FUM and BIK gene expression contribute to describe fumonisin and bikaverin synthesis in Fusarium verticillioides

Relationship Between Mycotoxin Production and Gene Expression in Fusarium graminearum Species Complex Strains Under Various Environmental Conditions

The Fusarium graminearum species complex (FGSC) can produce various mycotoxins and is a major concern for food quantity and quality worldwide. In this study, we determined the effects of water activity (a_w), temperature, incubation time and their interactions on mycotoxin accumulation and the expression levels of biosynthetic genes in FGSC strains from maize samples in China. The highest deoxynivalenol (DON), 3-acetyldeoxynivalenol(3ADON) and 15-acetyldeoxynivalenol (15ADON) levels of the F. boothii and F. graminearum strains were observed at 0.98 a_w/30 °C or 0.99 a_w/25 °C. F. asiaticum and F. meridionale reached maximum nivalenol (NIV) and 4-acetylnivalenol (4ANIV) contents at 0.99 a_w and 30 °C. With the extension of the incubation time, the concentrations of DON and NIV gradually increased, while those of their derivatives decreased. F. boothii, F. meridionale and one F. asiaticum strain had the highest zearalenone (ZEN) values at 0.95 a_w and 25 °C, while the optimum conditions for the other F. asiaticum strain and F. graminearum were 0.99 a_w and 30 °C. Four genes associated with trichothecene and zearalenone synthesis were significantly induced under higher water stress in the early stage of production. The results indicated independence of mycotoxin production and gene expression, as maximum amounts of these toxic metabolites were observed at higher a_w in most cases. This study provides useful information for the monitoring and prevention of such toxins entering the maize production chain.

Effect of Abiotic Conditions on Growth, Mycotoxin Production, and Gene Expression by Fusarium fujikuroi Species Complex Strains from Maize

Fusarium fujikuroi species complex (FFSC) strains are a major concern for food quantity and quality due to their strong ability to synthesize mycotoxins. The effects of interacting conditions of water activity, temperature, and incubation time on the growth rate, toxin production, and expression level of biosynthetic genes were examined. High temperature and water availability increased fungal growth. Higher water activity was in favor of toxin accumulation. The maximum amounts of fusaric acid (FA) and fumonisin B1 (FB1) were usually observed at 20–25 °C. F. andiyazi could produce a higher content of moniliformin (MON) in the cool environment than F. fujikuroi. The expression profile of biosynthetic genes under environmental conditions varied wildly; it was suggested that these genes might be expressed in a strain-dependent manner. FB1 concentration was positively related to the expression of FUM1, while a similar correlation of FUB8 and FUB12 with FA production could be observed in F. andiyazi, F. fujikuroi, and F. subglutinans. This study provides useful information in the monitoring and prevention of such toxins entering the maize production chain.

Bacillomycin D-C16 inhibits growth of Fusarium verticillioides and production of fumonisin B1 in maize kernels

Fusarium verticillioides causes ear and kernel rot in maize and produces mycotoxins, like fumonisin B₁ (FB₁). Bacillomycin D-C16 is a natural antimicrobial lipopeptide produced by Bacillus subtilis. In this study, the inhibitory effects of Bacillomycin D-C16 on the growth of F. verticillioides and on the production of FB₁ in maize were investigated. Bacillomycin D-C16 displayed strong fungicidal activity against F. verticillioides, with a minimum inhibitory concentration (MIC) of 32 g/L. Scanning electron microscopy (SEM) showed that Bacillomycin D-C16 altered the morphology of F. verticillioides mycelia. Bacillomycin D-C16 reduced the ergosterol content, increased the release of nucleic acids and proteins, and increased the levels of reactive oxygen species (ROS) in fungal mycelia. Bacillomycin D-C16 also significantly inhibited the production of FB₁ by inhibiting mycelial growth and decreasing the levels of fumonisin biosynthetic genes 1 (fum1), fum6 and fum14. The application of Bacillomycin D-C16 on maize kernels prior to storage inhibited the growth of F. verticillioides and the production of FB₁. Our results suggested that Bacillomycin D-C16 has a significant antifungal activity that could be used as a potential natural antimicrobial agent to control food contamination and to ensure food safety.

Fungal quinones: diversity, producers, and applications of quinones from Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium

Quinones represent an important group of highly structurally diverse, mainly polyketide-derived secondary metabolites widely distributed among filamentous fungi. Many quinones have been reported to have important biological functions such as inhibition of bacteria or repression of the immune response in insects. Other quinones, such as ubiquinones are known to be essential molecules in cellular respiration, and many quinones are known to protect their producing organisms from exposure to sunlight. Most recently, quinones have also attracted a lot of industrial interest since their electron-donating and -accepting properties make them good candidates as electrolytes in redox flow batteries, like their often highly conjugated double bond systems make them attractive as pigments. On an industrial level, quinones are mainly synthesized from raw components in coal tar. However, the possibility of producing quinones by fungal cultivation has great prospects since fungi can often be grown in industrially scaled bioreactors, producing valuable metabolites on cheap substrates. In order to give a better overview of the secondary metabolite quinones produced by and shared between various fungi, mainly belonging to the genera Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium, this review categorizes quinones into families such as emodins, fumigatins, sorbicillinoids, yanuthones, and xanthomegnins, depending on structural similarities and information about the biosynthetic pathway from which they are derived, whenever applicable. The production of these quinone families is compared between the different genera, based on recently revised taxonomy. KEY POINTS: • Quinones represent an important group of secondary metabolites widely distributed in important fungal genera such as Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium. • Quinones are of industrial interest and can be used in pharmacology, as colorants and pigments, and as electrolytes in redox flow batteries. • Quinones are grouped into families and compared between genera according to the revised taxonomy.

Natural blue pigments and bikaverin

In last years, the main studied microbial sources of natural blue pigments have been the eukaryotic algae, Rhodophytes and Cryptophytes, and the cyanobacterium Arthrospira (Spirulina) platensis, responsible for the production of phycocyanin, one of the most important blue compounds approved for food and cosmetic use. Recent research also includes the indigoidine pigment from the bacteria Erwinia, Streptomyces and Photorhabdus. Despite these advances, there are still few options of microbial blue pigments reported so far, but the interest in these products is high due to the lack of stable natural blue pigments in nature. Filamentous fungi are particularly attractive for their ability to produce pigments with a wide range of colors. Bikaverin is a red metabolite present mainly in species of the genus Fusarium. Although originally red, the biomass containing bikaverin changes its color to blue after heat treatment, through a mechanism still unknown. In addition to the special behavior of color change by thermal treatment, bikaverin has beneficial biological properties, such as antimicrobial and antiproliferative activities, which can expand its use for the pharmaceutical and medical sectors. The present review addresses the production natural blue pigments and focuses on the properties of bikaverin, which can be an important source of blue pigment with potential applications in the food industry and in other industrial sectors.

FvatfA regulates growth, stress tolerance as well as mycotoxin and pigment productions in Fusarium verticillioides

FvatfA from the maize pathogen Fusarium verticillioides putatively encodes the Aspergillus nidulans AtfA and Schizasaccharomyces pombe Atf1 orthologous bZIP-type transcription factor, FvAtfA. In this study, a ΔFvatfA deletion mutant was constructed and then genetically complemented with the fully functional FvatfA gene. Comparing phenotypic features of the wild-type parental, the deletion mutant and the restored strains shed light on the versatile regulatory functions played by FvAtfA in (i) the maintenance of vegetative growth on Czapek-Dox and Potato Dextrose agars and invasive growth on unwounded tomato fruits, (ii) the preservation of conidiospore yield and size, (iii) the orchestration of oxidative (H₂O₂, menadione sodium bisulphite) and cell wall integrity (Congo Red) stress defences and (iv) the regulation of mycotoxin (fumonisins) and pigment (bikaverin, carotenoid) productions. Expression of selected biosynthetic genes both in the fumonisin (fum1, fum8) and the carotenoid (carRA, carB) pathways were down-regulated in the ΔFvatfA strain resulting in defected fumonisin production and considerably decreased carotenoid yields. The expression of bik1, encoding the polyketide synthase needed in bikaverin biosynthesis, was not up-regulated by the deletion of FvatfA meanwhile the ΔFvatfA strain produced approximately ten times more bikaverin than the wild-type or the genetically complemented strains. The abolishment of fumonisin production of the ΔFvatfA strain may lead to the development of new-type, biology-based mycotoxin control strategies. The novel information gained on the regulation of pigment production by this fungus can be interesting for experts working on new, Fusarium-based biomass and pigment production technologies.

Key points • FvatfA regulates vegetative and invasive growths of F. verticillioides. • FvatfA also orchestrates oxidative and cell wall integrity stress defenses. • The ΔFvatfA mutant was deficient in fumonisin production. • FvatfA deletion resulted in decreased carotenoid and increased bikaverin yields.

Effect of Tebuconazole Enantiomers and Environmental Factors on Fumonisin Accumulation and FUM Gene Expression in Fusarium verticillioides

Fusarium verticillioides is an important corn pathogen that can produce fumonisins (FBs) under certain environmental conditions. In this study, we evaluated the enantioselective impact of tebuconazole enantiomers on the growth and FB production of F. verticillioides on maize-based media at different abiotic factors. The expression of FB biosynthetic genes ( FUM1 and FUM6) was quantified by real-time reverse transcription polymerase chain reaction. The results showed that water activity ( a_w), temperature, and types of tebuconazole significantly affected the growth of F. verticillioides. The order of fungicidal activity was (-)-tebuconazole > rac-tebuconazole > (+)-tebuconazole. (-)-tebuconazole exhibited the maximal selective fungicidal activity (242-fold) against F. verticillioides at 0.95 a_w and 35 °C. Production of fumonisin B₁ (FB₁) and fumonisin B₂ (FB₂) by F. verticillioides was influenced by a_w, temperature, types of tebuconazole, and dose. Under most conditions, (-)-tebuconazole showed stronger inhibition for FB₁ and FB₂ production than (+)-tebuconazole (1.87-2.85-fold reduction in FBs) and rac-tebuconazole. The optimal environmental condition for FB production was at 0.99 a_w and 25 °C. Tebuconazole enantiomers differently affected FB biosynthetic gene ( FUM1 and FUM6) expression, but the effects on FB production and gene expression showed no positive correlation. The present study provides a better understanding on ways to minimize FB production in corn treated with fungicides.

Dissecting Symptomatology and Fumonisin Contamination Produced by Fusarium verticillioides in Maize Ears

The fungus Fusarium verticillioides can infect maize ears, contaminating the grain with mycotoxins, including fumonisins. This global public health threat can be managed by breeding maize varieties that are resistant to colonization by F. verticillioides and by sorting grain after harvest to reduce fumonisin levels in food systems. Here, we employed two F. verticillioides inoculation techniques representing distinct infection pathways to dissect ear symptomatology and morphological resistance mechanisms in a diverse panel of maize inbred lines. The "point" method involved penetrating the ear with a spore-coated toothpick and the "inundative" method introduced a liquid spore suspension under the husk of the ear. We evaluated quantitative and qualitative indicators of external and internal symptom severity as low-cost proxies for fumonisin contamination, and found that kernel bulk density was predictive of fumonisin levels (78 to 84% sensitivity; 97 to 99% specificity). Inundative inoculation resulted in greater disease severity and fumonisin contamination than point inoculation. We also found that the two inoculation methods implicated different ear tissues in defense, with cob morphology being a more important component of resistance under point inoculation. Across both inoculation methods, traits related to cob size were positively associated with disease severity and fumonisin content. Our work demonstrates that (i) the use of diverse modes of inoculation is necessary for combining complementary mechanisms of genetic resistance, (ii) kernel bulk density can be used effectively as a proxy for fumonisin levels, and (iii) trade-offs may exist between yield potential and resistance to fumonisin contamination.

Mechanism of action of AMP-jsa9, a LI-F-type antimicrobial peptide produced by Paenibacillus polymyxa JSa-9, against Fusarium moniliforme

LI-F type peptides (AMP-jsa9) are a group of cyclic lipodepsipeptides that exhibit broad antimicrobial spectrum against Gram-positive bacteria and filamentous fungi. We sought to assess the toxicity of AMP-jsa9 and the mechanism of AMP-jsa9 action against Fusarium moniliforme. AMP-jsa9 exhibited weak hemolytic activity and weak cytotoxicity at antimicrobial concentrations (32μg/ml). Confocal laser microscopy, SEM, and TEM indicated that AMP-jsa9 primarily targets the cell wall, plasma membrane, and cytoskeleton, increases membranepermeability, and enhances cytoplasm leakage (e.g., K⁺, protein). Quantitative proteomic analysis using isobaric tags for relative and absolute quantitation (iTRAQ) detected a total of 162 differentially expressed proteins (59 up-regulated and 103 down-regulated) following treatment of F. moniliforme with AMP-jsa9. AMP-jsa9 treatment also led to reductions in chitin, ergosterol, NADH, NADPH, and ATP levels. Moreover, fumonisin B₁ expression and biosynthesis was suppressed in AMP-jsa9-treated F. moniliforme. Our results provide a theoretical basis for the application of AMP-jsa9 as a natural and effective antifungal agent in the agricultural, food, and animal feed industries.

Fumonisins and their modified forms, a matter of concern in future scenario?

Masked mycotoxins are found in grains and derived foods as a result of plant phase II metabolism. Recently, masked mycotoxins senso strictu, together with other covalently or non-covalently conjugated forms, even formed upon processing, have been classified as modified mycotoxins. In this context, the issue of modified fumonisins is of great interest, on account of the wide range of factors affecting their formation and accumulation in maize pre- and postharvest. Fumonisins, indeed, may undergo modification in plants, along the growing season, but also during storage and drying of maize kernels, and upon processing. All these modifications strongly affect the analytical outcome, thus making more difficult the assessment of maize compliance. Since the ratio between free and modified fumonisins is affected by maize composition and environmental factors, a deeper knowledge on the phenomena driving the production and accumulation of free and modified forms in plants may support the selection of resistant hybrids. This review provides a critical picture of the state of the art on this topic, mainly focusing on those events occurring in field, identified as crucial in determining amount and partitioning of contamination. Nevertheless, knowledge on modified fumonisins is still in its dawn, on account of the wide range of factors involved. Anyway, reported results, taking altogether, clearly indicate that modified fumonisins should be included in the monitoring plans to have an overview of the possible contribution to human exposure. Furthermore, next efforts should focus on the events occurring in field and on the cross-talk between the plant and the fungus, to support the identification of resistant hybrids and to provide data for predictive models, the most suitable tool to forecast what is going to happens in the future changing climate.

Influence of Butylated Hydroxyanisole on the Growth, Hyphal Morphology, and the Biosynthesis of Fumonisins in Fusarium proliferatum

Fusarium proliferatum as a common fungus pathogen in foods can produce toxic fumonisins, which can cause animal diseases and increase risks of human cancers. On contrary, butylated hydroxyanisole (BHA) as a synthetic antioxidant offers a clue for preventing growth of fungal species and inhibiting production of mycotoxins. Unfortunately, information of the inhibitory mechanism of BHA on Fusarium species is still limited. In this study, influence of BHA treatment on growth and inhibition of fumonisin production in relation to the expression of the fumonisin biosynthesis-related genes of the F. proliferatum ZYF was investigated, which revealed that BHA had a negative influence on growth and fumonisin production of F. proliferatum. To further elucidate the mechanism of BHA on the growth of F. proliferatum, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the F. proliferatum hyphae. The BHA treatment induced the loss of cytoplasm and cellular constituents, as well as distortion of mycelia, but it did not directly degrade the fumonisin. Furthermore, the BHA treatment markedly inhibited the expressions of FUM1 (a polyketide synthase encoding gene) and FUM8 (an aminotransferase encoding gene) genes, which resulted in the depression of metabolic pathway of F. proliferatum. The transcriptional analyses of the FUM1 and FUM8 genes confirmed a correlation between the fumonisin production and its gene expression. This study provided some insights into mechanisms of production of fumonisin and feasible prevention to reduce fumonisin contamination in favor of human and animal health.

Conservation and divergence of the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) pathway in two plant-pathogenic fungi: Fusarium graminearum and F. verticillioides

The cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) pathway is a central signalling cascade that transmits extracellular stimuli and governs cell responses through the second messenger cAMP. The importance of cAMP signalling in fungal biology has been well documented and the key conserved components, adenylate cyclase (AC) and the catalytic subunit of PKA (CPKA), have been functionally characterized. However, other genes involved in this signalling pathway and their regulation are not well understood in filamentous fungi. Here, we performed a comparative transcriptomics analysis of AC and CPKA mutants in two closely related fungi: Fusarium graminearum (Fg) and F. verticillioides (Fv). Combining available Fg transcriptomics and phenomics data, we reconstructed the Fg cAMP signalling pathway. We developed a computational program that combines sequence conservation and patterns of orthologous gene expression to facilitate global transcriptomics comparisons between different organisms. We observed highly correlated expression patterns for most orthologues (80%) between Fg and Fv. We also identified a subset of 482 (6%) diverged orthologues, whose expression under all conditions was at least 50% higher in one genome than in the other. This enabled us to dissect the conserved and unique portions of the cAMP-PKA pathway. Although the conserved portions controlled essential functions, such as metabolism, the cell cycle, chromatin remodelling and the oxidative stress response, the diverged portions had species-specific roles, such as the production and detoxification of secondary metabolites unique to each species. The evolution of the cAMP-PKA signalling pathway seems to have contributed directly to fungal divergence and niche adaptation.

Effect of fungicide application to control Fusarium head blight and 20 Fusarium and Alternaria mycotoxins in winter wheat (Triticum aestivum L.)

Azole fungicides have been reported to be the most effective active substances in the control of Fusarium Head Blight (FHB) and in the reduction of the main mycotoxins that occur in cereal grain, such as deoxynivalenol (DON). Four field experiments have been conducted in North West Italy, over a period of 2 growing seasons, in order to evaluate the effect of azole fungicide (prothioconazole) applications on the prevalence of emerging mycotoxins in common winter wheat under naturally-infected field conditions. Wheat samples have been analysed by means of a dilute-and-shoot multi-mycotoxin LC-MS/MS method. Twenty fungal metabolites were detected: enniatins, aurofusarin, moniliformin, equisetin, DON, deoxynivalenol-3-glucoside, culmorin, bikaverin, beauvericin, fumonisins, fusaric acid, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, nivalenol, zearalenone, decalonectrin, butenolide, tentoxin, alternariol and alternariol methyl ether. The most abundant fungal metabolites were DON and culmorin, with an average contamination in the untreated control of 1,360 μg/kg and 875 μg/kg, respectively, in the growing season with the highest disease pressure (2011-2012). On average, the results have shown that the fungicide application significantly reduced the enniatins (from 127 μg/kg to 46 μg/kg), aurofusarin (from 62 μg/kg to 21 μg/kg), moniliformin (from 32 μg/kg to 16 μg/kg), tentoxin (from 5.2 μg/kg to 2.5 μg/kg) and equisetin (from 0.72 μg/kg to 0.06 μg/kg) contents in all the experiments. However, DON, deoxynivalenol-3-glucoside and culmorin were only significantly reduced in the growing season with the highest disease pressure. The other fungal metabolites were mainly found in traces in the untreated plots. These results, which have been obtained in different environmental and agronomic conditions, have underlined for the first time that the fungicide usually applied to control the FHB and DON content, also consistently reduces the main emerging mycotoxins of winter wheat in temperate areas.

Role of the European corn borer (Ostrinia nubilalis) on contamination of maize with 13 Fusarium mycotoxins

The European corn borer (ECB) plays an important role in promoting Fusarium verticillioides infections and in the consequent fumonisin contamination in maize grain in temperate areas. The objective of this study was to evaluate whether the ECB feeding activity could also affect the occurrence of emerging mycotoxins in maize kernels. During the 2008-10 period, natural infestation of the insect was compared, in field research, with the protection of infestation, which was obtained by using an entomological net. The ears collected in the protected plots were free from ECB attack, while those subject to natural insect attacks showed a damage severity that varied from 10% to 25%. The maize samples were analysed by means of an LC-MS/MS-based multi-mycotoxin method, which led to the detection of various metabolites: fumonisins (FUMs), fusaproliferin (FUS), moniliformin (MON), bikaverin (BIK), beauvericin (BEA), fusaric acid (FA), equisetin (EQU), deoxynivalenol (DON), deoxynivalenol-3-glucoside (DON-3-G), zearalenone (ZEA), culmorin (CULM), aurofusarin (AUR) and butenolide (BUT). The occurrence of mycotoxins produced by Fusarium spp. of Liseola section was affected significantly by the ECB feeding activity. The presence of ECB injuries increased the FUMs from 995 to 4694 µg kg(-1), FUS from 17 to 1089 µg kg(-1), MON from 22 to 673 µg kg(-1), BIK from 58 to 377 µg kg(-1), BEA from 6 to 177 µg kg(-1), and FA from 21 to 379 µg kg(-1). EQU, produced by F. equiseti section Gibbosum, was also increased by the ECB activity, by 1-30 µg kg(-1) on average. Instead, the content of mycotoxins produced by Fusarium spp. of Discolor and Roseum sections was not significantly affected by ECB activity. As for FUMs, the application of a strategy that can reduce ECB damage could also be the most effective solution to minimise the other mycotoxins produced by Fusarium spp. of Liseola section.