Analyses of black Aspergillus species of peanut and maize for ochratoxins and fumonisins

Fumonisin distorts the cellular membrane lipid profile: A mechanistic insight

Monitoring modifications in membrane lipids in association with external stimuli/agents, including fumonisins (FUMs), is a widely employed approach to assess cellular metabolic response/status. FUMs are prevalent fusariotoxins worldwide that have diverse structures with varying toxicity across species; nevertheless, they can induce metabolic disturbances and disease, including cancer. The capacity of FUMs to disrupt membrane lipids, demonstrated across numerous species and organs/tissues, is ascribed to a multitude of factors/events, which range from direct to indirect effects. Certain events are well established, whereas the potential consequences of others remain speculative. The most notable effect is their resemblance to sphingoid bases, which impacts the synthesis of ceramides leading to numerous changes in lipids' composition that are not limited to sphingolipids' composition of the membranes. The next plausible scenario involves the induction of oxidative stress, which is considered an indirect/secondary effect of FUMs. Additional modes of action include modifications of enzyme activities and nuclear signals related to lipid metabolism, although these are likely not yet fully comprehended. This review provides in-depth insight into the current state of these events and their potential mechanistic actions in modifying membrane lipids, with a focus on long-chain fatty acids. This paper also presents a detailed description of the reported modifications to membrane lipids by FUMs.

Normalization of LC-MS mycotoxin determination using the N-alkylpyridinium-3-sulfonates (NAPS) retention index system

A major challenge for LC-MS analysis is the ability to compare data between laboratories and across instrument platforms. Currently, mycotoxin determination relies on dereplication strategies based on physicochemical properties such as the m/z of the precursor and product ions. Unlike these intrinsic properties, retention time (t_R) is an extrinsic property impacted by LC conditions, including mobile phases and column chemistry, making exchange of data between groups difficult. To address this, we are introducing the concept of incorporating an electrospray compatible, retention index (RI) system based on a series of N-alkylpyridinium-3-sulfonates (NAPS) into routine mycotoxin determination. These standards of differing alkyl chain length span RI units from 100 to 2000, are UV active and have fixed positive and negative charges for electrospray ionization in either mode. Using high resolution LC-MS/MS, the RIs of 96 mycotoxins and fungal secondary metabolites were normalized as a proof of concept with the NAPS RI system under multiple pH, column and gradient chromatographic conditions. This method was then applied to the analysis of a crude extract of Penicillium roqueforti, where we were able to decrease the number of false positives by implementing an RI filter as well as a secondary correction factor. Additionally, we developed software that allows users to convert published RIs to a predicted t_R values. Integration of the NAPS RI system into routine LC-MS analysis will improve compound identifications and help facilitate ease of data sharing.

Sphinganine-Analog Mycotoxins (SAMs): Chemical Structures, Bioactivities, and Genetic Controls

Sphinganine-analog mycotoxins (SAMs) including fumonisins and A. alternata f. sp. Lycopersici (AAL) toxins are a group of related mycotoxins produced by plant pathogenic fungi in the Fusarium genus and in Alternaria alternata f. sp. Lycopersici, respectively. SAMs have shown diverse cytotoxicity and phytotoxicity, causing adverse impacts on plants, animals, and humans, and are a destructive force to crop production worldwide. This review summarizes the structural diversity of SAMs and encapsulates the relationships between their structures and biological activities. The toxicity of SAMs on plants and animals is mainly attributed to their inhibitory activity against the ceramide biosynthesis enzyme, influencing the sphingolipid metabolism and causing programmed cell death. We also reviewed the detoxification methods against SAMs and how plants develop resistance to SAMs. Genetic and evolutionary analyses revealed that the FUM (fumonisins biosynthetic) gene cluster was responsible for fumonisin biosynthesis in Fusarium spp. Sequence comparisons among species within the genus Fusarium suggested that mutations and multiple horizontal gene transfers involving the FUM gene cluster were responsible for the interspecific difference in fumonisin synthesis. We finish by describing methods for monitoring and quantifying SAMs in food and agricultural products.

Mycotoxins and the Enteric Nervous System

Mycotoxins are secondary metabolites produced by various fungal species. They are commonly found in a wide range of agricultural products. Mycotoxins contained in food enter living organisms and may have harmful effects on many internal organs and systems. The gastrointestinal tract, which first comes into contact with mycotoxins present in food, is particularly vulnerable to the harmful effects of these toxins. One of the lesser-known aspects of the impact of mycotoxins on the gastrointestinal tract is the influence of these substances on gastrointestinal innervation. Therefore, the present study is the first review of current knowledge concerning the influence of mycotoxins on the enteric nervous system, which plays an important role, not only in almost all regulatory processes within the gastrointestinal tract, but also in adaptive and protective reactions in response to pathological and toxic factors in food.

Mycotoxins: A Fungal Genomics Perspective

The chemical and enzymatic diversity in the fungal kingdom is staggering. Large-scale fungal genome sequencing projects are generating a massive catalog of secondary metabolite biosynthetic genes and pathways. Fungal natural products are a boon and bane to man as valuable pharmaceuticals and harmful toxins. Understanding how these chemicals are synthesized will aid the development of new strategies to limit mycotoxin contamination of food and feeds as well as expand drug discovery programs. A survey of work focused on the fumonisin family of mycotoxins highlights technological advances and provides a blueprint for future studies of other fungal natural products. Expressed sequence tags led to the discovery of new fumonisin genes (FUM) and hinted at a role for alternatively spliced transcripts in regulation. Phylogenetic studies of FUM genes uncovered a complex evolutionary history of the FUM cluster, as well as fungi with the potential to synthesize fumonisin or fumonisin-like chemicals. The application of new technologies (e.g., CRISPR) could substantially impact future efforts to harness fungal resources.

Diversity of Mycotoxin-Producing Black Aspergilli in Canadian Vineyards

Several Aspergillus species produce ochratoxin A (OTA) and/or fumonisins on wine and table grapes. The relevant species and their mycotoxins have been investigated in a number of wine-producing regions around the world; however, similar data have not been reported for Canadian vineyards. A multiyear survey of black Aspergilli in Niagara, ON, vineyards was conducted to determine the diversity of species present and to assess the risk of OTA and fumonisin contamination of wine grapes from this region. From 2012 to 2014, 253 black Aspergilli were isolated from soil samples and the fruits of 10 varieties of grapes. The isolates were identified by DNA sequencing: Aspergillus welwitschiae (43%), Aspergillus uvarum (32%), Aspergillus brasiliensis (11%), Aspergillus tubingensis (9%), and Aspergillus niger (4%). Aspergillus carbonarius, the primary OTA producer on grapes in other parts of the world, was isolated only once, and this is the first report for it in Canada. All 10 A. niger strains produced fumonisins, but, in contrast, only 26% of the 109 A. welwitschiae isolates were producers, and no strains of either species produced OTA. Grape samples were analyzed for OTA and fumonisins from sites where strains with mycotoxigenic potential were isolated. Fumonisin B2 (FB2) was detected in 7 of 22 (32%) of these grape samples in the 1-15 ppb range, but no OTA was detected. Additionally, the recently reported nonaminated fumonisins were detected in 3 of 22 grape samples. These results suggest that fumonisin-producing Aspergilli can occur in Ontario vineyards but, at present, the risk of contamination of grapes appears low. The risk of OTA contamination in Niagara wine is also low because of the low prevalence of A. carbonarius.

Product ion filtering with rapid polarity switching for the detection of all fumonisins and AAL-toxins

RATIONALE

Fumonisins and AAL-toxins are structurally similar mycotoxins that contaminate agricultural crops and foodstuffs. Traditional analytical screening methods are designed to target the known compounds for which standards are available but there is clear evidence that many other derivatives exist and could be toxic. A fast, semi-targeted method for the detection of all known fumonisins, AAL-toxins and related emerging toxins is required.

METHODS

Strains of Fusarium verticillioides, Alternaria arborescens and Aspergillus welwitschiae were grown on their associated crops (maize, tomatoes, and grapes, respectively). Extracts were first analyzed in negative mode using product ion filtering to detect the tricarballylic ester product ion that is common to fumonisins and AAL-toxins (m/z 157.0142). During the same liquid chromatography (LC) run, rapid polarity switching was then used to collect positive mode tandem mass spectrometric (MS(2) ) data for characterization of the detected compounds.

RESULTS

Fumonisin B1 , B2 , B3 and B4 were detected on Fusarium contaminated maize, AAL-toxins TA, TB, TD, TE were detected on Alternaria inoculated tomatoes and fumonisin B2 , B4 and B6 on Aspergillus contaminated grapes. Additionally, over 100 structurally related compounds possessing a tricarballylic ester were detected from the mould inoculated plant material. These included a hydroxyl-FB1 from F. verticillioides inoculated maize, keto derivatives of AAL-toxins from A. arborescens inoculated tomatoes, and two previously unreported classes of non-aminated fumonisins from Asp. welwitschiae contaminated grapes.

CONCLUSIONS

A semi-targeted method for the detection of all fumonisins and AAL-toxins in foodstuffs was developed. The use of the distinctive tricarballylic ester product anion for detection combined with rapid polarity switching and positive mode MS(2) is an effective strategy for differentiating between known isomers such as FB1 and FB6 . This analytical tool is also effective for the identification of new compounds as evident from the discoveries of the previously unreported hydroxyl-FB1 , keto-AAL-toxins, and the two new families of non-aminated fumonisins.

An aptamer based surface plasmon resonance biosensor for the detection of ochratoxin A in wine and peanut oil

Ochratoxin A (OTA), as a kind of chlorophenolic mycotoxin, exist widely in plant origin food and is harmful to human. Herein, a surface plasmon resonance (SPR) biosensor using an anti-OTA aptamer immobilized sensor chip was developed to measure ochratoxin A (OTA) quantificationally through a straightforward direct binding assay. The streptavidin protein as a crosslinker was immobilized onto the surface of a sensor chip and the biotin-aptamer was captured through streptavidin-biotin interaction. The biosensor exhibited a detection range from 0.094 to 100ng/mL (linear range from 0.094 to 10ng/mL) of OTA with a lower detection limit of 0.005ng/mL. Detection of OTA in wine and peanut oil was further performed in the SPR biosensor using simple liquid-liquid extraction for sample pretreatments. Recoveries of ochratoxin A from spiked samples ranged from 86.9% to 116.5% and coefficients of variation (CVs) ranged from 0.2% to 6.9%. The developed methods in our studies showed good analytical performances with limits of detection much lower than the maximum residue limit, as well as a good reproducibility and stability.