From yellow rain to green wheat: 25 years of trichothecene biosynthesis research

Macrocyclic trichothecenes from Myrothecium verrucaria PA 57 and their cytotoxic activity

Four novel macrocyclic trichothecenes, termed mytoxins D-G (1-4), along with four known analogs (5-8), were isolated from the ethyl acetate extract of fermented rice inoculated with the fungus Myrothecium verrucaria PA57. Each compound features a tricyclic 12,13-epoxytrichothec-9-ene (EPT) core. Notably, mytoxin G (4) represents the first instance of a macrocyclic trichothecene incorporating a glucosyl unit within the trichothecene structure. The structures of the newly identified compounds were elucidated through comprehensive spectroscopic analysis combined with quantum chemical calculations. All isolated compounds demonstrated cytotoxic activity against the CAL27 and HCT116 cell lines, which are models for human oral squamous cell carcinoma and colorectal cancer, respectively. Specifically, mytoxin D (1) and mytoxin F (3) exhibited pronounced cytotoxic effects against both cancer cell lines, with IC50 values ranging from 3 to 6 nmol·L-1. Moreover, compounds 1 and 3 were found to induce apoptosis in HCT116 cells by activating caspase-3.

Attempting to Create a Pathway to 15-Deacetylcalonectrin with Limited Accumulation in Cultures of Fusarium Tri3 Mutants: Insight into Trichothecene Biosynthesis Machinery

The compound 15-deacetylcalonectrin (15-deCAL) is a common pathway intermediate in the biosynthesis of Fusarium trichothecenes. This tricyclic intermediate is metabolized to calonectrin (CAL) by trichothecene 15-O-acetyltransferase encoded by Tri3. Unlike other trichothecene pathway Tri gene mutants, the Δtri3 mutant produces lower amounts of the knocked-out enzyme's substrate 15-deCAL, and instead, accumulates higher quantities of earlier bicyclic intermediate and shunt metabolites. Furthermore, evolutionary studies suggest that Tri3 may play a role in shaping the chemotypes of trichothecene-producing Fusarium strains. To better understand the functional role of Tri3p in biosynthesis and evolution, we aimed to develop a method to produce 15-deCAL by using transgenic Fusarium graminearum strains derived from a trichothecene overproducer. Unfortunately, introducing mutant Tri3, encoding a catalytically impaired but structurally intact acetylase, did not improve the low 15-deCAL production level of the ΔFgtri3 deletion strain, and the bicyclic products continued to accumulate as the major metabolites of the active-site mutant. These findings are discussed in light of the enzyme responsible for 15-deCAL production in trichothecene biosynthesis machinery. To efficiently produce 15-deCAL, we tested an alternative strategy of using a CAL-overproducing transformant. By feeding a crude CAL extract to a Fusarium commune strain that was isolated in this study and capable of specifically deacetylating C-15 acetyl, 15-deCAL was efficiently recovered. The substrate produced in this manner can be used for kinetic investigations of this enzyme and its possible role in chemotype diversification.

A Role in 15-Deacetylcalonectrin Acetylation in the Non-Enzymatic Cyclization of an Earlier Bicyclic Intermediate in Fusarium Trichothecene Biosynthesis

The trichothecene biosynthesis in Fusarium begins with the cyclization of farnesyl pyrophosphate to trichodiene, followed by subsequent oxygenation to isotrichotriol. This initial bicyclic intermediate is further cyclized to isotrichodermol (ITDmol), a tricyclic precursor with a toxic trichothecene skeleton. Although the first cyclization and subsequent oxygenation are catalyzed by enzymes encoded by Tri5 and Tri4, the second cyclization occurs non-enzymatically. Following ITDmol formation, the enzymes encoded by Tri101, Tri11, Tri3, and Tri1 catalyze 3-O-acetylation, 15-hydroxylation, 15-O-acetylation, and A-ring oxygenation, respectively. In this study, we extensively analyzed the metabolites of the corresponding pathway-blocked mutants of Fusarium graminearum. The disruption of these Tri genes, except Tri3, led to the accumulation of tricyclic trichothecenes as the main products: ITDmol due to Tri101 disruption; a mixture of isotrichodermin (ITD), 7-hydroxyisotrichodermin (7-HIT), and 8-hydroxyisotrichodermin (8-HIT) due to Tri11 disruption; and a mixture of calonectrin and 3-deacetylcalonectrin due to Tri1 disruption. However, the ΔFgtri3 mutant accumulated substantial amounts of bicyclic metabolites, isotrichotriol and trichotriol, in addition to tricyclic 15-deacetylcalonectrin (15-deCAL). The ΔFgtri5ΔFgtri3 double gene disruptant transformed ITD into 7-HIT, 8-HIT, and 15-deCAL. The deletion of FgTri3 and overexpression of Tri6 and Tri10 trichothecene regulatory genes did not result in the accumulation of 15-deCAL in the transgenic strain. Thus, the absence of Tri3p and/or the presence of a small amount of 15-deCAL adversely affected the non-enzymatic second cyclization and C-15 hydroxylation steps.

Type A Trichothecene Metabolic Profile Differentiation, Mechanisms, Biosynthetic Pathways, and Evolution in Fusarium Species-A Mini Review

Trichothecenes are the most common Fusarium toxins detected in grains and related products. Type A trichothecenes are among the mycotoxins of greatest concern to food and feed safety due to their high toxicity. Recently, two different trichothecene genotypes within Fusarium species were reported. The available information showed that Tri1 and Tri16 genes are the key determinants of the trichothecene profiles of T-2 and DAS genotypes. In this review, polymorphisms in the Tri1 and Tri16 genes in the two genotypes were investigated. Meanwhile, the functions of genes involved in DAS and NEO biosynthesis are discussed. The possible biosynthetic pathways of DAS and NEO are proposed in this review, which will facilitate the understanding of the synthesis process of trichothecenes in Fusarium strains and may also inspire researchers to design and conduct further research. Together, the review provides insight into trichothecene profile differentiation and Tri gene evolutionary processes responsible for the structural diversification of trichothecene produced by Fusarium.

Regulatory mechanism of trichothecene biosynthesis in Fusarium graminearum

Among the genes involved in the biosynthesis of trichothecene (Tri genes), Tri6 and Tri10 encode a transcription factor with unique Cys₂His₂ zinc finger domains and a regulatory protein with no consensus DNA-binding sequences, respectively. Although various chemical factors, such as nitrogen nutrients, medium pH, and certain oligosaccharides, are known to influence trichothecene biosynthesis in Fusarium graminearum, the transcriptional regulatory mechanism of Tri6 and Tri10 genes is poorly understood. Particularly, culture medium pH is a major regulator in trichothecene biosynthesis in F. graminearum, but it is susceptible to metabolic changes posed by nutritional and genetic factors. Hence, appropriate precautions should be considered to minimize the indirect influence of pH on the secondary metabolism while studying the roles of nutritional and genetic factors on trichothecene biosynthesis regulation. Additionally, it is noteworthy that the structural changes of the trichothecene gene cluster core region exert considerable influence over the normal regulation of Tri gene expression. In this perspective paper, we consider a revision of our current understanding of the regulatory mechanism of trichothecene biosynthesis in F. graminearum and share our idea toward establishing a regulatory model of Tri6 and Tri10 transcription.

Cytotoxicity of the Fusarium mycotoxin deoxynivalenol on mammalian and avian cell lines

Trichothecenes are mycotoxins that occur in grains and can lead to acute and chronic poisoning in animals and humans. Deoxynivalenol (DON) is a type B trichothecene affecting protein synthesis, immune system, leading to brain, blood and kidney disorders. The aim of this work was to evaluate in vitro the cytotoxicity and the pathological effects of DON in short-term experiments on cells from non-tumour and tumour permanent cell lines and to compare their sensitivity. Cell cultivation of BALB/c 3T3, DEC 99, MDA-MB-231, MCF-7 and Hela cells was performed. Quantitative and qualitative methods evaluating cytotoxicity on the base of statistical and morphological analyses for determining the impact on the viability and proliferative activity were used: Neutral Red Uptake (NRU) cytotoxicity test, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test and fluorescence microscopy. The cytotoxic effect of DON was assessed after an exposure period of 24 h. DON treatment induced significant alterations in the growth and morphology of the cells, involving early and late apoptosis and necrosis signs. Statistically significant decrease of the viability of all cell lines was established at concentrations of DON starting from 1.9 µg/mL to 3.7 µg/mL, the mean IC50 concentrations were calculated. According to the IC50 values the hierarchical order of cell lines’ sensitivity was determined.

Characterisation of two unique sesquiterpenoids from Trichoderma hypoxylon

Two new sesquiterpenoids, 1-2, together with three known compounds, were isolated from Trichoderma hypoxylon. Among the known compounds, compound 4 was isolated as naturally occurring compound for the first time. The structures of these new compounds were characterized by HR-ESI-MS and spectroscopic methods including 1D and 2D NMR. The absolute configurations of 1-2 were assigned by electronic circular dichroism (ECD) calculations.

Impact of nitrogen metabolism-associated culture pH changes on regulation of Fusarium trichothecene biosynthesis: revision of roles of polyamine agmatine and transcription factor AreA

Fusarium graminearum produces trichothecene mycotoxins in infected grains and axenic liquid culture. A proposed regulatory model of trichothecene biosynthesis was examined in relation to nitrogen utilization. First, we showed that an important factor for the stimulation of trichothecene biosynthesis was not the occurrence of agmatine as a specific inducer molecule, but rather continuous acidification of the liquid culture medium arising from agmatine catabolism. When the pH of the L-Gln synthetic medium was frequently adjusted to the pH of the agmatine culture, trichothecene productivity of the L-Gln culture was equal to that of the agmatine culture. For efficient trichothecene biosynthesis, the culture pH should be lowered at an appropriate time point during the early growth stage. Second, we re-evaluated the role of the nitrogen regulatory GATA transcription factor AreA in trichothecene biosynthesis. Since Tri6 encodes a transcription factor indispensable for trichothecene biosynthesis, all fifteen AreA-binding consensus sequences in the Tri6 promoter were mutated. The mutant could catabolize L-Phe as the sole nitrogen source; furthermore, the pH profile of the synthetic L-Phe medium (initial pH 4.2) was the same as that of the wild-type (WT) strain. Under such conditions, the promoter mutant exhibited approximately 72% of the trichothecene productivity compared to the WT strain. Thus, F. graminearum AreA (FgAreAp) is dispensable for the functioning of the Tri6 promoter, but it contributes to the increased production of mycotoxin under mildly acidic conditions to some extent. Further investigations on the culture pH revealed that extremely low pH bypasses the function of FgAreAp.

New tricks for old dogs: Two new macrocyclic trichothecene epimers and absolute configuration of 16-hydroxyverrucarin B

Two new compounds, 3'-epi-16-hydroxyverrucarin A and 3'-epiverrucarin X, have been isolated and identified, and the characterization data of a series of known trichothecenes have been refined. The interesting structure and potent biological activities of macrocyclic trichothecenes have been of interest to the scientific community for several decades. However, some of the characterization data for the older analogues of this class are not well documented, either because of a lack of absolute configuration or a lack of clarity in the NMR data, largely due to technological limitations at the time they were discovered. NMR techniques, application of Mosher's esters analysis, and electronic circular dichroism were used here both to refine the characterization of known trichothecenes, as well as to uncover new structures. These studies demonstrate strategies that can be used to interrogate the characterization data of well-known secondary metabolites, thereby gaining greater insight into methods that can be used to refine previous literature.

Selection of Fusarium Trichothecene Toxin Genes for Molecular Detection Depends on TRI Gene Cluster Organization and Gene Function

Food security is a global concern. Fusarium are among the most economically important fungal pathogens because they are ubiquitous, disease management remains a challenge, they produce mycotoxins that affect food and feed safety, and trichothecene mycotoxin production can increase the pathogenicity of some Fusarium species depending on the host species. Although trichothecenes may differ in structure by their patterns of hydroxylation or acetylation, these small changes have a significant impact on toxicity and the biological activity of these compounds. Therefore, detecting and identifying which chemotype is present in a given population are important to predicting the specific toxins that may be produced and, therefore, to evaluating the risk of exposure. Due to the challenges of inducing trichothecene production by Fusarium isolates in vitro for subsequent chemical analysis, PCR assays using gene-specific primers, either singly or in combination, designed against specific genes of the trichothecene gene cluster of multiple species of Fusarium have been developed. The establishment of TRI genotypes that potentially correspond to a specific chemotype requires examination of an information and knowledge pipeline whose critical aspects in sequential order are: (i) understanding the TRI gene cluster organization which differs according to Fusarium species under study; (ii) knowledge of the re-arrangements to the core TRI gene cluster over evolutionary time, which also differs according to Fusarium species; (iii) the functions of the TRI genes in the biosynthesis of trichothecene analogs; and (iv) based on (i)⁻(iii), selection of appropriate target TRI gene(s) for primer design in PCR amplification for the Fusarium species under study. This review, therefore, explains this pipeline and its connection to utilizing TRI genotypes as a possible proxy to chemotype designation.

Mechanistic characterization of three sesquiterpene synthases from the termite-associated fungus Termitomyces

Three terpene synthases from the termite associated fungus Termitomyces were studied by isotopic labelling experiments and site-directed mutagenesis.

The Fungicidal Activity of Tebuconazole Enantiomers against Fusarium graminearum and Its Selective Effect on DON Production under Different Conditions

Tebuconazole, which consists of a pair of enantiomers with different fungicidal activities, is one of the most common fungicides used in the control of Fusarium graminearum. In this study, the fungicidal activity of rac-tebuconazole and its enantiomers against F. graminearum was determined at 0.997, 0.975, and 0.950 a_w and at 20, 25, and 30 °C on wheat-based media. Then, F. graminearum was treated with rac-tebuconazole and its enantiomers at the EC₁₀, EC₅₀, and EC₉₀ levels under different culture conditions, and DON production was measured. Finally, expression of the DON biosynthetic genes ( TRI5 and TRI6) was quantified by real-time RT-PCR after incubation with EC₅₀ doses of rac-tebuconazole and its enantiomers for 4, 8, and 14 days at 30 °C and a_w 0.997. The results showed that the fungicidal activity of tebuconazole was strongly influenced by temperature, a_w, and the combined factors. (-)-Tebuconazole is higher in fungicidal activity than (+)-tebuconazole and rac-tebuconazole with 24-99-fold and 1.8-6.7-fold, respectively. However, (-)-tebuconazole was generally more favorable for DON production than (+)-tebuconazole under the same conditions. Additionally, (-)-tebuconazole and rac-tebuconazole induced significantly increased expression of the DON biosynthetic genes ( TRI5 and TRI6) compared to the control by the 14th day of treatment. In this research, the combination condition of 30 °C and 0.997 a_w is the most suitable for DON production by F. graminearum. The test strains of F. graminearum treated with the EC₁₀ dose of (-)-tebuconazole produced the greatest amounts of DON.

Metabolic profile of the masked mycotoxin T-2 toxin-3-glucoside in rats (in vitro and in vivo) and humans (in vitro)

The metabolic profile of T-2 toxin-3-glucoside (T2-Glc) in humans and rats was investigated using ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-QTOF). When rat and human liver microsomes were incubated with T2-Glc, a total of five metabolites were detected. T2-Glc exposed a higher metabolic stability in rats and human than T-2 toxin (T-2). The metabolism of T2-Glc by the intestinal microbiota of human and rats was also investigated, and three metabolites were observed. T2-Glc was reconverted to T-2 during incubation with fresh faeces. Furthermore, in vivo metabolism of T2-Glc in rats after oral administration was carried out, and three metabolites were detected in rat urine and faeces (T-2, HT-2 toxin and 3'-OH-T2-Glc). In vivo metabolism results indicated that T2-Glc was mainly metabolised in the gastro-intestinal tract with a low absorption level in rats. The results demonstrated that hydroxylation (C-3' and C-4'), hydrolysis (C-4 and C-8) and deconjugation are the main metabolic pathways of T2-Glc in mammals.

Co-administration of amygdalin and deoxynivalenol disrupted regulatory proteins linked to proliferation of porcine ovarian cells in vitro

Deoxynivalenol (DON) represents one of the most prevalent trichothecene mycotoxin produced by Fusarium species, causing economic and health impacts. On the other hand, amygdalin has been demonstrated to possess both prophylactic and curative properties, thus it has been used as a traditional drug because of its wide range of medicinal benefits, including curing or preventing cancer, relieving fever, suppressing cough, and quenching thirst. The aim of this in vitro study was to evaluate potential effects of natural product amygdalin combined with mycotoxin deoxynivalenol (DON) on the key regulators of cell proliferation and apoptosis in porcine ovarian granulosa cells. Ovarian granulosa cells were incubated for 24h with amygdalin (1, 10, 100, 1000, 10 000 μg.mL-1) combined with deoxynivalenol (1 μg.mL-1), while the control group remained untreated. The presence of proliferative (cyclin B1, PCNA) and apoptotic markers (caspase-3) in porcine ovarian granulosa cells after amygdalin treatment (1, 10, 100, 1000, 10 000 μg.mL-1) combined with deoxynivalneol (1 μg.mL-1) was detected by immunocytochemistry. The presence of proliferative (cyclin B1, PCNA) and apoptotic markers (caspase-3) in porcine ovarian granulosa cells was detected by immunocytochemistry. Co-administration of amygdalin plus DON significantly (p <0.05) increased the number of granulosa cells containing cyclin B1 and PCNA at all tested concetrations, when compared to control. However, percentage of granulosa cells containing major apoptotic marker caspase-3 did not differ after co-administration of amygdalin and DON. In summary, results form this in vitro study indicate that co-exposure of amygdalin and deoxynivalenol  may act to stimulate proliferation-associated peptides in porcine ovarian granulosa cells, and thus alter cell proliferation and normal follicular development.

Identification of a trichothecene production inhibitor by chemical array and library screening using trichodiene synthase as a target protein

Trichothecene mycotoxins often accumulate in apparently normal grains of cereal crops. In an effort to develop an agricultural chemical to reduce trichothecene contamination, we screened trichothecene production inhibitors from the compounds on the chemical arrays. By using the trichodiene (TDN) synthase tagged with hexahistidine (rTRI5) as a target protein, 32 hit compounds were obtained from chemical library of the RIKEN Natural Product Depository (NPDepo) by chemical array screening. At 10μgmL^-1, none of the 32 chemicals inhibited trichothecene production by Fusarium graminearum in liquid culture. Against the purified rTRI5 enzyme, however, NPD10133 [progesterone 3-(O-carboxymethyl)oxime amide-bonded to phenylalanine] showed weak inhibitory activity at 10μgmL^-1 (18.7μM). For the screening of chemicals inhibiting trichothecene accumulation in liquid culture, 20 analogs of NPD10133 selected from the NPDepo chemical library were assayed. At 10μM, only NPD352 [testosterone 3-(O-carboxymethyl)oxime amide-bonded to phenylalanine methyl ester] inhibited rTRI5 activity and trichothecene production. Kinetic analysis suggested that the enzyme inhibition was of a mixed-type. The identification of NPD352 as a TDN synthase inhibitor lays the foundation for the development of a more potent inhibitor via systematic introduction of wide structural diversity on the gonane skeleton and amino acid residues.

L-Threonine and its analogue added to autoclaved solid medium suppress trichothecene production by Fusarium graminearum

Fusarium graminearum produces trichothecene mycotoxins under certain nutritional conditions. When L-Thr and its analogue L-allo-threonine were added to brown rice flour solid medium before inoculation, trichothecene production after 4 days of incubation was suppressed. A time-course analysis of gene expression demonstrated that L-Thr suppressed transcription of Tri6, a trichothecene master regulator gene, and a terpene cyclase Tri5 gene. Regulation of trichothecene biosynthesis by altering major primary metabolic processes may open up the possibility to develop safe chemicals for the reduction of mycotoxin contamination might be developed.

Killing of diverse eye pathogens (Acanthamoeba spp., Fusarium solani, and Chlamydia trachomatis) with alcohols

Background

Blindness is caused by eye pathogens that include a free-living protist (Acanthamoeba castellanii, A. byersi, and/or other Acanthamoeba spp.), a fungus (Fusarium solani), and a bacterium (Chlamydia trachomatis). Hand-eye contact is likely a contributor to the spread of these pathogens, and so hand washing with soap and water or alcohol–based hand sanitizers (when water is not available) might reduce their transmission. Recently we showed that ethanol and isopropanol in concentrations present in hand sanitizers kill walled cysts of Giardia and Entamoeba, causes of diarrhea and dysentery, respectively. The goal here was to determine whether these alcohols might kill infectious forms of representative eye pathogens (trophozoites and cysts of Acanthamoeba, conidia of F. solani, or elementary bodies of C. trachomatis).

Methodology/Principal findings

We found that treatment with 63% ethanol or 63% isopropanol kills >99% of Acanthamoeba trophozoites after 30 sec exposure, as shown by labeling with propidium iodide (PI) and failure to grow in culture. In contrast, Acanthamoeba cysts, which contain cellulose fibers in their wall, are relatively more resistant to these alcohols, particularly isopropanol. Depending upon the strain tested, 80 to 99% of Acanthamoeba cysts were killed by 63% ethanol after 2 min and 95 to 99% were killed by 80% ethanol after 30 sec, as shown by PI labeling and reduced rates of excystation in vitro. Both ethanol and isopropanol (63% for 30 sec) kill >99% of F. solani conidia, which have a wall of chitin and glucan fibrils, as demonstrated by PI labeling and colony counts on nutrient agar plates. Both ethanol and isopropanol (63% for 60 sec) inactivate 96 to 99% of elementary bodies of C. trachomatis, which have a wall of lipopolysaccharide but lack peptidoglycan, as measured by quantitative cultures to calculate inclusion forming units.

Conclusions/Significance

In summary, alcohols kill infectious forms of Acanthamoeba, F. solani, and C. trachomatis, although longer times and higher ethanol concentrations are necessary for Acanthamoeba cysts. These results suggest the possibility that expanded use of alcohol-based hand sanitizers in places where water is not easily available might reduce transmission of these important causes of blindness.

Hand washing with soap and water is an important public health tool for reducing transmission of viruses, bacteria, fungi, and protists. Alcohol-based hand sanitizers, which are widely dispensed in hospitals and public places, kill many of these same pathogens. What is not known is how effectively the alcohol-based hand sanitizers kill protists, fungi, or bacteria that cause eye disease. Here we show ethanol and isopropanol penetrate the walls and kill a free-living protist (Acanthamoeba castellanii, A. byersi, and other Acanthamoeba spp.), and a fungus (Fusarium solani), each of which causes keratitis, as well as a bacterium (Chlamydia trachomatis) that causes trachoma. These results suggest the possible benefit of hand sanitizers in the prevention of these eye pathogens.

2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) inhibits trichothecene production by Fusarium graminearum through suppression of Tri6 expression

Fusarium head blight (FHB) is a devastating disease of wheat (Triticum aestivum L.) caused by a mycotoxigenic fungus Fusarium graminearum resulting in significantly decreased yields and accumulation of toxic trichothecenes in grains. We tested 7 major secondary metabolites from wheat for their effect on trichothecene production in liquid cultures of F. graminearum producing trichothecene 15-acetyldeoxynivalenol (15-ADON). 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) benzoxazinoid completely abolished toxin production without any apparent effect on fungal growth. DIMBOA strongly affected the expression of Tri6, encoding a major transcriptional regulator of several genes of the trichothecene biosynthesis pathway. DIMBOA also repressed expression of Tri5, encoding trichodiene synthase, the first enzyme in the trichothecene biosynthesis pathway. Thus, DIMBOA could play an important role against the accumulation of trichothecenes in wheat grain. Breeding or engineering of wheat with increased levels of benzoxazinoids could provide varieties with increased resistance against trichothecene contamination of grain and lower susceptibility to FHB.

SnPKS19 Encodes the Polyketide Synthase for Alternariol Mycotoxin Biosynthesis in the Wheat Pathogen Parastagonospora nodorum

Alternariol (AOH) is an important mycotoxin from the Alternaria fungi. AOH was detected for the first time in the wheat pathogen Parastagonospora nodorum in a recent study. Here, we exploited reverse genetics to demonstrate that SNOG_15829 (SnPKS19), a close homolog of Penicillium aethiopicum norlichexanthone (NLX) synthase gene gsfA, is required for AOH production. We further validate that SnPKS19 is solely responsible for AOH production by heterologous expression in Aspergillus nidulans. The expression profile of SnPKS19 based on previous P. nodorum microarray data correlated with the presence of AOH in vitro and its absence in planta. Subsequent characterization of the ΔSnPKS19 mutants showed that SnPKS19 and AOH are not involved in virulence and oxidative stress tolerance. Identification and characterization of the P. nodorum SnPKS19 cast light on a possible alternative AOH synthase gene in Alternaria alternata and allowed us to survey the distribution of AOH synthase genes in other fungal genomes. We further demonstrate that phylogenetic analysis could be used to differentiate between AOH synthases and the closely related NLX synthases. This study provides the basis for studying the genetic regulation of AOH production and for development of molecular diagnostic methods for detecting AOH-producing fungi in the future.

Traversing the fungal terpenome

Fungi (Ascomycota and Basidiomycota) are prolific producers of structurally diverse terpenoid compounds. Classes of terpenoids identified in fungi include the sesqui-, di- and triterpenoids. Biosynthetic pathways and enzymes to terpenoids from each of these classes have been described. These typically involve the scaffold generating terpene synthases and cyclases, and scaffold tailoring enzymes such as e.g. cytochrome P450 monoxygenases, NAD(P)+ and flavin dependent oxidoreductases, and various group transferases that generate the final bioactive structures. The biosynthesis of several sesquiterpenoid mycotoxins and bioactive diterpenoids has been well-studied in Ascomycota (e.g. filamentous fungi). Little is known about the terpenoid biosynthetic pathways in Basidiomycota (e.g. mushroom forming fungi), although they produce a huge diversity of terpenoid natural products. Specifically, many trans-humulyl cation derived sesquiterpenoid natural products with potent bioactivities have been isolated. Biosynthetic gene clusters responsible for the production of trans-humulyl cation derived protoilludanes, and other sesquiterpenoids, can be rapidly identified by genome sequencing and bioinformatic methods. Genome mining combined with heterologous biosynthetic pathway refactoring has the potential to facilitate discovery and production of pharmaceutically relevant fungal terpenoids.

Biosynthesis of terpenoid natural products in fungi

Tens of thousands of terpenoid natural products have been isolated from plants and microbial sources. Higher fungi (Ascomycota and Basidiomycota) are known to produce an array of well-known terpenoid natural products, including mycotoxins, antibiotics, antitumor compounds, and phytohormones. Except for a few well-studied fungal biosynthetic pathways, the majority of genes and biosynthetic pathways responsible for the biosynthesis of a small number of these secondary metabolites have only been discovered and characterized in the past 5-10 years. This chapter provides a comprehensive overview of the current knowledge on fungal terpenoid biosynthesis from biochemical, genetic, and genomic viewpoints. Enzymes involved in synthesizing, transferring, and cyclizing the prenyl chains that form the hydrocarbon scaffolds of fungal terpenoid natural products are systematically discussed. Genomic information and functional evidence suggest differences between the terpenome of the two major fungal phyla--the Ascomycota and Basidiomycota--which will be illustrated for each group of terpenoid natural products.

Mushroom hunting by using bioinformatics: application of a predictive framework facilitates the selective identification of sesquiterpene synthases in basidiomycota

The Basidiomycota fungi represent a diverse source of natural products, particularly the sesquiterpenoids. Recently, genome sequencing, genome mining, and the subsequent discovery of a suite of sesquiterpene synthases in Omphalotus olearius was described. A predictive framework was developed to facilitate the discovery of sesquiterpene synthases in Basidiomycota. Phylogenetic analyses indicated a conservation of both sequence and initial cyclization mechanisms used. Here, the first robust application of this predictive framework is reported. It was used to selectively identify sesquiterpene synthases that follow 1,6-, 1,10-, and 1,11-cyclization mechanisms in the crust fungus Stereum hirsutum. The successful identification and characterization of a 1,6- and a 1,10-cyclizing sesquiterpene synthase, as well as three 1,11-cyclizing Δ(6) -protoilludene synthases, is described. This study verifies the accuracy and utility of the predictive framework as a roadmap for the discovery of specific sesquiterpene synthases from Basidiomycota, and thus represents an important step forward in natural product discovery.

Identification and characterization of an inhibitor of trichothecene 3-O-acetyltransferase, TRI101, by the chemical array approach

Trichothecene 3-O-acetyltransferase (TRI101) is an indispensable enzyme for the biosynthesis of trichothecenes, a group of mycotoxins produced by Fusarium graminearum. In this study, an inhibitor of TRI101 was identified by chemical array analysis using compounds from the RIKEN Natural Products Depository (NPDepo) library. Although the addition of the identified enzyme inhibitor to the fungal culture did not inhibit trichothecene production, it can serve as a candidate lead compound in the development of a mycotoxin inhibitor that inactivates fungal defense mechanisms.

Medical aspects of bio-terrorism

INTRODUCTION

Bioterrorism is a terrorist action involving the intentional release or dissemination of a biological warfare agent (BWA), which includes some bacteria, viruses, rickettsiae, fungi or biological toxins. BWA is a naturally occurring or human-modified form that may kill or incapacitate humans, animals or plants as an act of war or terrorism. BWA is a weapon of choice for mass destruction and terrorism, because of the incubation period, less effective amount than chemical warfare agents, easily distribution, odorless, colorless, difficult to detect, no need of specialized equipment for production and naturally distribution which can easily be obtained. BWA may be disseminating as an aerosol, spray, explosive device, and by food or water.

CLASSIFICATION

Based on the risk for human health, BWAs have been prioritized into three categories of A, B and C. Category A includes microorganisms or toxins that easily spread, leading to intoxication with high death rates such as Anthrax, Botulism, Plague, Smallpox, Tularemia and Viral hemorrhagic fevers. Category B has lower toxicity with wider range, including Staphylococcal Entrotoxin type B (SEB), Epsilon toxin of Clostridium perfringens, Ricin, Saxotoxins, Abrin and Trichothecene mycotoxins. The C category includes emerging pathogens that could also be engineered for mass spread such as Hanta viruses, multidrug-resistant tuberculosis, Nipah virus, the tick-borne encephalitis viruses, hemorrhagic fever viruses and yellow fever. CLINICAL MANIFESTATIONS OF BIOTOXINS IN HUMAN: Clinical features and severity of intoxication depend on the agent and exposed dose, route of entry, individual variation and environmental factors. Onset of symptoms varies from 2-24 h in Ricin to 24-96 h in Botulism. Clinical manifestations also vary from irritation of the eyes, skin and mucus membranes in T2 toxin to an acute flaccid paralysis of bilateral cranial nerve impairment of descending manner in botulism. Most of the pyrogenic toxins such as SEB produce the same signs and symptoms as toxic shock syndrome including a rapid drop in blood pressure, elevated temperature, and multiple organ failure.

MANAGEMENT

There is no specific antidote or effective treatment for most of the biotoxins. The clinical management is thus more supportive and symptomatic. Fortunately vaccines are now available for most of BWA. Therefore, immunization of personnel at risk of exposure is recommended.

CONCLUSION

Biotoxins are very wide and bioterrorism is a heath and security threat that may induce national and international problems. Therefore, the security authorities, health professional and even public should be aware of bioterrorism.

Comprehensive gene expression analysis of type B trichothecenes

Type B trichothecenes, deoxynivalenol (DON) and nivalenol (NIV), are secondary metabolites of Fusarium species and are major pollutants in food and feed products. Recently, the production trend of their derivatives, 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON), and 4-acetylnivalenol (4-AcNIV or fusarenon-X), has been changing in various regions worldwide. Although in vivo behavior has been reported, it is necessary to acquire more detailed information about these derivatives. Here, the yeast PDR5 mutant was used for toxicity evaluation, and the growth test revealed that DON, 15-AcDON, and 4-AcNIV had higher toxicity compared to 3-AcDON and NIV. 15-AcDON exerted the most significant gene expression changes, and cellular localization clustering exhibited repression of mitochondrial ribosomal genes. This study suggests that the toxicity trends of both DON products (DON and its derivatives) and NIV products (NIV and its derivatives) are similar to those observed in mammalian cells, with a notable toxic response to 15-AcDON.

Current and future experimental strategies for structural analysis of trichothecene mycotoxins--a prospectus

Fungal toxins, such as those produced by members of the order Hypocreales, have widespread effects on cereal crops, resulting in yield losses and the potential for severe disease and mortality in humans and livestock. Among the most toxic are the trichothecenes. Trichothecenes have various detrimental effects on eukaryotic cells including an interference with protein production and the disruption of nucleic acid synthesis. However, these toxins can have a wide range of toxicity depending on the system. Major differences in the phytotoxicity and cytotoxicity of these mycotoxins are observed for individual members of the class, and variations in toxicity are observed among different species for each individual compound. Furthermore, while diverse toxicological effects are observed throughout the whole cellular system upon trichothecene exposure, the mechanism of toxicity is not well understood. In order to comprehend how these toxins interact with the cell, we must first have an advanced understanding of their structure and dynamics. The structural analysis of trichothecenes was a subject of major interest in the 1980s, and primarily focused on crystallographic and solution-state Nuclear Magnetic Resonance (NMR) spectroscopic studies. Recent advances in structural determination through solution- and solid-state NMR, as well as computation based molecular modeling is leading to a resurgent interest in the structure of these and other mycotoxins, with the focus shifting in the direction of structural dynamics. The purpose of this work is to first provide a brief overview of the structural data available on trichothecenes and a characterization of the methods commonly employed to obtain such information. A summary of the current understanding of the relationship between structure and known function of these compounds is also presented. Finally, a prospectus on the application of new emerging structural methods on these and other related systems is discussed.

Compartmentalization and molecular traffic in secondary metabolism: a new understanding of established cellular processes

Great progress has been made in understanding the regulation of expression of genes involved in secondary metabolism. Less is known about the mechanisms that govern the spatial distribution of the enzymes, cofactors, and substrates that mediate catalysis of secondary metabolites within the cell. Filamentous fungi in the genus Aspergillus synthesize an array of secondary metabolites and provide useful systems to analyze the mechanisms that mediate the temporal and spatial regulation of secondary metabolism in eukaryotes. For example, aflatoxin biosynthesis in Aspergillus parasiticus has been studied intensively because this mycotoxin is highly toxic, mutagenic, and carcinogenic in humans and animals. Using aflatoxin synthesis to illustrate key concepts, this review focuses on the mechanisms by which sub-cellular compartmentalization and intra-cellular molecular traffic contribute to the initiation and completion of secondary metabolism within the cell. We discuss the recent discovery of aflatoxisomes, specialized trafficking vesicles that participate in the compartmentalization of aflatoxin synthesis and export of the toxin to the cell exterior; this work provides a new and clearer understanding of how cells integrate secondary metabolism into basic cellular metabolism via the intra-cellular trafficking machinery.

Spotlights on advances in mycotoxin research

A remarkable feature of filamentous fungi is their ability to produce small yet structurally complex and often bioactive natural products. In this mini-review, we cover advances in the research on fungal secondary metabolites, particularly mycotoxins, and focus on biosynthetic aspects as well as on the complex regulatory mechanisms which control the expression of biosynthetic genes. We also highlight the increasing impact of genomics and transcriptomics, which help explore the realm of secondary metabolism of fungi.