Byssochlamys nivea with patulin-producing capability has an isoepoxydon dehydrogenase gene (idh) with sequence homology to Penicillium expansum and P. griseofulvum

Immunosuppressive effects of the mycotoxin patulin in macrophages

Patulin (PAT) is a fungi-derived secondary metabolite produced by numerous fungal species, especially within Aspergillus, Byssochlamys, and Penicillium genera, amongst which P. expansum is the foremost producer. Similar to other fungi-derived metabolites, PAT has been shown to have diverse biological features. Initially, PAT was used as an effective antimicrobial agent against Gram-negative and Gram-positive bacteria. Then, PAT has been shown to possess immunosuppressive properties encompassing humoral and cellular immune response, immune cell function and activation, phagocytosis, nitric oxide and reactive oxygen species production, cytokine release, and nuclear factor-κB and mitogen-activated protein kinases activation. Macrophages are a heterogeneous population of immune cells widely distributed throughout organs and connective tissue. The chief function of macrophages is to engulf and destroy foreign bodies through phagocytosis; this ability was fundamental to his discovery. However, macrophages play other well-established roles in immunity. Thus, considering the central role of macrophages in the immune response, we review the immunosuppressive effects of PAT in macrophages and provide the possible mechanisms of action.

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.

Paecilomyces Rot: A New Apple Disease

Paecilomyces niveus is an important food spoilage fungus that survives thermal processing in fruit products, where it produces the mycotoxin patulin. Spoilage of products has been attributed to soil contamination; however, little is known about the ecology of this organism. In this study, orchard soils and culled apple fruit were surveyed and the ability of P. niveus to infect apple was tested on two popular apple varieties. P. niveus was found in 34% of sampled orchard soils from across New York. Completing Koch's postulates, P. niveus was demonstrated to cause postharvest disease in Gala and Golden Delicious apple. Symptoms of this disease, named Paecilomyces rot, resemble several other apple diseases, including black rot, bitter rot, and bull's-eye rot. External symptoms of Paecilomyces rot include brown, circular, concentrically ringed lesions, with an internal rot that is firm and cone-shaped. Both Gala and Golden Delicious apple fruit inoculated with P. niveus developed lesions ≥43 mm in size at 22 days after inoculation. There is some evidence that the size of lesions and rate of infection differ between Gala and Golden Delicious, which may indicate differing resistance to P. niveus. This work shows that P. niveus is common in New York orchard soil and can cause a novel postharvest fruit disease. Whether infected fruit can serve as an overlooked source of inoculum in heat-processed apple products requires further study.

Apple Intrinsic Factors Modulating the Global Regulator, LaeA, the Patulin Gene Cluster and Patulin Accumulation During Fruit Colonization by Penicillium expansum

The mycotoxin patulin is produced in colonized tissue by Penicillium expansum during storage of apples and is significantly affected by environmental factors that contribute to its accumulation. Few reports have, however, examined the effect of natural intrinsic factors associated with the fruit on the production of patulin. Here, we find that with advancing maturity, Golden Delicious apples show increased concentrations of total soluble solids (TSS) from 14 to 17% associated with the increased expression of the global transcription factor involved in regulation of secondary metabolite biosynthesis in filamentous fungi, laeA expression and patulin accumulation. However, the apple cultivar Granny Smith, with similar TSS values but differing in pH levels and malic acid concentrations, showed reduced expression levels of laeA and the patulin biosynthesis gene cluster (pat genes) and patulin accumulation, suggesting a complexity of host factors contribution to patulin accumulation during P. expansum colonization. To start elucidating these apple intrinsic factors, we examined their in vitro impact on laeA and pat gene expression concomitant with patulin synthesis. Increasing sucrose concentrations from 15 to 175 mM repressed laeA and pat gene expression and patulin production. However, this affect was modified and often reversed and sometimes accentuated by changes in pH, or the addition of malic acid or the major apple phenolic compounds, chlorogenic acid and epicatechin. While the increase in malic acid from 0 to 1% increased laeA and pat gene expression, the decrease in pH from 3.5 to 2.5 reduced their expression. Also the increased laeA and pat genes expressions at increasing epicatechin concentrations from 0 to 1 mM, was reversed by increasing sucrose concentrations, all together suggesting the complexity of the interactions in vivo.

Lichen Biosynthetic Gene Clusters Part II: Homology Mapping Suggests a Functional Diversity

Lichens are renowned for their diverse natural products though little is known of the genetic programming dictating lichen natural product biosynthesis. We sequenced the genome of Cladonia uncialis and profiled its secondary metabolite biosynthetic gene clusters. Through a homology searching approach, we can now propose specific functions for gene products as well as the biosynthetic pathways that are encoded in several of these gene clusters. This analysis revealed that the lichen genome encodes the required enzymes for patulin and betaenones A-C biosynthesis, fungal toxins not known to be produced by lichens. Within several gene clusters, some (but not all) genes are genetically similar to genes devoted to secondary metabolite biosynthesis in Fungi. These lichen clusters also contain accessory tailoring genes without such genetic similarity, suggesting that the encoded tailoring enzymes perform distinct chemical transformations. We hypothesize that C. uncialis gene clusters have evolved by shuffling components of ancestral fungal clusters to create new series of chemical steps, leading to the production of hitherto undiscovered derivatives of fungal secondary metabolites.

Colonization of grapes berries and cider by potential producers of patulin

The aim of this study was to detect potential producers of mycotoxin patulin from grapes (berries, surface sterilized berries - endogenous mycobiota and grape juice) of Slovak origin. We analyzed 47 samples of grapes, harvested in 2011, 2012 and 2013 from various wine-growing regions. For the isolation of species we used the method of direct plating berries and surface-sterilized berries (using 1% freshly pre-pared chlorine) berries on DRBC (Dichloran Rose Bengal Chloramphenicol agar). For the determination of fungal contamination of grape juice we used plate-dilution method and DRBC and DG18 (Dichloran 18% Glycerol agar) as media. The cultivation in all modes of inoculation was carried at 25 ±1 °C, for 5 to 7 days. After incubation Aspergillus and Pencillium isolates were inoculated on the identification media. The potential producers of patulin were isolated from 23 samples berries, 19 samples of surface-sterilized berries and 6 samples of grape juice. Overall, the representatives of producers of patulin were detected in 32 (68.1%) samples (75 isolates). In this work we focused on the detection of potential producers of patulin, Penicillium expansum (the most important producer of patulin in fruits), Penicillium griseofulvum and Aspergillus clavatus were isolated. Chosen isolates of potential patulin producers were tested for the ability to produce relevant mycotoxins in in vitro conditions using thin layer chromatography method. The ability to produce patulin in in vitro condition was detected in 82% of isolates of Penicillium expansum, 65% of Penicillium griseofuvum and 100% of Aspergillus clavatus. Some isolates of Penicillium expansum were able to produce citrinin and roquefortine C, Penicillium griseofulvum cyclopiazonic acid, griseofulvin and roquefortin C, also.

Sequencing, physical organization and kinetic expression of the patulin biosynthetic gene cluster from Penicillium expansum

Patulin is a polyketide-derived mycotoxin produced by numerous filamentous fungi. Among them, Penicillium expansum is by far the most problematic species. This fungus is a destructive phytopathogen capable of growing on fruit, provoking the blue mold decay of apples and producing significant amounts of patulin. The biosynthetic pathway of this mycotoxin is chemically well-characterized, but its genetic bases remain largely unknown with only few characterized genes in less economic relevant species. The present study consisted of the identification and positional organization of the patulin gene cluster in P. expansum strain NRRL 35695. Several amplification reactions were performed with degenerative primers that were designed based on sequences from the orthologous genes available in other species. An improved genome Walking approach was used in order to sequence the remaining adjacent genes of the cluster. RACE-PCR was also carried out from mRNAs to determine the start and stop codons of the coding sequences. The patulin gene cluster in P. expansum consists of 15 genes in the following order: patH, patG, patF, patE, patD, patC, patB, patA, patM, patN, patO, patL, patI, patJ, and patK. These genes share 60-70% of identity with orthologous genes grouped differently, within a putative patulin cluster described in a non-producing strain of Aspergillus clavatus. The kinetics of patulin cluster genes expression was studied under patulin-permissive conditions (natural apple-based medium) and patulin-restrictive conditions (Eagle's minimal essential medium), and demonstrated a significant association between gene expression and patulin production. In conclusion, the sequence of the patulin cluster in P. expansum constitutes a key step for a better understanding of the mechanisms leading to patulin production in this fungus. It will allow the role of each gene to be elucidated, and help to define strategies to reduce patulin production in apple-based products.

Influence of package, type of apple juice and temperature on the production of patulin by Byssochlamys nivea and Byssochlamys fulva

Although the production of patulin in apple fruits is mainly by Penicillium expansum, there is no information on the ability of heat resistant moulds that may survive pasteurization to produce this mycotoxin in juice packages during storage and distribution. In this study, the production of patulin by Byssochlamys spp (Byssochlamys nivea FRR 4421, B. nivea ATCC 24008 and Byssochlamys fulva IOC 4518) in cloudy and clarified apple juices packaged in laminated paperboard packages or in polyethylene terephthalate bottles (PET) and stored at both 21 degrees C and 30 degrees C, was investigated. The three Byssochlamys strains were able to produce patulin in both cloudy and clarified apple juices. Overall, the lower the storage temperature, the lower the patulin levels and mycelium dry weight in the apple juices (p<0.05). The greatest variations in pH and degrees Brix were observed in the juices from which the greatest mycelium dry weights were recovered. The maximum levels of patulin recovered from the juices were ca. 150 microg/kg at 21 degrees C and 220 microg/kg at 30 degrees C. HPLC-UV, HPCL-DAD and mass spectrometry analyses confirmed the ability of B. fulva IOC 4518 to produce patulin. Due to the heat resistance of B. nivea and B. fulva and their ability to produce patulin either in PET bottles or in laminated paperboard packages, the control of contamination and the incidence of these fungi should be a matter of concern for food safety. Control measures taken by juice industries must also focus on controlling the ascospores of heat resistant moulds.

Biosynthesis and toxicological effects of patulin

Patulin is a toxic chemical contaminant produced by several species of mold, especially within Aspergillus, Penicillium and Byssochlamys. It is the most common mycotoxin found in apples and apple-derived products such as juice, cider, compotes and other food intended for young children. Exposure to this mycotoxin is associated with immunological, neurological and gastrointestinal outcomes. Assessment of the health risks due to patulin consumption by humans has led many countries to regulate the quantity in food. A full understanding of the molecular genetics of patulin biosynthesis is incomplete, unlike other regulated mycotoxins (aflatoxins, trichothecenes and fumonisins), although the chemical structures of patulin precursors are now known. The biosynthetic pathway consists of approximately 10 steps, as suggested by biochemical studies. Recently, a cluster of 15 genes involved in patulin biosynthesis was reported, containing characterized enzymes, a regulation factor and transporter genes. This review includes information on the current understanding of the mechanisms of patulin toxinogenesis and summarizes its toxicological effects.

A gene having sequence homology to isoamyl alcohol oxidase is transcribed during patulin production in Penicillium griseofulvum

The genes for the patulin biosynthetic pathway are most likely arranged in a cluster, as is often the case for other mycotoxins. With this in mind, GeneWalking has been performed to identify genes both upstream and downstream of the isoepoxydon dehydrogenase (idh) gene. A gene present in Penicillium griseofulvum NRRL 2159A had high sequence homology to the isoamyl alcohol oxidase (iao) gene and was detected downstream of the idh gene and in the same orientation. By virtue of the presence of a signal peptide sequence, the newly identified gene coded for a secreted protein with an FAD-binding domain and potential for N-glycosylation. An open reading frame consisted of 1946 nucleotides, containing four putative introns and encoding a 22 amino acid signal peptide. The 571 amino acid mature protein contained nine cysteine residues and had 11 potential N-linked glycosylation sites. Searches using GenBank indicated that Aspergillus terreus, A. oryzae, A. fumigatus, and Gibberella zeae contain genes coding for a putative isoamyl alcohol oxidase. When the translated query was compared with the translated database, the highest scores were seen with A. clavatus (E value of 0.00), A. fumigatus (E value of 8e(-142)), and A. oryzae and A. terreus (each having an E value of 2e(-141)). Reverse transcription-polymerase chain reaction analysis confirmed that the iao gene was transcribed. The amplified products were sequenced for confirmation of their identities. This is the first report of an isoamyl alcohol oxidase gene in a species of the genus Penicillium.

The inability of Byssochlamys fulva to produce patulin is related to absence of 6-methylsalicylic acid synthase and isoepoxydon dehydrogenase genes

Byssochlamys species are responsible for spoilage and degradation of fruits and silages. Under specific conditions they are able to produce mycotoxins. The aim of this study was to evaluate the potential of 19 different strains of Byssochlamys nivea and Byssochlamys fulva to produce patulin in relation with the presence of two genes involved in the patulin biosynthesis pathways in the genome of these fungal strains. The strains were characterized by macroscopic, microscopic examinations, internal transcribed spacer (ITS) rRNA and beta-tubulin fragment amplification and sequencing. All of the 8 B. nivea strains tested produced patulin. By contrast, none of the 11 strains of B. fulva produce this toxin. Two genes of the patulin biosynthetic pathway, a polyketide synthase (pks) and the isoepoxydon dehydrogenase (idh) were cloned from B. nivea. The deduced amino acid sequence of the polyketide synthase was 74% identical to the 6-methylsalicylic acid synthase gene of Penicillium griseofulvum and had the five functional domains characteristic of fungal type I polyketide synthases (beta-ketosynthase, acyltransferase, dehydratase, beta-ketoreductase and acyl carrier protein). The complete coding sequence of idh gene displayed after translation 88% of identity with P. griseofulvum IDH and 85% with P. expansum IDH, respectively. Both pks and idh messengers were strongly co-expressed during the production of 6-methylsalicylic acid and patulin. The presence of these genes was then investigated in the genome of B. nivea and B. fulva strains by PCR. All B. nivea strains possess the two genes, by contrast none of the B. fulva strains display these genes. The absence of 6-methylsalicylic acid and isoepoxydon dehydrogenase genes can explain the inability of B. fulva to produce patulin. In conclusion, B. fulva don't seem to be responsible for the occurrence of patulin by lack of genes.

The sequence of the isoepoxydon dehydrogenase gene of the patulin biosynthetic pathway in Penicillium species

Interest in species of the genus Penicillium is related to their ability to produce the mycotoxin patulin and to cause spoilage of fruit products worldwide. The sequence of the isoepoxydon dehydrogenase (idh) gene, a gene in the patulin biosynthetic pathway, was determined for 28 strains representing 12 different Penicillium species known to produce the mycotoxin patulin. Isolates of Penicillium carneum, Penicillium clavigerum, Penicillium concentricum, Penicillium coprobium, Penicillium dipodomyicola, Penicillium expansum, Penicillium gladioli, Penicillium glandicola, Penicillium griseofulvum, Penicillium paneum, Penicillium sclerotigenum and Penicillium vulpinum were compared. Primer pairs for DNA amplification and sequencing were designed from the P. griseofulvum idh gene (GenBank AF006680). The two introns present were removed from the nucleotide sequences, which were translated to produce the IDH sequences of the 12 species for comparison. Phylogenetic relationships among the species were determined from rDNA (ITS1, 5.8 S, ITS2 and partial sequence of 28S rDNA) and from the idh nucleotide sequences minus the two introns. Maximum parsimony analysis showed trees based on rDNA and idh sequences to be congruent. It is anticipated that the genetic information obtained in the present study will aid in the design of probes, specific for patulin biosynthetic pathway genes, to identify the presence of these mycotoxigenic fungi.