided the structural rationale. Our results provide insights to design more efficient risk assessment studies expanding knowledge over the group toxicity.

Isolation, characterization and toxicological potential of Alternaria-mycotoxins (TeA, AOH and AME) in different Alternaria species from various regions of India

Alternaria species produce various sorts of toxic metabolites during their active growth and causes severe diseases in many plants by limiting their productivity. These toxic metabolites incorporate various mycotoxins comprising of dibenzo-α-pyrone and some tetramic acid derivatives. In this study, we have screened out total 48 isolates of Alternaria from different plants belonging to different locations in India, on the basis of their pathogenic nature. Pathogenicity testing of these 48 strains on susceptible tomato variety (CO-3) showed 27.08% of the strains were highly pathogenic, 35.41% moderately pathogenic and 37.5% were less pathogenic. Phylogenetic analysis showed the presence of at least eight evolutionary cluster of the pathogen. Toxins (TeA, AOH and AME) were isolated, purified on the basis of column chromatography and TLC, and further confirmed by the HPLC-UV chromatograms using standards. The final detection of toxins was done by the LC-MS/MS analysis by their mass/charge ratio. The present study develops an approach to classify the toxicogenic effect of each of the individual mycotoxins on tomato plant and focuses their differential susceptibility to develop disease symptoms. This study represents the report of the natural occurrence and distribution of Alternaria toxins in various plants from India.

Alternaria Toxins: Potential Virulence Factors and Genes Related to Pathogenesis

Alternaria is an important fungus to study due to their different life style from saprophytes to endophytes and a very successful fungal pathogen that causes diseases to a number of economically important crops. Alternaria species have been well-characterized for the production of different host-specific toxins (HSTs) and non-host specific toxins (nHSTs) which depend upon their physiological and morphological stages. The pathogenicity of Alternaria species depends on host susceptibility or resistance as well as quantitative production of HSTs and nHSTs. These toxins are chemically low molecular weight secondary metabolites (SMs). The effects of toxins are mainly on different parts of cells like mitochondria, chloroplast, plasma membrane, Golgi complex, nucleus, etc. Alternaria species produce several nHSTs such as brefeldin A, tenuazonic acid, tentoxin, and zinniol. HSTs that act in very low concentrations affect only certain plant varieties or genotype and play a role in determining the host range of specificity of plant pathogens. The commonly known HSTs are AAL-, AK-, AM-, AF-, ACR-, and ACT-toxins which are named by their host specificity and these toxins are classified into different family groups. The HSTs are differentiated on the basis of bio-statistical and other molecular analyses. All these toxins have different mode of action, biochemical reactions and signaling mechanisms to cause diseases. Different species of Alternaria produced toxins which reveal its biochemical and genetic effects on itself as well as on its host cells tissues. The genes responsible for the production of HSTs are found on the conditionally dispensable chromosomes (CDCs) which have been well characterized. Different bio-statistical methods like basic local alignment search tool (BLAST) data analysis used for the annotation of gene prediction, pathogenicity-related genes may provide surprising knowledge in present and future.

Characterization of small-spored Alternaria from Argentinean crops through a polyphasic approach

Small-spored Alternaria have been isolated from a wide variety of food crops, causing both economic losses and human health risk due to the metabolites produced. Their taxonomy has been discussed widely, but no scientific consensus has been established in this field to date. Argentina is a major exporter of agricultural products, so it is essential to thoroughly understand the physiological behaviour of this pathogen in a food safety context. Thus, the objective of this work was to characterize small-spored Alternaria spp. obtained from tomato fruits, pepper fruits, wheat grains and blueberries from Argentina by a polyphasic approach involving metabolomic and phylogenetic analyses based on molecular and morphological characters. Morphological analysis divided the population studied into three groups; A. arborescens sp.-grp., A. tenuissima sp.-grp., and A. alternata sp.-grp. However, when these characters were simultaneously analysed with molecular data, no clearly separated groups were obtained. Haplotype network and phylogenetic analysis (both Bayesian and maximum parsimony) of a conserved region yielded the same result, suggesting that all isolates belong to the same species. Furthermore, no correlation could be established between morphological species-groups and a metabolite or group of metabolites synthesized. Thus, the whole set of analyses carried out in the present work supports the hypothesis that these small-spored Alternaria isolates from food belong to the same species. Identification at species level through classical morphology or modern molecular techniques does not seem to be a useful tool to predict toxicological risk in food matrices. The detection of any small-spored Alternaria from Section Alternaria (D.P. Lawr., Gannibal, Peever & B.M. Pryor 2013) in food implies a potential toxicological risk.

The major Alternaria alternata allergen, Alt a 1: A reliable and specific marker of fungal contamination in citrus fruits

The ubiquitously present spores of Alternaria alternata can spoil a wide variety of foodstuffs, including a variety of fruits belonging to the Citrus genus. The major allergenic protein of A. alternata, Alt a 1, is a species-specific molecular marker that has been strongly associated with allergenicity and phytopathogenicity of this fungal species. This study aimed to evaluate the potential of the detection of Alt a 1 as a reliable indicator of A. alternata contamination in citrus fruits. To accomplish this aim, sixty oranges were artificially infected with a spore suspension of A. alternata. Internal fruit material was collected at different incubation times (one, two and three weeks after the fungal inoculation) and used for both total RNA extraction and protein extraction. Alt a 1 detection was then performed by polymerase chain reaction (PCR) amplification using Alt a 1 specific primers and by enzyme-linked immunosorbent assay (ELISA). The experimental model presented in this work was effective to simulate the typical Alternaria black rot phenotype and its progression. Although both PCR and ELISA techniques have been successfully carried out for detecting Alt a 1 allergen in A. alternata infected oranges, the PCR method was found to be more sensitive than ELISA. Nevertheless, ELISA results were highly valuable to demonstrate that considerable amounts of Alt a 1 are produced during A. alternata fruit infection process, corroborating the recently proposed hypothesis that this protein plays a role in the pathogenicity and virulence of Alternaria species. Such evidence suggests that the detection of Alt a 1 by PCR-based assay may be used as a specific indicator of the presence of pathogenic and allergenic fungal species, A. alternata, in fruits. This knowledge can be employed to control the fungal infection and mitigate agricultural losses as well as human exposure to A. alternata allergens and toxins.

Experimental Paper. The effect of colour grading of milk thistle (Silybum marianum (L.) Gaertn.) seeds on their quality for sowing

Introduction: Milk thistle (Silybum marianum (L.) Gaertn.) is a medicinal plant belonging to Asteraceae family. Extract from milk thistle achenes (termed in practice as seeds) contains sylimarin, which protects liver cells against inorganic and organic toxic compounds. Objective: The aim of the research was to evaluate the effect of colour grading on the quality of milk thistle seeds. Methods: Seeds were graded manually by colour according to the Royal Horticultural Society Colour Chart, issued in Great Britain. In three samples two fractions of seeds were separated: beige and brown, whereas seeds of the fourth sample were graded into three fractions: yellow, beige and brown. The 1000-seed weight and germination of graded and non-graded seeds were evaluated. Infestation of graded seeds with fungi was assessed. Results: Brown seeds had a higher 1000-seed weight than beige or yellow ones. Germination at the final count of beige seeds did not differ as compared to that of brown seeds or was even better. Milk thistle seeds were infested with numerous fungi, however Alternaria alternata and Ulocladium consortiale predominated. Conclusions: Less mature beige seeds can be used as sowing material because their germination at the final count did not differ as compared to that of fully mature brown seeds or was even better. Infestation of these seeds with some of the fungi was lower than brown seeds.

Establishment of CRISPR/Cas9 in Alternaria alternata

The filamentous fungus Alternaria alternata is a potent producer of many secondary metabolites, some of which like alternariol or alternariol-methyl ether are toxic and/or cancerogenic. Many Alternaria species do not only cause post-harvest losses of food and feed, but are aggressive plant pathogens. Despite the great economic importance and the large number of research groups working with the fungus, the molecular toolbox is rather underdeveloped. Gene deletions often result in heterokaryotic strains and therefore, gene-function analyses are rather tedious. In addition, A. alternata lacks a sexual cycle and classical genetic approaches cannot be combined with molecular biological methods. Here, we show that CRISPR/Cas9 can be efficiently used for gene inactivation. Two genes of the melanin biosynthesis pathway, pksA and brm2, were chosen as targets. Several white mutants were obtained after several rounds of strain purification through protoplast regeneration or spore inoculation. Mutation of the genes was due to deletions from 1bp to 1.5kbp. The CRISPR/Cas9 system was also used to inactivate the orotidine-5-phosphate decarboxylase gene pyrG to create a uracil-auxotrophic strain. The strain was counter-selected with fluor-orotic acid and could be re-transformed with pyrG from Aspergillus fumigatus and pyr-4 from Neurospora crassa. In order to test the functioning of GFP, the fluorescent protein was fused to a nuclear localization signal derived from the StuA transcription factor of Aspergillus nidulans. After transformation bright nuclei were visible.

Alternaria Species and Their Associated Mycotoxins

The genus Alternaria includes more than 250 species. The traditional methods for identification of Alternaria species are based on morphological characteristics of the reproductive structures and sporulation patterns under controlled culture conditions. Cladistics analyses of "housekeeping genes" commonly used for other genera, failed to discriminate among the small-spored Alternaria species. The development of molecular methods achieving a better agreement with morphological differences is still needed. The production of secondary metabolites has also been used as a means of classification and identification. Alternaria spp. can produce a wide variety of toxic metabolites. These metabolites belong principally to three different structural groups: (1) the dibenzopyrone derivatives, alternariol (AOH), alternariol monomethyl ether (AME), and altenuene (ALT); (2) the perylene derivative altertoxins (ATX-I, ATX-II, and ATX II); and (3) the tetramic acid derivative, tenuazonic acid (TeA). TeA, AOH, AME, ALT, and ATX-I are the main. Certain species in the genus Alternaria produce host-specific toxins (HSTs) that contribute to their pathogenicity and virulence. Alternaria species are plant pathogens that cause spoilage of agricultural commodities with consequent mycotoxin accumulation and economic losses. Vegetable foods infected by Alternaria rot could introduce high amounts of these toxins to the human diet. More investigations on the toxic potential of these toxins and their hazard for human consumption are needed to make a reliable risk assessment of dietary exposure.

Targeting Conserved Genes in Alternaria Species

Real-time polymerase chain reaction (PCR) is a molecular biology technique based on the detection of the fluorescence produced by a reporter molecule, which increases as the reaction proceeds proportionally to the accumulation of the PCR product within each amplification cycle. The fluorescent reporter molecules include dyes that bind to the double-stranded DNA (i.e., SYBR^® Green) or sequence-specific probes (i.e., Molecular Beacons or TaqMan^® Probes). Real-time PCR provides a tool for accurate and sensitive quantification of target fungal DNA. Here, we describe a TaqMan real-time PCR method for specific detection and quantification of Alternaria spp. The method uses Alternaria-specific primers and probe, targeting the internal transcribed spacer regions ITS1 and ITS2 of the rRNA gene, and a positive amplification control based on 18S rRNA gene.

Mycotoxins: An Underhand Food Problem

Among the food safety issues, the occurrence of fungal species able to produce toxic metabolites on the agro-food products has acquired a general attention. These compounds, the mycotoxins, generally provided of low molecular weight, are the result of the secondary metabolism of the toxigenic fungi. They may have toxic activity toward the plants, but mostly represent a serious risk for human and animal health worldwide, since they can be accumulated on many final crop products and they have a broad range of toxic biological activities. In particular, mainly cereals are the most sensitive crops to the colonization of toxigenic fungal species which accumulate in the grains the related mycotoxins both in the field, until the harvest stage, and in the storage. According to a Food and Agriculture Organization study, approximately 25 % of the global food and feed output is contaminated by mycotoxins. Therefore, since a large proportion of the world's population consumes, as a staple food, the cereals, the consumption of mycotoxin-contaminated cereals is a main issue for health risk worldwide. Furthermore, mycotoxin contamination can have a huge economic and social impact, especially when mycotoxin occurrence on the food commodities is over the regulation limits established by different national and transnational institutions, implying that contaminated products must be discarded. Finally, the climate change due to the global warming can alter stages and rates of toxigenic fungi development and modify host-resistance and host-pathogen interactions, influencing deeply also the conditions for mycotoxin production that vary for each individual pathogen. New combinations of mycotoxins/host plants/geographical areas are arising to the attention of the scientific community and require new diagnostic tools and deeper knowledge of both biology and genetics of toxigenic fungi. Moreover, to spread awareness and knowledge at international level on both the hazard that mycotoxins represent for consumers and costs for stakeholders is of key importance for developing all possible measures aimed to control such dangerous contaminants worldwide.

AlternariaMycotoxins in Food and Feed: An Overview

Alternariais one of the major mycotoxigenic fungal genera with more than 70 reported metabolites.Alternariamycotoxins showed notably toxicity, such as mutagenicity, carcinogenicity, induction of DNA strand break, sphingolipid metabolism disruption, or inhibition of enzymes activity and photophosphorylation. This review reports on the toxicity, stability, metabolism, current analytical methods, and prevalence ofAlternariamycotoxins in food and feed through the most recent published research. Half of the publications were focused on fruits, vegetables, and derived products—mainly tomato and apples—while cereals and cereal by-products represented 38%. The most studied compounds were alternariol, alternariol methyl ether, tentoxin, and tenuazonic acid, but altenuene, altertoxins (I, II, and III), and macrosporin have been gaining importance in recent years. Solid-liquid extraction (50%) with acetonitrile or ethyl acetate was the most common extraction methodology, followed by QuEChERS and dilution-direct injection (both 14%). High- and ultraperformance liquid chromatography coupled with tandem mass spectrometry was the predominant determination technique (80%). The highest levels of alternariol and alternariol methyl ether were found in lentils, oilseeds, tomatoes, carrots, juices, wines, and cereals. Tenuazonic acid highest levels were detected in cereals followed by beer, while alternariol, alternariol methyl ether, tenuazonic acid, and tentoxin were found in legumes, nuts, and oilseeds.

Rapid screening of Alternaria mycotoxins using MALDI-TOF mass spectrometry

BACKGROUND

Members of the Alternaria genus produce various toxins whose occurrence in agricultural commodities is a major concern for humans and the environment. The present study developed a simple and efficient matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method for the rapid detection of Alternaria toxins.

RESULTS

A new method for the detection of alternariol (AOH), alternariol monomethyl ether (AME) and tentoxin (TEN) by MALDI-TOF MS was developed. Different solid phase extraction (SPE) clean-up methods were tried to optimize the purification of wheat matrix, and an optimal extraction method was designed to recover the three Alternaria toxins. In addition, various MALDI matrices were examined and α-cyano-4-hydroxycinnamic acid (CHCA) matrix gave good repeatability for all three Alternaria toxins.

CONCLUSION

This is the first study to report the detection of three important Alternaria toxins concurrently using MALDI-TOF MS and opens up the possibility of rapid screening of Alternaria toxins in several other cereals and food products. © 2016 Her Majesty the Queen in Right of Canada Journal of the Science of Food and Agriculture © 2016 Society of Chemical Industry.

Sulfoglucosides as Novel Modified Forms of the Mycotoxins Alternariol and Alternariol Monomethyl Ether

The mycotoxins alternariol and alternariol-9-O-methyl ether have recently been reported to be extensively conjugated with glucose and malonyl glucose in tobacco suspension cells. However, only trace amounts of glucosylated conjugates were detected in tomatoes inoculated with Alternaria alternata in the present study. Instead, mostly sulfate conjugates were observed. In studies using cultures of A. alternata and incubations of alternariol and alternariol-9-O-methyl ether with tomato tissue in the absence of the fungus, it was clarified that sulfate conjugates were produced by the fungus, whereas tomato tissues converted alternariol and alternariol-9-O-methyl ether to glucosylated metabolites. Alternariol-3-sulfate, alternariol-9-sulfate, and alternariol-9-O-methyl ether-3-sulfate were unambiguously identified as fungal metabolites using MS and 1H and 13C NMR spectroscopy. When these sulfate conjugates were incubated with tobacco suspension cells or ex planta tomato tissues, three sulfoglucosides of alternariol and one sulfoglucoside of alternariol-9-O-methyl ether were formed. Using NMR spectroscopy, the chemical structures of alternariol-3-sulfate-9-glucoside, alternariol-9-sulfate-3-glucoside, and alternariol-9-O-methyl ether-3-sulfate-7-glucoside were established. These conjugates were also detected in the A. alternata-inoculated tomato. This is the first report on a mixed sulfate/glucoside diconjugate of a mycotoxin. Diconjugates of this novel type may be formed by all mycotoxins and their phase I metabolites with two or more hydroxyl groups and should be taken into account in the future analysis of modified mycotoxins.

Spotlight on the Underdogs-An Analysis of Underrepresented Alternaria Mycotoxins Formed Depending on Varying Substrate, Time and Temperature Conditions

Alternaria (A.) is a genus of widespread fungi capable of producing numerous, possibly health-endangering Alternaria toxins (ATs), which are usually not the focus of attention. The formation of ATs depends on the species and complex interactions of various environmental factors and is not fully understood. In this study the influence of temperature (7 °C, 25 °C), substrate (rice, wheat kernels) and incubation time (4, 7, and 14 days) on the production of thirteen ATs and three sulfoconjugated ATs by three different Alternaria isolates from the species groups A. tenuissima and A. infectoria was determined. High-performance liquid chromatography coupled with tandem mass spectrometry was used for quantification. Under nearly all conditions, tenuazonic acid was the most extensively produced toxin. At 25 °C and with increasing incubation time all toxins were formed in high amounts by the two A. tenuissima strains on both substrates with comparable mycotoxin profiles. However, for some of the toxins, stagnation or a decrease in production was observed from day 7 to 14. As opposed to the A. tenuissima strains, the A. infectoria strain only produced low amounts of ATs, but high concentrations of stemphyltoxin III. The results provide an essential insight into the quantitative in vitro AT formation under different environmental conditions, potentially transferable to different field and storage conditions.

Development and Validation of a LC-ESI-MS/MS Method for the Determination of Alternaria Toxins Alternariol, Alternariol Methyl-Ether and Tentoxin in Tomato and Tomato-Based Products

Alternaria species are capable of producing several secondary toxic metabolites in infected plants and in agricultural commodities, which play important roles in food safety. Alternaria alternata turn out to be the most frequent fungal species invading tomatoes. Alternariol (AOH), alternariol monomethyl ether (AME), and tentoxin (TEN) are some of the main Alternaria mycotoxins that can be found as contaminants in food. In this work, an analytical method based on liquid chromatography (LC) tandem mass spectrometry (MS/MS) detection for the simultaneous quantification of AOH, AME, and TEN in tomato and tomato-based products was developed. Mycotoxin analysis was performed by dispersive liquid-liquid microextraction (DLLME) combined with LC-ESI-MS/MS. Careful optimization of the MS/MS parameters was performed with an LC/MS system with the ESI interface in the positive ion mode. Mycotoxins were efficiently extracted from sample extract into a droplet of chloroform (100 µL) by DLLME technique using acetonitrile as a disperser solvent. Method validation following the Commission Decision No. 2002/657/EC was carried out by using tomato juice as a blank matrix. Limits of detection and quantitation were, respectively, in the range 0.7 and 3.5 ng/g. Recovery rates were above 80%. Relative standard deviations of repeatability (RSDr) and intermediate reproducibility (RSDR) were ≤ 9% and ≤ 15%, respectively, at levels of 25 and 50 ng/g. Five out of 30 analyzed samples resulted positive to at least one Alternaria toxin investigated. AOH was the most common Alternaria toxin found, but at levels close to LOQ (average content: 3.75 ng/g).

Characterization of Citrus-Associated Alternaria Species in Mediterranean Areas

Alternaria brown spot is one of the most important diseases of tangerines and their hybrids worldwide. Recently, outbreaks in Mediterranean areas related to susceptible cultivars, refocused attention on the disease. Twenty representatives were selected from a collection of 180 isolates of Alternaria spp. from citrus leaves and fruit. They were characterized along with reference strains of Alternaria spp. Micro- and macroscopic characteristics separated most Alternaria isolates into six morphotypes referable to A. alternata (5) and A. arborescens (1). Phylogenetic analyses, based on endopolygalacturonase (endopg) and internal transcribed spacer (ITS), confirmed this finding. Moreover, a five-gene phylogeny including two anonymous genomics regions (OPA 1-3 and OPA 2-1), and the beta-tubulin gene (ß-tub), produced a further clustering of A. alternata into three clades. This analysis suggested the existence of intra-species molecular variability. Investigated isolates showed different levels of virulence on leaves and fruit. In particular, the pathogenicity on fruit seemed to be correlated with the tissue of isolation and the clade. The toxigenic behavior of Alternaria isolates was also investigated, with tenuazonic acid (TeA) being the most abundant mycotoxin (0.2-20 mg/L). Isolates also synthesized the mycotoxins alternariol (AOH), its derivate alternariol monomethyl ether (AME), and altenuene (ALT), although to a lesser extent. AME production significantly varied among the six morphotypes. The expression of pksJ/pksH, biosynthetic genes of AOH/AME, was not correlated with actual toxin production, but it was significantly different between the two genotypes and among the four clades. Finally, ten isolates proved to express the biosynthetic genes of ACTT1 phytotoxin, and thus to be included in the Alternaria pathotype tangerine. A significant correlation between pathogenicity on leaves and ACTT1 gene expression was recorded. The latter was significantly dependent on geographical origin. The widespread occurrence of Alternaria spp. on citrus fruit and their ability to produce mycotoxins might represent a serious concern for producers and consumers.

Bioactive Dibenzo-α-pyrone Derivatives from the Endophytic Fungus Rhizopycnis vagum Nitaf22

Six new dibenzo-α-pyrones, rhizopycnolides A (1) and B (2) and rhizopycnins A-D (3-6), together with eight known congeners (7-14), were isolated from the endophytic fungus Rhizopycnis vagum Nitaf22 obtained from Nicotiana tabacum. The structures of the new compounds were unambiguously elucidated using NMR, HRESIMS, TDDFT ECD calculation, and X-ray crystallography data. Rhizopycnolides A (1) and B (2) feature an uncommon γ-butyrolactone-fused dibenzo-α-pyrone tetracyclic skeleton (6/6/6/5), while rhizopycnin B (4) was the first amino group containing dibenzo-α-pyrone. Rhizopycnolides A (1) and B (2) are proposed to be biosynthesized from polyketide and tricarboxylic acid cycle pathways. The isolated compounds were tested for their antibacterial, antifungal, and cytotoxic activities. Among them, rhizopycnolide A (1), rhizopycnins C (5) and D (6), TMC-264 (8), penicilliumolide D (11), and alternariol (12) were active against the tested pathogenic bacteria Agrobacterium tumefaciens, Bacillus subtilis, Pseudomonas lachrymans, Ralstonia solanacearum, Staphylococcus hemolyticus, and Xanthomonas vesicatoria with MIC values in the range 25-100 μg/mL. Rhizopycnin D (6) and TMC-264 (8) strongly inhibited the spore germination of Magnaporthe oryzae with IC50 values of 9.9 and 12.0 μg/mL, respectively. TMC-264 (8) showed potent cytotoxicity against five human cancer cell lines (HCT-116, HepG2, BGC-823, NCI-H1650, and A2780) with IC50 values of 3.2-7.8 μM.

Natural occurrence of mycotoxins and toxigenic capacity of Alternaria strains from mouldy peppers

Sweet pepper (Capsicum annuum) is an important crop cultivated worldwide, with Argentina being one of the major producers in South America. The fruit is susceptible to several fungal diseases, leading to severe economic losses for producers. In this study, Alternaria was found as the prevalent genus in mouldy peppers (50% fruits infected). Morphological identification revealed that all 64 Alternaria isolates belonged to small-spored species, most of them corresponding to A. tenuissima, A. arborescens and A. alternata species-groups. Their secondary metabolite profile was evaluated in vitro; alternariols were synthesized by most of the isolates (91% for alternariol and 92% for alternariol monomethyl ether). A high number of Alternaria spp. also produced tenuazonic acid (64%), altenuene (84%) and tentoxin (72%). In addition, damaged pepper fruits were analysed for the presence of tenuazonic acid and alternariols. A total 32 out of 48 spoiled pepper fruits were contaminated with at least one of these metabolites. Half of the samples were positive for tenuazonic acid (range 8-11,422μg/kg), while alternariol and its monomethyl ether were less frequently detected (21 and 29%, respectively) and at lower concentrations. This is the first report on the natural occurrence of Alternaria mycotoxins in Argentinean sweet pepper, and highlights a consumer risk when mouldy fruits are used in industrialized products because these compounds are not destroyed by conventional heat treatments.

Possibility of Alternaria toxins reduction by extrusion processing of whole wheat flour

This study represents the first report about possibility of reduction of Alternaria toxins in wheat using the extrusion process. Effects of extrusion processing parameters - moisture content (w=16, 20, 24g/100g), feeding rate (q=15, 20, 25kg/h), and screw speed (v=300, 390, 480rpm), on reduction rate of tenuazonic acid (TeA), alternariol (AOH) and alternariol monomethyl ether (AME), in whole wheat flour were investigated. Temperature ranged between 111.1 and 160.8°C, while the absolute pressure was from 0.17 to 0.23MPa. The simultaneous influence of w and v was the most important for TeA reduction (p<0.05), while v and q were the most influential for AOH reduction (p<0.01). Level of AME reduction was mostly influenced by w and v (p<0.10). Optimal parameters for reduction of all three Alternaria toxins were as follows: w=24g/100g, q=25kg/h, v=390rpm, with a reduction of 65.6% for TeA, 87.9% for AOH and 94.5% for AME.

Validated UPLC-MS/MS Methods To Quantitate Free and Conjugated Alternaria Toxins in Commercially Available Tomato Products and Fruit and Vegetable Juices in Belgium

Ultraperformance liquid chromatography tandem mass spectrometry and Quick, Easy, Cheap, Effective, Rugged, and Safe based analytical methodologies to quantitate both free (alternariol (1), alternariol monomethyl ether (2), tenuazonic acid (3), tentoxin (4), altenuene (5), altertoxin-I (6)) and conjugated (sulfates and glucosides of 1 and 2) Alternaria toxins in fruit and vegetable juices and tomato products were developed and validated. Acceptable limits of quantitation (0.7-5.7 μg/kg), repeatability (RSDr < 15.7%), reproducibility (RSDR < 17.9%), and apparent recovery (87.0-110.6%) were obtained for all analytes in all matrices investigated. 129 commercial foodstuffs were analyzed, and 3 was detected in 100% of tomato product samples (<LOQ to 333 μg/kg), while 1, 2, 4, and 5 were also frequently detected (21-86%, <LOQ to 62 μg/kg). Moreover, low levels (<LOQ to 9.9 μg/kg) of modified Alternaria toxins (sulfates of 1 and 2) were repeatedly detected. A deterministic dietary exposure assessment revealed the possible risk for human health related to the presence of 1 and 2 in tomato based foodstuffs, whereas 3 is unlikely to be of human health concern.

Presence of Fusarium Species and Other Toxigenic Fungi in Malting Barley and Multi-Mycotoxin Analysis by Liquid Chromatography-High-Resolution Mass Spectrometry

A study was carried out on 43 malting barley samples collected in 2013 across the Umbria region (central Italy) to determine the incidence of the principal mycotoxigenic fungal genera, to identify the Fusarium species isolated from the grains, and to detect the presence of 34 fungal secondary metabolites by liquid chromatography-high-resolution mass spectrometry. The multimycotoxin-method development involved the evaluation of both a two-step solvent and QuEChERS protocol for metabolite extraction. The former protocol was selected because of better accuracy, which was evaluated on the basis of spike-recovery experiments. The most frequently isolated fungal species belonged to the genera Alternaria and Fusarium. The predominant Fusarium species was F. avenaceum, followed by F. graminearum. HT-2 toxin was the most frequently detected mycotoxin, followed by enniatin B, enniatin B1, T-2 toxin, and nivalenol. As a consequence of the observed mixed fungal infections, mycotoxin co-occurrence was also detected. A combination of mycological and mycotoxin analyses allowed the ability to obtain comprehensive information about the presence of mycotoxigenic fungi and their contaminants in malting barley cultivated in a specific geographic area.

Evaluation of Alternaria mycotoxins in strawberries: quantification and storage condition

Alternariol (AOH), alternariol methyl ether (AME) and tentoxin (TEN) are Alternaria mycotoxins produced by the most common post-harvest pathogens of fruits. The production of these metabolites depends on several environmental factors, mainly temperature, water activity, pH and the technological treatments that have been applied to the product. In this study, the occurrence of AOH, AME and TEN was evaluated in strawberries samples stored at different temperatures ranges (at 22 ± 2 or 6 ± 2°C) and different periods (up to 1 month) simulating the current practice of consumer's storage conditions. Sample extraction was performed using a liquid-liquid extraction method prior to LC-MS/MS analysis. AOH was the most prevalent mycotoxins with a 42% at strawberries stored at (22 ± 2)°C and 37% stored at (6 ± 2)°C. The highest AOH levels were found in samples conserved at (22 ± 2)°C ranging between 26 and 752 ng g(-1). AME levels ranged between 11 and 137 ng g(-)(1), which were found mainly in stored samples at (6 ± 2)°C for more than 28 days. None sample presented levels of TEN in either of the studied conditions.

New cytotoxic compounds of endophytic fungus Alternaria sp. isolated from Broussonetia papyrifera (L.) Vent

From the ethyl acetate extract of a culture of the endophytic fungus Alternaria species G7 in Broussonetia papyrifera, a new compound altertoxin IV (1) together with nine known compounds were isolated and identified by means of bioassay-guided fractionation. The structures of these compounds were established on the basis of spectroscopic methods, among which the absolute configuration of compound 1, a new tetrahydroperylenone derivative, was determined by means of X-Ray Crystallographic analysis. The isolated compounds were subjected to cytotoxic activity against three human cancer cell lines (A549, MG-63, and SMMC-7721). Compound 2 showed significant cytotoxic activities against tested cell lines, with IC50 values of 1.47, 2.11 and 7.34 μg/mL, respectively. Additionally, compound 4 also exhibited significant cytotoxic activities against cell lines MG-63 and SMMC-7721, with IC50 values of 0.53 and 2.92 μg/mL. Endophytic fungi Alternaria from B. papyrifera might be promising sources of natural bioactive and novel metabolites.

Temporal changes in fungal communities from buckwheat seeds and their effects on seed germination and seedling secondary metabolism

Seed-associated fungal communities affect multiple parameters of seed quality at all stages of production, from seed development to post-harvest storage and germination. We therefore investigated the diversity and dynamics of fungal communities in the seeds of common buckwheat (Fagopyrum esculentum) and Tartary buckwheat (F. tataricum) from harvest to 1 y of storage. Fungal populations in seeds were relatively stable, comprised mainly of field fungi. Incidence of fungi was most likely determined by fungal interspecies direct interactions, as well as by their synthesis of volatile organic compounds. Most prominent antagonistic interactions were seen for two plant pathogens, Alternaria alternata on Botrytis cinerea. Detrimental effects of the fungi on seed germination and seedling development were related to fungal extracellular enzyme activity, and in particular to amylase, cellulase and, polyphenol oxidase. Polyphenol and tannin concentrations in buckwheat seedlings were related to fungal growth rate and intensity of fungal cellulase activity, respectively, which suggests that physical penetration of the fungi through the host tissues is probably the stimulus for the activation of plant defence reactions in these seedlings.

Alternaria toxins of the alternariol type are not metabolised by human faecal microbiota

The metabolism of the Alternaria toxins alternariol (AOH), alternariol-9-O-methyl ether (AME) and altenuene (ALT) by the microbiota present in faeces from three human volunteers was studied. Faecal cultures were prepared as a 5% faeces suspension in brain-heart infusion broth and incubated with 50 μM of the toxins under anaerobic conditions for 72 h at 37 °C. The metabolism of AOH was also studied in pure bacterial cultures with either Escherichia coli DH5α or Lactobacillus plantarum BFE 5092 for 72 h at 37 °C. The three parent toxins were stable in uninoculated, heat-treated medium over a 72 h incubation period with a recovery of more than 90%. As a control for the activity of the faecal microbiota, the isoflavone daidzein was incubated with the faecal cultures and was transformed to its expected metabolites. In contrast, no metabolites of AOH, AME and ALT could be detected in the faecal cultures from the same volunteers, indicating that the gut microbiota was not capable of metabolising these substances. The Alternaria toxins could be shown to be at least partially bound to bacterial cells in a non-covalent manner, which may serve as a mechanism for their removal from the gut.

Colonization of grapes berries by Alternaria sp. and their ability to produce mycotoxins

Our research focused on identify the Alternaria species from grapes (surface sterilized berries and non-surface sterilized berries) of Slovak origin and characterize their toxinogenic potential in in vitro conditions. We analyzed 47 samples of grapes, harvested in years 2011, 2012 and 2013 from various wine-growing regions. For the isolation of species, the method of direct plating berries and surface-sterilized berries (using 1 % freshly pre-pared chlorine) on DRBC (Dichloran Rose Bengal Chloramphenicol agar) was used. For each analysis was used 50 berries. Only undamaged berries have been used for analysis. The cultivation was carried at 25 ±1°C, for 5 to 7 days in dark. After incubation, the colonies of Alternaria were transferred on PCA - potato-carrot agar and CYA - Czapek-yeast extract agar and cultured for 7 days at room temperature and natural light. A total 4 species-groups of the genus Alternaria were isolated from grapes berries: Alternaria alternata (1369 isolates), Alternaria arborescens (734 isolates), Alternaria infectoria (143 isolates), and Alternaria tenuissima (3579 isolates). According to European Union legislation mycotoxins produced by species genus Alternaria are not monitored in foods and food commodities. Mycotoxins such as alternariol and alternariol monomethylether are mutagenic and genotoxic in various in vitro systems. Selected strains were tested for production of altenuene, alternariol monomethylether and alternariol. In neither case of A. infectoria species-group isolates was confirmed the production of tested mycotoxins in in vitro conditions by TLC method. The ability to produce altenuene, alternariol monomethylether and alternariol in in vitro conditions was detected in isolates of Alternaria alternata, Alternaria arborescens and Alternaria tenuissima species-groups. Isolates of Alternaria alternata species-group (44 tested isolates) were able to produce altenuene (24 isolates), alternariol monomethyleter (42 isolates) and alternariol (43 isolates). Only one isolate did not produce any mycotoxins. Isolates of Alternaria arborescens species-group (38 tested isolates) were able to produce altenuene (24 isolates), alternariol monomethyleter (33 isolates) and alternariol (36 isolates). Only two isolates did not produce any mycotoxins. Isolates of Alternaria tenuissima species-group (87 tested isolates) were able to produce altenuene (42 isolates), alternariol monomethyleter (41 isolates) and alternariol (73 isolates). Thirteen isolates did not produce any mycotoxins.

Fluorescent Pseudomonads in the Phyllosphere of Wheat: Potential Antagonists Against Fungal Phytopathogens

Fluorescent pseudomonads isolated from wheat leaves were characterized regarding their antagonistic potential and taxonomy in relation to protect crop plants from infestation by Fusarium and Alternaria fungi causing diseases in wheat. Using a dual culture assay, inhibition of fungal growth was found for 40 isolates of 175 fluorescent pseudomonads. Twenty-two of the antagonists were able to suppress strains of Fusarium as well as Alternaria. By means of real-time qPCR, the phlD gene encoding the antibiotic 2,4-diacetylphloroglucinol was detected in 20 isolates. On the basis of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry spectral patterns, the isolates with antagonistic activity were assigned to the phylogenetic subgroup Pseudomonas fluorescens and the closely related Pseudomonas gessardii subgroup. The results of the study suggest that pseudomonads in the phyllosphere of crop plants may possibly contribute to natural plant protection.

A single-step solid phase extraction for the simultaneous determination of 8 mycotoxins in fruits by ultra-high performance liquid chromatography tandem mass spectrometry

A simple and rapid extraction procedure for the simultaneous determination of eight mycotoxins (Alternaria toxins, ochratoxin A, patulin, citrinin) in a variety of fruit matrices has been developed using ultra high performance liquid chromatography coupled to tandem mass spectrometry. The procedure involves a one-step cleanup using homemade solid phase extraction (SPE) cartridges. By comparative evaluation among six various adsorbents (C18, PSA, HLB, MCX, Silica, NH2), the combination of MCX and NH2 was found to provide the most effective cleanup, removing the greatest number of matrix interferences and also allowing the quantification of all analyzed mycotoxins in fruits. The optimized extraction conditions including acidified aqueous acetonitrile and an additional salt-out step using NaCl were employed before SPE cleanup. Method validation was performed by analyzing samples spiked at three levels (LOQ, 2 LOQ and 10 LOQ). Four fruits including apple, sweet cherry, tomato and orange fruits were selected, and accuracy (recovery%), precision (RSD%), limits of quantification (LOQ), linearity and matrix effect were evaluated during validation. Matrix-matched linearity with correlation coefficients ≥ 0.9921 was established in the range of 5-200 ng mL(-1) for patulin and 1-200 ng mL(-1) for other mycotoxins, respectively. Recoveries between 74.2% and 102.4% and relative standard deviations lower than 4.7% were obtained for all tested fruits. The matrix effect observed was low (≤ ± 17%) in all three fruit matrixes with the exception of orange, for which strong ion suppression was observed for alternariol (25.3%), ochratoxin A (31.6%) and citrinin (40.3%). Therefore, matrix-matched calibration was used for a correct quantification in order to compensate for matrix effect. The limits of quantification (LOQ), ranging from 1 to 5 μg kg(-1) depending on mycotoxins type, were always lower than maximum permitted levels for every regulated mycotoxin by the current European legislation.

Phenotypic and phylogenetic segregation of Alternaria infectoria from small-spored Alternaria species isolated from wheat in Germany and Russia

AIMS

To identify the taxonomic differences between phytopathogenic small-spored Alternaria strains isolated from wheat kernels in Germany and Russia by a polyphasic approach.

METHODS AND RESULTS

Ninety-five Alternaria (A.) strains were characterized by their colony colour, their three-dimensional sporulation patterns, mycotoxin production and phylogenetic relationships based on sequence variation in translation elongation factor 1-α (TEF1-α). The examination of toxin profiles and the phylogenetic features via TEF1-α resulted in two distinct clusters, in each case containing Alternaria infectoria isolates (92 and 96% respectively) in the first and the Alternaria alternata, Alternaria arborescens and Alternaria tenuissima isolates (77 and 79% respectively) in the other combined cluster. The production of Alternariol, Altertoxin and Altenuene has not been reported previously in the A. infectoria species group. The isolates from Germany and Russia differ slightly in species composition and mycotoxin production capacity.

CONCLUSIONS

We identified that the A. infectoria species group can be differentiated from the A. alternata, A. arborescens and A. tenuissima species group by colour, low mycotoxin production and by the sequence variation in TEF1-α gene.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results allow a reliable toxic risk assessment when detecting different Alternaria fungi on cereals.