Production of fusaric acid by Fusarium species

Back to the roots: a reappraisal of Neocosmospora

The genus Neocosmospora (Fusarium solani species complex) contains saprobes, plant endophytes and pathogens of major economic significance as well as opportunistic animal pathogens. Advances in biological and phylogenetic species recognition revealed a rich species diversity which has largely remained understudied. Most of the currently recognised species lack formal descriptions and Latin names, while the taxonomic utility of old names is hampered by the lack of nomenclatural type specimens. Therefore, to stabilise the taxonomy and nomenclature of these important taxa, we examined type specimens and representative cultures of several old names by means of morphology and phylogenetic analyses based on rDNA (ITS and LSU), rpb2 and tef1 sequences. Sixty-eight species are accepted in Neocosmospora, 29 of them described herein as new; while 13 new combinations are made. Eleven additional phylogenetic species are recognized, but remain as yet undescribed. Lectotypes are proposed for eight species, seven species are epitypified and two species are neotypified. Notes on an additional 17 doubtful or excluded taxa are provided.

Improvement of bioactive metabolite production in microbial cultures-A systems approach by OSMAC and deconvolution-based 1 HNMR quantification

Traditionally, the screening of metabolites in microbial matrices is performed by monocultures. Nonetheless, the absence of biotic and abiotic interactions generally observed in nature still limit the chemical diversity and leads to "poorer" chemical profiles. Nowadays, several methods have been developed to determine the conditions under which cryptic genes are activated, in an attempt to induce these silenced biosynthetic pathways. Among those, the one strain, many compounds (OSMAC) strategy has been applied to enhance metabolic production by a systematic variation of growth parameters. The complexity of the chemical profiles from OSMAC experiments has required increasingly robust and accurate techniques. In this sense, deconvolution-based ¹ HNMR quantification have emerged as a promising methodology to decrease complexity and provide a comprehensive perspective for metabolomics studies. Our present work shows an integrated strategy for the increased production and rapid quantification of compounds from microbial sources. Specifically, an OSMAC design of experiments (DoE) was used to optimize the microbial production of bioactive fusaric acid, cytochalasin D and 3-nitropropionic acid, and Global Spectral Deconvolution (GSD)-based ¹ HNMR quantification was carried out for their measurement. The results showed that OSMAC increased the production of the metabolites by up to 33% and that GSD was able to extract accurate NMR integrals even in heavily coalescence spectral regions. Moreover, GSD-¹ HNMR quantification was reproducible for all species and exhibited validated results that were more selective and accurate than comparative methods. Overall, this strategy up-regulated important metabolites using a reduced number of experiments and provided fast analyte monitor directly in raw extracts.

Histological and Gene Expression Analyses in Banana Reveals the Pathogenic Differences between Races 1 and 4 of Banana Fusarium Wilt Pathogen

Fusarium oxysporum f. sp. cubense, the causative agent of Panama disease, is classified into three races: Foc1, Foc2, and Foc4. However, the histological characteristics, the accumulation of fusaric acid (FA), and resistant gene expression in banana infected with different races remain unclear. In this study, we compared the infection processes, FA contents, and gene expression levels in a Cavendish banana cultivar (Musa AAA Brazilian) inoculated with Foc1 and Foc4. Results showed that Foc4 can rapidly extend from the roots to the leaves, whereas Foc1 expands slowly from the roots to the rhizomes but cannot expand further upward. In addition, the colonization of plants by Foc4 was significantly higher compared with Foc1, as was the content of FA in those infected plant tissues. We observed that a large amount of starch granules was produced in the rhizomes and the number of starch granules was significantly higher after infection with Foc1 than after infection with Foc4. We further found that starch has an important inhibitory effect on the phytotoxicity induced by FA, thus leading to more resistance to the pathogens in the plants with high amounts of starch accumulation than in those with a low amount of starch accumulation. Moreover, the expression levels of 10 defense-related genes were analyzed and the results showed that the induction levels of those genes were higher after infection with Foc1 than after infection with Foc4. These results suggest that the observed differences in the invasion of host tissues and FA accumulation, and the number of starch granules and expression of defense-related genes, may contribute to a difference in virulence between the two races and the resulting difference in host resistance response, respectively.

Dose-dependent neuroprotective effect of oriental phyto-derived glycyrrhizin on experimental neuroterminal norepinephrine depletion in a rat brain model

The dose-dependent neuroprotective role of licorice-derived glycyrrhizin during subacute neuroterminal norepinephrine (NE) depletion was studied in rat brain. Experimental design included thirty 5-week-old male rats randomly divided into five groups. Compared to the saline-injected control group, the group receiving daily intraperitoneal injection of fusaric acid (FA; 5 mg/kg/b.w.) for 30 days showed pharmacological depletion of NE. The neuroprotective effects of three successively increasing oral doses of glycyrrhizin were examined in FA-treated rats. Neurochemical parameters and histo-/immunohistopathological changes in the hippocampus were examined. FA generated global hippocampal stress with altered neurobiochemical parameters, accompanied by immune-confirmed inflammatory tissue damage, and noticeable behavioral changes. Although glycyrrhizin after FA-induced intoxication did not correct the recorded drop in the NE level, it decreased the dopamine levels to control levels. Similarly, glycyrrhizin at a high dose restored the serotonin level to its normal value and blocked the FA-induced increase in the level of its metabolite, 5-hydroxyindoleacetic acid. The FA-induced rise in γ-aminobutyric acid (GABA) and histamine was alleviated after administration of a high dose of glycyrrhizin. This was accompanied by improvements in the bioenergetic status and neuronal regenerative capacity through recovery of ATP and brain-derived neurotrophic factor levels to the pre-intoxicated values. High doses of glycyrrhizin also ameliorated the FA-generated behavioral changes and oxidative damage, manifested by the reduction in the expression of cortical pro-apoptotic caspase 3 in the same group. This study suggests that glycyrrhizin can potentially mend most of the previously evoked neuronal damage induced by FA intoxication in the brain of an experimental rat model.

Crop Diseases and Mycotoxin Accumulation in Temperate Agroforestry Systems

Background: Temperate agroforestry is regarded as a sustainable alternative to monoculture agriculture due to enhanced provisioning of ecosystem services. Plant health and food safety are crucial requirements for sustainable agriculture; however, studies of fungal diseases and mycotoxin contamination of crops grown under temperate agroforestry are lacking. This study therefore aimed to compare fungal colonization and mycotoxin contamination of crops grown in temperate agroforestry against conventional monoculture. Methods: The biomass of plant pathogenic fungi in oilseed rape plants and barley and wheat grain harvested in 2016 to 2018 at four paired agroforestry and monoculture sites was quantified using species-specific real-time PCR. Mycotoxin content of barley and wheat grain was determined by HPLC-MS/MS. Results: The colonization of oilseed rape plants with the vascular pathogen Verticillium longisporum and wheat grain with the head blight pathogen Fusarium tricinctum was lower in agroforestry than in conventional monoculture. Mycotoxin content of barley and wheat grain did not differ between agroforestry and monoculture systems and did not exceed the legal limits of the EU. Remarkably, fumonisin B1 was detected in wheat grains at two sites in two years, yet the low levels found do not raise food safety concerns. No differences were found between the two production systems with regard to infection of wheat and barley grain with five Fusarium species (F. avenaceum, F. culmorum, F. graminearum, F. poae, and F. proliferatum) and oilseed rape with fungal pathogens Leptosphaeria biglobosa, Leptosphaeria maculans, and Sclerotinia sclerotiorum. Conclusions: Temperate agroforestry does not negatively affect the infection of wheat, barley and oilseed rape with major fungal pathogens though it may suppress the infection of oilseed rape with V. longisporum and wheat grain with F. tricinctum. Furthermore, temperate agroforestry does not increase mycotoxin contamination of barley and wheat. Therefore, temperate agroforestry does not negatively affect food safety.

Fusaric acid-induced promoter methylation of DNA methyltransferases triggers DNA hypomethylation in human hepatocellular carcinoma (HepG2) cells

Fusaric acid (FA), a mycotoxin contaminant of maize, displays toxicity in plants and animals; however, its epigenetic mechanism is unknown. DNA methylation, an epigenetic modification that regulates gene expression, is mediated by DNA methyltransferases (DNMTs; DNMT1, DNMT3A, and DNMT3B) and demethylases (MBD2). The expression of DNMTs and demethylases are regulated by promoter methylation, microRNAs (miR-29b) and post-translational modifications (ubiquitination). Alterations in these DNA methylation modifying enzymes affect DNA methylation patterns and offer novel mechanisms of FA toxicity. We determined the effect of FA on global DNA methylation as well as a mechanism of FA-induced changes in DNA methylation by transcriptional (promoter methylation), post-transcriptional (miR-29b) and post-translational (ubiquitination) regulation of DNMTs and MBD2 in the human hepatocellular carcinoma (HepG2) cell line. FA induced global DNA hypomethylation (p < 0.0001) in HepG2 cells. FA decreased the mRNA and protein expression of DNMT1 (p < 0.0001), DNMT3A (p < 0.0001), and DNMT3B (p < 0.0001) by upregulating miR-29b (p < 0.0001) and inducing promoter hypermethylation of DNMT1 (p < 0.0001) and DNMT3B (p < 0.0001). FA decreased the ubiquitination of DNMT1 (p = 0.0753), DNMT3A (p = 0.0008), and DNMT3B (p < 0.0001) by decreasing UHRF1 (p < 0.0001) and USP7 (p < 0.0001). FA also induced MBD2 promoter hypomethylation (p < 0.0001) and increased MBD2 expression (p < 0.0001). Together these results indicate that FA induces global DNA hypomethylation by altering DNMT promoter methylation, upregulating miR-29b, and increasing MBD2 in HepG2 cells.

Antifungal Evaluation of Hypericum Triquetrifolium Polar Extracts against Fusarium spp

The chemical composition of different kinds of Hypericum triquetrifolium extracts was analyzed by LC-DAD-ESI-MS. Hyperoside, rutin, isoquercitrin and biapigenin were the main constituents. As these natural compounds were reported in the literature for their antifungal activity, the total extracts were tested for their antifungal activity against eight phytopathogenic strains of Fusarium species.

One-step loop-mediated isothermal amplification (LAMP) for the rapid and sensitive detection of Fusarium fujikuroi in bakanae disease through NRPS31, an important gene in the gibberellic acid bio-synthesis

Rice bakanae disease caused by Fusarium fujikuroi is one of the most famous seed borne diseases. If infected seeds are used, this disease will occur with serious impacts. Thus, a simple, reliable, specific and sensitive method for surveillance is urgently needed to screen infected seeds and seedlings at early developmental stages. In this study, a rapid and efficient loop-mediated isothermal amplification (LAMP) method was developed to detect F. fujikuroi in contaminated rice seeds and seedlings for diagnosis of bakanae disease. NRPS31 gene plays an important role in the gibberellic acid (GA) bio-synthesis of F. fujikuroi, and is not present in any other sequenced fungal genome, and thus was adopted as the target for LAMP primer design. The LAMP assay enables the fast detection of as little as 1 fg of pure genomic F. fujikuroi DNA within 60 minutes. Further tests indicated that the LAMP assay was more sensitive and faster than the traditional isolation method for F. fujikuroi detection in rice seeds and seedlings. Our results show that this LAMP assay is a useful and convenient tool for detecting F. fujikuroi, and it can be applied widely in seed quarantine of bakanae disease, providing valid data for disease prevention.

Fusaricates H-K and fusolanones A-B from a mangrove endophytic fungus Fusarium solani HDN15-410

Seven compounds including four undescribed fusaric acid derivatives, namely fusaricates H-K, and two undescribed γ-pyrone derivatives, named fusolanones A-B, as well as a known compound fusaric acid, were isolated from a mangrove endophytic fungus Fusarium solani. Fusaricates H-K represent the first cases of fusaric acid butanediol esters and are diastereoisomers. Their structures including absolute configurations were elucidated based on NMR, MS, chemical synthesis, chiral HPLC analysis and ECD calculations. The antibacterial activity of all undescribed compounds were tested and fusolanone B showed the best activity with MIC value 6.25 μg/mL on Vibrio parahaemolyticus.

Rhizosphere Microenvironments of Eight Common Deciduous Fruit Trees Were Shaped by Microbes in Northern China

The rhizosphere microenvironment is the site of nutrient circulation and microbial community formation, and thus is an ongoing topic of research. Although research on this topic is extensive, studies into the rhizosphere microenvironment of fruit trees remain rare. To elucidate the mechanisms driving the fruit tree rhizosphere microenvironment, we assessed soil physicochemical properties, enzyme activities, the community-level physiological profile (CLPP) and microbial diversity in rhizospheric soils of eight common deciduous fruit trees in northern China. We found that the available minerals, pH, enzyme activities, microbial utilization of six types of carbon (C) substrates, and microbial diversity in the rhizosphere varied among tree species. Redundancy analysis (RDA) showed that rhizosphere microenvironmental parameters (ammonia nitrogen content, soil pH and invertase activity) were closely related to the soil microbial community. Further analysis revealed that the soil microbial utilization of six C sources, nitrate nitrogen content, and invertase activity were negatively correlated with Ambiguous species and Alternaria; however, these groups were positively correlated with pH. The ammonia nitrogen content was positively correlated with C source utilization and negatively correlated with Ambiguous, Lysobacter, Nitrospira, Alternaria, Fusarium, and Colletotrichum. Interestingly, invertase was closely linked to the microbial community, especially fungal diversity, and was positively correlated with plant-beneficial microbes such as Mortierella, Geomyces, Lysobacter, and Chaetomium, but negatively correlated with pathogenic microbes such as Alternaria, Fusarium, and Colletotrichum. Hence, rhizosphere soil physicochemical properties, enzyme activities and microbial community were significantly affected by tree species. Additionally, a variety of environmental factors were closely related to the microbial community in the rhizospheric soils of eight species of deciduous fruit trees.

Environmental pH modulates transcriptomic responses in the fungus Fusarium sp. associated with KSHB Euwallacea sp. near fornicatus

BACKGROUND

The Ambrosia Fusarium Clade phytopathogenic Fusarium fungi species have a symbiotic relationship with ambrosia beetles in the genus Euwallacea (Coleoptera: Curculionidae). Related beetle species referred to as Euwallacea sp. near fornicatus have been spread in California, USA and are recognized as the causal agents of Fusarium dieback, a disease that causes mortality of many plant species. Despite the importance of this fungi, no transcriptomic resources have been generated. The datasets described here represent the first ever transcripts available for these species. We focused our study on the isolated species of Fusarium that is associated with one of the cryptic species referred to as Kuroshio Shot Hole Borer (KSHB) Euwallacea sp. near fornicatus.

RESULTS

Hydrogen concentration is a critical signal in fungi for growth and host colonization, the aim of this study was to evaluate the effect of different pH conditions on growth and gene expression of the fungus Fusarium sp. associated with KSHB. An RNA-seq approach was used to compare the gene expression of the fungus grown for 2 weeks in liquid medium at three different pH levels (5.0, 6.0, and 7.0). An unbuffered treatment was included to evaluate the capability of the fungus to change the pH of its environment and the impact in gene expression. The results showed that the fungus can grow and modulate its genetic expression at different pH conditions; however, growth was stunted in acidic pH in comparison with neutral pH. The results showed a differential expression pattern in each pH condition even when acidic conditions prevailed at the end of the experiment. After comparing transcriptomics data from the three treatments, we found a total of 4,943 unique transcripts that were differentially expressed.

CONCLUSIONS

We identified transcripts related to pH signaling such as the conserved PAL/RIM pathway, some transcripts related to secondary metabolism and other transcripts that were differentially expressed. Our analysis suggests possible mechanisms involved in pathogenicity in this novel Fusarium species. This is the first report that shows transcriptomic data of this pathogen as well as the first report of genes and proteins involved in their metabolism identifying potential virulence factors.

Evaluation of the cytotoxic and genotoxic effects of mycotoxin fusaric acid

Fusaric acid (FA) is produced by several Fusarium species and is commonly found in grains. This investigation was performed to evaluate the cytotoxic and genotoxic effects of FA either in human cervix carcinoma (HeLa) cell line using 3-(4,5-dimethylthiazolyl-2)-2,5 diphenyltetrazolium bromide (MTT) assay and in human lymphocytes using chromosome aberrations (CAs), sister chromatid exchanges (SCEs), micronuclei (MN) as well as comet assay in vitro. The cells were treated with 0.78, 1.56, 3.125, 6.25, 12.50, 25, 50, 100, 200, and 400 µg/mL concentrations of FA. It has potent cytotoxic effect on HeLa cell line measured by MTT assay especially at higher concentrations (200, 400 µg/mL). The half of inhibitory concentration (IC₅₀) evidenced by FA in the HeLa cells was 200 μg/mL at 24 h and between 200 and 400 μg/mL at 48 h. It was also observed that FA produced a significant decrease in mitotic index (MI) at 12.50 µg/mL compared to solvent control. Furthermore, it indicated a cytotoxic effect at the concentrations ranging from 25 to 400 μg/mL in human lymphocytes. The results of this research point out that being exposed to FA at high concentrations show cytotoxicity. Besides FA induced comet tail intensity at 3.125, 6.25, and 12.50 µg/mL concentrations in isolated human lymphocytes. On the other hand, no genotoxic effects were seen in human lymphocytes in vitro using CA, SCE and MN assays.

Evolution and Diversity of Biosynthetic Gene Clusters in Fusarium

Plant pathogenic fungi in the Fusarium genus cause severe damage to crops, resulting in great financial losses and health hazards. Specialized metabolites synthesized by these fungi are known to play key roles in the infection process, and to provide survival advantages inside and outside the host. However, systematic studies of the evolution of specialized metabolite-coding potential across Fusarium have been scarce. Here, we apply a combination of bioinformatic approaches to identify biosynthetic gene clusters (BGCs) across publicly available genomes from Fusarium, to group them into annotated families and to study gain/loss events of BGC families throughout the history of the genus. Comparison with MIBiG reference BGCs allowed assignment of 29 gene cluster families (GCFs) to pathways responsible for the production of known compounds, while for 57 GCFs, the molecular products remain unknown. Comparative analysis of BGC repertoires using ancestral state reconstruction raised several new hypotheses on how BGCs contribute to Fusarium pathogenicity or host specificity, sometimes surprisingly so: for example, a gene cluster for the biosynthesis of hexadehydro-astechrome was identified in the genome of the biocontrol strain Fusarium oxysporum Fo47, while being absent in that of the tomato pathogen F. oxysporum f.sp. lycopersici. Several BGCs were also identified on supernumerary chromosomes; heterologous expression of genes for three terpene synthases encoded on the Fusarium poae supernumerary chromosome and subsequent GC/MS analysis showed that these genes are functional and encode enzymes that each are able to synthesize koraiol; this observed functional redundancy supports the hypothesis that localization of copies of BGCs on supernumerary chromosomes provides freedom for evolutionary innovations to occur, while the original function remains conserved. Altogether, this systematic overview of biosynthetic diversity in Fusarium paves the way for targeted natural product discovery based on automated identification of species-specific pathways as well as for connecting species ecology to the taxonomic distributions of BGCs.

Insights into the Genome Sequence of Chromobacterium amazonense Isolated from a Tropical Freshwater Lake

Members of the genus Chromobacterium have been isolated from geographically diverse ecosystems and exhibit considerable metabolic flexibility, as well as biotechnological and pathogenic properties in some species. This study reports the draft assembly and detailed sequence analysis of Chromobacterium amazonense strain 56AF. The de novo-assembled genome is 4,556,707 bp in size and contains 4294 protein-coding and 95 RNA genes, including 88 tRNA, six rRNA, and one tmRNA operon. A repertoire of genes implicated in virulence, for example, hemolysin, hemolytic enterotoxins, colicin V, lytic proteins, and Nudix hydrolases, is present. The genome also contains a collection of genes of biotechnological interest, including esterases, lipase, auxins, chitinases, phytoene synthase and phytoene desaturase, polyhydroxyalkanoates, violacein, plastocyanin/azurin, and detoxifying compounds. Importantly, unlike other Chromobacterium species, the 56AF genome contains genes for pore-forming toxin alpha-hemolysin, a type IV secretion system, among others. The analysis of the C. amazonense strain 56AF genome reveals the versatility, adaptability, and biotechnological potential of this bacterium. This study provides molecular information that may pave the way for further comparative genomics and functional studies involving Chromobacterium-related isolates and improves our understanding of the global genomic diversity of Chromobacterium species.

Screening of Bacillus mojavensis biofilms and biosurfactants using laser ablation electrospray ionization mass spectroscopy

AIMS

Biofilms are composed of micro-organisms within a matrix of chemically complex polymer compounds and from these structures many unknown competitive factors are suggested that many considered are important consequences for biological control. This research was undertaken to study further the endophyte, Bacillus mojavensis and its relationships to biofilm and two classes of lipopeptides considered relevant for biocontrol of plant pathogens.

METHODS AND RESULTS

Laser ablation electrospray ionization mass spectrometry and conventional MS/MS were used to study in situ biofilm production and the production of lipopeptides fengycin and surfactin in different strains of B. mojavensis in plate and test tube culture on two media. All strains were capable of producing biofilm in vitro along with the accumulation of surfactin and fengycin although no concentration-dependent relationship between lipopeptide accumulation and biofilm was observed.

CONCLUSION

All strains studied produce biofilms in culture with the accumulated surfactin and fengycin, demonstrating that endophytic bacteria also produced biofilms.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates that this endophytic species produced biofilms along with two biocontrol compounds of which one, surfactin, considered by others as a quorum sensor, highlighting its ecological role as a signalling mechanism in planta.

Fusaric acid contributes to virulence of Fusarium oxysporum on plant and mammalian hosts

Fusaric acid (FA) is amongst the oldest identified secondary metabolites produced by Fusarium species, known for a long time to display strong phytotoxicity and moderate toxicity to animal cells; however, the cellular targets of FA and its function in fungal pathogenicity remain unknown. Here, we investigated the role of FA in Fusarium oxysporum, a soil-borne cross-kingdom pathogen that causes vascular wilt on more than 100 plant species and opportunistic infections in humans. Targeted deletion of fub1, encoding a predicted orthologue of the polyketide synthase involved in FA biosynthesis in F. verticillioides and F. fujikuroi, abolished the production of FA and its derivatives in F. oxysporum. We further showed that the expression of fub1 was positively controlled by the master regulator of secondary metabolism LaeA and the alkaline pH regulator PacC through the modulation of chromatin accessibility at the fub1 locus. FA exhibited strong phytotoxicity on tomato plants, which was rescued by the exogenous supply of copper, iron or zinc, suggesting a possible function of FA as a chelating agent of these metal ions. Importantly, the severity of vascular wilt symptoms on tomato plants and the mortality of immunosuppressed mice were significantly reduced in fub1Δ mutants and fully restored in the complemented strains. Collectively, these results provide new insights into the regulation and mode of action of FA, as well as on the function of this phytotoxin during the infection process of F. oxysporum.

The main phytotoxic metabolite produced by a strain of Fusarium oxysporum inducing grapevine plant declining in Italy

A strain of Fusarium oxysporum was isolated from grapevine showing heavy decline disease in a vineyard of Veneto region in Italy. The fungus showed to produce phytotoxic metabolites when grown in liquid culture. The main metabolite was identified as fusaric acid produced for the first time as a phytotoxin by a strain of F. oxysporom isolated from diseased grapevine plants. Its quantification in the fungus cultures filtrates was accomplished by HPLC. When tested on tobacco by leaf-puncture assay fusaric acid at 0.5 mg/mL induced the formation of extensive necrosis.

Species composition of and fumonisin production by the Fusarium fujikuroi species complex isolated from Korean cereals

To assess the risk of fumonisin contamination in Korean cereals, we isolated colonies of the Fusarium fujikuroi species complex (FFSC) from barley, maize, rice and soybean samples from 2011 to 2015. A total of 878 FFSC strains were isolated mostly from maize and rice, and species identity of the isolates were determined using the DNA sequence of the translation elongation factor 1-α (TEF-1α) and RNA polymerase II (RPB2) genes. Fusaria recovered from Korean cereals included F. fujikuroi (317 isolates and a frequency of 36%), F. proliferatum (212 isolates and 24.1%), F. verticillioides (170 isolates and 19.4%), F. concentricum (86 strains and 9.8%), F. andiyazi (56 isolates and 6.4%), F. subglutinans (28 isolates and 3.2%), F. thapsinum (5 isolates and 0.6%), and F. circinatum (2 isolates and 0.2%). The rice samples were dominated by F. fujikuroi (47.4%), F. proliferatum (27.3%), and F. concentricum (15.1%), whereas maize samples were dominated by F. verticillioides (33.9%), F. fujikuroi (25.3%), and F. proliferatum (21.1%). A phylogenetic analysis of 70 representative isolates demonstrated that each species was resolved as genealogically exclusive in the ML tree. Fumonisin production potential was evaluated using a PCR assay for the fumonisin biosynthesis gene, FUM1 in all of the isolates. Most of the isolates tested (94%) were positive for FUM1. All of the isolates assigned to F. fujikuroi, F. proliferatum, F. verticillioides and F. thapsinum were positive for FUM1 irrespective of their host origin. Seventy-seven representative isolates positive for FUM1 were examined for fumonisin production in rice medium. The majority of F. proliferatum (26/27, 96.3%), F. verticillioides (16/17, 94.1%) and F. fujikuroi (19/25, 76.0%) produced both FB₁ and FB₂. Notably, 16 of 19 fumonisin-producing F. fujikuroi produced >1000μg/g of fumonisins (FB₁+FB₂) in rice medium, which is higher than that in previous reports. These results suggest that F. fujikuroi can produce high levels of fumonisins similar to F. verticillioides and F. proliferatum.

Secondary metabolism in Fusarium fujikuroi: strategies to unravel the function of biosynthetic pathways

The fungus Fusarium fujikuroi causes bakanae disease of rice due to its ability to produce the plant hormones, the gibberellins. The fungus is also known for producing harmful mycotoxins (e.g., fusaric acid and fusarins) and pigments (e.g., bikaverin and fusarubins). However, for a long time, most of these well-known products could not be linked to biosynthetic gene clusters. Recent genome sequencing has revealed altogether 47 putative gene clusters. Most of them were orphan clusters for which the encoded natural product(s) were unknown. In this review, we describe the current status of our research on identification and functional characterizations of novel secondary metabolite gene clusters. We present several examples where linking known metabolites to the respective biosynthetic genes has been achieved and describe recent strategies and methods to access new natural products, e.g., by genetic manipulation of pathway-specific or global transcritption factors. In addition, we demonstrate that deletion and over-expression of histone-modifying genes is a powerful tool to activate silent gene clusters and to discover their products.

Antifungal Activity and Action Mode of Cuminic Acid from the Seeds of Cuminum cyminum L. against Fusarium oxysporum f. sp. Niveum (FON) Causing Fusarium Wilt on Watermelon

In order to develop a novel biofungicide, the antifungal activity and action mode of cuminic acid from the seed of Cuminum cyminum L. against Fusarium oxysporum f. sp. niveum (FON) on watermelon was determined systematically. In this study, the median effective concentration (EC50) value for cuminic acid in inhibiting mycelial growth of FON was 22.53 μg/mL. After treatment with cuminic acid, the mycelial morphology was seriously influenced; cell membrane permeability and glycerol content were increased markedly, but pigment and mycotoxin (mainly fusaric acid) were significantly decreased. Synthesis genes of bikaverin (Bike1, Bike2 and Bike3) and fusaric acid (FUB1, FUB2, FUB3 and FUB4) both were downregulated compared with the control, as confirmed by quantitative RT-PCR. In greenhouse experiments, cuminic acid at all concentrations displayed significant bioactivities against FON. Importantly, significant enhancement of activities of SOD, POD, CAT and decrease of MDA content were observed after in vivo cuminic acid treatment on watermelon leaves. These indicated that cuminic acid not only showed high antifungal activity, but also could enhance the self-defense system of the host plant. Above all, cuminic acid showed the potential as a biofungicide to control FON.

Role of fusaric acid in the development of 'Fusarium wilt' symptoms in tomato: Physiological, biochemical and proteomic perspectives

Fusarium wilt is one of the most prevalent and damaging diseases of tomato. Among various toxins secreted by the Fusarium oxysporum f. sp. lycopersici (causal agent of Fusarium wilt of tomato), fusaric acid (FA) is suspected to be a potent pathogenicity factor in tomato wilt disease development. With this rationale the present study was carried out with physiological, biochemical and proteomic perspectives. Treatment of FA was given to the leaves of tomato directly through infiltration to show the characteristic features of Fusarium wilt of tomato. The phytotoxic effect of FA was assessed in the form of cell death in tomato leaves which was observed by increased uptake of Evans blue stain. The measurement of electrolyte leakage was used as an indicator of the extent of cell death. The influence of FA on the leaf photosynthesis of tomato plant was investigated and it was found that FA strongly reduced the photosynthetic pigment contents of tomato leaves resulting to heavy suppression of leaf photosynthesis processes, which therefore affected leaf physiology finally leading to leaf wilting and necrosis. This cell death inducer (FA) produced an enormous oxidative burst during which large quantities of reactive oxygen species (ROS) like H₂O₂ was generated in the treated leaf tissues of tomato plants which was evident from enhancement in lipid peroxidation. To assess the involvement of proteolysis in the cell death cascade induced by FA treatment, total protease activity was measured in the leaf tissues and it was found that the total protease activity increased with the treatment and leading to cell death. Furthermore, proteomic study was used as a powerful tool to understand the alterations in cellular protein expression in response to FA exposure. Differential expression in several proteins was observed in the present study. Proteomic analyses, thus, clearly indicate that proteins belonging to different functional classes are significantly affected in the plant leaf tissues after FA exposure leading to deterioration of structure and metabolism of cells. Thus, it is concluded that FA plays an important role in fungal pathogenicity by decreasing cell viability.

Emerging Mycotoxins: Beyond Traditionally Determined Food Contaminants

Modern analytical techniques can determine a multitude of fungal metabolites contaminating food and feed. In addition to known mycotoxins, for which maximum levels in food are enforced, also currently unregulated, so-called "emerging mycotoxins" were shown to occur frequently in agricultural products. The aim of this review is to critically discuss the relevance of selected emerging mycotoxins to food and feed safety. Acute and chronic toxicity as well as occurrence data are presented for enniatins, beauvericin, moniliformin, fusaproliferin, fusaric acid, culmorin, butenolide, sterigmatocystin, emodin, mycophenolic acid, alternariol, alternariol monomethyl ether, and tenuazonic acid. By far not all of the detected compounds are toxicologically relevant at their naturally occurring levels and are therefore of little or no health concern to consumers. Still, gaps in knowledge have been identified for several compounds. These gaps should be closed by the scientific community in the coming years to allow a proper risk assessment.

Is Quorum Signaling by Mycotoxins a New Risk-Mitigating Strategy for Bacterial Biocontrol of Fusarium verticillioides and Other Endophytic Fungal Species?

Bacterial endophytes are used as biocontrol organisms for plant pathogens such as the maize endophyte Fusarium verticillioides and its production of fumonisin mycotoxins. However, such applications are not always predictable and efficient. In this work, we hypothesize and review work that quorum sensing inhibitors are produced either by fungi or by pathogenic bacteria for competitive purposes, altering the efficiency of the biocontrol organisms. Recently, quorum sensing inhibitors have been isolated from several fungi, including Fusarium species, three of which are mycotoxins. Thus, we further postulate that other mycotoxins are inhibitors or quenching metabolites that prevent the protective abilities and activities of endophytic biocontrol bacteria within intercellular spaces. To test the aforementioned suppositions, we review work detailing the use of bioassay bacteria for several mycotoxins for quorum activity. We specifically focus on the quorum use of endophytic bacteria as biocontrols for mycotoxic fungal endophytes, such as the Fusarium species and the fumonisin mycotoxins.

Detection of Fumonisins in Fresh and Dehydrated Commercial Garlic

An epidemic fungal disease caused by Fusarium proliferatum, responsible for fumonisin production (FB1, FB2, and FB3), has been reported in the main garlic-producing countries in recent years. Fumonisins are a group of structurally related toxic metabolites produced by this pathogen. The aim of this work was to establish an enzyme-linked immunosorbent assay (ELISA) procedure, mostly applied to cereals, that is suitable for fumonisin detection in garlic and compare these results to those obtained by high-performance liquid chromatography (HPLC) and screening of fresh and dehydrated garlic for toxicological risk. The results show good correlation between the two analytical methods. In fresh symptomatic garlic, fumonisin levels were higher in the basal plates than those in the portions with necrotic spots. Among the 56 commercially dehydrated garlic samples screened, three were positive by ELISA test and only one was above the limit of quantitation. The same samples analyzed by HPLC showed the presence of FB1 in trace amounts that was below the limit of quantitation; FB2 and FB3 were absent. The results are reassuring, because no substantial contamination by fumonisins was found in commercial garlic.

Fusaric Acid immunotoxicity and MAPK activation in normal peripheral blood mononuclear cells and Thp-1 cells

Fusaric acid (FA), a food-borne mycotoxin, is a potent divalent metal chelator. The human immune system is complex and susceptible to environmental insult however, the immunotoxity of FA remains unknown. We investigated the immunotoxicity of FA on human peripheral blood mononuclear cells (PBMCs) and Thp-1 cells. FA was cytotoxic to PBMCs (IC₅₀-240.8 μg/ml) and Thp-1 (IC₅₀-107.7 μg/ml) cells at 24 h. FA induced early apoptosis but significantly decreased caspase activity in PBMCs, a characteristic of paraptosis. In Thp-1 cells, FA induced apoptosis and increased caspase -9 and -3/7 activities. In PBMCs, FA maintained mitochondrial membrane potential and decreased protein expression of Bax whilst increasing expression of p-Bcl-2; FA induced oxidative stress and depleted ATP levels in both cell types. In Thp-1 cells, FA increased mitochondrial membrane depolarization and decreased p-Bcl-2 expression. In PBMCs, FA significantly up-regulated the MAPK protein expression of p-ERK and p-JNK but down-regulated p-p38 expression. In Thp-1 cells, FA up-regulated MAPK protein expression of p-ERK whilst p-JNK and p-p38 expression were down-regulated. In conclusion FA induced programmed cell death and altered MAPK signaling in healthy PBMCs and Thp-1 cells strongly suggesting a possible mechanism of FA induced immunotoxicity in vitro.

Fusaric Acid Induces DNA Damage and Post-Translational Modifications of p53 in Human Hepatocellular Carcinoma (HepG2 ) Cells

Fusaric acid (FA), a common fungal contaminant of maize, is known to mediate toxicity in plants and animals; however, its mechanism of action is unclear. p53 is a tumor suppressor protein that is activated in response to cellular stress. The function of p53 is regulated by post-translational modifications-ubiquitination, phosphorylation, and acetylation. This study investigated a possible mechanism of FA induced toxicity in the human hepatocellular carcinoma (HepG₂ ) cell line. The effect of FA on DNA integrity and post-translational modifications of p53 were investigated. Methods included: (a) culture and treatment of HepG₂ cells with FA (IC₅₀ : 580.32 μM, 24 h); (b) comet assay (DNA damage); (c) Western blots (protein expression of p53, MDM2, p-Ser-15-p53, a-K382-p53, a-CBP (K1535)/p300 (K1499), HDAC1 and p-Ser-47-Sirt1); and (d) Hoechst 33342 assay (apoptosis analysis). FA caused DNA damage in HepG₂ cells relative to the control (P < 0.0001). FA decreased the protein expression of p53 (0.24-fold, P = 0.0004) and increased the expression of p-Ser-15-p53 (12.74-fold, P = 0.0126) and a-K382-p53 (2.24-fold, P = 0.0096). This occurred despite the significant decrease in the histone acetyltransferase, a-CBP (K1535)/p300 (K1499) (0.42-fold, P = 0.0023) and increase in the histone deacetylase, p-Ser-47-Sirt1 (1.22-fold, P = 0.0020). The expression of MDM2, a negative regulator of p53, was elevated in the FA treatment compared to the control (1.83-fold, P < 0.0001). FA also inhibited cell proliferation and induced apoptosis in HepG₂ cells as evidenced by the Hoechst assay. Together, these results indicate that FA is genotoxic and post-translationally modified p53 leading to HepG₂ cell death. J. Cell. Biochem. 118: 3866-3874, 2017. © 2017 Wiley Periodicals, Inc.

Nitrate Increased Cucumber Tolerance to Fusarium Wilt by Regulating Fungal Toxin Production and Distribution

Cucumber Fusarium wilt, induced by Fusarium oxysporum f. sp. cucumerinum (FOC), causes severe losses in cucumber yield and quality. Nitrogen (N), as the most important mineral nutrient for plants, plays a critical role in plant-pathogen interactions. Hydroponic assays were conducted to investigate the effects of different N forms (NH₄⁺ vs. NO₃‒) and supply levels (low, 1 mM; high, 5 mM) on cucumber Fusarium wilt. The NO₃‒-fed cucumber plants were more tolerant to Fusarium wilt compared with NH₄⁺-fed plants, and accompanied by lower leaf temperature after FOC infection. The disease index decreased as the NO₃‒ supply increased but increased with the NH₄⁺ level supplied. Although the FOC grew better under high NO₃- in vitro, FOC colonization and fusaric acid (FA) production decreased in cucumber plants under high NO₃- supply, associated with lower leaf membrane injury. There was a positive correlation between the FA content and the FOC number or relative membrane injury. After the exogenous application of FA, less FA accumulated in the leaves under NO₃- feeding, accompanied with a lower leaf membrane injury. In conclusion, higher NO₃- supply protected cucumber plants against Fusarium wilt by suppressing FOC colonization and FA production in plants, and increasing the plant tolerance to FA.

Fusaric acid and analogues as Gram-negative bacterial quorum sensing inhibitors

Taking advantage of microwave-assisted synthesis, efficient and expedite procedures for preparation of a library of fusaric acid and 39 analogues are reported. The fusaric acid analogues were tested in cell-based screening assays for inhibition of the las and rhl quorum sensing system in Pseudomonas aeruginosa and the lux quorum sensing system in Vibrio fischeri. Eight of the 40 compounds in the library including fusaric acid inhibited lux quorum sensing and one compound inhibited activity of the las quorum sensing system. To our delight, none of the compounds showed growth inhibitory effects in the tested concentration ranges.

Nitrate Protects Cucumber Plants Against Fusarium oxysporum by Regulating Citrate Exudation

Fusarium wilt causes severe yield losses in cash crops. Nitrogen plays a critical role in the management of plant disease; however, the regulating mechanism is poorly understood. Using biochemical, physiological, bioinformatic and transcriptome approaches, we analyzed how nitrogen forms regulate the interactions between cucumber plants and Fusarium oxysporum f. sp. cucumerinum (FOC). Nitrate significantly suppressed Fusarium wilt compared with ammonium in both pot and hydroponic experiments. Fewer FOC colonized the roots and stems under nitrate compared with ammonium supply. Cucumber grown with nitrate accumulated less fusaric acid (FA) after FOC infection and exhibited increased tolerance to chemical FA by decreasing FA absorption and transportation in shoots. A lower citrate concentration was observed in nitrate-grown cucumbers, which was associated with lower MATE (multidrug and toxin compound extrusion) family gene and citrate synthase (CS) gene expression, as well as lower CS activity. Citrate enhanced FOC spore germination and infection, and increased disease incidence and the FOC population in ammonium-treated plants. Our study provides evidence that nitrate protects cucumber plants against F. oxysporum by decreasing root citrate exudation and FOC infection. Citrate exudation is essential for regulating disease development of Fusarium wilt in cucumber plants.

Effects of fusaric acid treatment on the protocorm-like bodies of Dendrobium sonia-28

Dendrobium sonia-28 is a popular orchid hybrid due to its flowering recurrence and dense inflorescences. Unfortunately, it is being decimated by fungal diseases, especially those caused by Fusarium proliferatum. In this study, selection of F. proliferatum-tolerant protocorm-like bodies (PLBs) was carried out by assessing the effects of differing concentrations of fusaric acid (FA). PLBs were cultured on Murashige and Skoog (MS) medium supplemented with 0.05 to 0.2 millimolar (mM) concentrations of FA. Higher concentrations of FA increased mortality of PLBs and reduced their growth. The survival rate for 0.05 mM FA was 20 % but only 1 % at the highest dose of 0.2 mM. Additionally, two different size ranges of PLBs were investigated, and growth increased more at lower FA concentrations for larger PLBs, whilst the growth rate of smaller PLBs was inhibited at an FA concentration of 0.2 mM. Histological examination using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses disclosed severe cell wall and organelle damage, as well as stomatal closure in PLBs treated with the high FA concentrations. Reductions in plantlet growth were much greater at the highest concentrations of FA. Some randomly amplified polymorphic DNA (RAPD) markers clearly discriminated between selected and non-selected variants of Dendrobium sonia-28, showing different banding patterns for each FA concentration and specific bands for selected and control plants.

A Rapid Method with UPLC for the Determination of Fusaric Acid in Fusarium Strains and Commercial Food and Feed Products

A rapid, sensitive and validated method for the determination of fusaric acid (FA) in several Fusarium strains and different commercial food and feed products is reported based on ultra-performance liquid chromatography. This method requires only crude sample by a simple extraction with methanol, and requires a very short time of 8 min for completion. Separation of FA was performed at injection volume of 1 μl with a 20:80 (v/v) water/acetonitrile mobile phase containing 0.1 % formic acid at a flow rate of 0.05 ml/min and detected with UV at 220 nm. Nice linearity and good correlation coefficient (R² > 0.99) were obtained in the concentration range of 1-200 μg/ml. Validation was demonstrated using blank samples spiked at three different concentrations with standard solution, and the method yielded more than 98.2 % recovery efficiencies and below 2.56 % R.S.D. when applied in the analysis of FA produced by Fusarium verticillioides and a set of transgenic strains of this fungus. Satisfactory recoveries in the range of 79.1-105.8 % and R.S.D lower than 10 % were also obtained for the tested commercial food and feed products. The concentration FA detection in the transgenic strains ranged from 9.65 to 135 μg/kg (0.29-4.05 μg per gram of biomass). However, FA was not detected in most of the commercial products with the exception of niblet, oatmeal, red kidney bean and soybean, for which the concentrations of FA ranged from 2.5 to 18 μg/kg (below the permitted maximum). These results show that the proposed method has a great potential application to analyze FA from different sources rapidly.

Fusaric acid induces mitochondrial stress in human hepatocellular carcinoma (HepG2) cells

Fusarium spp are common contaminants of maize and produce many mycotoxins, including the fusariotoxin fusaric acid (FA). FA is a niacin related compound, chelator of divalent cations, and mediates toxicity via oxidative stress and possible mitochondrial dysregulation. Sirtuin 3 (SIRT3) is a stress response deacetylase that maintains proper mitochondrial function. We investigated the effect of FA on SIRT3 and oxidative and mitochondrial stress pathways in the hepatocellular carcinoma (HepG2) cell line. We determined FA toxicity (24 h incubation; IC50 = 104 μg/ml) on mitochondrial output, cellular and mitochondrial stress responses, mitochondrial biogenesis and markers of cell death using spectrophotometry, luminometry, qPCR and western blots. FA caused a dose dependent decrease in metabolic activity along with significant depletion of intracellular ATP. FA induced a significant increase in lipid peroxidation, despite up-regulation of the antioxidant transcription factor, Nrf2. FA significantly decreased expression of SIRT3 mRNA with a concomitant decrease in protein expression. Lon protease was also significantly down-regulated. FA induced aberrant mitochondrial biogenesis as evidenced by significantly decreased protein expressions of: PGC-1α, p-CREB, NRF1 and HSP70. Finally, FA activated apoptosis as noted by the significantly increased activity of caspases 3/7 and also induced cellular necrosis. This study provides insight into the molecular mechanisms of FA (a neglected mycotoxin) induced hepatotoxicity.

Production of Fusaric Acid by Fusarium spp. in Pure Culture and in Solid Medium Co-Cultures

The ability of fungi isolated from nails of patients suffering from onychomycosis to induce de novo production of bioactive compounds in co-culture was examined. Comparison between the metabolite profiles produced by Sarocladium strictum, by Fusarium oxysporum, and by these two species in co-culture revealed de novo induction of fusaric acid based on HRMS. Structure confirmation of this toxin, using sensitive microflow NMR, required only three 9-cm Petri dishes of fungal culture. A targeted metabolomics study based on UHPLC-HRMS confirmed that the production of fusaric acid was strain-dependent. Furthermore, the detected toxin levels suggested that onychomycosis-associated fungal strains of the F. oxysporum and F. fujikuroi species complexes are much more frequently producing fusaric acid, and in higher amount, than strains of the F. solani species complex. Fusarium strains producing no significant amounts of this compound in pure culture, were shown to de novo produce that compound when grown in co-culture. The role of fusaric acid in fungal virulence and defense is discussed.

The Fusarium solani species complex: ubiquitous pathogens of agricultural importance

Members of the Fusarium solani species complex (FSSC) are capable of causing disease in many agriculturally important crops. The genomes of some of these fungi include supernumerary chromosomes that are dispensable and encode host-specific virulence factors. In addition to genomics, this review summarizes the known molecular mechanisms utilized by members of the FSSC in establishing disease.

TAXONOMY

Kingdom Fungi; Phylum Ascomycota; Class Sordariomycetes; Order Hypocreales; Family Nectriaceae; Genus Fusarium.

HOST RANGE

Members of the FSSC collectively have a very broad host range, and have been subdivided previously into formae speciales. Recent phylogenetic analysis has revealed that formae speciales correspond to biologically and phylogenetically distinct species.

DISEASE SYMPTOMS

Typically, FSSC causes foot and/or root rot of the infected host plant, and the degree of necrosis correlates with the severity of the disease. Symptoms on above-ground portions of the plant can vary greatly depending on the specific FSSC pathogen and host plant, and the disease may manifest as wilting, stunting and chlorosis or lesions on the stem and/or leaves.

CONTROL

Implementation of agricultural management practices, such as crop rotation and timing of planting, can reduce the risk of crop loss caused by FSSC. If available, the use of resistant varieties is another means to control disease in the field.

USEFUL WEBSITES

http://genome.jgi-psf.org/Necha2/Necha2.home.html.

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.

Determination of oral bioavailability of fusaric acid in male Sprague-Dawley rats

Head and neck squamous cell cancer accounts for 3 % of new cancer cases and 2 % of cancer mortality annually in the United States. Current treatment options for most head and neck cancers continue to be surgical excision with or without radiation, radiation alone, or chemotherapy with radiation depending on location, stage of disease, and patient preference. Fusaric acid (FA) is a novel compound from a novel class of nicotinic acid derivatives that have activity against head and neck squamous cell carcinoma (HNSCC). Although its exact mechanism is still unknown, FA is thought to be active by increasing damage to DNA and preventing its synthesis and repair. The novel mechanism of FA provides an alternative to present therapies, as a single agent whether given parenterally or orally. It has synergy with conventional agents taxol, carboplatin, and erlotinib. In order to determine if FA has reasonable oral bioavailability, we have determined the pharmacokinetics of FA in male Sprague Dawley rats following administration by gavage and by intravenous injection. The bioavailability of FA was sufficient (58 %) to suggest that FA may be viable as an orally administered medication. Despite the encouraging bioavailability of FA, the intravenous (IV) pharmacokinetics suggested non-linear behavior within the IV dose range of 10, 25, and 75 mg/kg. These results demonstrate that further pharmacokinetic and toxicity studies in larger animals such as dogs and non-human primates are warranted.

Identification of a 12-gene Fusaric Acid Biosynthetic Gene Cluster in Fusarium Species Through Comparative and Functional Genomics

In fungi, genes involved in biosynthesis of a secondary metabolite (SM) are often located adjacent to one another in the genome and are coordinately regulated. These SM biosynthetic gene clusters typically encode enzymes, one or more transcription factors, and a transport protein. Fusaric acid is a polyketide-derived SM produced by multiple species of the fungal genus Fusarium. This SM is of concern because it is toxic to animals and, therefore, is considered a mycotoxin and may contribute to plant pathogenesis. Preliminary descriptions of the fusaric acid (FA) biosynthetic gene (FUB) cluster have been reported in two Fusarium species, the maize pathogen F. verticillioides and the rice pathogen F. fujikuroi. The cluster consisted of five genes and did not include a transcription factor or transporter gene. Here, analysis of the FUB region in F. verticillioides, F. fujikuroi, and F. oxysporum, a plant pathogen with multiple hosts, indicates the FUB cluster consists of at least 12 genes (FUB1 to FUB12). Deletion analysis confirmed that nine FUB genes, including two Zn(II)2Cys6 transcription factor genes, are required for production of wild-type levels of FA. Comparisons of FUB cluster homologs across multiple Fusarium isolates and species revealed insertion of non-FUB genes at one or two locations in some homologs. Although the ability to produce FA contributed to the phytotoxicity of F. oxysporum culture extracts, lack of production did not affect virulence of F. oxysporum on cactus or F. verticillioides on maize seedlings. These findings provide new insights into the genetic and biochemical processes required for FA production.

Water balance altered in cucumber plants infected with Fusarium oxysporum f. sp. cucumerinum

Fusarium wilt is caused by the infection and growth of the fungus Fusarium oxysporum in the xylem of host plants. The physiological responses of cucumbers that are infected with Fusarium oxysporum f. sp. cucumerinum (FOC) was studied in pot and hydroponic experiments in a greenhouse. The results showed that although water absorption and stem hydraulic conductance decreased markedly in infected plants, large amounts of red ink accumulated in the leaves of infected cucumber plants. The transpiration rate (E) and stomatal conductance (gs) of the infected plants were significantly reduced, but the E/gs was higher than healthy plants. We further found that there was a positive correlation between leaf membrane injury and E/gs, indicating that the leaf cell membrane injury increased the non-stomatal water loss from infected plants. The fusaric acid (FA), which was detected in the infected plant, resulted in damage to the leaf cell membranes and an increase in E/gs, suggesting that FA plays an important role in non-stomatal water loss. In conclusion, leaf cell membrane injury in the soil-borne Fusarium wilt of cucumber plants induced uncontrolled water loss from damaged cells. FA plays a critical role in accelerating the development of Fusarium wilt in cucumber plants.

Production of siderophores increases resistance to fusaric acid in Pseudomonas protegens Pf-5

Fusaric acid is produced by pathogenic fungi of the genus Fusarium, and is toxic to plants and rhizobacteria. Many fluorescent pseudomonads can prevent wilt diseases caused by these fungi. This study was undertaken to evaluate the effect of fusaric acid on P. protegens Pf-5 and elucidate the mechanisms that enable the bacterium to survive in the presence of the mycotoxin. The results confirm that fusaric acid negatively affects growth and motility of P. protegens. Moreover, a notable increase in secretion of the siderophore pyoverdine was observed when P. protegens was grown in the presence of fusaric acid. Concomitantly, levels of enzymes involved in the biosynthesis of pyoverdine and enantio-pyochelin, the second siderophore encoded by P. protegens, increased markedly. Moreover, while similar levels of resistance to fusaric acid were observed for P. protegens mutants unable to synthesize either pyoverdine or enanto-pyochelin and the wild type strain, a double mutant unable to synthesize both kinds of siderophores showed a dramatically reduced resistance to this compound. This reduced resistance was not observed when this mutant was grown under conditions of iron excess. Spectrophotometric titrations revealed that fusaric acid binds not only Fe2+ and Fe3+, but also Zn2+, Mn2+ and Cu2+, with high affinity. Our results demonstrate that iron sequestration accounts at least in part for the deleterious effect of the mycotoxin on P. protegens.

Inhibition of bacterial quorum sensing by extracts from aquatic fungi: first report from marine endophytes

In our search for quorum-sensing (QS) disrupting molecules, 75 fungal isolates were recovered from reef organisms (endophytes), saline lakes and mangrove rhizosphere. Their QS inhibitory activity was evaluated in Chromobacterium violaceum CVO26. Four strains of endophytic fungi stood out for their potent activity at concentrations from 500 to 50 μg mL⁻¹. The molecular characterization, based on the internal transcribed spacer (ITS) region sequences (ITS1, 5.8S and ITS2) between the rRNA of 18S and 28S, identified these strains as belonging to four genera: Sarocladium (LAEE06), Fusarium (LAEE13), Epicoccum (LAEE14), and Khuskia (LAEE21). Interestingly, three came from coral species and two of them came from the same organism, the coral Diploria strigosa. Metabolic profiles obtained by Liquid Chromatography-High Resolution Mass Spectrometry (LC-HRMS) suggest that a combination of fungal secondary metabolites and fatty acids could be the responsible for the observed activities. The LC-HRMS analysis also revealed the presence of potentially new secondary metabolites. This is, to the best of our knowledge, the first report of QS inhibition by marine endophytic fungi.

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.

Screening survey of co-production of fusaric acid, fusarin C, and fumonisins B₁, B₂ and B₃ by Fusarium strains grown in maize grains

Fusarium species isolated from Belgian maize were screened for their ability to produce fusarin C, fusaric acid, fumonisins B1 (FB1), FB2 and FB3 in maize grains. First, cultivation of Fusarium species in Myro liquid medium allowed overcoming the shortage of the standard of fusarin C on the market. All Fusarium verticillioides produced much higher contents of mycotoxins in Myro compared to Fusarium graminearum or Fusarium venenatum. The optimization of the LC-MS/MS method resulted in low limits of detection and quantification for fusarin C, fusaric acid, FB1, FB2 and FB3 determination in maize grains. Its application for screening the potential toxin production ability evidenced that the concentrations of the analytes were significantly increased at various levels when F. verticillioides strains were cultivated in maize grains and reached 441 mg kg(-1) for fusaric acid, 74 mg kg(-1) for fusarin C, 1,301 mg kg(-1) for FB1, 367 mg kg(-1) for FB2 and 753 mg kg(-1) for FB3.