Dissection of patulin biosynthesis, spatial control and regulation mechanism in Penicillium expansum

UvVelC is important for conidiation and pathogenicity in the rice false smut pathogen Ustilaginoidea virens

Rice false smut disease is one of the most significant rice diseases worldwide. Ustilaginoidea virens is the causative agent of this disease. Although several developmental and pathogenic genes have been identified and functionally analyzed, the pathogenic molecular mechanisms of U. virens remain elusive. The velvet family regulatory proteins are involved in fungal development, conidiation, and pathogenicity. In this study, we demonstrated the function of the VelC homolog UvVELC in U. virens. We identified the velvet family protein UvVELC and characterized its functions using a target gene deletion-strategy. Deletion of UvVELC resulted in conidiation failure and pathogenicity. The UvVELC expression levels during infection suggested that this gene might be involved in the early infection process. UvVELC is also important in resistance to abiotic stresses, the utilization efficiency of glucose, stachyose, raffinose, and other sugars, and the expression of transport-related genes. Moreover, UvVELC could physically interact with UvVEA in yeast, and UvVELC/UvVEA double-knockout mutants also failed in conidiation and pathogenicity. These results indicate that UvVELC play a critical role in the conidiation and pathogenicity in U. virens. Functional analysis indicated that UvVELC-mediated conidiation and nutrient acquisition from rice regulates the pathogenicity of U. virens. Understanding the function of the UvVELC homolog could provide a potential molecular target for controlling rice false smut disease.

Several secondary metabolite gene clusters in the genomes of ten Penicillium spp. raise the risk of multiple mycotoxin occurrence in chestnuts

Penicillium spp. produce a great variety of secondary metabolites, including several mycotoxins, on food substrates. Chestnuts represent a favorable substrate for Penicillium spp. development. In this study, the genomes of ten Penicillium species, virulent on chestnuts, were sequenced and annotated: P. bialowiezense. P. pancosmium, P. manginii, P. discolor, P. crustosum, P. palitans, P. viridicatum, P. glandicola, P. taurinense and P. terrarumae. Assembly size ranges from 27.5 to 36.8 Mb and the number of encoded genes ranges from 9,867 to 12,520. The total number of predicted biosynthetic gene clusters (BGCs) in the ten species is 551. The most represented families of BGCs are non ribosomal peptide synthase (191) and polyketide synthase (175), followed by terpene synthases (87). Genome-wide collections of gene phylogenies (phylomes) were reconstructed for each of the newly sequenced Penicillium species allowing for the prediction of orthologous relationships among our species, as well as other 20 annotated Penicillium species available in the public domain. We investigated in silico the presence of BGCs for 10 secondary metabolites, including 5 mycotoxins, whose production was validated in vivo through chemical analyses. Among the clusters present in this set of species we found andrastin A and its related cluster atlantinone A, mycophenolic acid, patulin, penitrem A and the cluster responsible for the synthesis of roquefortine C/glandicoline A/glandicoline B/meleagrin. We confirmed the presence of these clusters in several of the Penicillium species conforming our dataset and verified their capacity to synthesize them in a chestnut-based medium with chemical analysis. Interestingly, we identified mycotoxin clusters in some species for the first time, such as the andrastin A cluster in P. flavigenum and P. taurinense, and the roquefortine C cluster in P. nalgiovense and P. taurinense. Chestnuts proved to be an optimal substrate for species of Penicillium with different mycotoxigenic potential, opening the door to risks related to the occurrence of multiple mycotoxins in the same food matrix.

Effects of temperature, pH, and relative humidity on the growth of Penicillium paneum OM1 isolated from pears and its patulin production

Patulin is a mycotoxin produced by several species of Penicillium sp., Aspergillus sp., and Byssochlamys sp. on apples and pears. Most studies have been focused on Penicillium expansum, a common postharvest pathogen, but little is known about the characteristics of Penicillium paneum. In the present study, we evaluated the effects of temperature, pH, and relative humidity (RH) on the growth of P. paneum OM1, which was isolated from pears, and its patulin production. The fungal strain showed the highest growth rate at 25 °C and pH 4.5 on pear puree agar medium (PPAM) under 97 % RH, while it produced the highest amount of patulin at 20 °C and pH 4.5 on PPAM under 97 % RH. Moreover, RT-qPCR analysis of relative expression levels of 5 patulin biosynthetic genes (patA, patE, patK, patL, and patN) in P. paneum OM1 exhibited that the expression of the 4 patulin biosynthetic genes except patL was up-regulated in YES medium (patulin conducive), while it was not in PDB medium (patulin non-conducive). Our data demonstrated that the 3 major environmental parameters had significant impact on the growth of P. paneum OM1 and its patulin production. These results could be exploited to prevent patulin contamination by P. paneum OM1 during pear storage.

The small GTPase Ypt7 of Penicillium expansum is required for growth, patulin biosynthesis and virulence

Ypt GTPases are the largest subfamily of small GTPases involved in membrane transport. Here, a PeYpt7 gene deletion mutant of P. expansum was constructed. The ΔPeYpt7 mutant showed reduced colony growth with abnormal mycelial growth, reduced conidiation, and insufficient spore development. The mutation rendered the pathogen susceptible to osmotic stress and cell wall stressors. In addition, the absence of PeYpt7 reduced patulin production in P. expansum and significantly limited gene expression (PatG, PatH, PatI, PatD, PatF, and PatL). In addition, the mutant showed attenuated virulence in infected fruit and reduced expression of pathogenic factors was (PMG, PG, PL, and GH1). Thus, PeYpt7 modulates the growth, morphology, patulin accumulation, and pathogenicity of P. expansum by limiting the expression of related genes.

Targeting of Specialized Metabolites Biosynthetic Enzymes to Membranes and Vesicles by Posttranslational Palmitoylation: A Mechanism of Non-Conventional Traffic and Secretion of Fungal Metabolites

In nature, the formation of specialized (secondary) metabolites is associated with the late stages of fungal development. Enzymes involved in the biosynthesis of secondary metabolites in fungi are located in distinct subcellular compartments including the cytosol, peroxisomes, endosomes, endoplasmic reticulum, different types of vesicles, the plasma membrane and the cell wall space. The enzymes traffic between these subcellular compartments and the secretion through the plasma membrane are still unclear in the biosynthetic processes of most of these metabolites. Recent reports indicate that some of these enzymes initially located in the cytosol are later modified by posttranslational acylation and these modifications may target them to membrane vesicle systems. Many posttranslational modifications play key roles in the enzymatic function of different proteins in the cell. These modifications are very important in the modulation of regulatory proteins, in targeting of proteins, intracellular traffic and metabolites secretion. Particularly interesting are the protein modifications by palmitoylation, prenylation and miristoylation. Palmitoylation is a thiol group-acylation (S-acylation) of proteins by palmitic acid (C16) that is attached to the SH group of a conserved cysteine in proteins. Palmitoylation serves to target acylated proteins to the cytosolic surface of cell membranes, e.g., to the smooth endoplasmic reticulum, whereas the so-called toxisomes are formed in trichothecene biosynthesis. Palmitoylation of the initial enzymes involved in the biosynthesis of melanin serves to target them to endosomes and later to the conidia, whereas other non-palmitoylated laccases are secreted directly by the conventional secretory pathway to the cell wall space where they perform the last step(s) of melanin biosynthesis. Six other enzymes involved in the biosynthesis of endocrosin, gliotoxin and fumitremorgin believed to be cytosolic are also targeted to vesicles, although it is unclear if they are palmitoylated. Bioinformatic analysis suggests that palmitoylation may be frequent in the modification and targeting of polyketide synthetases and non-ribosomal peptide synthetases. The endosomes may integrate other small vesicles with different cargo proteins, forming multivesicular bodies that finally fuse with the plasma membrane during secretion. Another important effect of palmitoylation is that it regulates calcium metabolism by posttranslational modification of the phosphatase calcineurin. Mutants defective in the Akr1 palmitoyl transferase in several fungi are affected in calcium transport and homeostasis, thus impacting on the biosynthesis of calcium-regulated specialized metabolites. The palmitoylation of secondary metabolites biosynthetic enzymes and their temporal distribution respond to the conidiation signaling mechanism. In summary, this posttranslational modification drives the spatial traffic of the biosynthetic enzymes between the subcellular organelles and the plasma membrane. This article reviews the molecular mechanism of palmitoylation and the known fungal palmitoyl transferases. This novel information opens new ways to improve the biosynthesis of the bioactive metabolites and to increase its secretion in fungi.

Exploring the Biocontrol Capability of Non-Mycotoxigenic Strains of Penicillium expansum

Penicillium expansum is one the major postharvest pathogens of pome fruit during postharvest handling and storage. This fungus also produces patulin, which is a highly toxic mycotoxin that can contaminate infected fruits and their derived products and whose levels are regulated in many countries. In this study, we investigated the biocontrol potential of non-mycotoxigenic strains of Penicillium expansum against a mycotoxigenic strain. We analyzed the competitive behavior of two knockout mutants that were unable to produce patulin. The first mutant (∆patK) involved the deletion of the patK gene, which is the initial gene in patulin biosynthesis. The second mutant (∆veA) involved the deletion of veA, which is a global regulator of primary and secondary metabolism. At the phenotypic level, the ∆patK mutant exhibited similar phenotypic characteristics to the wild-type strain. In contrast, the ∆veA mutant displayed altered growth characteristics compared with the wild type, including reduced conidiation and abnormal conidiophores. Neither mutant produced patulin under the tested conditions. Under various stress conditions, the ∆veA mutants exhibited reduced growth and conidiation when exposed to stressors, including cell membrane stress, oxidative stress, osmotic stress, and different pH values. However, no significant changes were observed in the ∆patK mutant. In competitive growth experiments, the presence of non-mycotoxigenic strains reduced the population of the wild-type strain during in vitro growth. Furthermore, the addition of either of the non-mycotoxigenic strains resulted in a significant decrease in patulin levels. Overall, our results suggest the potential use of non-mycotoxigenic mutants, particularly ∆patK mutants, as biocontrol agents to reduce patulin contamination in food and feed.

A Mushroom P450-Monooxygenase Enables Regio- and Stereoselective Biocatalytic Synthesis of Epoxycyclohexenones

An epoxycyclohexenone (ECH) moiety occurs in natural products of both bacteria and ascomycete and basidiomycete fungi. While the enzymes for ECH formation in bacteria and ascomycetes have been identified and characterized, it remained obscure how this structure is biosynthesized in basidiomycetes. In this study, we i) identified a genetic locus responsible for panepoxydone biosynthesis in the basidiomycete mushroom Panus rudis and ii) biochemically characterized PanH, the cytochrome P450 enzyme catalyzing epoxide formation in this pathway. Using a PanH-producing yeast as a biocatalyst, we synthesized a small library of bioactive ECH compounds as a proof of concept. Furthermore, homology modeling, molecular dynamics simulation, and site directed mutation revealed the substrate specificity of PanH. Remarkably, PanH is unrelated to ECH-forming enzymes in bacteria and ascomycetes, suggesting that mushrooms evolved this biosynthetic capacity convergently and independently of other organisms.

Structure elucidation and characterization of patulin synthase, insights into the formation of a fungal mycotoxin

Patulin synthase (PatE) from Penicillium expansum is a flavin-dependent enzyme that catalyses the last step in the biosynthesis of the mycotoxin patulin. This secondary metabolite is often present in fruit and fruit-derived products, causing postharvest losses. The patE gene was expressed in Aspergillus niger allowing purification and characterization of PatE. This confirmed that PatE is active not only on the proposed patulin precursor ascladiol but also on several aromatic alcohols including 5-hydroxymethylfurfural. By elucidating its crystal structure, details on its catalytic mechanism were revealed. Several aspects of the active site architecture are reminiscent of that of fungal aryl-alcohol oxidases. Yet, PatE is most efficient with ascladiol as substrate confirming its dedicated role in biosynthesis of patulin.

Whole genome sequencing and annotation of Scleroderma yunnanense, the only edible Scleroderma species

Scleroderma yunnanense, an ectomycorrhizal fungus, is a popular edible mushroom within the Yunnan Province of Southwest China that holds great ecological and economic implications. However, despite its significance, there remains limited information about this species. Therefore, we sequenced S. yunnanense genome to identify the functional genes of S. yunnanense involved in secondary metabolite and carbohydrate production pathways. First, we present the 40.43 Mb high-quality reference genome for S. yunnanense, distributed across 35 contigs; moreover, the N50 contig size was found to reach 3.31 Mb and contained 8877 functional genes. Finally, genome annotation was conducted to compare the functional genes of S. yunnanense with protein sequences from different publicly available databases. Taken together, we identified 12 biosynthetic gene clusters across 10 contigs; among these were 13 key mevalonate (MVA) pathway enzymes, a key tyrosinase enzyme in the 3,4-dihydroxyphenylalanine (DOPA) pathway that is responsible for producing DOPA melanins, and 16 enzymes involved in uridine diphosphate glucose biosynthesis. Overall, this study presents the first genome assembly and annotation of S. yunnanense; ultimately, this information will be important in the elucidation of the biological activities and artificial domestication of this fungus.

The Identification and Comparative Analysis of Non-Coding RNAs in Spores and Mycelia of Penicillium expansum

Penicillium expansum is the most popular post-harvest pathogen and causes blue mold disease in pome fruit and leads to significant economic losses worldwide every year. However, the fundamental regulation mechanisms of growth in P. expansum are unclear. Recently, non-coding RNAs (ncRNAs) have attracted more attention due to critical roles in normalizing gene expression and maintaining cellular genotypes in organisms. However, the research related to ncRNAs in P. expansum have not been reported. Therefore, to provide an overview of ncRNAs on composition, distribution, expression changes, and potential targets in the growth process, a comparative transcriptomic analysis was performed on spores and mycelia of P. expansum in the present study. A total of 2595 novel mRNAs, 3362 long non-coding RNAs (lncRNAs), 10 novel microRNAs (miRNAs), 86 novel small interfering RNAs (siRNAs), and 11,238 circular RNAs (circRNAs) were predicted and quantified. Of these, 1482 novel mRNAs, 5987 known mRNAs, 2047 lncRNAs, 40 miRNAs, 38 novel siRNAs, and 9235 circRNAs were differentially expressed (DE) in response to the different development stages. Afterward, the involved functions and pathways of DE RNAs were revealed via Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) database enrichment analysis. The interaction networks between mRNAs, lncRNAs, and miRNAs were also predicted based on their correlation coefficient of expression profiles. Among them, it was found that miR168 family members may play important roles in fungal growth due to their central location in the network. These findings will contribute to a better understanding on regulation machinery at the RNA level on fungal growth and provide a theoretical basis to develop novel control strategies against P. expansum.

Set1/COMPASS regulates growth, pathogenicity, and patulin biosynthesis of Penicillium expansum via H3K4 methylation and the interaction with PeVelB

INTRODUCTION

Penicillium expansum is a harmful plant fungal pathogen that causes blue mold disease and produces mycotoxin patulin, leading to huge economic losses and food safety hazard. Set1 associated complex Set1/COMPASS deposits the methylation at lysine 4 of histone H3, which is associated with gene expression in diverse biological processes of fungi. However, the function and underlying mechanisms of Set1/COMPASS are poorly defined in P. expansum.

OBJECTIVES

The study aimed to identify Set1/COMPASS and investigate its regulation mechanisms on growth, pathogenicity, and patulin biosynthesis of P. expansum.

METHODS

Analyses of phylogenetic relationship, conserved structural domain, and gene deletion were used to identify components of Set1/COMPASS. Phenotype analysis and stress tolerance test of gene deletion mutants were conducted to analyze the function of these components. Yeast two-hybrid, Co-Immunoprecipitation (Co-IP), and point mutation were performed to verify the protein interaction. Western blot was conducted for detection of H3K4 methylation levels.

RESULTS

P. expansum owns six components of Set1/COMPASS besides PeSet1. Absence of each component resulted in reduction of H3K4 methylation levels and impaired growth, pathogenicity, and patulin biosynthesis, as well as altered stress responses of P. expansum. One component PeBre2p was found to interact with the conserved global regulator PeVelB (VelvetLike protein B) at Asp294 of PeBre2p. This interaction affected fungal growth and utilization of fructose, lactose, glycine, and proline in P. expansum.

CONCLUSION

This study revealed the important roles of Set1/COMPASS in P. expansum and clarified for the first time the combined regulation of PeBre2p and PeVelB in fungal growth and nutrition utilization. These results will provide potential targets for the control of blue mold disease.

PeAP1-mediated oxidative stress response plays an important role in the growth and pathogenicity of Penicillium expansum

Penicillium expansum is the causal agent of post-harvest blue mold in various fruits and serves as a model for understanding fungal pathogenicity and mycotoxin production. The relevance of oxidative stress response in the growth and virulence of P. expansum has been largely unexplored. Here, we identify the transcriptional factor PeAP1 as a regulator of oxidative stress response in P. expansum. Gene expression and protein abundance of PeAP1, as well as its nuclear localization, are specifically induced by H2O2. Deletion of PeAP1 results in increased sensitivity to H2O2, and PeAP1 mutants exhibit a variety of defects in hyphal growth and virulence. PeAP1 prevents the accumulation of both intracellular H2O2 during vegetative growth and host-derived H2O2 during biotrophic growth. Application of an antioxidant glutathione and a NADPH oxidase inhibitor, diphenylene iodonium, to the PeAP1 mutant partially restored fungal growth and virulence. RNA sequencing analysis revealed 144 H2O2-induced PeAP1 target genes, including four antioxidant-related genes, PeGST1, PePrx1, PePrx2, and PeTRX2, that were also demonstrated to be involved in oxidative stress response and/or virulence. Collectively, our results demonstrate the global regulatory role of PeAP1 in response to oxidative stress and provide insights into the critical role of the PeAP1-mediated oxidative stress response to regulate growth and virulence of P. expansum. IMPORTANCE Reactive oxygen species are the core of host plant defense and also play a vital role in the successful invasion of host plants by pathogenic fungi. Despite its importance, the relevance of oxidative stress response in fungal growth and virulence is poorly understood in P. expansum. In this study, we reveal that the transcription factor PeAP1 acts as a central regulator of oxidative stress response in P. expansum and that there is a major link between PeAP1-mediated oxidative stress response and fungal growth and virulence. To explore the underlying mechanisms, we performed comparative transcriptomic studies and identified a number of H2O2-induced PeAP1 target genes, including four novel ones, PePrx1, PePrx2, PeGST1, and PeTRX2, whose functions were linked to PeAP1 and pathogenicity. These findings provide novel insights into the regulation mechanism of PeAP1 on growth and virulence, which might offer promising targets for control of blue mold and patulin contamination.

Strategies for the Development of Industrial Fungal Producing Strains

The use of microorganisms in industry has enabled the (over)production of various compounds (e.g., primary and secondary metabolites, proteins and enzymes) that are relevant for the production of antibiotics, food, beverages, cosmetics, chemicals and biofuels, among others. Industrial strains are commonly obtained by conventional (non-GMO) strain improvement strategies and random screening and selection. However, recombinant DNA technology has made it possible to improve microbial strains by adding, deleting or modifying specific genes. Techniques such as genetic engineering and genome editing are contributing to the development of industrial production strains. Nevertheless, there is still significant room for further strain improvement. In this review, we will focus on classical and recent methods, tools and technologies used for the development of fungal production strains with the potential to be applied at an industrial scale. Additionally, the use of functional genomics, transcriptomics, proteomics and metabolomics together with the implementation of genetic manipulation techniques and expression tools will be discussed.

Ena Proteins Respond to PacC-Mediated pH Signaling Pathway and Play a Crucial Role in Patulin Biosynthesis

Penicillium expansum is a main producer of patulin that causes severe postharvest decay and food safety issues in the fruit industry. Development, pathogenicity, and patulin production of P. expansum are strongly influenced by the PacC-pH signaling pathway. Global transcription factor PacC regulates various fungal biological processes through a complicated molecular network. In the present study, three Ena family genes (PeEnas), PeEnaA, PeEnaB, and PeEnaC, as important downstream targets of PePacC, were identified in P. expansum. Deletion of PeEnaA, PeEnaB, and PeEnaC showed little effect on mycelial growth under alkaline or high salinity conditions, but double and triple deletion of these genes impaired the virulence of P. expansum on apple fruit. Notably, patulin biosynthesis of P. expansum was distinctly inhibited in the deletion mutants of PeEnas. PeEnas regulated expressions of the patulin gene cluster, AP1, CreA, Sge1, and Hog1 at the transcriptional level and played roles in maintaining membrane potential. Overexpression of PeEnaC in ΔPePacC restored the patulin production defect of ΔPePacC. Our results indicated that, as downstream targets of PePacC, the PeEna family proteins play a crucial role in patulin biosynthesis in P. expansum.

Ultrastructural observation and transcriptome analysis provide insights into mechanisms of Penicillium expansum invading apple wounds

Penicillium expansum is a pathogen causing enormous postharvest losses of fruits, especially apples. In this study, we first investigated the morphological changes of P. expansum within apple wounds during infectious process by microscopic observation. We found that conidia swelled and secreted potential hydrophobin in 4 h, germinated in 8 h, and finally formed conidiophores in 36 h, a critical control time point to prevent the second contamination of spores. We then compared the transcript accumulation of P. expansum in apple tissues and liquid culture at 12 h. In total, 3168 and 1318 up-regulated and down-regulated genes were identified. Among them, genes regarding the biosynthesis of substances such as ergosterol, organic acid, cell wall degrading enzymes, and patulin were induced in expression. Pathways were activated, including autophagy, the mitogen-activated protein kinase, and pectin degradation. Our findings provide insights into the lifestyle and the mechanisms of P. expansum invading apple fruits.

Current Insights in Fungal Importance-A Comprehensive Review

Besides plants and animals, the Fungi kingdom describes several species characterized by various forms and applications. They can be found in all habitats and play an essential role in the excellent functioning of the ecosystem, for example, as decomposers of plant material for the cycling of carbon and nutrients or as symbionts of plants. Furthermore, fungi have been used in many sectors for centuries, from producing food, beverages, and medications. Recently, they have gained significant recognition for protecting the environment, agriculture, and several industrial applications. The current article intends to review the beneficial roles of fungi used for a vast range of applications, such as the production of several enzymes and pigments, applications regarding food and pharmaceutical industries, the environment, and research domains, as well as the negative impacts of fungi (secondary metabolites production, etiological agents of diseases in plants, animals, and humans, as well as deteriogenic agents).

Immobilized short-chain dehydrogenase/reductase on Fe3O4 particles acts as a magnetically recoverable biocatalyst component in patulin bio-detoxification system

Patulin is one of the most important mycotoxins that contaminates fruit-derived products and causes acute or chronic toxicity in humans. In the present study, a novel patulin-degrading enzyme preparation was developed by taking a short-chain dehydrogenase/reductase and covalently linking it to dopamine/polyethyleneimine co-deposited magnetic Fe₃O₄ particles. Optimum immobilization provided 63% immobilization efficiency and 62% activity recovery. Moreover, the immobilization protocol substantially improved thermal and storage stabilities, proteolysis resistance, and reusability. Using reduced nicotinamide adenine dinucleotide phosphate as a cofactor, the immobilized enzyme exhibited a detoxification rate of 100% in phosphate-buffered saline and a detoxification rate of more than 80% in apple juice. The immobilized enzyme did not cause adverse effects on juice quality and could be magnetically separated quickly after detoxification to ensure convenient recycling. Moreover, it did not exhibit cytotoxicity against a human gastric mucosal epithelial cell line at a concentration of 100 mg/L. Consequently, the immobilized enzyme as a biocatalyst had the characteristics of high efficiency, stability, safety, and easy separation, establishing the first step in building a bio-detoxification system to control patulin contamination in juice and beverage products.

Aggressiveness and Patulin Production in Penicillium expansum Multidrug Resistant Strains with Different Expression Levels of MFS and ABC Transporters, in the Presence or Absence of Fludioxonil

Penicillium expansum is the most common postharvest pathogen of apple fruit, causing blue mold disease. Due to the extensive use of fungicides, strains resistant to multiple chemical classes have been selected. A previous study by our group proposed that the overexpression of MFS (major facilitator superfamily) and ABC (ATP binding cassette) transporters constitute an alternative resistance mechanism in Multi Drug resistant (MDR) strains of this pathogen. This study was initiated to determine two main biological fitness parameters of MDR strains: aggressiveness against apple fruit and patulin production. In addition, the expression pattern of efflux transporters and hydroxylase-encoding genes that belong to the patulin biosynthesis pathway, in the presence or absence of fludioxonil and under in vitro and in vivo conditions were investigated. Results showed that the MDR strains produced higher concentrations of patulin but showed a lower pathogenicity compared to the wild-type isolates. Moreover, expression analysis of patC, patM and patH genes indicated that the higher expression levels do not correlate with the detected patulin concentration. The selection of MDR strains in P. expansum populations and the fact that they produce more patulin, constitutes a serious concern not only for successful disease control but also for human health. The above-mentioned data represent the first report of MDR in P. expansum associated with its patulin-production ability and the expression level of patulin biosynthesis pathway genes.

Histone H3K4 Methyltransferase PeSet1 Regulates Colonization, Patulin Biosynthesis, and Stress Responses of Penicillium expansum

Fruit blue mold disease and patulin contamination caused by Penicillium expansum lead to huge economic losses and food safety concerns worldwide. Many genes have been proven to be involved in the regulation of pathogenic and toxigenic processes of P. expansum. Histone H3 lysine 4 (H3K4) methylation is well recognized for its association with chromatin regulation and gene transcription. However, it is not clear whether H3K4 methylation is related to infection and patulin biosynthesis in Penicillium. Here, we characterized PeSet1, which is responsible for H3K4me1/me2/me3 in P. expansum. The deletion of PeSet1 caused severe defects in hyphal growth, conidiation, colonization, patulin biosynthesis, and stress responses. Moreover, we demonstrated that PeSet1 is involved in the regulation of patulin biosynthesis by mediating the expression of patulin cluster genes and crucial global regulatory factors. Likewise, PeSet1 positively regulated key genes in β-1,3-glucan biosynthesis and the reactive oxygen species scavenging process to modulate cell wall integrity and oxidative stress responses, respectively. Collectively, we have proven for the first time the function of Set1 in patulin biosynthesis and the crucial role of Set1 in colonization and stress responses in P. expansum. IMPORTANCE Penicillium expansum is one of the most important plant fungal pathogens, which not only causes blue mold rot in various fruits, leading to huge decay losses, but also produces mycotoxin patulin, posing a threat to human health. Both pathogenesis and patulin biosynthesis in P. expansum are regulated by complex and sophisticated networks. We focused on the epigenetic modification and identified a conserved histone H3K4 methyltransferase PeSet1 in P. expansum. Our work revealed the important role of PeSet1 in growth, development, colonization, patulin production, and stress responses of P. expansum. In particular, we originally described the regulation of Set1 on patulin biosynthetic pathway. These findings will provide new targets for the prevention and control of blue mold disease and patulin contamination.

Comprehensive review on patulin and Alternaria toxins in fruit and derived products

Mycotoxins are toxic secondary metabolites produced by certain fungi, which can contaminate various food commodities, including fruits and their derived products. Patulin and Alternaria toxins are among the most commonly encountered mycotoxins in fruit and their derived products. In this review, the sources, toxicity, and regulations related to these mycotoxins, as well as their detection and mitigation strategies are widely discussed. Patulin is a mycotoxin produced mainly by the fungal genera Penicillium, Aspergillus, and Byssochlamys. Alternaria toxins, produced by fungi in the Alternaria genus, are another common group of mycotoxins found in fruits and fruit products. The most prevalent Alternaria toxins are alternariol (AOH) and alternariol monomethyl ether (AME). These mycotoxins are of concern due to their potential negative effects on human health. Ingesting fruits contaminated with these mycotoxins can cause acute and chronic health problems. Detection of patulin and Alternaria toxins in fruit and their derived products can be challenging due to their low concentrations and the complexity of the food matrices. Common analytical methods, good agricultural practices, and contamination monitoring of these mycotoxins are important for safe consumption of fruits and derived products. And Future research will continue to explore new methods for detecting and managing these mycotoxins, with the ultimate goal of ensuring the safety and quality of fruits and derived product supply.

Genetic Regulation of Mycotoxin Biosynthesis

Mycotoxin contamination in food poses health hazards to humans. Current methods of controlling mycotoxins still have limitations and more effective approaches are needed. During the past decades of years, variable environmental factors have been tested for their influence on mycotoxin production leading to elucidation of a complex regulatory network involved in mycotoxin biosynthesis. These regulators are putative targets for screening molecules that could inhibit mycotoxin synthesis. Here, we summarize the regulatory mechanisms of hierarchical regulators, including pathway-specific regulators, global regulators and epigenetic regulators, on the production of the most critical mycotoxins (aflatoxins, patulin, citrinin, trichothecenes and fumonisins). Future studies on regulation of mycotoxins will provide valuable knowledge for exploring novel methods to inhibit mycotoxin biosynthesis in a more efficient way.

Ultraviolet Applications to Control Patulin Produced by Penicillium expansum CMP-1 in Apple Products and Study of Further Patulin Degradation Products Formation and Toxicity

Patulin is a mycotoxin whose presence in apple-derived products and fruit juices is legally regulated, being its maximum limits established in the legislation of multiple countries. However, the management of contaminated batches is still an issue for producers. This investigation aims to evaluate ultraviolet light (254 nm, UV-C254nm) irradiation to find solutions that can be applied at different stages of the apple juice production chain. In this regard, 8.8 (UV-1) and 35.1 (UV-2) kJ m−2 treatments inactivated spores of Penicillium expansum CMP-1 on the surface of apples. Although the same treatments applied to wounded apples (either before the infection or after the infection, immediately or when the lesion had appeared) did not show any effect on the growth rate of P. expansum during storage (up to 14 days, at 4 or 25 °C), they reduced patulin content per lesion size in apples treated after the infection had occurred (patulin decreased from 2.24 (control) to 0.65 µg kg−1 cm−2 (UV-2 treated apples)). Additionally, the treatment of juice with patulin with ultraviolet light up to 450.6 kJ m−2 resulted in more than 98 % reduction of patulin. Degradation products of patulin after UV-C254nm treatments were tentatively identified by HPLC–MS, and toxicity and biological activities were assessed in silico, and results indicated that such products did not pose an increased risk when compared to patulin.

Comparative Penicillium spp. Transcriptomics: Conserved Pathways and Processes Revealed in Ungerminated Conidia and during Postharvest Apple Fruit Decay

Blue mold, caused by Penicillium spp., is an impactful postharvest disease resulting in significant economic losses due to reduced pome fruit quality and mycotoxin contamination. Using two Penicillium species with different levels of aggressiveness, transcriptomics were implemented in order to identify genes expressed during apple fruit decay and loci expressed in ungerminated conidia. Total RNA was isolated from ungerminated conidia and decayed apple fruit infected with P. expansum R19 or P. polonicum RS1. There were 2442 differentially expressed genes (DEGs) between the R19 and RS1 in apple. Comparisons within species between apple and conidia revealed 4404 DEGs for R19 and 2935 for RS1, respectively. Gene ontology (GO) analysis revealed differential regulation in fungal transport and metabolism genes during decay, suggesting a flux in nutrient acquisition and detoxification strategies. In R19, the oxidoreductase GO category comprised 20% of all DEG groups in apple verses conidia. Ungerminated conidia from both species showed DEGs encoding the glyoxylate shunt and beta-oxidation, specifying the earliest metabolic requirements for germination. This is the first study to identify pre-loaded transcripts in conidia from blue mold fungi, reveal unique genes between species expressed during apple decay, and show the expression dynamics of known fungal virulence factors. These findings will enable development of targeted approaches for blue mold abatement strategies.

Degradation of Patulin in Pear Juice and Apple Juice by Ascorbic Acid and the Combination of Ascorbic Acid and Ferrous Iron

Patulin (PAT) is a toxic secondary metabolite produced by certain species of Penicillium sp. and Aspergillus sp. on apples and pears. In this study, we investigated the effects of ascorbic acid and the combination of ascorbic acid and ferrous iron on degradation of PAT in 100% pure pear juice and apple juice using high-performance liquid chromatography UV detector (HPLC-UVD). The addition of 2 different levels of ascorbic acid (143 or 286 μg/mL) into pear juice or apple juice containing 0.08 or 0.4 μg/mL of PAT showed 87.7-100% and 67.3-68.7% of PAT degradation rates, respectively, after 24 h incubation at 25 °C. Moreover, the addition of both ascorbic acid (143 or 286 μg/mL) and ferrous iron (0.033 or 0.11 μmol/mL) into pear juice or apple juice containing the same level of PAT exhibited higher PAT degradation rates (100 and 75-94%, respectively) than the addition of only ascorbic acid after 24 h incubation at 25 °C. Our data demonstrated that ascorbic acid plus ferrous iron as well as ascorbic acid were highly effective on degradation of PAT in pear juice and apple juice and that addition of both ascorbic acid and ferrous iron produced higher PAT degradation rates than addition of only ascorbic acid.

Current Review of Mycotoxin Biodegradation and Bioadsorption: Microorganisms, Mechanisms, and Main Important Applications

Mycotoxins are secondary metabolites produced by fungi. Food/feed contamination by mycotoxins is a great threat to food safety. The contamination can occur along the food chain and can cause many diseases in humans and animals, and it also can cause economic losses. Many detoxification methods, including physical, chemical, and biological techniques, have been established to eliminate mycotoxins in food/feed. The biological method, with mycotoxin detoxification by microorganisms, is reliable, efficient, less costly, and easy to use compared with physical and chemical ones. However, it is important to discover the metabolite's toxicity resulting from mycotoxin biodegradation. These compounds can be less or more toxic than the parent. On the other hand, mechanisms involved in a mycotoxin's biological control remain still unclear. Mostly, there is little information about the method used by microorganisms to control mycotoxins. Therefore, this article presents an overview of the most toxic mycotoxins and the different microorganisms that have a mycotoxin detoxification ability. At the same time, different screening methods for degradation compound elucidation are given. In addition, the review summarizes mechanisms of mycotoxin biodegradation and gives some applications.

Modulating Activity Evaluation of Gut Microbiota with Versatile Toluquinol

Gut microbiota have important implications for health by affecting the metabolism of diet and drugs. However, the specific microbial mediators and their mechanisms in modulating specific key intermediate metabolites from fungal origins still remain largely unclear. Toluquinol, as a key versatile precursor metabolite, is commonly distributed in many fungi, including Penicillium species and their strains for food production. The common 17 gut microbes were cultivated and fed with and without toluquinol. Metabolic analysis revealed that four strains, including the predominant Enterococcus species, could metabolize toluquinol and produce different metabolites. Chemical investigation on large-scale cultures led to isolation of four targeted metabolites and their structures were characterized with NMR, MS, and X-ray diffraction analysis, as four toluquinol derivatives (1–4) through O1/O4-acetyl and C5/C6-methylsulfonyl substitutions, respectively. The four metabolites were first synthesized in living organisms. Further experiments suggested that the rare methylsulfonyl groups in 3–4 were donated from solvent DMSO through Fenton’s reaction. Metabolite 1 displayed the strongest inhibitory effect on cancer cells A549, A2780, and G401 with IC₅₀ values at 0.224, 0.204, and 0.597 μM, respectively, while metabolite 3 displayed no effect. Our results suggest that the dominant Enterococcus species could modulate potential precursors of fungal origin and change their biological activity.

Highly efficient removal of patulin using immobilized enzymes of Pseudomonas aeruginosa TF-06 entrapped in calcium alginate beads

Patulin is a toxic secondary metabolite produced by several moulds, which contaminates fruits and their products posing serious threats to human health. Though several microorganisms and enzymes have been reported to effectively degrade patulin, separation of them from fruit juice challenges the commercial applications. Here, a Pseudomonas aeruginosa strain TF-06 was isolated, its patulin degradation mechanism and optimum conditions for enzyme immobilization were investigated. The results indicated that TF-06 could degrade patulin into non-cytotoxic E/Z-ascladiol mainly by the activity of intracellular enzymes. For easy separation of enzymes, calcium alginate was selected for immobilization of intracellular enzymes from TF-06. The immobilized enzyme beads were effective in detoxification of patulin in apple juice. The mitigation rate was reached 95%, while there was no negative effect on juice quality. The study provides a promising way to resolve the issue of enzyme separation during mycotoxin biological detoxification in fruit juice.

Subcellular localization of fungal specialized metabolites

Fungal specialized metabolites play an important role in the environment and have impacted human health and survival significantly. These specialized metabolites are often the end product of a series of sequential and collaborating biosynthetic enzymes that reside within different subcellular compartments. A wide variety of methods have been developed to understand fungal specialized metabolite biosynthesis in terms of the chemical conversions and the biosynthetic enzymes required, however there are far fewer studies elucidating the compartmentalization of the same enzymes. This review illustrates the biosynthesis of specialized metabolites where the localization of all, or some, of the biosynthetic enzymes have been determined and describes the methods used to identify the sub-cellular localization.

More than a Virulence Factor: Patulin Is a Non-Host-Specific Toxin that Inhibits Postharvest Phytopathogens and Requires Efflux for Penicillium Tolerance

Mycotoxin contamination is a leading cause of food spoilage and waste on a global scale. Patulin, a mycotoxin produced by Penicillium spp. during postharvest pome fruit decay, causes acute and chronic effects in humans, withstands pasteurization, and is not eliminated by fermentation. While much is known about the impact of patulin on human health, there are significant knowledge gaps concerning the effect of patulin during postharvest fruit-pathogen interactions. Application of patulin on six apple cultivars reproduced some blue mold symptoms that were cultivar-independent and dose-dependent. Identical symptoms were also observed in pear and mandarin orange. Six Penicillium isolates exposed to exogenous patulin exhibited delayed germination after 24 h, yet all produced viable colonies in 7 days. However, four common postharvest phytopathogenic fungi were completely inhibited by patulin during conidial germination and growth, suggesting the toxin is important for Penicillium to dominate the postharvest niche. Using clorgyline, a broad-spectrum efflux pump inhibitor, we demonstrated that efflux plays a role in Penicillium auto-resistance to patulin during conidial germination. The work presented here contributes new knowledge of patulin auto-resistance, its mode of action, and inhibitory role in fungal-fungal interactions. Our findings provide a solid foundation to develop toxin and decay mitigation approaches.

Biosynthesis of fungal polyketides by collaborating and trans-acting enzymes

Covering: 1999 up to 2021Fungal polyketides encompass a range of structurally diverse molecules with a wide variety of biological activities. The giant multifunctional enzymes that synthesize polyketide backbones remain enigmatic, as do many of the tailoring enzymes involved in functional modifications. Recent advances in elucidating biosynthetic gene clusters (BGCs) have revealed numerous examples of fungal polyketide synthases that require the action of collaborating enzymes to synthesize the carbon backbone. This review will discuss collaborating and trans-acting enzymes involved in loading, extending, and releasing polyketide intermediates from fungal polyketide synthases, and additional modifications introduced by trans-acting enzymes demonstrating the complexity encountered when investigating natural product biosynthesis in fungi.

Impact of the antifungal protein PgAFP on the proteome and patulin production of Penicillium expansum on apple-based medium

Apples are prone to be contaminated with Penicillium expansum, which produces the mycotoxin patulin, posing a risk for human health. Antifungal treatments are required to control this fungal pathogen, although consumers demand products free of synthetic additives. Then, the use of antifungal proteins produced by moulds represents a novel and promising strategy. Although its inhibitory effect on P. expansum has been reported, the impact of these proteins on patulin production has been scarcely studied, pointing to a possible patulin overproduction. The aim of this work was to evaluate the effect of the antifungal protein PgAFP on the proteome and patulin biosynthesis of P. expansum grown in apple-based agar, intending to decipher these effects without the apple in vivo physiological response to the fungal infection. PgAFP increased the production of patulin on three of the five P. expansum strains evaluated. The proteome of the PgAFP-treated P. expansum showed five proteins involved in patulin biosynthesis in higher abundance (fold change 2.8-9.8), as well as proteins related to pathogenicity and virulence that suggest lower ability to infect fruits. Additionally, several proteins associated with oxidative stress, such as glutathione peroxidase, redoxin, or heat shock proteins were found in higher abundance, pointing to a response against oxidative stress elicited by PgAFP. These results provide evidence to be cautious in applying this antifungal protein in apples, being of utmost relevance to provide knowledge about the global response of P. expansum against an antifungal protein with many shared characteristics with others. These findings significantly contribute to future studies of assessment and suitability of not only these antifungal proteins but also new antifungal compounds.

Xylarins A-D, Two Pairs of Diastereoisomeric Isoindoline Alkaloids from the Endolichenic Fungus Xylaria sp

Two pairs of diastereoisomeric isoindoline alkaloids, xylarins A-D (1-4), were isolated from the endolichenic fungus Xylaria sp. Xylarins A and B (1 and 2) possess a previously undescribed 5/6/5-5/6 polycyclic scaffold, featuring a combination of a novel dihydrobenzofurone unit and an isoindoline unit, while xylarins C and D (3 and 4) contain an additional N,N-dimethylaniline at the C-3' position. Their structures were elucidated by comprehensive spectroscopic analyses combined with single-crystal X-ray diffraction and electronic circular dichroism calculations. The plausible biosynthetic pathways and gene clusters for 1-4 were proposed. Compound 1 exhibited significant antithrombotic activity.

Arginine Methyltransferase PeRmtC Regulates Development and Pathogenicity of Penicilliumexpansum via Mediating Key Genes in Conidiation and Secondary Metabolism

Penicillium expansum is one of the most common and destructive post-harvest fungal pathogens that can cause blue mold rot and produce mycotoxins in fruit, leading to significant post-harvest loss and food safety concerns. Arginine methylation by protein arginine methyltransferases (PRMTs) modulates various cellular processes in many eukaryotes. However, the functions of PRMTs are largely unknown in post-harvest fungal pathogens. To explore their roles in P. expansum, we identified four PRMTs (PeRmtA, PeRmtB, PeRmtC, and PeRmt2). The single deletion of PeRmtA, PeRmtB, or PeRmt2 had minor or no impact on the P. expansum phenotype while deletion of PeRmtC resulted in decreased conidiation, delayed conidial germination, impaired pathogenicity and pigment biosynthesis, and altered tolerance to environmental stresses. Further research showed that PeRmtC could regulate two core regulatory genes, PeBrlA and PeAbaA, in conidiation, a series of backbone genes in secondary metabolism, and affect the symmetric ω-N^G, N’^G-dimethylarginine (sDMA) modification of proteins with molecular weights of primarily 16–17 kDa. Collectively, this work functionally characterized four PRMTs in P. expansum and showed the important roles of PeRmtC in the development, pathogenicity, and secondary metabolism of P. expansum.

De novo biosynthesis and gram-level production of m-cresol in Aspergillus nidulans

The industrially important meta-cresol (m-cresol, 3-methylphenol) is mainly produced from fossil resources by chemical methods. The microbial production of m-cresol was rarely investigated. Herein, we constructed a platform for the overproduction of m-cresol in a modified fungus Aspergillus nidulans FGSC no. A1145∆ST∆EM, which gave a gram-level titer using starch as carbon resource. For the biosynthesis of m-cresol, the 6-methyl salicylic acid synthase (MSAS)-encoding gene patK and 6-methyl salicylic acid decarboxylase-encoding gene patG from A. clavatus were co-expressed in the host A. nidulans. Multiple strategies, including promotor engineering, gene multiplication, and fed-batch fermentation, were applied to raise the production of m-cresol, which resulted in the titers of 1.29 g/L in shaking flasks and 2.03 g/L in fed-batch culture. The chassis cell A. nidulans A1145∆ST∆EM was proved to possess better tolerance to m-cresol than yeast, as it could grow in the liquid medium containing up to 2.5 g/L of m-cresol. These results showed that A. nidulans has great potential to be further engineered for industrial production of m-cresol.Key points• m-Cresol was de novo biosynthesized by a fungal chassis cell Aspergillus nidulans.• Promoter engineering and gene multiplication implemented the fine-tuned genes expression.• The titer of m-cresol reached 2.03 g/L via fed-batch culture.

Effect of Ambient pH on Growth, Pathogenicity, and Patulin Production of Penicillium expansum

Penicillium expansum is an important postharvest pathogen of pomaceous fruit and a causal agent of blue mold or soft rot. In this study, we investigated the effect of ambient pH on growth, ultrastructure alteration, and pathogenicity of P. expansum, as well as accumulation of patulin and expression of genes involved in patulin biosynthesis. Under different pH, the fungus was routinely cultured and collected for growth, pathogenicity, patulin production, and gene expression studies using transmission electron microscopy, apple inoculation, HPLC, and RT-qPCR methods. Different ambient pH had significant impact on expression of genes and growth factors involved in patulin biosynthesis. Under same range of pH, gene expression profile, growth factors, and patulin accumulation (in vivo and in vitro) all showed similar changing trends. A well-developed cell was observed in addition to upregulation of genes at pH between pH 5.0 and 7.0, while the opposite was observed when pH was too basic (8.5) or too acid (2.5). Additionally, ambient pH had direct or indirect influence on expression of PecreaA, PelaeA, and PepacC. These findings will help in understanding the effect of ambient pH on growth, pathogenicity, and patulin production and support the development of successful methods for combating P. expansum infection on apple fruits.

PeMetR-mediated sulfur assimilation is essential for virulence and patulin biosynthesis in Penicillium expansum

Penicillium expansum, as the causal agent of blue mould and a main producer of mycotoxin patulin, is a global concern for economic and food safety. To date, the nutritional requirements of the pathogen during infection and patulin biosynthesis are poorly understood. Here, we genetically characterized the role of the bZIP transcription factor PeMetR in sulfur metabolism, virulence and patulin biosynthesis of P. expansum. The PeMetR regulator is crucial for normal germination and growth on inorganic S-sources but dispensable for utilization of organic S-sources. Accordingly, it is involved in regulating the expression of genes in sulfur assimilation pathway rather than methionine metabolic processes. Disruption of PeMetR resulted in a complete loss of virulence on various fruits. Additionally, the mutant showed a remarkably reduced ability to produce patulin. Exogenous methionine could partially or completely rescue the impaired phenotypes of the mutant. Inactivation of the sulfur assimilation pathway genes, PesA, PesB, PesC, PesF, generated growth, virulence and patulin production defects similar to those of ΔPeMetR. Overall, our study provides evidence that PeMetR-mediated sulfur assimilation is essential for growth and infection and shows for the first time that regulation of sulfur assimilation affects biosynthesis of an important mycotoxin patulin in P. expansum.

Aspergillus derived mycotoxins in food and the environment: Prevalence, detection, and toxicity

Aspergillus species are the paramount ubiquitous fungi that contaminate various food substrates and produce biochemicals known as mycotoxins. Aflatoxins (AFTs), ochratoxin A (OTA), patulin (PAT), citrinin (CIT), aflatrem (AT), secalonic acids (SA), cyclopiazonic acid (CPA), terrein (TR), sterigmatocystin (ST) and gliotoxin (GT), and other toxins produced by species of Aspergillus plays a major role in food and human health. Mycotoxins exhibited wide range of toxicity to the humans and animal models even at nanomolar (nM) concentration. Consumption of detrimental mycotoxins adulterated foodstuffs affects human and animal health even trace amounts. Bioaerosols consisting of spores and hyphal fragments are active elicitors of bronchial irritation and allergy, and challenging to the public health. Aspergillus is the furthermost predominant environmental contaminant unswervingly defile lives with a 40-90 % mortality risk in patients with conceded immunity. Genomics, proteomics, transcriptomics, and metabolomics approaches useful for mycotoxins' detection which are expensive. Antibody based detection of toxins chemotypes may result in cross-reactivity and uncertainty. Aptamers (APT) are single stranded DNA (ssDNA/RNA), are specifically binds to the target molecules can be generated by systematic evolution of ligands through exponential enrichment (SELEX). APT are fast, sensitive, simple, in-expensive, and field-deployable rapid point of care (POC) detection of toxins, and a better alternative to antibodies.

Patulin in food: A mycotoxin concern for human health and its management strategies

The mycotoxin patulin is primarily produced as a secondary metabolite by numerous fungal species and predominantly by Aspergillus, Byssochlamys, and Penicillium species. It is generally associated with fungal infected food materials. Penicillium expansum is considered the only fungal species liable for patulin contamination in pome fruits, especially in apples and apple-based products. This toxin in food poses serious health concerns and economic threat, which has aroused the need to adopt effective detection and mitigation strategies. Understanding its origin sources and biosynthetic mechanism stands essential for efficiently designing a management strategy against this fungal contamination. This review aims to present an updated outline of the sources of patulin occurrence in different foods and their biosynthetic mechanisms. It further provides information regarding the detrimental effects of patulin on human and agriculture as well as its effective detection, management, and control strategies.

Fungal Toxins and Host Immune Responses

Fungi are ubiquitous organisms that thrive in diverse natural environments including soils, plants, animals, and the human body. In response to warmth, humidity, and moisture, certain fungi which grow on crops and harvested foodstuffs can produce mycotoxins; secondary metabolites which when ingested have a deleterious impact on health. Ongoing research indicates that some mycotoxins and, more recently, peptide toxins are also produced during active fungal infection in humans and experimental models. A combination of innate and adaptive immune recognition allows the host to eliminate invading pathogens from the body. However, imbalances in immune homeostasis often facilitate microbial infection. Despite the wide-ranging effects of fungal toxins on health, our understanding of toxin-mediated modulation of immune responses is incomplete. This review will explore the current understanding of fungal toxins and how they contribute to the modulation of host immunity.

The Good, the Bad, and the Ugly: Mycotoxin Production During Postharvest Decay and Their Influence on Tritrophic Host-Pathogen-Microbe Interactions

Mycotoxins are a prevalent problem for stored fruits, grains, and vegetables. Alternariol, aflatoxin, and patulin, produced by Alternaria spp., Aspergillus spp., and Penicillium spp., are the major mycotoxins that negatively affect human and animal health and reduce fruit and produce quality. Control strategies for these toxins are varied, but one method that is increasing in interest is through host microbiome manipulation, mirroring a biocontrol approach. While the majority of mycotoxins and other secondary metabolites (SM) produced by fungi impact host–fungal interactions, there is also an interplay between the various organisms within the host microbiome. In addition to SMs, these interactions involve compounds such as signaling molecules, plant defense and growth hormones, and metabolites produced by both the plants and microbial community. Therefore, studies to understand the impact of the various toxins impacting the beneficial and harmful microorganisms that reside within the microbiome is warranted, and could lead to identification of safe analogs for antimicrobial activity to reduce fruit decay. Additionally, exploring the composition of the microbial carposphere of host plants is likely to shed light on developing a microbial consortium to maintain quality during storage and abate mycotoxin contamination.

Patulin and Trichothecene: characteristics, occurrence, toxic effects and detection capabilities via clinical, analytical and nanostructured electrochemical sensing/biosensing assays in foodstuffs

Patulin and Trichothecene as the main groups of mycotoxins in significant quantities can cause health risks from allergic reactions to death on both humans and animals. Accordingly, rapid and highly sensitive determination of these toxics agents is of great importance. This review starts with a comprehensive outlook regarding the characteristics, occurrence and toxic effects of Patulin and Trichothecene. In the following, numerous clinical and analytical approaches have been extensively discussed. The main emphasis of this review is placed on the utilization of novel nanomaterial based electrochemical sensing/biosensing tools for highly sensitive determination of Patulin and Trichothecene. Furthermore, a detailed and comprehensive comparison has been performed between clinical, analytical and sensing methods. Subsequently, the nanomaterial based electrochemical sensing platforms have been approved as reliable tools for on-site analysis of Patulin and Trichothecene in food processing and manufacturing industries. Different nanomaterials in improving the performance of detecting assays were investigated and have various benefits toward clinical and analytical methods. This paper would address the limitations in the current developments as well as the future challenges involved in the successful construction of sensing approaches with the functionalized nanomaterials and also allow exploring into core-research works regarding this area.

Diverse Taxonomies for Diverse Chemistries: Enhanced Representation of Natural Product Metabolism in UniProtKB

The UniProt Knowledgebase UniProtKB is a comprehensive, high-quality, and freely accessible resource of protein sequences and functional annotation that covers genomes and proteomes from tens of thousands of taxa, including a broad range of plants and microorganisms producing natural products of medical, nutritional, and agronomical interest. Here we describe work that enhances the utility of UniProtKB as a support for both the study of natural products and for their discovery. The foundation of this work is an improved representation of natural product metabolism in UniProtKB using Rhea, an expert-curated knowledgebase of biochemical reactions, that is built on the ChEBI (Chemical Entities of Biological Interest) ontology of small molecules. Knowledge of natural products and precursors is captured in ChEBI, enzyme-catalyzed reactions in Rhea, and enzymes in UniProtKB/Swiss-Prot, thereby linking chemical structure data directly to protein knowledge. We provide a practical demonstration of how users can search UniProtKB for protein knowledge relevant to natural products through interactive or programmatic queries using metabolite names and synonyms, chemical identifiers, chemical classes, and chemical structures and show how to federate UniProtKB with other data and knowledge resources and tools using semantic web technologies such as RDF and SPARQL. All UniProtKB data are freely available for download in a broad range of formats for users to further mine or exploit as an annotation source, to enrich other natural product datasets and databases.

Characterization of a short-chain dehydrogenase/reductase and its function in patulin biodegradation in apple juice

Biodegradation based on microbial enzymes is considered to be one of the promising ways for controlling patulin contamination. However, few patulin degrading enzymes have been isolated and characterized until now. Here, a short-chain dehydrogenase/reductase (SDR) gene, CgSDR, was cloned from a yeast strain Candida guilliermondii, and expressed in Escherichia coli. The expression of CgSDR conferred a strong patulin tolerance and degradation ability to E. coli, and purified CgSDR could transform patulin into E-ascladiol in vitro with NADPH as a coenzyme. Moreover, addition of CgSDR at 150 μg/mL could reduce 80% of patulin in apple juice and the biodegradation process did not affect the quality of the apple juice. A molecular docking analysis and site-directed mutagenesis indicated that CgSDR might interact with patulin via VAL188 as an active binding sites. The findings provide new insights for developing enzymic formulations for mycotoxin detoxification in fruit derived products.

Targeting mitochondrial metabolite transporters in Penicillium expansum for reducing patulin production

There is an increasing need of alternative treatments to control fungal infection and consequent mycotoxin accumulation in harvested fruits and vegetables. Indeed, only few biological targets of antifungal agents have been characterized and can be used for limiting fungal spread from decayed fruits/vegetables to surrounding healthy ones during storage. On this concern, a promising target of new antifungal treatments may be represented by mitochondrial proteins due to some species-specific functions played by mitochondria in fungal morphogenesis, drug resistance and virulence. One of the most studied mycotoxins is patulin produced by several species of Penicillium and Aspergillus genera. Patulin is toxic to many biological systems including bacteria, higher plants and animalia. Although precise biochemical mechanisms of patulin toxicity in humans are not completely clarified, its high presence in fresh and processed apple fruits and other apple-based products makes necessary developing a strategy for limiting its presence/accumulation. Patulin biosynthetic pathway consists of an enzymatic cascade, whose first step is represented by the synthesis of 6-methylsalicylic acid, obtained from the condensation of one acetyl-CoA molecule with three malonyl-CoA molecules. The most abundant acetyl-CoA precursor is represented by citrate produced by mitochondria. In the present investigation we report about the possibility to control patulin production through the inhibition of mitochondrial/peroxisome transporters involved in the export of acetyl-CoA precursors from mitochondria and/or peroxisomes, with specific reference to the predicted P. expansum mitochondrial Ctp1p, DTC, Sfc1p, Oac1p and peroxisomal PXN carriers.

Targeting Penicillium expansum GMC Oxidoreductase with High Affinity Small Molecules for Reducing Patulin Production

Simple Summary

With the urgent necessity of potential treatments for limiting mycotoxin production and postharvest fungal rots, we propose a combined in silico/in vitro/in vivo strategy for the rapid and effective identification of bioactive small molecules, chosen among a chemical library hosting approved drugs and phytochemicals, to be used after harvest. The molecular target of our analysis was the GMC oxidoreductase from Penicillium expansum involved in the biosynthesis of patulin, a mycotoxin that can contaminate many foods, especially fruits and fruit-based products. The employed in silico/in vitro/in vivo assays described in our study proved the effectiveness of our strategy and in particular of two small molecules, 6-hydroxycoumarin (structurally related to umbelliferon, an already characterized patulin synthase inhibitor) and meticrane (an already approved drug) in reducing patulin accumulation. Our findings highly recommend the mentioned ligands to be subjected to further analysis for being used in the next future in place of other more toxic compounds, in postharvest treatments based on dipping or drenching methods.

Abstract

Flavine adenine dinucleotide (FAD) dependent glucose methanol choline oxidoreductase (GMC oxidoreductase) is the terminal key enzyme of the patulin biosynthetic pathway. GMC oxidoreductase catalyzes the oxidative ring closure of (E)-ascladiol to patulin. Currently, no protein involved in the patulin biosynthesis in Penicillium expansum has been experimentally characterized or solved by X-ray diffraction. Consequently, nothing is known about P. expansum GMC oxidoreductase substrate-binding site and mode of action. In the present investigation, a 3D comparative model for P. expansum GMC oxidoreductase has been described. Furthermore, a multistep computational approach was used to identify P. expansum GMC oxidoreductase residues involved in the FAD binding and in substrate recognition. Notably, the obtained 3D comparative model of P. expansum GMC oxidoreductase was used for performing a virtual screening of a chemical/drug library, which allowed to predict new GMC oxidoreductase high affinity ligands to be tested in in vitro/in vivo assays. In vitro assays performed in presence of 6-hydroxycoumarin and meticrane, among the highly affinity predicted binders, confirmed a dose-dependent inhibition (17–81%) of patulin production by 6-hydroxycoumarin (10 µM–1 mM concentration range), whereas the approved drug meticrane inhibited patulin production by 43% already at 10 µM. Furthermore, 6-hydroxycoumarin and meticrane caused a 60 and 41% reduction of patulin production, respectively, in vivo on apples at 100 µg/wound.