Production of fusaric acid by Fusarium species

Endophytic Alternaria and Fusarium species associated to potato plants (Solanum tuberosum L.) in Iran and their capability to produce regulated and emerging mycotoxins

Endophytic fungi live inside virtually every plant species, without causing any apparent disease or damage to the host. Nevertheless, under particular conditions, mutualistic lifestyle of endophytes may change to pathogenic. In this study, the biodiversity of Alternaria and Fusarium species, the two most abundant endophytic fungi isolated from healthy potato plants in two climatically different regions of Iran, Ardebil in the north-west and Kerman in the south-east, was investigated. Seventy-five Fusarium strains and 83 Alternaria strains were molecularly characterized by multi-locus gene sequencing. Alternaria strains were characterized by the sequences of gpd and caM gene fragments and the phylogenetic tree was resolved in 3 well-separated clades. Seventy-three strains were included in the clade A, referred as Alternaria section, 6 strains were included in clade B, referred as Ulocladioides section, and 4 strains were included in clade C, referred as Infectoriae section. Fusarium strains, identified by sequencing the translation elongation factor 1α (tef1), β-tubulin (tub2) and internal transcribed spacer (ITS) genomic regions, were assigned to 13 species, viz. F. brachygibosum, F. clavum, F. equiseti, F. flocciferum, F. incarnatum, F. nirenbergiae, F. nygamai, F. oxysporum, F. proliferatum, F. redolens, F. sambucinum, F. solani and F. thapsinum. Twenty-six selected strains, representative of F. equiseti, F. nirenbergiae, F. oxysporum, F. nygamai, F. proliferatum, and F. sambucinum, were also tested for production of the mycotoxins deoxynivalenol (DON), nivalenol (NIV), diacetoxyscirpenol (DAS), T-2 toxin (T-2), beauvericin (BEA), enniatins (ENNs), fumonisins (FBs), fusaric acid (FA) and moniliformin (MON). None of the tested strains produced trichothecene toxins (DON, NIV, DAS and T-2). Two out of 2 F. equiseti isolates, 1/6 F. oxysporum, 1/3 F. proliferatum, and 1/9 F. nygamai did not produce any of the tested toxins; the rest of strains produced one or more BEA, ENNs, FBs, FA and MON toxins. The most toxigenic strain, F. nygamai ITEM-19012, produced the highest quantities of FBs (7946, 4693 and 4333 μg/g of B1, B2, and B3 respectively), along with the highest quantities of both BEA (4190 μg/g) and MON (538 μg/g). These findings suggest that contamination of potato tubers with mycotoxins in the field or at post-harvest, due to a change in lifestyle of endophytic microflora, should be carefully considered and furtherly investigated.

Genetic dissection of the degradation pathways for the mycotoxin fusaric acid in Burkholderia ambifaria T16

IMPORTANCE

Fusaric acid (FA) is an important virulence factor produced by several Fusarium species. These fungi are responsible for wilt and rot diseases in a diverse range of crops. FA is toxic for animals, humans and soil-borne microorganisms. This mycotoxin reduces the survival and competition abilities of bacterial species able to antagonize Fusarium spp., due to its negative effects on viability and the production of antibiotics effective against these fungi. FA biodegradation is not a common characteristic among bacteria, and the determinants of FA catabolism have not been identified so far in any microorganism. In this study, we identified genes, enzymes, and metabolic pathways involved in the degradation of FA in the soil bacterium Burkholderia ambifaria T16. Our results provide insights into the catabolism of a pyridine-derivative involved in plant pathogenesis by a rhizosphere bacterium.

Virulence factors of the genus Fusarium with targets in plants

Fusarium spp. comprise various species of filamentous fungi that cause severe diseases in plant crops of both agricultural and forestry interest. These plant pathogens produce a wide range of molecules with diverse chemical structures and biological activities. Genetic functional analyses of some of these compounds have shown their role as virulence factors (VF). However, their mode of action and contributions to the infection process for many of these molecules are still unknown. This review aims to analyze the state of the art in Fusarium VF, emphasizing their biological targets on the plant hosts. It also addresses the current experimental approaches to improve our understanding of their role in virulence and suggests relevant research questions that remain to be answered with a greater focus on species of agroeconomic importance. In this review, a total of 37 confirmed VF are described, including 22 proteinaceous and 15 non-proteinaceous molecules, mainly from Fusarium oxysporum and Fusarium graminearum and, to a lesser extent, in Fusarium verticillioides and Fusarium solani.

Evaluation of Hydrangea Cultivars for Tolerance Against Root Rot Caused by Fusarium oxysporum

Root rot caused by Fusarium oxysporum Schltdl. is a newly identified disease in oakleaf hydrangea. Some cultivars such as Pee Wee and Queen of Hearts grown in pot-in-pot container systems showed root rot symptoms after late spring frost in May 2018 with 40 and 60% incidence in the infected nursery, respectively. This experiment was carried out to evaluate the tolerance among different hydrangea cultivars against root rot caused by F. oxysporum. Fifteen hydrangea cultivars from four different species were selected, and rooted cuttings were prepared from new spring flushes. Twelve plants from each cultivar were transplanted in a 1-gallon pot. Half of transplanted plants (six single plants) were inoculated by drenching 150 ml of F. oxysporum conidial suspension to maintain the concentration of 1 × 106 conidia/ml. Half of the plants remain noninoculated (control) and were drenched with sterile water. After 4 months, root rot was assessed using a scale of 0 to 100% root area affected, and recovery of F. oxysporum was recorded by plating 1-cm root sections in Fusarium selective medium. Fusaric acid (FA) and mannitol were extracted from the roots of inoculated and noninoculated plants to see the effect and role on pathogenesis. Further, mannitol concentration was analyzed using absorption wavelength in a spectrophotometer, and FA was analyzed using high-performance liquid chromatography (HPLC). Results indicated that no cultivars were resistant to F. oxysporum. Cultivars from Hydrangea arborescens, H. macrophylla, and H. paniculata were more tolerant to F. oxysporum compared to cultivars from H. quercifolia. Among H. quercifolia, cultivars Snowflake, John Wayne, and Alice were more tolerant to F. oxysporum.

Exploring the chemical diversity of phytopathogenic fungi infecting edible fruits

Two fungi, Fusarium guttiforme and Colletotrichum horii, were cultured under different conditions to obtain fourteen compounds. The axenic cultures of F. guttiforme and C. horii in potato dextrose broth (PDB) medium yielded fusaric acid (1), 9,10-dehydrofusaric acid (2), and tyrosol, whereas their co-cultivation produced fusarinol (5), a fusaric acid complex with magnesium (3), 9,10-dehydrofusaric acid complex with magnesium (4), and 5-butyl-5-(hydroxymethyl) dihydrofuranone (9). Upon changing the medium from PDB to Czapek, different compounds (uracil, p-hydroxy acetophenone, and cyclo(L-Leu-L-Pro) were obtained. Fusaric acid (1) was biotransformed into fusarinol (5) by C. horii, suggesting a detoxification process, and three other compounds were obtained: 7-hydroxyfusarinol (7), 9,10-dehydrofusarinol (6), and fusarinyl acetate (8). Epigenetic modulation of suberohydroxamic acid against F. guttiforme afforded gibepyrone B (10). These compounds were subjected to a papain inhibition enzymatic assay; the highest inhibitory activity was displayed by the two magnesium complexes, at 56 and 54% inhibition, respectively.

The intrinsic resistance of Fusarium solani to the Fusarium-specific fungicide phenamacril is attributed to the natural variation of both T218S and K376M in myosin5

Fusarium solani is responsible for causing root rot in various crops, resulting in wilting and eventual demise. Phenamacril, a specific inhibitor of myosin5 protein, has gained recognition as an effective fungicide against a broad spectrum of Fusarium species. It has been officially registered for controlling Fusarium diseases through spray application, root irrigation, and seed dipping. In this study, phenamacril was observed to exhibit negligible inhibitory effects on F. solani causing crop root rot, despite the absence of prior exposure to phenamacril. Considering the high selectivity of phenamacril, this phenomenon was attributed to intrinsic resistance and further investigated for its underlying mechanism. Sequence alignment analysis of myosin5 proteins across different Fusarium species revealed significant differences at positions 218 and 376. Subsequent homology modeling and molecular docking results indicated that substitutions T218S, K376M, and T218S&K376M impaired the binding affinity between phenamacril and myosin5 in F. solani. Mutants carrying these substitutions were generated via site-directed mutagenesis. A phenamacril-sensitivity test showed that the EC50 values of mutants carrying T218S, K376M, and T218S&K376M were reduced by at least 6.13-fold, 9.66-fold, and 761.90-fold respectively compared to the wild-type strain. Fitness testing indicated that mutants carrying K376M or T218S&K376M had reduced sporulation compared to the wild-type strain. Additionally, mutants carrying T218S exhibited an enhanced virulence compared to the wild-type strain. However, there were no significant differences observed in mycelial growth rates between the mutants and the wild-type strain. Thus, the intrinsic differences observed at positions 218 and 376 in myosin5 between F. solani and other Fusarium species are specifically associated with phenamacril resistance. The identification of these resistance-associated positions in myosin5 of F. solani has significantly contributed to the understanding of phenamacril resistance mechanisms, thereby discouraging the use of phenamacril for controlling F. solani.

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

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

Alkaline pH, Low Iron Availability, Poor Nitrogen Sources and CWI MAPK Signaling Are Associated with Increased Fusaric Acid Production in Fusarium oxysporum

Fusaric acid (FA) is one of the first secondary metabolites isolated from phytopathogenic fungi belonging to the genus Fusarium. This molecule exerts a toxic effect on plants, rhizobacteria, fungi and animals, and it plays a crucial role in both plant and animal pathogenesis. In plants, metal chelation by FA is considered one of the possible mechanisms of action. Here, we evaluated the effect of different nitrogen sources, iron content, extracellular pH and cellular signalling pathways on the production of FA siderophores by the pathogen Fusarium oxysporum (Fol). Our results show that the nitrogen source affects iron chelating activity and FA production. Moreover, alkaline pH and iron limitation boost FA production, while acidic pH and iron sufficiency repress it independent of the nitrogen source. FA production is also positively regulated by the cell wall integrity (CWI) mitogen-activated protein kinase (MAPK) pathway and inhibited by the iron homeostasis transcriptional regulator HapX. Collectively, this study demonstrates that factors promoting virulence (i.e., alkaline pH, low iron availability, poor nitrogen sources and CWI MAPK signalling) are also associated with increased FA production in Fol. The obtained new insights on FA biosynthesis regulation can be used to prevent both Fol infection potential and toxin contamination.

Total Heterologous Biosynthesis of Fungal Natural Products in Aspergillus nidulans

Fungal natural products comprise a wide range of bioactive compounds including important drugs and agrochemicals. Intriguingly, bioinformatic analyses of fungal genomes have revealed that fungi have the potential to produce significantly more natural products than what have been discovered so far. It has thus become widely accepted that most biosynthesis pathways of fungal natural products are silent or expressed at very low levels under laboratory cultivation conditions. To tap into this vast chemical reservoir, the reconstitution of entire biosynthetic pathways in genetically tractable fungal hosts (total heterologous biosynthesis) has become increasingly employed in recent years. This review summarizes total heterologous biosynthesis of fungal natural products accomplished before 2020 using Aspergillus nidulans as heterologous hosts. We review here Aspergillus transformation, A. nidulans hosts, shuttle vectors for episomal expression, and chromosomal integration expression. These tools, collectively, not only facilitate the discovery of cryptic natural products but can also be used to generate high-yield strains with clean metabolite backgrounds. In comparison with total synthesis, total heterologous biosynthesis offers a simplified strategy to construct complex molecules and holds potential for commercial application.

Mixtures of mycotoxins, phytoestrogens and pesticides co-occurring in wet spent brewery grains (BSG) intended for dairy cattle feeding in Austria

Spent brewery grains (BSG) are the main by-product of beer production and are incorporated in rations of food-delivering animals, mainly dairy cows. Like other agricultural commodities, BSG can be contaminated by a broad spectrum of natural and synthetic undesirable substances, which can be hazardous to animal and human health as well as to the environment. The co-occurrence of mycotoxins, phytoestrogens, other fungal and plant secondary metabolites, along with pesticides, was investigated in 21 BSG samples collected in dairy farms in Austria. For this purpose, a validated multi-metabolite liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) was employed. Metabolites derived from Fusarium, Aspergillus, Alternaria and pesticide residues, were ubiquitous in the samples. Zearalenone (ZEN), T-2 and HT-2 toxins were the only regulated mycotoxin detected, albeit at concentrations below the European guidance values for animal feeds. Ergot alkaloids, Penicillium-derived metabolites, and phytoestrogens had occurrence rates of 90, 48 and 29%, respectively. Penicillium metabolites presented the highest levels among the fungal compounds, indicating contamination during storage. Aflatoxins (AFs), ochratoxins and deoxynivalenol (DON) were not detected. Out of the 16 detected pesticides, two fungicides, ametoctradin (9.5%) and mandipropamid (14.3%) revealed concentrations exceeding their respective maximum residue level (MRL) (0.01 mg kg^-1) for barley in two samples. Although based on European guidance and MRL values the levels of the detected compounds probably do not pose acute risks for cattle, the impact of the long-time exposure to such mixtures of natural and synthetic toxicants on animal health and food safety are unknown and must be elucidated.

Biosensor approach for electrochemical quantitative assessment and qualitative characterization of the effect of fusaric acid on a culture-receptor

Fusaric acid (FA) is a secondary fungal metabolite, which is widespread on corn and corn-based feed and food; FA has non-specific toxicity. Biosensor method is an express and easy-to-use method for quantitative and qualitative assessment of FA effect. Search for cultures has been performed for the formation of laboratory models of FA biosensor with the Clark-type oxygen electrode as transducer: respiration intensity of chosen cultures changed in the presence of FA. Resting cells of Fusarium oxysporum f. sp. vasinfectum and Bacillus subtilis were used as receptors of the amperometric biosensor for FA determination in aqueous solution. To enhance the sensitivity of detection, induction by substrate was performed for Bacillus subtilis. Response-concentration linear dependencies were obtained in a range of 0.5-500 FA mg/L. Biosensor models were applied to characterize influence of FA on microbial cells and investigate some features of FA transport. The dependences of the cells' response to FA on FA concentration were obtained; the kinetic parameters S_0.5 and V_max were determined for each culture. Inhibition-threshold FA (S^it) concentrations were similar for both studied cultures. At concentrations lower than S^it, the process of simple diffusion governed FA transport into cells and caused the cells' response to FA for non-induced culture.

Fusarium Head Blight of Small Grains in Pennsylvania: Unravelling Species Diversity, Toxin Types, Growth, and Triazole Sensitivity

Fusarium graminearum is the main causal species of Fusarium head blight (FHB) globally. Recent changes in the trichothecene (toxin) types in the North American FHB pathogens support the need for continued surveillance. In this study, 461 isolates were obtained from symptomatic spikes of wheat, spelt, barley, and rye crops during 2018 and 2019. These were all identified to species and toxin types using molecular-based approaches. An additional set of 77 F. graminearum isolates obtained from overwintering crop residues during winter 2012 were molecularly identified to toxin types. A subset of 31 F. graminearum isolates (15 15-acetyl-deoxynivalenol [15ADON] and 16 3-acetyl-deoxynivalenol [3ADON]) were assessed for mycelial growth, macroconidia, perithecia, and ascospore production, and sensitivity to two triazoles. Ninety percent of isolates obtained from the symptomatic spikes (n = 418) belonged to F. graminearum, with four other species found at a lower frequency (n = 39). The F. graminearum isolates from symptomatic spikes were mainly of the 15ADON (95%), followed by 3ADON (4%), nivalenol (0.7%), and NX-2 (0.3%) toxin types. All F. graminearum isolates obtained from overwintering residue were of the 15ADON type. The toxin types could not be differentiated based on the multivariate analysis of growth and reproduction traits. All isolates were sensitive to tebuconazole and metconazole fungicides in vitro. This study confirms the dominance of F. graminearum and suggests ecological and environmental factors, to be further identified, that lead to similar composition of toxin types in the northern United States. Our results may be useful to assess the sustainability of FHB management practices and provide a baseline for future FHB surveys.

Fungal species and mycotoxins in mouldy spots of grass and maize silages in Austria

Fungi and mycotoxins in silage can have detrimental consequences for both cattle and human health. This pilot study identified, via the routinary direct plating method, the dominant cultivable fungi in mouldy grass silages (GS) (n = 19) and maize silages (MS) (n = 28) from Austria. The profiles of regulated, modified, and emerging mycotoxins together with other fungal metabolites were analysed via LC-(ESI)MS/MS. Penicillium roqueforti, Saccharomyces spp., Geotrichum candidum, Aspergillus fumigatus and Monascus ruber were the most frequent fungal organisms identified. Other species including Mucor circinelloides, Fusarium spp. and Paecilomyces niveus were detected at lower frequencies. The presence of complex mixtures of toxic and potentially toxic compounds was evidenced by high levels and occurrences (≥ 50%) of Penicillium-produced compounds such as mycophenolic acid (MPA), roquefortines (ROCs), andrastins (ANDs) and marcfortine A. Mouldy silages contained toxins commonly produced by genus Fusarium (e.g. zearalenone (ZEN) and trichothecenes), Alternaria (like tenuazonic acid (TeA) and alternariol (AHO)) and Aspergillus (such as sterigmatocystin (STC)). Compared to those in GS, mouldy spots in MS presented significantly higher fungal counts and more diverse toxin profiles, in addition to superior levels of Fusarium spp., Penicillium spp. and total fungal metabolites. Generally, no correlation between mould counts and corresponding metabolites was detected, except for the counts of P. roqueforti, which were positively correlated with Penicillium spp. metabolites in mouldy MS. This study represents a first assessment of the fungal diversity in mouldy silage in Austria and highlights its potential role as a substantial contributor to contamination with complex mycotoxin mixtures in cattle diets.

m6A modification: recent advances, anticancer targeted drug discovery and beyond

Abnormal N6-methyladenosine (m6A) modification is closely associated with the occurrence, development, progression and prognosis of cancer, and aberrant m6A regulators have been identified as novel anticancer drug targets. Both traditional medicine-related approaches and modern drug discovery platforms have been used in an attempt to develop m6A-targeted drugs. Here, we provide an update of the latest findings on m6A modification and the critical roles of m6A modification in cancer progression, and we summarize rational sources for the discovery of m6A-targeted anticancer agents from traditional medicines and computer-based chemosynthetic compounds. This review highlights the potential agents targeting m6A modification for cancer treatment and proposes the advantage of artificial intelligence (AI) in the discovery of m6A-targeting anticancer drugs.

Graphical abstract

Three stages of m6A-targeting anticancer drug discovery: traditional medicine-based natural products, modern chemical modification or synthesis, and artificial intelligence (AI)-assisted approaches for the future.

Genome-wide transcriptional response of the causal soybean sudden death syndrome pathogen Fusarium virguliforme to a succinate dehydrogenase inhibitor fluopyram

BACKGROUND

Succinate dehydrogenase inhibitors (SDHIs) have been widely used to manage plant diseases caused by phytopathogenic fungi. Although attention to and use of SDHI fungicides has recently increased, molecular responses of fungal pathogens to SDHIs have often not been investigated. A SDHI fungicide, fluopyram, has been used as a soybean seed treatment and has displayed effective control of Fusarium virguliforme, one of the causal agents of soybean sudden death syndrome. To examine genome-wide gene expression of F. virguliforme to fluopyram, RNA-seq analysis was conducted on two field strains of F. virguliforme with differing SDHI fungicide sensitivity in the absence and presence of fluopyram.

RESULTS

The analysis indicated that several xenobiotic detoxification-related genes, such as those of deoxygenase, transferases and transporters, were highly induced by fluopyram. Among the genes, four ATP-binding cassette (ABC) transporters were characterized by the yeast expression system. The results revealed that expression of three ABCG transporters was associated with reduced sensitivity to multiple fungicides including fluopyram. In addition, heterologous expression of a major facilitator superfamily (MFS) transporter that was highly expressed in the fluopyram-insensitive F. virguliforme strain in the yeast system conferred decreased sensitivity to fluopyram.

CONCLUSION

This study demonstrated that xenobiotic detoxification-related genes were highly upregulated in response to fluopyram, and expression of ABC or MFS transporter genes was associated with reduced sensitivity to the SDHI fungicide. This is the first transcriptomic analysis of the fungal species response to fluopyram and the finding will help elucidate the molecular mechanisms of SDHI resistance. © 2021 Society of Chemical Industry.

Weeds Harbor Fusarium Species that Cause Malformation Disease of Economically Important Trees in Western Mexico

Mango malformation disease (MMD) caused by Fusarium spp. is an important limiting factor in most production areas worldwide. Fusarium mexicanum and F. pseudocircinatum have been reported as causing MMD in Mexico. These two pathogens also cause a similar disease in Swietenia macrophylla (big-leaf mahogany malformation disease) in central western Mexico, and F. pseudocircinatum was recently reported as causing malformation disease in Tabebuia rosea (rosy trumpet) in the same region. These studies suggest that additional plant species, including weeds, might be hosts of these pathogens. The role that weed hosts might have in the disease cycle is unknown. The objectives of this work were to recover Fusarium isolates from understory vegetation in mango orchards with MMD, identify the Fusarium isolates through DNA sequence data, and determine whether F. mexicanum is capable of inducing disease in the weedy legume Senna uniflora (oneleaf senna). Additional objectives in this work were to compare Fusarium isolates recovered from weeds and mango trees in the same orchards by characterizing their phylogenetic relationships, assessing in vitro production of mycotoxins, and identifying their mating type idiomorph. A total of 59 Fusarium isolates from five species complexes were recovered from apical and lateral buds from four weed species. Two of the species within the F. fujikuroi species complex are known to cause MMD in Mexico. Trichothecene production was detected in five isolates, including F. sulawense and F. irregulare in the F. incarnatum-equiseti species complex and F. boothii in the F. sambucinum species complex. Both mating types were present among mango and weed isolates. This is the first report of herbaceous hosts harboring Fusarium species that cause mango malformation in Mexico. The information provided should prove valuable for further study of the epidemiological role of weeds in MMD and help manage the disease.

Plant Responses to Biotic Stress: Old Memories Matter

Plants are fascinating organisms present in most ecosystems and a model system for studying different facets of ecological interactions on Earth. In the environment, plants constantly encounter a multitude of abiotic and biotic stresses. The zero-avoidance phenomena make them more resilient to such environmental odds. Plants combat biotic stress or pathogenic ingression through a complex orchestration of intracellular signalling cascades. The plant-microbe interaction primarily relies on acquired immune response due to the absence of any specialised immunogenic cells for adaptive immune response. The generation of immune memory is mainly carried out by T cells as part of the humoral immune response in animals. Recently, prodigious advancements in our understanding of epigenetic regulations in plants invoke the "plant memory" theory afresh. Current innovations in cutting-edge genomic tools have revealed stress-associated genomic alterations and strengthened the idea of transgenerational memory in plants. In plants, stress signalling events are transferred as genomic imprints in successive generations, even without any stress. Such immunogenic priming of plants against biotic stresses is crucial for their eco-evolutionary success. However, there is limited literature capturing the current knowledge of the transgenerational memory of plants boosting biotic stress responses. In this context, the present review focuses on the general concept of memory in plants, recent advancements in this field and comprehensive implications in biotic stress tolerance with future perspectives.

Antifungal activity of volatile compounds generated by endophytic fungi Sarocladium brachiariae HND5 against Fusarium oxysporum f. sp. cubense

The soil-born filamentous fungal pathogen Fusarium oxysporum f. sp. cubense (FOC), which causes vascular wilt disease in banana plants, is one of the most economically important Fusarium species. Biocontrol using endophytic microorganisms is among the most effective methods for controlling banana Fusarium wilt. In this study, volatile organic compounds (VOCs) showed strong antifungal activity against FOC. Seventeen compounds were identified from the VOCs produced by endophytic fungi Sarocladium brachiariae HND5, and three (2-methoxy-4-vinylphenol, 3,4-dimethoxystyrol and caryophyllene) showed antifungal activity against FOC with 50% effective concentrations of 36, 60 and 2900 μL/L headspace, respectively. Transmission electron microscopy (TEM) and double fluorescence staining revealed that 2-methoxy-4-vinylphenol and 3,4-dimethoxystyrol damaged the plasma membranes, resulting in cell death. 3,4-dimethoxystyrol also could induce expression of chitin synthases genes and altered the cell walls of FOC hyphae. Dichloro-dihydro-fluorescein diacetate staining indicated the caryophyllene induced accumulation of reactive oxygen species (ROS) in FOC hyphae. FOC secondary metabolism also responded to active VOC challenge by producing less fusaric acid and expressions of genes related to fusaric acid production were interrupted at sublethal concentrations. These findings indicate the potential of S. brachiariae HND5 as a biocontrol agent against FOC and the antifungal VOCs as fumigants.

Deciphering the effect of FUB1 disruption on fusaric acid production and pathogenicity in Fusarium circinatum

Fusarium circinatum is an important pathogen of pine trees. However, little is known regarding the molecular processes underlying its pathogenesis. We explored the potential role of the phytotoxin fusaric acid (FA) in the pathogenicity of the fungus. FA is produced by products of the FUB biosynthesis gene cluster, containing FUB1-12. Of these, FUB1 encodes the core polyketide synthase, which we disrupted. We used the resulting mutant strain to investigate whether FUB1 and FA production play a role in the virulence of F. circinatum on pine. Our results showed that FA production was abolished both in vitro and in planta. However, bikaverin production was increased in the knockout mutant. FUB1 disruption also corresponded with downregulation of a F. circinatum homologue of LaeA, a master transcriptional regulator of secondary metabolism. Lesion lengths produced by the FUB1 knockout mutant on inoculated Pinus patula seedlings were significantly smaller than those produced by the wild type strain. Collectively, these results show that FUB1 plays a role in FA production in F. circinatum, and that this gene contributes to the aggressiveness of F. circinatum on P. patula. This study will contribute to the limited knowledge we have about the molecular basis of pathogenicity in this fungus.

Sequencing of non-virulent strains of Fusarium fujikuroi reveals genes putatively involved in bakanae disease of rice

Bakanae, one of the most important diseases of rice, is caused by the fungal pathogen Fusarium fujikuroi. The elongation of internodes is the most common symptom induced by the pathogen, and it is related to the production of gibberellins. Despite this, the pathogenicity mechanism of F. fujikuroi is still not completely clear, and there are some strains inducing stunting instead of elongation. Even if there are relatively many genomes of F. fujikuroi strains available in online databases, none of them belongs to an isolate of proven non-virulence, and therefore there has been no comparative genomics study conducted between virulent and non-virulent strains. In the present work, the genomes of non-virulent strain SG4 and scarcely virulent strain C2S were compared to the ones of 12 available virulent isolates. Genes present in the majority of available virulent strains, but not in the non-virulent one, underwent functional annotation with multiple tools, and their expression level during rice infection was checked using pre-existing data. Nine genes putatively related to pathogenicity in F. fujikuroi were identified throughout comparative and functional analyses. Among these, many are involved in the degradation of plant cell wall, which is poorly studied in F. fujikuroi-rice interactions. Three of them were validated through qPCR, showing higher expression in the virulent strain and low to no expression in the low virulent and non virulent strains during rice infection. This work helps to clarify the mechanisms of pathogenicity of F. fujikuroi on rice.

Physiological Response of Cape Gooseberry Plants to Fusarium oxysporum f. sp. physali, Fusaric Acid, and Water Deficit in a Hydrophonic System

Cape gooseberry production has been limited by vascular wilt caused by Fusarium oxysporum f. sp. physali (Foph). Fusaric acid (FA) is a mycotoxin produced by many Fusarium species such as F. oxysporum formae speciales. The effects of the interaction between this mycotoxin and plants (such as cape gooseberry) under biotic stress (water deficit, WD) have been little explored. Three experiments were carried out. The objectives of this study were to evaluate (i) different Foph inoculum densities (1 × 104 and 1 × 106 conidia ml-1; experiment (1); (ii) the effect of times of exposure (0, 6, 9, and 12 h) and FA concentrations (0, 12.5, 25, 50, and 100 mg L-1; experiment (2), and (iii) the interaction between Foph (1 × 104 conidia mL-1) or FA (25 mg L-1 × 9 h), and WD conditions (experiment 3) on the physiological (plant growth, leaf stomatal conductance (g s ), and photochemical efficiency of PSII (Fv/Fm ratio) and biochemical [malondialdehyde (MDA) and proline] responses of cape gooseberry seedling ecotype Colombia. The first experiment showed that Foph inoculum density of 1 × 106 conidia ml-1 caused the highest incidence of the disease (100%). In the second experiment, g s (~40.6 mmol m-2 s-1) and Fv/Fm ratio (~0.59) decreased, whereas MDA (~9.8 μmol g-1 FW) increased in plants with exposure times of 9 and 12 h and an FA concentration of 100 mg L-1 compared with plants without FA exposure or concentrations (169.8 mmol m-2 s-1, 0.8, and 7.2 μmol g-1 FW for g s , Fv/Fm ratio and MDA, respectively). In the last experiment, the interaction between Foph or FA and WD promoted a higher area under the disease progress curve (AUDPC) (Foph × WD = 44.5 and FA × WD = 37) and lower g s (Foph × WD = 6.2 mmol m-2 s-1 and FA × WD = 9.5 mmol m-2 s-1) compared with plants without any interaction. This research could be considered as a new approach for the rapid scanning of responses to the effects of FA, Foph, and WD stress not only on cape gooseberry plants but also on other species from the Solanaceae family.

Co-Occurrence of 35 Mycotoxins: A Seven-Year Survey of Corn Grain and Corn Silage in the United States

Mycotoxins contaminate crops worldwide and play a role in animal health and performance. Multiple mycotoxins may co-occur which may increase the impact on the animal. To assess the multiple mycotoxin profile of corn (Zea mays), we conducted a 7-year survey of new crop corn grain and silage in the United States. A total of 711 grain and 1117 silage samples were collected between 2013 and 2019 and analyzed for the simultaneous presence of 35 mycotoxins using ultra-performance liquid chromatography–tandem mass spectrometry. The measured mean number of mycotoxins per sample were 4.8 (grain) and 5.2 (silage), ranging from 0 to 13. Fusaric acid (FA) was most frequently detected in 78.1 and 93.8% of grains and silages, respectively, followed by deoxynivalenol (DON) in 75.7 and 88.2% of samples. Fumonisin B1 (FB1), fumonisin B2 and 15-acetyl-deoxynivalenol (15ADON) followed. The greatest (p < 0.05) co-occurrence was between FA and DON in 59.1% of grains and 82.7% of silages, followed by FA with FB1, DON with 15ADON, and FA with 15ADON. Although many samples had lower mycotoxin concentrations, 1.6% (grain) and 7.9% (silage) of tested samples had DON ≥ 5000 µg/kg. Fumonisins were detected ≥ 10,000 µg/kg in 9.6 and 3.9% of grain and silage samples, respectively. Concentrations in grain varied by year for eight mycotoxin groups (p < 0.05), while all 10 groups showed yearly variations in silage. Our survey suggest that multiple mycotoxins frequently co-occur in corn grain and silage in the United States, and some of the more prevalent mycotoxins are those that may not be routinely analyzed (i.e., FA and 15ADON). Assessment of multiple mycotoxins should be considered when developing management programs.

Characterization of the Exo-Metabolome of the Emergent Phytopathogen Fusarium kuroshium sp. nov., a Causal Agent of Fusarium Dieback

Fusarium kuroshium is the fungal symbiont associated with the ambrosia beetle Euwallacea kuroshio, a plague complex that attacks avocado, among other hosts, causing a disease named Fusarium dieback (FD). However, the contribution of F. kuroshium to the establishment of this disease remains unknown. To advance the understanding of F. kuroshium pathogenicity, we profiled its exo-metabolome through metabolomics tools based on accurate mass spectrometry. We found that F. kuroshium can produce several key metabolites with phytotoxicity properties and other compounds with unknown functions. Among the metabolites identified in the fungal exo-metabolome, fusaric acid (FA) was further studied due to its phytotoxicity and relevance as a virulence factor. We tested both FA and organic extracts from F. kuroshium at various dilutions in avocado foliar tissue and found that they caused necrosis and chlorosis, resembling symptoms similar to those observed in FD. This study reports for first-time insights regarding F. kuroshium associated with its virulence, which could lead to the potential development of diagnostic and management tools of FD disease and provides a basis for understanding the interaction of F. kuroshium with its host plants.

Phloroglucinol Derivatives in Plant-Beneficial Pseudomonas spp.: Biosynthesis, Regulation, and Functions

Plant-beneficial Pseudomonas spp. aggressively colonize the rhizosphere and produce numerous secondary metabolites, such as 2,4-diacetylphloroglucinol (DAPG). DAPG is a phloroglucinol derivative that contributes to disease suppression, thanks to its broad-spectrum antimicrobial activity. A famous example of this biocontrol activity has been previously described in the context of wheat monoculture where a decline in take-all disease (caused by the ascomycete Gaeumannomyces tritici) has been shown to be associated with rhizosphere colonization by DAPG-producing Pseudomonas spp. In this review, we discuss the biosynthesis and regulation of phloroglucinol derivatives in the genus Pseudomonas, as well as investigate the role played by DAPG-producing Pseudomonas spp. in natural soil suppressiveness. We also tackle the mode of action of phloroglucinol derivatives, which can act as antibiotics, signalling molecules and, in some cases, even as pathogenicity factors. Finally, we discuss the genetic and genomic diversity of DAPG-producing Pseudomonas spp. as well as its importance for improving the biocontrol of plant pathogens.

Fusarium cerealis causing Fusarium head blight of durum wheat and its associated mycotoxins

Fusarium Head Blight (FHB) is a very important fungal disease that affects small grain cereals worldwide. This disease not only causes yield loses but also crops contamination with mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). Species within the Fusarium graminearum species complex have been described as the main causal agents of this disease, however lately there have been few reports of Fusarium cerealis causing the disease in wheat and barley in different parts of the world. This study evaluated the aggressiveness of F. cerealis to durum wheat cultivars and also mycotoxin production in planta. Moreover, the mycotoxin profile of F. cerealis strains was characterized molecularly and chemically. All durum wheat cultivars showed typical FHB symptoms but the disease severity varied among them in levels up to 66%. In addition, seventeen different compounds were detected in the infected heads including DON, NIV and nivalenol-3-β-d-glucose (NIV3G). NIV was detected in all cultivars and was the most produced mycotoxin with levels ranging from 1.04 to 6.8 mg/kg. On the other hand, the molecular analysis of F. cerealis strains showed that all of them possessed NIV genotype while the chemical assessment showed that the strains were able to produce not only this toxin in vitro but also DON, zearalenone and other twenty-one secondary metabolites. The increasing incidence of F. cerealis and the possible contamination of crops with the mycotoxins that it produces are of great concern for food security and world cereal trade since it has been reported that NIV is more toxic for humans and animals than DON.

Production of antimicrobial metabolites against pathogenic bacteria and yeasts by Fusarium oxysporum in submerged culture processes

The antimicrobial activity of the metabolites produced by Fusarium oxysporum PR-33 in submerged culture was evaluated against Gram-positive and Gram-negative bacteria and yeasts. Metabolites were determined by HPLC-DAD-MS/MS. An extract was obtained following the removal of mycelium by centrifugation and lyophilisation of the supernatant. The compounds in this extract demonstrated broad-spectrum antimicrobial action, with rates of inhibition between 60 and 80%, depending on the species and extract tested. The major compounds of the extracts were identified as fusarinolic acid and its isomer [56.9% flask extract (FE)] and 59.2% bioreactor extract (BE), dehydrofusaric acid (35.7% FE and 31.6% BE), and fusaric acid (6.5% FE and 1.1% BE). Fusaric acid has been shown to be responsible for antimicrobial activity. The cytotoxicity of the extracts was evaluated in culture of HEK-293 and SH-SY5Y animal cells and toxicity of these extracts was verified even in the lowest tested concentrations. Therefore, our results indicate that the compounds identified exhibit potential as antimicrobial agents.

Fungal natural products galaxy: Biochemistry and molecular genetics toward blockbuster drugs discovery

Secondary metabolites synthesized by fungi have become a precious source of inspiration for the design of novel drugs. Indeed, fungi are prolific producers of fascinating, diverse, structurally complex, and low-molecular-mass natural products with high therapeutic leads, such as novel antimicrobial compounds, anticancer compounds, immunosuppressive agents, among others. Given that these microorganisms possess the extraordinary capacity to secrete diverse chemical scaffolds, they have been highly exploited by the giant pharma companies to generate small molecules. This has been made possible because the isolation of metabolites from fungal natural sources is feasible and surpasses the organic synthesis of compounds, which otherwise remains a significant bottleneck in the drug discovery process. Here in this comprehensive review, we have discussed recent studies on different fungi (pathogenic, non-pathogenic, commensal, and endophytic/symbiotic) from different habitats (terrestrial and marines), the specialized metabolites they biosynthesize, and the drugs derived from these specialized metabolites. Moreover, we have unveiled the logic behind the biosynthesis of vital chemical scaffolds, such as NRPS, PKS, PKS-NRPS hybrid, RiPPS, terpenoids, indole alkaloids, and their genetic mechanisms. Besides, we have provided a glimpse of the concept behind mycotoxins, virulence factor, and host immune response based on fungal infections.

Liquid Fungal Cocultivation as a Strategy to Access Bioactive Metabolites

Fungi are a rich source of bioactive compounds. Fungal cocultivation is a method of potentiating chemical interactions and, consequently, increasing bioactive molecule production. In this study, we evaluated the bactericidal, antiprotozoal, and cathepsin V inhibition activities of extracts from axenic cultures of 6 fungi (Fusarium guttiforme, Pestalotiopsis diospyri, Phoma caricae-papayae, Colletotrichum horii, Phytophthora palmivora, and C. gloeosporioides) that infest tropical fruits and 57 extracts obtained by their cocultivation. Our results reveal that fungal cocultivation enhances the biological activity of the samples, since all extracts that were active on Gram-positive bacteria, Gram-negative bacteria, Trypanosoma cruzi, and Leishmania infantum were obtained from cocultivation. Bacterial growth is either totally or partially inhibited by 46% of the extracts. Two extracts containing mainly fusaric and 9,10-dehydrofusaric acids were particularly active. The presence of the fungus F. guttiforme in co-cultures that give rise to extracts with the highest activities against L. infantum. An axenic culture gave rise to the most active extract for the inhibition of cathepsin V; however, other coculture extracts also exhibited activity toward this biological target. Therefore, the results of the biological activities indicate that fungal cocultivation increased the biological potential of samples, likely due to the hostile and competitive environment that pushes microorganisms to produce substances important for defense and allows access to metabolic routes then silenced in milder cultivation conditions.

Fusarochromene, a novel tryptophan-derived metabolite from Fusarium sacchari

Fusarochromene isolated from the plant pathogenic fungus, Fusarium sacchari is closely related to a group of mycotoxins including fusarochromanone previously isolated from various Fusaria spp. Despite their assumed polyketide biogenesis, incorporation studies with 13C-labelled acetate, glycerol and tryptophans show that fusarochromene is unexpectedly derived via oxidative cleavage of the aromatic amino acid tryptophan. A putative biosynthetic gene cluster has been identified.

Pyridine alkaloids with activity in the central nervous system

This review discusses all pyridine alkaloids with CNS activity, their therapeutic potential, and the interesting array of sources whence they originate.

Biosynthesis of Mycotoxin Fusaric Acid and Application of a PLP-Dependent Enzyme for Chemoenzymatic Synthesis of Substituted l-Pipecolic Acids

Fusaric acid (FA) is a well-known mycotoxin that plays an important role in plant pathology. The biosynthetic gene cluster for FA has been identified, but the biosynthetic pathway remains unclarified. Here, we elucidated the biosynthesis of FA, which features a two-enzyme catalytic cascade, a pyridoxal 5'-phosphate (PLP)-dependent enzyme (Fub7), and a flavin mononucleotide (FMN)-dependent oxidase (Fub9) in synthesizing the picolinic acid scaffold. FA biosynthesis also involves an off-line collaboration between a highly reducing polyketide synthase (HRPKS, Fub1) and a nonribosomal peptide synthetase (NRPS)-like carboxylic acid reductase (Fub8) in making an aliphatic α,β-unsaturated aldehyde. By harnessing the stereoselective C-C bond-forming activity of Fub7, we established a chemoenzymatic route for stereoconvergent synthesis of a series of 5-alkyl-, 5,5-dialkyl-, and 5,5,6-trialkyl-l-pipecolic acids of high diastereomeric ratio.

Potato dry rot disease: current status, pathogenomics and management

Potato dry rot disease caused by Fusarium species is a major threat to global potato production. The soil and seed-borne diseases influence the crop stand by inhibiting the development of potato sprouts and cause severe rots in seed tubers, table and processing purpose potatoes in cold stores. The symptoms of the dry rot include sunken and wrinkled brown to black tissue patches on tubers having less dry matter and shriveled flesh. Fungal infection accompanied by toxin development in the rotten tubers raises more concern for consumer health. The widespread dry rot causing fungal species (Fusarium graminearum) is reported to have a hemibiotrophic lifestyle. A cascade of enzymes, toxins and small secreted proteins are involved in the pathogenesis of these hemibiotrophs. With the availability of the genome sequence of the most devastating species Fusarium sambucinum, it is important to identify the potential pathogenicity factors and small secreted proteins that will help in designing management strategies. Limited resistant cultivars and the emergence of fungicide-resistant strains have made it more threatening for potato cultivation and trade. Several novel fungicide molecules (Azoxystrobin, chlorothalonil and fludioxonil), are found very effective as tuber treatment chemicals. Besides, many beneficial bioagents and safer chemicals have shown antibiosis and mycoparasitism against this pathogen. Germplasm screening for dry rot resistance is important to assist the resistance breeding program for the development of resistant cultivars. This review aims to draw attention to the symptomatology, infection process, pathogenomics, the role of toxins and management approaches for potato dry rot disease, which is very much critical in designing better management strategies.

Occurrence, Pathogenicity, and Mycotoxin Production of Fusarium temperatum in Relation to Other Fusarium Species on Maize in Germany

Fusarium subglutinans is a plant pathogenic fungus infecting cereal grain crops. In 2011, the species was divided in Fusarium temperatumsp. nov. and F. subglutinans sensu stricto. In order to determine the occurrence and significance of F. temperatum and F. subglutinans on maize, a monitoring of maize ears and stalks was carried out in Germany in 2017 and 2018. Species identification was conducted by analysis of the translation elongation factor 1α (TEF-1α) gene. Ninety-four isolates of F. temperatum and eight isolates of F. subglutinans were obtained during two years of monitoring from 60 sampling sites in nine federal states of Germany. Inoculation of maize ears revealed a superior aggressiveness for F. temperatum, followed by Fusarium graminearum, Fusarium verticillioides, and F. subglutinans. On maize stalks, F. graminearum was the most aggressive species while F. temperatum and F. subglutinans caused only small lesions. The optimal temperature for infection of maize ears with F. temperatum was 24 °C and 21 °C for F. subglutinans. All strains of F. temperatum and F. subglutinans were pathogenic on wheat and capable to cause moderate to severe head blight symptoms. The assessment of mycotoxin production of 60 strains of F. temperatum cultivated on rice revealed that all strains produced beauvericin, moniliformin, fusaric acid, and fusaproliferin. The results demonstrate a higher prevalence and aggressiveness of F. temperatum compared to F. subglutinans in German maize cultivation areas.

Fungal diversity and metabolomic profiles in GM and isogenic non-GM maize cultivars from Brazil

There is little knowledge of the microbial diversity, mycotoxins and associated secondary metabolites in GM maize and isogenic non-GM cultivars (cvs). This study has quantified the microbial populations and dominant fungal genera in 6 cvs of each type representative of herbicide, pesticide or stacked resistance to both. The predominant mycotoxins and targeted metabolomics profiles were also compared between the two sets of cvs. This showed that the overall fungal populations were 8.8 CFUs g⁻¹ maize. The dominant genera, isolated from maize samples, whether surface-sterilised or not, in all maize cvs were Fusarium, followed by Penicillium, Aspergillus and occasionally Cladosporium and Alternaria. The analysis of the targeted metabolomics showed that approx. 29 different metabolites were detected. These were dominated by fumonisins and minor Penicillium spp. metabolites (questiomycin A and rugulovasine A). Interestingly, the range and number of mycotoxins present in the GM cvs were significantly lower than in the non-GM maize samples. This suggests that while the fungal diversity of the two types of maize appeared to be very similar, the major contaminant mycotoxins and range of toxic secondary metabolites were much lower in the GM cvs.

The Impact of Natural Dietary Compounds and Food-Borne Mycotoxins on DNA Methylation and Cancer

Cancer initiation and progression is an accumulation of genetic and epigenetic modifications. DNA methylation is a common epigenetic modification that regulates gene expression, and aberrant DNA methylation patterns are considered a hallmark of cancer. The human diet is a source of micronutrients, bioactive molecules, and mycotoxins that have the ability to alter DNA methylation patterns and are thus a contributing factor for both the prevention and onset of cancer. Micronutrients such as betaine, choline, folate, and methionine serve as cofactors or methyl donors for one-carbon metabolism and other DNA methylation reactions. Dietary bioactive compounds such as curcumin, epigallocatechin-3-gallate, genistein, quercetin, resveratrol, and sulforaphane reactivate essential tumor suppressor genes by reversing aberrant DNA methylation patterns, and therefore, they have shown potential against various cancers. In contrast, fungi-contaminated agricultural foods are a source of potent mycotoxins that induce carcinogenesis. In this review, we summarize the existing literature on dietary micronutrients, bioactive compounds, and food-borne mycotoxins that affect DNA methylation patterns and identify their potential in the onset and treatment of cancer.

Fusarium fujikuroi Species Complex Associated With Rice, Maize, and Soybean From Jiangsu Province, China: Phylogenetic, Pathogenic, and Toxigenic Analysis

Species belonging to the Fusarium fujikuroi species complex (FFSC) are of vital importance and are a major concern for food quantity and quality worldwide, as they not only cause serious diseases in crops but also produce various mycotoxins. To characterize the population structure and evaluate the risk of poisonous secondary metabolites, a total of 237 candidate strains were isolated from rice, maize, and soybean samples in Jiangsu Province, China. Species identification of the individual strain was accomplished by sequencing the translation elongation factor 1α gene (TEF-1α) and the fumonisin (FB) synthetic gene (FUM1). The distribution of Fusarium species among the different crops was observed. The maize seeds were dominated by F. proliferatum (teleomorph, Gibberella intermedia) and F. verticillioides (teleomorph, G. moniliformis), whereas F. fujikuroi (teleomorph, G. fujikuroi) was the most frequently isolated species from rice and soybean samples. In addition, phylogenetic analyses of these strains were performed, and the results suggested clear groups showing no obvious relationship with the origin source. FFSC species pathogenicity and toxigenicity were studied. All of the species reduced the rice seed germination rate, with no significant differences. F. fujikuroi showed two distinct patterns of influencing the length of rice seedlings, which were correlated with FBs and gibberellic acid synthesis. FBs were mainly produced by F. verticillioides and F. proliferatum. F. proliferatum and F. fujikuroi also produced moniliformin and beauvericin. The toxigenicity of F. andiyazi (teleomorph, G. andiyazi) was extremely low. Further analysis indicated that the sequence variations in TEF-1α and the differences in the expression levels of the toxin synthesis genes were associated with the diversity of secondary metabolites in F. fujikuroi strains. These findings provide insight into the population-level characterization of the FFSC and might be helpful in the development of strategies for the management of diseases and mycotoxins.

Enhancement of gibberellic acid production from Fusarium fujikuroi by mutation breeding and glycerol addition

Gibberellic acid (GA₃) is a natural plant growth hormone that has been widely used in agriculture and horticulture. To obtain higher GA₃ producing strains, the method of screening the strains for resistance to simvastatin was used after treatment with nitrosoguanidine (NTG) and gamma rays. The rationale for the strategy was that mutants showing simvastatin resistance were likely to be high GA₃ producers, as their activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is relatively more effective. GA₃ yield of mutant S109 increased by 14.2% than that of the original strain. The GA₃ production ability in mutant S109 remained relatively stable after ten generations. With the addition of 0.4 g glycerol on the 5th day during the fermentation process in Erlenmeyer flask, maximum GA₃ production of 2.7 g/L was achieved by this mutant, exhibiting 28.6% increase compared with original strain. Furthermore, we also achieved 2.8 g/L GA₃ and had a 33.3% increase with addition 20 g glycerol on the 5th day during the fermentation process in a 5-L bioreactor. Our results indicated efficient GA₃ production could be achieved on the condition that the supply of glycerol at the suitable conditions. This study would lay a foundation for industrial production of GA₃.

Fusarium fujikuroi species complex in Brazilian rice: Unveiling increased phylogenetic diversity and toxigenic potential

Fusarium fujikuroi species complex (FFSC) species are commonly encountered infecting rice, but knowledge of the diversity and toxigenic potential of the species is lacking in Brazil, the largest rice-producing country outside Asia. One hundred FFSC isolates obtained from national rice were identified using morphology and phylogeny of TEF, CAL and TUB genes. Eight previously known and one novel Fusarium species were identified. Three species accounted for around 60% of the strains: F. fujikuroi (n = 23), F. proliferatum (n = 22) and F. verticillioides (n = 16). The less frequent species were F. volatile (n = 8), F. anthophilum (n = 6), F. pseudocircinatum (n = 4), F. sterilihyphosum (n = 2) and F. begoniae (n = 1). The novel Fusarium species was represented by 18 isolates. All species produced at least one of the analyzed mycotoxins [beauvericin (BEA), fumonisins (FBs), moniliformin (MON) and enniatins (ENNs)]. BEA was produced by all species but F. verticillioides. The FBs (mainly FB1) were produced mostly by F. fujikuroi, F. proliferatum and F. verticillioides. F. begoniae and F. verticillioides did not produce ENNs and F. sterilihyphosum and F. begoniae did not produce MON, while the other species produced MON and ENNs. Our results add new knowledge of the diversity, geographical distribution and host range of FFSC species.

Effect of interacting conditions of water activity, temperature and incubation time on Fusarium thapsinum and Fusarium andiyazi growth and toxin production on sorghum grains

This study examined the effect of interacting conditions of water activity (a_W, 0.995, 0.98 and 0.95) and temperature (15, 25 and 30 °C) on growth rate of two Fusarium thapsinum and one F. andiyazi strains isolated from sorghum in Argentina. In addition, the effect of interacting conditions (a_W × temperature × incubation time (7, 14, 21 and 28 days)) on mycotoxin production (moniliformin (MON), fusaric acid (FA) and fusarin C (FUS C)) on a sorghum grain substrate was evaluated. Statistical analysis showed that a_W and temperature significantly affected growth of both species, mainly the a_W. Incubation time significantly influenced mycotoxin production by both species as well, mostly for FA. Maximum growth rates of the F. thapsinum strains were obtained at the highest a_W (0.995) and 25 °C and growth rate decreased as a_W and temperature were reduced. The same growth profile was observed for F. andiyazi RCFA09 (maximum growth rates at 0.995-25 °C). Mycotoxin production by both species was detected at the highest a_W levels whereas at 0.95 a_W only low amounts of MON were produced by F. thapsinum. Maximum MON and FUS C production by both F. thapsinum strains was observed at 0.995 a_W and 25-30 °C after 28 days of incubation. Also, F. thapsinum strains showed maximum FA production at the highest a_W and temperature but after 14 days; after this incubation time toxin levels significantly decreased. The responses to a_W and temperature of F. andiyazi were similar to that of F. thapsinum strains in relation to FA and FUS C production. Maximum levels of FA were detected at the highest a_W after 14 days of incubation at 25-30 °C. Fusarin C was produced at all assayed temperatures but maximum levels were detected at 30 °C and 0.995 a_W after 28 days of incubation. Two-dimensional profiles on the interactions of a_W by temperature were developed from these data to identify conditions that indicate a significant risk from MON, FA and FUS C accumulation on sorghum grains. The results of this study suggest that sorghum grains could be colonized by these species and toxin production can occur, especially during development stages under field conditions at high water activity of grains or during grain storage if the drying process is slow or deficient. To our knowledge, this study described for the first time FUS C production by F. thapsinum and F. andiyazi under interacting conditions of a_W, temperature and incubation time on sorghum grains.

Different Phenotypes, Similar Genomes: Three Newly Sequenced Fusarium fujikuroi Strains Induce Different Symptoms in Rice Depending on Temperature

Bakanae, caused by the hemibiotrophic fungus Fusarium fujikuroi, is one of the most important diseases of rice and is attributed to up to 75% of losses, depending on the strain and environmental conditions. Some strains cause elongation and thin leaves, whereas others induce stunting and chlorotic seedlings. Differences in symptoms are attributed to genetic differences in the strains. F. fujikuroi strains Augusto2, CSV1, and I1.3 were sequenced with Illumina MiSeq, and pathogenicity trials were conducted on rice cultivar Galileo, which is susceptible to bakanae. By performing gene prediction, single nucleotide polymorphism (SNP) calling, and structural variant analysis with a reference genome, we show how an extremely limited number of polymorphisms in genes not commonly associated with bakanae disease can cause strong differences in phenotype. CSV1 and Augusto2 were particularly close, with only 21,887 SNPs between them, but they differed in virulence, reaction to temperature, induced symptoms, colony morphology and color, growth speed, fumonisin, and gibberellin production. Genes potentially involved in the shift in phenotype were identified. Furthermore, we show how temperature variation may result in different symptoms even in rice plants inoculated with the same F. fujikuroi strain. Moreover, all of the F. fujikuroi strains became more virulent at higher temperatures. Significant differences were likewise observed in gibberellic acid production and in the expression of both fungal and plant gibberellin biosynthetic genes.

Molecular docking and mechanisms of fusaric acid induced mitochondrial sirtuin aberrations in glycolytically and oxidatively poised human hepatocellular carcinoma (HepG2) cells

Fusaric acid (FA) is a ubiquitous yet neglected mycotoxin. The toxicity of FA is associated with mitochondrial dysfunction and oxidative stress. Sirtuins (SIRTs) are key mediators of cell stress responses through deacetylation of antioxidant, mitochondrial maintenance and energy metabolism proteins. Dietary bioactive compounds have profound effects on SIRT activity, however little is known regarding common foodborne toxins and SIRTs. In this study the interaction of FA with mitochondrial SIRTs - SIRT3 and SIRT5, were firstly studied by molecular docking. Thereafter we substantiated the in silico findings by investigating the effect of FA on expression profiles of SIRT3 and SIRT5, and transcriptional and post-transcriptional regulators, PGC-1α and miRNA-30c using western blots and qPCR in vitro. FA was predicted to bind to the active site of SIRT3 and SIRT5 having implications for biological activity. Furthermore, protein expression of SIRT3 and SIRT5 was down-regulated despite elevated mRNA levels. Further experimentation revealed post-transcriptional regulation of both SIRTs as evidenced by elevated miRNA-30c despite induction of PGC-1α. This study highlights the potential of a diet contaminated with FA to dysregulate mitochondrial specific proteins that can lead to initiation and progression of sirtuin related diseases including cancer and insulin resistance.

Putative metabolic pathway for the bioproduction of bikaverin and intermediates thereof in the wild Fusarium oxysporum LCP531 strain

Fungal naphthoquinones, like red bikaverin, are of interest due to their growing applications in designing pharmaceutical products. Though considerable work has been done on the elucidation of bikaverin biosynthesis pathway in Fusarium fujikuroi, very few reports are available regarding its bioproduction in F. oxysporum. We are hereby proposing a putative metabolic pathway for bikaverin bioproduction in a wild F. oxysporum strain by cross-linking the pigment profiles we obtained under two different fermentation conditions with literature. Naphthoquinone pigments were extracted with a pressurized liquid extraction method, and characterized by HPLC–DAD and UHPLC-HRMS. The results led to the conclusions that the F. oxysporum LCP531 strain was able to produce bikaverin and its various intermediates, e.g., pre-bikaverin, oxo-pre-bikaverin, dinor-bikaverin, me-oxo-pre-bikaverin, and nor-bikaverin, in submerged cultures in various proportions. To our knowledge, this is the first report of the isolation of these five bikaverin intermediates from F. oxysporum cultures, providing us with steady clues for confirming a bikaverin metabolic pathway as well as some of its regulatory patterns in the F. oxysporum LCP531 strain, based on the previously reported model in F. fujikuroi. Interestingly, norbikaverin accumulated along with bikaverin in mycelial cells when the strain grew on simple carbon and nitrogen sources and additional cofactors. Along bikaverin production, we were able to describe the excretion of the toxin beauvericin as main extrolite exclusively in liquid medium containing complex nitrogen and carbon sources, as well as the isolation of ergosterol derivate in mycelial extracts, which have potential for pharmaceutical uses. Therefore, culture conditions were also concluded to trigger some specific biosynthetic route favoring various metabolites of interest. Such observation is of great significance for selective production of pigments and/or prevention of occurrence of others (aka mycotoxins).