FAM Tag Size Separation-Based Capture-Systematic Evolution of Ligands by Exponential Enrichment for Sterigmatocystin-Binding Aptamers with High Specificity.

Sterigmatocystin (ST) is a known toxin whose aptamer has rarely been reported because ST is a water-insoluble small-molecule target with few active sites, leading to difficulty in obtaining its aptamer using traditional target fixation screening methods. To obtain aptamer for ST, we incorporated FAM tag size separation into the capture-systematic evolution of ligands by exponential enrichment and combined it with molecular activation for aptamer screening. The screening process was monitored using a quantitative polymerase chain reaction fluorescence amplification curve and recovery of negative-, counter-, and positive-selected ssDNA. The affinity and specificity of the aptamer were verified by constructing an aptamer-affinity column, and the binding sites were predicted using molecular docking simulations. The results showed that the Kd value of the H Seq02 aptamer was 25.3 nM. The aptamer-affinity column based on 2.3 nmol of H Seq02 exhibited a capacity of about 80 ng, demonstrating better specificity than commercially available antibody affinity columns. Molecular simulation docking predicted the binding sites for H Seq02 and ST, further explaining the improved specificity. In addition, circular dichroism and isothermal titration calorimetry were used to verify the interaction between the aptamer and target ST. This study lays the foundation for the development of a new ST detection method.

In Vivo Genotoxicity and Toxicity Assessment of Sterigmatocystin Individually and in Mixture with Aflatoxin B1.

Mycotoxins are natural food and feed contaminants produced by several molds. The primary mode of exposure in humans and animals is through mixtures. Aflatoxin B1 (AFB1) and sterigmatocystin (STER) are structurally related mycotoxins that share the same biosynthetic route. Few in vivo genotoxicity assays have been performed with STER. In the present genotoxicity study, Wistar rats were dosed orally with STER (20 mg/kg b.w.), AFB1 (0.25 mg/kg b.w.) or a mixture of both in an integrated micronucleus (bone marrow) and comet study (liver and kidney). STER was dosed at the highest feasible dose in corn oil. No increase in the percentage of micronuclei in bone marrow was observed at any condition. Slight DNA damage was detected in the livers of animals treated with AFB1 or the mixture (DNA strand breaks and Fpg (Formamidopyrimidine DNA glycosylase)-sensitive sites, respectively). Plasma, liver, and kidney samples were analyzed with LC-MS/MS demonstrating exposure to both mycotoxins. General toxicity parameters (organs absolute weight, biochemistry, and histopathology) were not altered either individually or in the mixture. The overall absence of individual genotoxicity did not allow us to set any type of interaction in the mixture. However, a possible toxicokinetic interaction was observed.

Study of co-occurrence of mycotoxins in cocoa beans in Brazil by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

In this study, 135 samples of cocoa beans collected in the Amazon and Atlantic Forest regions of Brazil were analysed to evaluate the possible co-occurrence of 34 mycotoxins. The results indicate that 42% of the cocoa samples exhibited quantifiable levels for 11 mycotoxins: aflatoxins (AFs) B1, B2 and G1; ochratoxin A; citrinin; cyclopiazonic acid; tenuazonic acid; paxilline; sterigmatocystin; zearalenone and fumonisin B2. Of the samples, 18% exhibited the co-occurrence of up to six mycotoxins. No toxins belonging to the groups of trichothecenes or ergot alkaloids were detected. Contingency analysis of the incidence of mycotoxins did not show significant differences between the two regions evaluated. Seven samples were contaminated with AFs, while only one contained ochratoxin A above 10 µg kg-1. The accuracy of the method was evaluated by proficiency testing for ochratoxin A, where satisfactory Z-scores were obtained.

Rapid but narrow - Evolutionary adaptation and transcriptional response of Drosophila melanogaster to toxic mould.

Insects have adapted to a multitude of environmental conditions, including the presence of xenobiotic noxious substances. Environmental microorganisms, particularly rich on ephemeral resources, employ these noxious chemicals in a chemical warfare against predators and competitors, driving co-evolutionary adaptations. In order to analyse how environmental microbes may be driving such evolutionary adaptations, we experimentally evolved Drosophila melanogaster populations by exposing larvae to the toxin-producing mould Aspergillus nidulans that infests the flies' breeding substrate. To disentangle the effects of the mycotoxin Sterigmatocystin from other substrate modifications inflicted by the mould, we used the following four selection regimes: (i) control without fungus, (ii) A. nidulans wild type, (iii) a mutant of A. nidulans ΔlaeA with impaired toxin production, (iv) synthetic Sterigmatocystin. Experimental evolution was carried out in five independent D. melanogaster populations each, for a total of 11 generations. We further combined our evolution experiment with transcriptome analysis to identify evolutionary shifts in gene expression due to the selection regimes and mould confrontation. Populations that evolved in presence of the toxin-producing mould or the pure mycotoxin rapidly adapted to the respective conditions and showed higher viability in subsequent confrontations. Yet, mycotoxin-selected populations had no advantage in A. nidulans wild type confrontation. Moreover, distinctive changes in gene expression related to the selection-regime contrast were only associated with the toxin-producing-fungus regime and comprised a narrow set of genes. Thus, it needs the specific conditions of the selection agent to enable adaptation to the fungus.

Co-Occurrence of Mycotoxins in Feed for Cattle, Pigs, Poultry, and Sheep in Navarra, a Region of Northern Spain.

Mycotoxins, toxic compounds produced by fungi on raw materials, such as cereals, represent a serious health hazard. Animals are exposed to them mainly through the ingestion of contaminated feed. This study presents data about the presence and co-occurrence of nine mycotoxins: aflatoxins B1, B2, G1, and G2, ochratoxins A and B, zearalenone (ZEA), deoxynivalenol (DON), and sterigmatocystin (STER), in 400 samples of compound feed for cattle, pigs, poultry, and sheep (100 samples each) collected in Spain (2019-2020). Aflatoxins, ochratoxins, and ZEA were quantified using a previously validated HPLC method using fluorescence detection; whereas DON and STER were quantified using ELISA. Moreover, the obtained results were compared with those obtained in this country and published in the last 5 years. The mycotoxin presence in Spanish feed, especially for ZEA and DON, has been demonstrated. The maximum individual levels found were: AFB1: 6.9 µg/kg in a sample of feed for poultry; OTA: 65.5 µg/kg in a sample of feed for pigs, DON: 887 µg/kg in a sample of feed for sheep, and ZEA: 816 µg/kg in a sample of feed for pigs. Nevertheless, regulated mycotoxins appear, in general, at levels below those regulated by the EU; in fact, the percentage of samples containing concentrations above these limits was very low (from 0% for DON to 2.5% for ZEA). The co-occurrence of mycotoxins has also been demonstrated: 63.5% of the analyzed samples presented detectable levels of two to five mycotoxins. Due to the fact that the distribution of mycotoxins in raw materials can change greatly from year to year with climate conditions or market globalization, regular mycotoxin monitorization in feed is needed to prevent the integration of contaminated materials in the food chain.

Cyclodextrin-Based Displacement Strategy of Sterigmatocystin from Serum Albumin as a Novel Approach for Acute Poisoning Detoxification.

This study demonstrates that sterigmatocystin (STC) interacts non-covalently with various cyclodextrins (CDs), showing the highest binding affinity for sugammadex (a γ-CD derivative) and γ-CD, and an almost order of magnitude lower affinity for ß-CD. This difference in affinity was studied using molecular modelling and fluorescence spectroscopy, which demonstrated a better insertion of STC into larger CDs. In parallel, we showed that STC binds to human serum albumin (HSA) (a blood protein known for its role as a transporter of small molecules) with an almost two order of magnitude lower affinity compared to sugammadex and γ-CD. Competitive fluorescence experiments clearly demonstrated an efficient displacement of STC from the STC-HSA complex by cyclodextrins. These results are a proof-of-concept that CDs can be used to complex STC and related mycotoxins. Similarly, as sugammadex extracts neuromuscular relaxants (e.g., rocuronium and vecuronium) from blood and blocks their bioactivity, it could also be used as first aid upon acute intoxication to encapsulate a larger part of the STC mycotoxin from serum albumin.

Hollow-structured molecularly imprinted polymers enabled specific enrichment and highly sensitive determination of aflatoxin B1 and sterigmatocystin against complex sample matrix.

The biotoxins with high toxicity have the potential to be manufactured into biochemical weapons, seriously threatening international public security. Developing robust and applicable sample pretreatment platforms and reliable quantification methods has been recognized as the most promising and practical approach to solving these problems. Through the integration of the hollow-structured microporous organic networks (HMONs) as the imprinting carriers, we proposed a molecular imprinting platform (HMON@MIP) with enhanced adsorption performance in terms of specificity, imprinting cavity density as well as adsorption capacity. The HMONs core of MIPs provided a hydrophobic surface that enhanced the adsorption of biotoxin template molecules during the imprinting process, resulting in an increased imprinting cavity density. The HMON@MIP adsorption platform could produce a series of MIP adsorbents by changing the biotoxin template, such as aflatoxin and sterigmatocystin, and showed promising generalizability. The limits of detection (LOD) of the HMON@MIP-based preconcentration method for AFT B1 and ST were 4.4 and 6.7 ng L-1, respectively, and the method was applicable to food sample with satisfied recoveries of 81.2-95.1%. And the specific recognition and adsorption sites left on HMON@MIP by the imprinting process can achieve outstanding selectivity for AFT B1 and ST. The developed imprinting platforms hold great potential for application in the identification and determination of various food hazards in complex food sample matrices and contribute to precise food safety inspection.

Isolation of the Main Pathogens Causing Postharvest Disease in Fresh Angelica sinensis during Different Storage Stages and Impacts of Ozone Treatment on Disease Development and Mycotoxin Production.

Angelica sinensis, a Chinese herbal medicine, is susceptible to molds during storage, reducing its quality, and even generating mycotoxins with toxic effects on human health. Fresh A. sinensis was harvested from Min County of Gansu Province in China and kept at room temperature. Naturally occurring symptoms were observed during different storage stages. Molds were isolated and identified from the diseased A. sinensis using morphological and molecular biology methods. The impact of ozone treatment on postharvest disease development and mycotoxin production was investigated. The results indicated that A. sinensis decay began on day 7 of storage and progressed thereafter. Nine mold species were isolated and characterized: day 7, two Mucormycetes; day 14, Clonostachys rosea; day 21, two Penicillium species and Aspergillus versicolor; day 28, Alternaria alternata and Trichoderma atroviride; and day 49, Fusarium solani. Ozone treatment markedly inhibited the development of postharvest disease and the mycotoxin production (such as, patulin, 15-acetyl-deoxynivalenol, and sterigmatocystin) in the rotten tissue of A. sinensis inoculated with the nine isolates.

[Establishment of non-targeted screening database and confirmation method for 18 mycotoxins in grains using ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry].

A mass spectral library of 18 mycotoxins was developed based on ultra performance liquid chromatography-quadrupole-time of flight mass spectrometry (UPLC-Q-TOF/MS), which was used to establish a non-targeted screening method for mycotoxins in rice and wheat matrices. Eighteen mycotoxin standards were separated on an HSS T3 column, and data were collected for both positive and negative ionization under the MSE mode of the UPLC-Q-TOF/MS. Details including formulas, retention times, theoretical exact masses, measured exact masses of the adduct and fragment ions, and ion abundance ratios were recorded to establish the mass spectral library of the 18 mycotoxins in UNIFI Software. Analyte detection was based on a retention time deviation of 0.3 min, and the exact mass deviation of the adduct ions and fragment ions was set to 5×10-6. The screening detection limit (SDL) was used as the main threshold for verifying the screening method. In the validation process, 18 mycotoxins were classified into two types: with maximum levels (MLs) and without MLs. The results showed that the mycotoxins with MLs could be accurately screened at their limited level, and the mycotoxins without MLs had a range of SDL concentration from 2 to 800 µg/kg. The matrix effect results showed that 14 mycotoxins in rice and 11 in wheat had moderate matrix effects. Finally, 25 batches of rice and wheat were purified using QuEChERS and HLB columns after acetonitrile extraction and screening were performed by employing the established method. The results revealed that aflatoxin G1 (AFG1), aflatoxin G2 (AFG2), fumonisins B1 (FB1), and sterigmatocystin (ST) were detected in one batch of rice, FB1 and ST were detected in another batch of rice, FB1 and ochratoxin A (OTA) were detected in two batches of wheat, and no other mycotoxins were detected. This method is characterized by high throughput, simplicity, rapidity, accuracy, and can be applied to accurately screen mycotoxins with concentrations higher than the SDLs and qualitatively screen various mycotoxins in rice and wheat without standards.

Urease and Carbonic Anhydrase Inhibitory Effect of Xanthones from Aspergillus nidulans, an Endophytic Fungus of Nyctanthes arbor-tristis.

Urease plays a major role in the pathogenesis of peptic and gastric ulcer and also causes acute pyelonephritis and development of infection-induced reactive arthritis. Carbonic anhydrases (CA) cause pathological disorders such as epilepsy (CA I), glaucoma, gastritis, renal, pancreatic carcinomas, and malignant brain tumors (CA II). Although various synthetic urease and carbonic anhydrase inhibitors are known, these have many side effects. Hence, present studies were undertaken on ethyl acetate extract of Aspergillus nidulans, an endophytic fungus separated from the leaves of Nyctanthes arbor-tristis Linn. and led to the isolation of five furanoxanthones, sterigmatin (1: ), sterigmatocystin (3: ), dihydrosterigmatocystin (4: ), oxisterigmatocystin C (5: ), acyl-hemiacetal sterigmatocystin (6: ), and a pyranoxanthone (2: ). Acetylation of 3: gave compound O-acetyl sterigmatocystin (7: ). Their chemical structures were elucidated by 1H and 13C NMR and MS. The inhibitory effect of isolated compounds was evaluated on urease and carbonic anhydrase (bCA II) enzymes in vitro. Compounds 3: and 6: showed significant urease inhibition (IC50 19 and 21 µM), while other compounds exhibited varying degrees of urease inhibition (IC50 33 - 51 µM). Compounds 4, 6: and 7: exhibited significant inhibition of bCA II (IC50 values 21, 25 and 18 µM respectively), compounds 1: -3: displayed moderate inhibition (IC50 61, 76 and 31 µM respectively) while 5: showed no inhibition. A mechanistic study of the most active urease inhibitors was also performed using enzyme kinetics and molecular docking. All compounds were found non-toxic on the NIH-3T3 cell line.

New application of Aspergillus versicolor in promoting plant growth after suppressing sterigmatocystin production via genome mining and engineering.

Aspergillus genus is a key component in fermentation and food processing. However, sterigmatocystin (STE)-a mycotoxin produced by several species of Aspergillus-limits the use of some Aspergillus species (such as Aspergillus versicolor, Aspergillus inflatus, and Aspergillus parasiticus) because of its toxicity and carcinogenicity. Here, we engineered an STE-free Aspergillus versicolor strain based on genome mining techniques. We sequenced and assembled the Aspergillus versicolor D5 genome (34.52 Mb), in which we identified 16 scaffolds and 54 biosynthetic gene clusters (BGCs). We silenced cytochrome P450 coding genes STC17 and STC27 by insertional inactivation. The production of STE in the Δstc17 mutant strain was increased by 282% but no STE was detected in the Δstc27 mutant. Metabolites of Δstc27 mutant exhibited growth-promoting effect on plants. Our study makes significant progress in improving the application of some Aspergillus strains by restricting their production of toxic and carcinogenic compounds.

The Putative C2H2 Transcription Factor VadH Governs Development, Osmotic Stress Response, and Sterigmatocystin Production in Aspergillus nidulans.

The VosA-VelB hetero-dimeric complex plays a pivotal role in regulating development and secondary metabolism in Aspergillus nidulans. In this work, we characterize a new VosA/VelB-activated gene called vadH, which is predicted to encode a 457-amino acid length protein containing four adjacent C2H2 zinc-finger domains. Mutational inactivation of vosA or velB led to reduced mRNA levels of vadH throughout the lifecycle, suggesting that VosA and VelB have a positive regulatory effect on the expression of vadH. The deletion of vadH resulted in decreased asexual development (conidiation) but elevated production of sexual fruiting bodies (cleistothecia), indicating that VadH balances asexual and sexual development in A. nidulans. Moreover, the vadH deletion mutant exhibited elevated susceptibility to hyperosmotic stress compared to wild type and showed elevated production of the mycotoxin sterigmatocystin (ST). Genome-wide expression analyses employing RNA-Seq have revealed that VadH is likely involved in regulating more genes and biological pathways in the developmental stages than those in the vegetative growth stage. The brlA, abaA, and wetA genes of the central regulatory pathway for conidiation are downregulated significantly in the vadH null mutant during asexual development. VadH also participates in regulating the genes, mat2, ppgA and lsdA, etc., related to sexual development, and some of the genes in the ST biosynthetic gene cluster. In summary, VadH is a putative transcription factor with four C2H2 finger domains and is involved in regulating asexual/sexual development, osmotic stress response, and ST production in A. nidulans.

Metabolomic and regular analysis reveal phytotoxic mechanisms of sterigmatocystin in Amaranthus retroflexus L.

Sterigmatocystin (STE) is a common hepatotoxic and nephrotoxic contaminant in cereals, however, its phytotoxicity and mechanisms are poorly understood. Here, the phytotoxic mechanisms of STE were investigated via the metabolomics of Amaranthus retroflexus L. A total of 140 and 113 differential metabolites were detected in the leaves and stems, respectively, among which amino acids, lipids, and phenolic compounds were significantly perturbed. Valine, leucine, isoleucine, and lysine biosynthesis were affected by STE. These metabolic responses revealed that STE might be toxic to plants by altering the plasma membrane and inducing oxidative damage, which was verified by measuring the relative electrical conductivity and quantification of reactive oxygen species. The elevated amino acids, as well as the decreased of D-sedoheptuiose-7-phosphate indicated increased proteolysis and carbohydrate metabolism restriction. Furthermore, the IAA level also decreased. This study provides a better understanding of the impacts of STE on the public health, environment and food security.

Centrifugation-Assisted Solid-Phase Extraction Coupled with UPLC-MS/MS for the Determination of Mycotoxins in ARECAE Semen and Its Processed Products.

Mycotoxins can occur naturally in a variety of agriculture products, including cereals, feeds, and Chinese herbal medicines (TCMs), via pre- and post-harvest contamination and are regulated worldwide. However, risk mitigation by monitoring for multiple mycotoxins remains a challenge using existing methods due to their complex matrices. A multi-toxin method for 22 mycotoxins (aflatoxin B1, B2, G1, G2, M1, M2; ochratoxin A, B, C; Fumonisin B1, B2, B3; 15-acetyldeoxynivalenol, 3-acetyldeoxynivalenol, diace-toxyscirpenol, HT-2, T-2, deepoxy-deoxynivalenol, deoxynivalenol, neosolaniol, zearalenone, and sterigmatocystin) using centrifugation-assisted solid-phase extraction (SPE) clean-up prior to ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) analysis for Arecae Semen and its processed products was developed and validated. Several experimental parameters affecting the extraction and clean-up efficiency were systematically optimized. The results indicated good linearity in the range of 0.1-1000 µg/kg (r2 > 0.99), low limits of detection (ranging from 0.04 µg/kg to 1.5 µg/kg), acceptable precisions, and satisfactory recoveries for the selected mycotoxins. The validated method was then applied to investigate mycotoxin contamination levels in Areca catechu and its processed products. The mycotoxins frequently contaminating Areca catechu were aflatoxins (AFs), and the average contamination level and number of co-occurring mycotoxins in the Arecae Semen slices (Binlangpian) were higher than those in commercially whole Arecae Semen and Arecae Semen Tostum (Jiaobinlang). Sterigmatocystin was detected in 5 out of 30 Arecae Semen slices. None of the investigated mycotoxins were detected in Arecae pericarpium (Dafupi). The results demonstrated that centrifugation-assisted SPE coupled with UHPLC-MS/MS can be a useful tool for the analysis of multiple mycotoxins in Areca catechu and its processed products.

Monitoring of sterigmatocystin biosynthesis using RT-qPCR in airborne Aspergillus species of the series Versicolores.

Aspergilli series Versicolores have been shown to be explanatory variables for different symptoms like coughing and dizziness experienced by residents of mold-damaged homes. Among these species, eight are particularly recurrent in bioaerosols: Aspergillus amoenus, A. creber, A. fructus, A. jensenii, A. protuberus, A. puulaauensis, A. sydowii and A. tabacinus. In order to monitor the biosynthesis of sterigmatocystin (a mycotoxin associated with a risk of cancer development) and the development of these molds, we developed an RT-qPCR tool by targeting the aflR and rho1 genes. A total of 30 fungal isolates representing these eight species were included. For each of them, sterigmatocystin was quantified by UPLC-HRMS and (1 â†’ 3)-ß-D-glucan by visible spectrophotometry using Endosafe®-PTS™-Glucan Cartridges. After validation of our method by RT-qPCR, the direct assay was compared to the amount of aflR and rho1 cDNA. The sterigmatocystin and aflR assays showed a significant correlation between these two approaches (p < 0.0001), demonstrated for the first time the production of sterigmatocystin by A. tabacinus and suggested the ability of A. sydowii to synthesize sterigmatocystin. Assays conducted on (1 â†’ 3)-ß-D-glucan and rho1 did not show a correlation, supporting the multiplicity of functions performed in fungal cells by the RHO1 GTPase. The proposed tool could allow monitoring of sterigmatocystin biosynthesis by Aspergillus of the series Versicolores under different culture and climatic conditions.

The role of the Aspergillus nidulans high mobility group B protein HmbA, the orthologue of Saccharomyces cerevisiae Nhp6p.

The mammalian HMGB1 is a high-mobility-group B protein, which is both an architectural and functional element of chromatin. Nhp6p, the extensively studied fungal homologue of HMGB1 in Saccharomyces cerevisiae has pleiotropic physiological functions. Despite the existence of Nhp6p orthologues in filamentous ascomycetes, little is known about their physiological roles besides their contribution to sexual development. Here we study the function of HmbA, the Aspergillus nidulans orthologue of Nhp6p. We show that HmbA influences the utilization of various carbon- and nitrogen sources, stress tolerance, secondary metabolism, hyphae elongation and maintenance of polarized growth. Additionally, by conducting heterologous expression studies, we demonstrate that HmbA and Nhp6p are partially interchangeable. HmbA restores SNR6 transcription and fitness of nhp6AΔBΔ mutant and reverses its heat sensitivity. Nhp6Ap complements several phenotypes of hmbAΔ, including ascospore formation, utilization of various carbon- and nitrogen-sources, radial growth rate, hypha elongation by polarized growth. However, Nhp6Ap does not complement sterigmatocystin production in a hmbAΔ strain. Finally, we also show that HmbA is necessary for the normal expression of the endochitinase chiA, a cell wall re-modeller that is pivotal for the normal mode of maintenance of polar growth.

Graphene oxide-mediated fluorescence turn-on GO-FAM-FRET aptasensor for detection of sterigmatocystin.

Sterigmatocystin (STC) is a toxic fungal secondary metabolite recognized by the FAO and WHO as a genotoxic and carcinogenic substance. STC contaminates several foods and feed commodities, posing a health risk to humans. The present study proposes to develop a graphene oxide-mediated aptasensor platform for the one-step detection of STC. In this study, DNA aptamers were generated against STC by using a target immobilization-free graphene oxide (GO)-SELEX protocol. The champion aptamers were subjected to in silico maturation using a genetic algorithm to improve binding affinity. Further, MSA-C6 and STC interactions were characterized by MD simulation, bio-layer interferometry (KD 27.9 nM) and flow cytometry. GO was immobilized on a polypropylene surface and functionalized with FAM labelled MSA-C6 to develop a simple one-step fluorescence turn-on aptasensor. The linear detection range of the aptasensor was found to be 80-720 ppb with LOD 23.56 ± 4.93 ppb and LOQ 132.43 ± 3.25 ppb. Insignificant interference of salts and detergents as well as negligible cross-reactivity with other structurally similar mycotoxins were observed. Recovery studies in simulated contaminated samples indicated appreciable recoveries (71-89%) using aptasensing assay. The results of the study indicate the successful development of a simple one-step detection platform for STC, useful for the measurement and monitoring of samples for the presence of STC. It also reports a high-affinity aptamer, which can be exploited in other sensing platforms.

Asperemestrins A-D, Emestrin Hybrid Polymers with Bridged Skeletons from the Endophytic Fungus Aspergillus nidulans.

Four emestrin hybrid polymers, asperemestrins A-D (1-4, respectively), were isolated from the fungus Aspergillus nidulans. Asperemestrins A-C are the first examples of emestrin-sterigmatocystin heterodimers bearing a 7/5/6/6/5/5/6/6/6 nonacyclic system with a 2,5-diazabicyclo[2.2.2]octane-3,6-dione core, while asperemestrin D features an unprecedented 2,15-dithia-17,19-diazabicyclo[14.2.2]icosa-4,8-diene-12,18,20-trione core skeleton. Their structures were determined by extensive spectroscopic data, electronic circular dichroism calculations, and single-crystal X-ray diffraction. Asperemestrin B showed moderate cytotoxicity against cancer cell lines, including SU-DHL-2, HEPG2, and HL-60.

The KdmB-EcoA-RpdA-SntB chromatin complex binds regulatory genes and coordinates fungal development with mycotoxin synthesis.

Chromatin complexes control a vast number of epigenetic developmental processes. Filamentous fungi present an important clade of microbes with poor understanding of underlying epigenetic mechanisms. Here, we describe a chromatin binding complex in the fungus Aspergillus nidulans composing of a H3K4 histone demethylase KdmB, a cohesin acetyltransferase (EcoA), a histone deacetylase (RpdA) and a histone reader/E3 ligase protein (SntB). In vitro and in vivo evidence demonstrate that this KERS complex is assembled from the EcoA-KdmB and SntB-RpdA heterodimers. KdmB and SntB play opposing roles in regulating the cellular levels and stability of EcoA, as KdmB prevents SntB-mediated degradation of EcoA. The KERS complex is recruited to transcription initiation start sites at active core promoters exerting promoter-specific transcriptional effects. Interestingly, deletion of any one of the KERS subunits results in a common negative effect on morphogenesis and production of secondary metabolites, molecules important for niche securement in filamentous fungi. Consequently, the entire mycotoxin sterigmatocystin gene cluster is downregulated and asexual development is reduced in the four KERS mutants. The elucidation of the recruitment of epigenetic regulators to chromatin via the KERS complex provides the first mechanistic, chromatin-based understanding of how development is connected with small molecule synthesis in fungi.

The function of a conidia specific transcription factor CsgA in Aspergillus nidulans.

Aspergillus spp. mainly reproduce asexually via asexual spores called conidia. In this study, we identified CsgA, a conidia-specific Zn2Cys6 transcription factor containing the GAL4-like zinc-finger domain, and characterized the roles of CsgA in the model organism Aspergillus nidulans. In A. nidulans, the ΔcsgA strain produced abnormal conidiophores and exhibited increased conidial production. The deletion of csgA resulted in impaired production of sexual fruiting bodies (cleistothecia) and lower mutA expression levels. Overexpression of csgA led to decreased conidia production but increased cleistothecia production, suggesting that CsgA is essential for proper asexual and sexual development in A. nidulans. In conidia, the deletion of csgA resulted in increased trehalose content, higher spore viability, and increased tolerance to thermal and oxidative stresses. Transcriptomic analysis revealed that the loss of csgA affects the expression of genes related to conidia germination, DNA repair, and secondary metabolite biosynthesis. Further analysis revealed that the ΔcsgA strain exhibited delayed conidial germination and abnormal germ tube length. Additionally, the production of sterigmatocystin increased in the ΔcsgA conidia compared to that in the controls. Overall, these results suggest that CsgA is crucial for proper fungal development, spore viability, conidial germination, and sterigmatocystin production in A. nidulans.