Production of culmorin compounds and other secondary metabolites by Fusarium culmorum and F. graminearum strains isolated from Norwegian cereals

New Cytotoxic Secondary Metabolites from Two Deep-Sea-Derived Fungi and the Co-Culture Impact on the Secondary Metabolic Patterns

In this study, chemical profiles for two co-existing deep-sea-derived Penicillium fungal strains were thoroughly investigated. Two new compounds and 11 known compounds were identified from Penicillium sp. LXY140-R, while one new compound and 12 known compounds were isolated from Penicillium sp. LXY140-3. Their structures were elucidated by extensive 1D and 2D NMR experiments, which were supported by HR-ESI-MS data. The antiproliferative activities of all isolates against HCT-116, A549 and Bel-7402 cell lines were also evaluated. Compounds 2, 5, 6, 10 and 13 showed potent antiproliferative activity. To reveal the metabolic relationship of the two strains, we conducted co-culture experiments to discover cross-talk molecules by a device that allows only small molecule to communicate. Extensive HPLC/MS² experiments were applied to identify the disturbance of the chemical profiles within the synthetic Penicillium-Penicillium community. The fungal strain LXY140-R was found to accumulate mono or multiple-acetylation derivatives of deoxynivalenol (DON) sesquiterpenes as responsible molecules by the disturbance of the metabolites produced by the LXY140-3 strain.

Multiple Fungal Metabolites Including Mycotoxins in Naturally Infected and Fusarium-Inoculated Wheat Samples

In this study, the occurrence of multiple fungal metabolites including mycotoxins was determined in four different winter wheat varieties in a field experiment in Croatia. One group was naturally infected, while the second group was inoculated with a Fusarium graminearum and F. culmorum mixture to simulate a worst-case infection scenario. Data on the multiple fungal metabolites including mycotoxins were acquired with liquid chromatography with mass spectrometry (LC-MS/MS) multi-(myco)toxin method. In total, 36 different fungal metabolites were quantified in this study: the Fusarium mycotoxins deoxynivalenol (DON), DON-3-glucoside (D3G), 3-acetyldeoxynivalenol (3-ADON), culmorin (CULM), 15-hydroxyculmorin, 5-hydroxyculmorin, aurofusarin, rubrofusarin, enniatin (Enn) A, Enn A1, Enn B, Enn B1, Enn B2, Enn B3, fumonisin B1, fumonisin B2, chrysogin, zearalenone (ZEN), moniliformin (MON), nivalenol (NIV), siccanol, equisetin, beauvericin (BEA), and antibiotic Y; the Alternaria mycotoxins alternariol, alternariolmethylether, altersetin, infectopyron, tentoxin, tenuazonic acid; the Aspergillus mycotoxin kojic acid; unspecific metabolites butenolid, brevianamid F, cyclo(L-Pro-L-Tyr), cyclo(L-Pro-L-Val), and tryptophol. The most abundant mycotoxins in the inoculated and naturally contaminated samples, respectively, were found to occur at the following average concentrations: DON (19,122/1504 µg/kg), CULM (6109/1010 µg/kg), 15-hydroxyculmorin (56,022/1301 µg/kg), 5-hydroxyculmorin (21,219/863 µg/kg), aurofusarin (43,496/1266 µg/kg). Compared to naturally-infected samples, Fusarium inoculations at the flowering stage increased the concentrations of all Fusarium mycotoxins, except enniatins and siccanol in Ficko, the Aspergillus metabolite kojic acid, the Alternaria mycotoxin altersetin, and unspecific metabolites brevianamid F, butenolid, cyclo(L-Pro-L-Tyr), and cyclo(L-Pro-L-Val). In contrast to these findings, because of possible antagonistic actions, Fusarium inoculation decreased the concentrations of the Alternaria toxins alternariol, alternariolmethylether, infectopyron, tentoxin, tenuazonic acid, as well as the concentration of the nonspecific metabolite tryptophol.

Changes in masked forms of deoxynivalenol and their co-occurrence with culmorin in cereal-based products: A systematic review and meta-analysis

This study was aimed to evaluate the fate of D3G, 3-ADON, and 15-ADON during various processing steps (milling, fermentation, baking and cooking with water) of different cereal-based products, as well as the co-occurrence of culmorin (CUL) and its derivatives (15-Hydroxy-CUL and 5-Hydroxy-CUL. Some databases such as Science Direct, PubMed, Scopus, and Embase were screened to collect the relevant published papers between January 1983 to October 2018, and 23 articles with 319 data were included. The baking resulted in reductions in the concentration of all types of investigated masked mycotoxins, i.e., 15-ADON (-25%) > 3-ADON (-15%) > D3G (-6%). Also, rank order of CUL and its derivatives based on occurrence was CUL (70%) > 15-Hydroxy-CUL (47%) > 5-Hydroxy-CUL (15%) and their rank based on their concentration was 5-Hydroxy-CUL (99.21 µg/kg) > CUL (48.84 µg/kg) > 15-Hydroxy-CUL (9.39 µg/kg) > Hydroxy -CUL (0.06 µg/kg) > 12-Hydroxy-CUL (0.05 µg/kg) > 14-Hydroxy-CUL (0.01 µg/kg).

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.

Comprehensive Description of Fusarium graminearum Pigments and Related Compounds

Several studies have explored in depth the biochemistry and genetics of the pigments present in Fusarium graminearum, but there is a need to discuss their relationship with the mold's observable surface color pattern variation throughout its lifecycle. Furthermore, they require basic cataloguing, including a description of their major features known so far. Colors are a viable alternative to size measurement in growth studies. When grown on yeast extract agar (YEA) at 25 °C, F. graminearum initially exhibits a whitish mycelium, developing into a yellow-orange mold by the sixth day and then turning into wine-red. The colors are likely due to accumulation of the golden yellow polyketide aurofusarin and the red rubrofusarin, but the carotenoid neurosporaxanthin also possibly plays a major role in the yellow or orange coloration. Torulene might contribute to red tones, but it perhaps ends up being converted into neurosporaxanthin. Culmorin is also present, but it does not contribute to the color, though it was initially isolated in pigment studies. Additionally, there is the 5-deoxybostrycoidin-based melanin, but it mostly occurs in the teleomorph's perithecium. There is still a need to chemically quantify the pigments throughout the lifecycle, and analyze their relationships and how much each impacts F. graminearum's surface color.

Mycotoxin Biosynthesis and Central Metabolism Are Two Interlinked Pathways in Fusarium graminearum, as Demonstrated by the Extensive Metabolic Changes Induced by Caffeic Acid Exposure

Fusarium graminearum is a major plant pathogen that causes devastating diseases of cereals and produces type B trichothecene (TCTB) mycotoxins in infected grains. A comprehensive understanding of the molecular and biochemical mechanisms underlying the regulation of TCTB biosynthesis is required for improving strategies to control the TCTB contamination of crops and ensuring that these strategies do not favor the production of other toxic metabolites by F. graminearum Elucidation of the association of TCTB biosynthesis with other central and specialized processes was the focus of this study. Combined 1H nuclear magnetic resonance (1H NMR) and liquid chromatography-quadrupole time of flight-mass spectrometry (LC-QTOF-MS) analyses were used to compare the exo- and endometabolomes of F. graminearum grown under toxin-inducing and -repressing caffeic acid conditions. Ninety-five metabolites were putatively or unambiguously identified, including 26 primary and 69 specialized metabolites. Our data demonstrated that the inhibition of TCTB production induced by caffeic acid exposure was associated with significant changes in the secondary and primary metabolism of F. graminearum, although the fungal growth was not affected. The main metabolic changes were an increase in the accumulation of several polyketides, including toxic ones, alterations in the tricarboxylic organic acid cycle, and modifications in the metabolism of several amino acids and sugars. While these findings provide insights into the mechanisms that govern the inhibition of TCTB production by caffeic acid, they also demonstrate the interdependence between the biosynthetic pathway of TCTB and several primary and specialized metabolic pathways. These results provide further evidence of the multifaceted role of TCTB in the life cycle of F. graminearumIMPORTANCEFusarium graminearum is a major plant pathogen that causes devastating diseases of cereal crops and produces type B trichothecene (TCTB) mycotoxins in infected grains. The best way to restrict consumer exposure to TCTB is to limit their production before harvest, which requires increasing the knowledge on the mechanisms that regulate their biosynthesis. Using a metabolomics approach, we investigated the interconnection between the TCTB production pathway and several fungal metabolic pathways. We demonstrated that alteration in the TCTB biosynthetic pathway can have a significant impact on other metabolic pathways, including the biosynthesis of toxic polyketides, and vice versa. These findings open new avenues for identifying fungal targets for the design of molecules with antimycotoxin properties and therefore improving sustainable strategies to fight against diseases caused by F. graminearum Our data further demonstrate that analyses should consider all fungal toxic metabolites rather than the targeted family of mycotoxins when assessing the efficacy of control strategies.

Chemical synthesis of culmorin metabolites and their biologic role in culmorin and acetyl-culmorin treated wheat cells

The Fusarium metabolite culmorin (1) is receiving increased attention as an "emerging mycotoxin". It co-occurs with trichothecene mycotoxins and potentially influences their toxicity. Its ecological role and fate in plants is unknown. We synthesized sulfated and glucosylated culmorin conjugates as potential metabolites, which are expected to be formed in planta, and used them as reference compounds. An efficient procedure for the synthesis of culmorin sulfates was developed. Diastereo- and regioselective glucosylation of culmorin (1) was achieved by exploiting or preventing unexpected acyl transfer when using different glucosyl donors. The treatment of a wheat suspension culture with culmorin (1) revealed an in planta conversion of culmorin into culmorin-8-glucoside (6) and culmorin acetate, but no sulfates or culmorin-11-glucoside (7) was found. The treatment of wheat cells with the fungal metabolite 11-acetylculmorin (2) revealed its rapid deacetylation, but also showed the formation of 11-acetylculmorin-8-glucoside (8). These results show that plants are capable of extensively metabolizing culmorin.

From malt to wheat beer: A comprehensive multi-toxin screening, transfer assessment and its influence on basic fermentation parameters

The aim was to determine the mycotoxin transfer rate into beer during a semi-industrial production process and the effect of fungicide treatment in the field on mycotoxins concentrations in beer. To ensure the usual practical agronomical conditions, sample A was treated with fungicide Prosaro® 250, and sample B was infected with Fusarium culmorum spores, in order to obtain infected malt. Malt was produced using standard procedure and beer was produced in a semi-industrial unit. During fermentation measurement of sugars (maltotriose and maltose), glycerol and ethanol content was performed on a daily basis. Multiple toxins were determined in malt and beer. Deoxynivalenol (DON), its modified plant metabolite DON-3-glucoside (DON-glucoside), brevianamide F, tryptophol, linamarin, lotaustralin, culmorin (CUL), 15-hydroxy-CUL and 5-hydroyx-CUL were detected in all samples. Results indicate that F. culmorum infection did not influence the fermentation process or the alcohol concentration.

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.

Mycotoxigenic potentials of the genera: Aspergillus, Fusarium and Penicillium isolated from houseflies (Musca domestica L.)

A study on the potential of houseflies (Musca domestica L.) to spread fungal spores in Gauteng Province, South Africa proved that houseflies are vectors for fungal spores. Therefore, there is a need to determine the toxigenic potentials and to identify the mycotoxins produced by fungal isolates derived from this study. In total 377 potentially toxigenic isolates of Aspergillus (186), Fusarium (85) and Penicillium (106) species (spp.) were isolated. These isolates were further tested for their ability to produce aflatoxins (AFs) [aflatoxin B₁, B₂, G₁ and G₂], deoxynivalenol (DON), fumonisin B₁ (FB₁) ochratoxin A (OTA), and zearalenone (ZEA) by high-performance liquid chromatography (HPLC) respectively. Strains of A. flavus and A. parasiticus belonging to the genera of Aspergillus were found to be the main producers of AFB₁, AFB₂, AFG₁, and AFG₂, while A. carbonarius, A. niger and A. ochraceus produced OTA. Fumonisin B₁ was produced by F. verticillioides and F. proliferatum with concentrations ranging from 20 to 1834μg/kg and 79 to 262μg/kg respectively. Deoxynivalenol produced mainly by F. culmorum (2-6μg/kg), F. graminearum (1-4μg/kg), F. poae (1-3μg/kg), and F. sporotrichioides (2-3μg/kg) species was the least detected toxin in this study. The high mycotoxins levels produced in isolates from houseflies in this study are regarded as unsafe, especially when international legislated tolerance levels for mycotoxins are considered. Thus, possible human exposure to mycotoxins may pose concerns with respect to human health and demands constant and consistent investigation.

Hydroxylation of Longiborneol by a Clm2-Encoded CYP450 Monooxygenase to Produce Culmorin in Fusarium graminearum

A second structural gene required for culmorin biosynthesis in the plant pathogen Fusarium graminearum is described. Clm2 encodes a regio- and stereoselective cytochrome P450 monooxygenase for C-11 of longiborneol (1). Clm2 gene disruptants were grown in liquid culture and assessed for culmorin production via HPLC-evaporative light scattering detection. The analysis indicated a complete loss of culmorin (2) from the liquid culture of the ΔClm2 mutants. Culmorin production resumed in a ΔClm2 complementation experiment. A detailed analysis of the secondary metabolites extracted from the large-scale liquid culture of disruptant ΔClm2D20 revealed five new natural products: 3-hydroxylongiborneol (3), 5-hydroxylongiborneol (4), 12-hydroxylongiborneol (5), 15-hydroxylongiborneol (6), and 11-epi-acetylculmorin (7). The structures of the new compounds were elucidated by a combination of HRMS, 1D and 2D NMR, and X-ray crystallography.

Secondary metabolites in fungus-plant interactions

Fungi and plants are rich sources of thousands of secondary metabolites. The genetically coded possibilities for secondary metabolite production, the stimuli of the production, and the special phytotoxins basically determine the microscopic fungi-host plant interactions and the pathogenic lifestyle of fungi. The review introduces plant secondary metabolites usually with antifungal effect as well as the importance of signaling molecules in induced systemic resistance and systemic acquired resistance processes. The review also concerns the mimicking of plant effector molecules like auxins, gibberellins and abscisic acid by fungal secondary metabolites that modulate plant growth or even can subvert the plant defense responses such as programmed cell death to gain nutrients for fungal growth and colonization. It also looks through the special secondary metabolite production and host selective toxins of some significant fungal pathogens and the plant response in form of phytoalexin production. New results coming from genome and transcriptional analyses in context of selected fungal pathogens and their hosts are also discussed.

Fusarium species, chemotype characterisation and trichothecene contamination of durum and soft wheat in an area of central Italy

BACKGROUND

Fusarium head blight (FHB) of wheat is an important disease causing yield losses and mycotoxin contamination. The aim of the work was to detect and characterise trichothecene producing Fusarium species in durum and soft wheat cultivated in an area of central Italy in 2009 and 2010 and to determine trichothecene contamination by LC-MS/MS in the grain.

RESULTS

F. graminearum s. str. was the most frequent species. In 2009, the occurrence of F. avenaceum and F. poae was higher than in 2010. Among F. graminearum strains, the 15-acetyl deoxynivalenol (15-ADON) chemotype could be found more frequently, followed by nivalenol (NIV) and 3-ADON chemotypes, while all F. culmorum isolates belonged to the 3-ADON chemotype. All F. poae strains were NIV chemotypes. In vitro trichothecene production confirmed molecular characterisation. Durum wheat was characterised by a higher average DON contamination with respect to soft wheat, NIV was always detected at appreciable levels while type-A trichothecenes were mostly found in durum wheat samples in 2009 with 6% of samples exceeding the contamination level recently recommended by the European Union.

CONCLUSION

Climatic conditions were confirmed to be predominant factors influencing mycotoxigenic species composition and mycotoxin contaminations. However, NIV contamination was found to occur irrespective of climatic conditions, suggesting that it may often represent an under-estimated risk to be further investigated.

Mycotoxins and other fungal metabolites in grain dust from Norwegian grain elevators and compound feed mills

Employees at grain elevators and compound feed mills are exposed to large amounts of grain dust during work, frequently leading to airway symptoms and asthma. Although the exposure to grain dust, microorganisms, β-1→3-glucans and endotoxins has been extensively studied, the focus on the mycotoxin content of grain dust has previously been limited to one or few mycotoxins. Our objective was therefore to screen settled grain dust from grain elevators and compound feed mills for fungal metabolites by LC/MS-MS and explore differences between work places, seasons and climatic zones. Seventy fungal metabolites and two bacterial metabolites were detected. Trichothecenes, depsipeptides, ergot alkaloids, and other metabolites from Fusarium, Claviceps, Alternaria, Penicillium, Aspergillus, and other fungi were represented. The prevalence of individual metabolites was highly variable, and the concentration of each metabolite varied considerably between samples. The prevalence and concentration of most metabolites were higher in grain elevators compared to compound feed mills. Differences between seasons and climatic zones were inconclusive. All samples contained multiple mycotoxins, indicating a highly complex pattern of possible inhalational exposure. A mean exposure of 20 ng/m3 of fungal metabolites was estimated, whereas a worst case scenario estimated as much as 10 ?g/m3. Although many of these compounds may be linked to toxicological and immunological effects through experimental or epidemiological studies, it still remains to be determined whether the detected concentrations implicate adverse health outcomes when inhaled.

A Simple Method with Liquid Chromatography/Tandem Mass Spectrometry for the Determination of the Six Trichothecene Mycotoxins in Rice Medium

A selective and speedy LC-MS/MS method was developed to determine six trichothecene mycotoxins (nivalenol, deoxynivalenol, fusarenon X, 15-acetyldeoxynivalenol, 3-acetyldeoxynivalenol, and T-2 toxin) in rice medium where Fusarium graminearum were cultivated for in vitro tests. The analytes were extracted from the rice medium with acetonitrile/water (85/15, v/v), and diluted with acetonitrile/water (5/95, v/v) in order to minimize the effects of matrices. Diluted solutions were analyzed by LC-MS/MS with electrospray ionization (ESI) interface in negative or positive ion mode and the multiple reaction monitoring mode. Recovery rates were 76-106% with a spiked level at 1-6 microg/kg of mycotoxins that corresponded to the limit of quantitation. The method was applied to study the time courses of trichothecene production and the biomass of fungi by three Fusarium graminearum strains. Three strains have different mycotoxin biosynthesis pathways, wFg14 and 03E-1 were DON producer, and 03N-1 was NIV producer.

Fusarium culmorum: causal agent of foot and root rot and head blight on wheat

Fusarium culmorum is a ubiquitous soil-borne fungus able to cause foot and root rot and Fusarium head blight on different small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in contamination of the grain with mycotoxins. This review summarizes recent research activities related to F. culmorum, including studies into its population diversity, mycotoxin biosynthesis, mechanisms of pathogenesis and resistance, the development of diagnostic tools and preliminary genome sequence surveys. We also propose potential research areas that may expand our basic understanding of the wheat-F. culmorum interaction and assist in the management of the disease caused by this pathogen.

TAXONOMY

Fusarium culmorum (W.G. Smith) Sacc. Kingdom Fungi; Phylum Ascomycota; Subphylum Pezizomycotina; Class Sordariomycetes; Subclass Hypocreomycetidae; Order Hypocreales; Family Nectriaceae; Genus Fusarium.

DISEASE SYMPTOMS

Foot and root rot (also known as Fusarium crown rot): seedling blight with death of the plant before or after emergence; brown discoloration on roots and coleoptiles of the infected seedlings; brown discoloration on subcrown internodes and on the first two/three internodes of the main stem; tiller abortion; formation of whiteheads with shrivelled white grains; Fusarium head blight: prematurely bleached spikelets or blighting of the entire head, which remains empty or contains shrunken dark kernels. IDENTIFICATION AND DETECTION: Morphological identification is based on the shape of the macroconidia formed on sporodochia on carnation leaf agar. The conidiophores are branched monophialides, short and wide. The macroconidia are relatively short and stout with an apical cell blunt or slightly papillate; the basal cell is foot-shaped or just notched. Macroconidia are thick-walled and curved, usually 3-5 septate, and mostly measuring 30-50 × 5.0-7.5 μm. Microconidia are absent. Oval to globose chlamydospores are formed, intercalary in the hyphae, solitary, in chains or in clumps; they are also formed from macroconidia. The colony grows very rapidly (1.6-2.2 cm/day) on potato dextrose agar (PDA) at the optimum temperature of 25 °C. The mycelium on PDA is floccose, whitish, light yellow or red. The pigment on the reverse plate on PDA varies from greyish-rose, carmine red or burgundy. A wide array of polymerase chain reaction (PCR) and real-time PCR tools, as well as complementary methods, which are summarised in the first two tables, have been developed for the detection and/or quantification of F. culmorum in culture and in naturally infected plant tissue.

HOST RANGE

Fusarium culmorum has a wide range of host plants, mainly cereals, such as wheat, barley, oats, rye, corn, sorghum and various grasses. In addition, it has been isolated from sugar beet, flax, carnation, bean, pea, asparagus, red clover, hop, leeks, Norway spruce, strawberry and potato tuber. Fusarium culmorum has also been associated with dermatitis on marram grass planters in the Netherlands, although its role as a causal agent of skin lesions appears questionable. It is also isolated as a symbiont able to confer resistance to abiotic stress, and has been proposed as a potential biocontrol agent to control the aquatic weed Hydrilla spp.

USEFUL WEBSITES

http://isolate.fusariumdb.org/; http://sppadbase.ipp.cnr.it/; http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://plantpath.psu.edu/facilities/fusarium-research-center; http://www.phi-base.org/; http://www.uniprot.org/; http://www.cabi.org/; http://www.indexfungorum.org/

Verification of the effectiveness of SCAR (sequence characterized amplified region) primers for the identification of Polish strains of Fusarium culmorum and their potential ability to produce B-trichothecenes and zearalenone

Rapid and sensitive methods to detect Fusarium culmorum and trichothecene and zearalenone producing strains in food and feed are valuable in predicting potential contamination. In this study the effectiveness of primers, recommended in the literature, for species identification of F. culmorum and basic genes encoding for mycotoxin production was tested. A total of 68 isolates of F. culmorum were collected from cereals and potato between 2005 and 2008 from different Polish provinces. It was shown that from among the four primer pairs enabling the identification of F. culmorum, and therefore also to establish its presence in the material, only primers Fc01F/Fc01R seem to be fully effective in the case of Polish strains. Determination of material contamination by F. culmorum, however, is only a first step in determining food safety. It is also extremely important to identify genes encoding the potential ability to produce mycotoxins. It was shown that three pairs of primers (tox5-1/tox5-2, HATriF/HATriR and Tri5F/Tri5R) enable a fully effective identification of the presence of the Tri5 gene responsible for producing trichothecenes. Determination of the DON-chemotype, and thus identification of the strains of F. culmorum potentially producing deoxynivalenol, is enabled equally by MinusTri7F/MinusTri7F, Tri7F/Tri7DON and Tri13F/Tri13DONR. However, a determination of the NIV-chemotype, and thus identification of the strains potentially producing nivalenol, is enabled by Tri7F/Tri7R, Tri7F/Tri7NIV and Tri13NIVF/Tri13R. The potential ability of isolates to produce ZEA can be determined to the same degree in assay with PKS4-PS.1/PKS4-PS.2 and F1/R1.

Electron ionisation mass spectrometry of the pentafluoropropionate esters of trichothecene analogues and culmorin compounds from Fusarium species

This paper reports the mass spectra, obtained after electron ionisation (EI) at 70 eV, of 34 trichothecenes and five culmorin compounds after acylation with pentafluoropropionic anhydride. The derivatised fungal metabolites were separated by gas chromatography, and the mass spectra were obtained by scanning of a single quadrupole mass filter in the scan range m/z 200-900. The fragmentation pathways of three trichothecenes (triacetyl-deoxynivalenol, 4,15-diacetoxy-scirpenol, T-2 toxin) have been studied in more detail by linked scan-high-resolution mass spectrometry. The most common trichothecenes are today more often routinely analysed using LC/MS-based methodologies. However, EI-MS may give complementary structural information, and the data that are summarised in this article may help to identify analogues of one of the largest class of mycotoxins, the tricothecenes, as well as culmorin compounds that are commonly co-produced by Fusarium culmorum and F. graminearum in cultures or naturally contaminated samples.

Terpenes from marine-derived fungi

Terpenes from marine-derived fungi show a pronounced degree of structural diversity, and due to their interesting biological and pharmacological properties many of them have aroused interest from synthetic chemists and the pharmaceutical industry alike. The aim of this paper is to give an overview of the structural diversity of terpenes from marine-derived fungi, highlighting individual examples of chemical structures and placing them in a context of other terpenes of fungal origin. Wherever possible, information regarding the biological activity is presented.

CLM1 of Fusarium graminearum encodes a longiborneol synthase required for culmorin production

Fusarium graminearum is a fungal pathogen of cereal crops (e.g., wheat, barley, maize) and produces a number of mycotoxins, including 15-acetyldeoxynivalenol, butenolide, zearalenone, and culmorin. To identify a biosynthetic gene for the culmorin pathway, an expressed-sequence-tag database was examined for terpene cyclase genes. A gene designated CLM1 was expressed under trichothecene-inducing conditions. Expression of CLM1 in yeast (Saccharomyces cerevisiae) resulted in the production of a sesquiterpene alcohol, longiborneol, which has the same ring structure as culmorin. Gene disruption and add-back experiments in F. graminearum showed that CLM1 was required for culmorin biosynthesis. CLM1 gene disruptants were able to convert exogenously added longiborneol to culmorin. Longiborneol accumulated transiently in culmorin-producing strains. The results indicate that CLM1 encodes a longiborneol synthase and is required for culmorin biosynthesis in F. graminearum.

Inactivation of a cytochrome P-450 is a determinant of trichothecene diversity in Fusarium species

Species of the genus Fusarium produce a great diversity of agriculturally important trichothecene toxins that differ from each other in their pattern of oxygenation and esterification. T-2 toxin, produced by Fusarium sporotrichioides, and nivalenol (NIV), produced by some strains of F. graminearum, contain an oxygen at the C-4 position. Deoxynivalenol (DON), produced by other strains of F. graminearum, lacks a C-4 oxygen. NIV and DON are identical except for this difference, whereas T-2 differs from these trichothecenes at three other carbon positions. Sequence and Northern analyses of the F. sporotrichioides genomic region upstream of the previously described core trichothecene gene cluster have extended the cluster by two genes: TRI13 and TRI14. TRI13 shares significant similarity with the cytochrome P-450 class of enzymes, but TRI14 does not share similarity with any previously characterized proteins. Gene disruption and fermentation studies in F. sporotrichioides indicate that TRI13 is required for the addition of the C-4 oxygen of T-2 toxin, but that TRI14 is not required for trichothecene biosynthesis. PCR and sequence analyses indicate that the TRI13 homolog is functional in NIV-producing strains of F. graminearum but nonfunctional in DON-producing strains of the fungus. These genetic observations are consistent with chemical observations that biosynthesis of T-2 toxin and NIV requires a C-4 hydroxylase while biosynthesis of DON does not.

The occurrence of culmorin and hydroxy-culmorins in cereals

Forty-five samples from 1988-1995 of naturally contaminated grain, barley, wheat and oats, three samples of mixed feed, and 16 samples of grain artificially inoculated with Fusarium culmorum during the flowering stage were analysed for deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-acetyl-DON), culmorin and hydroxy-culmorins. These compounds are secondary metabolites produced by the fungal species F. culmorum and F. graminearum. Acetonitrile-water extract of the samples was purified on a Mycosep #225 column, derivetized using penta-fluoropropionic anhydride (PFPA) and analysed by gas chromatography-mass spectrometry (GC-MS). The amount of each of culmorin, 5-, 12-, 14 and 15-hydroxy-culmorin and one unknown hydroxy-culmorin were determined relative to the amount of DON plus 3-acetyl DON for each sample. The ratio between the total amount of culmorin compounds and the DON compounds ranged from 0.14 to 1.07 in the samples. This study shows that there is a strong correlation between the amount of DON present in the grain and the amount of culmorin and hydroxy-culmorins present. The ratio of each of the culmorin compounds relative to the amount of DON compounds were in the same range in the grain artificially inoculated by F. culmorum as found in an earlier study for F. culmorum strains cultivated on rice, while the hydroxy-culmorin profile in the naturally contaminated grain was more similar to what was found for the F. graminearum cultures in the same study. These results indicate that F. graminearum may be a relatively important source for DON in grain also in relatively cold areas.