Study on the role of patulin on pathogenicity and virulence of Penicillium expansum

Transcriptomic investigation of the interaction between a biocontrol yeast, Papiliotrema terrestris strain PT22AV, and the postharvest fungal pathogen Penicillium expansum on apple

Biocontrol strategies offer a promising alternative to control plant pathogens achieving food safety and security. In this study we apply a RNAseq analysis during interaction between the biocontrol agent (BCA) Papiliotrema terrestris, the pathogen Penicillium expansum, and the host Malus domestica. Analysis of the BCA finds overall 802 upregulated DEGs (differentially expressed genes) when grown in apple tissue, with the majority being involved in nutrients uptake and oxidative stress response. This suggests that these processes are crucial for the BCA to colonize the fruit wounds and outcompete the pathogen. As to P. expansum analysis, 1017 DEGs are upregulated when grown in apple tissue, with the most represented GO categories being transcription, oxidation reduction process, and transmembrane transport. Analysis of the host M. domestica finds a higher number of DEGs in response to the pathogen compared to the BCA, with overexpression of genes involved in host defense signaling pathways in the presence of both of them, and a prevalence of pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) only during interaction with P. expansum. This analysis contributes to advance the knowledge on the molecular mechanisms that underlie biocontrol activity and the tritrophic interaction of the BCA with the pathogen and the host.

The Influence of Long-Term Storage on the Epiphytic Microbiome of Postharvest Apples and on Penicillium expansum Occurrence and Patulin Accumulation

Patulin is a secondary metabolite primarily synthesized by the fungus Penicillium expansum, which is responsible for blue mold disease on apples. The latter are highly susceptible to fungal infection in the postharvest stages. Apples destined to produce compotes are processed throughout the year, which implies that long periods of storage are required under controlled atmospheres. P. expansum is capable of infecting apples throughout the whole process, and patulin can be detected in the end-product. In the present study, 455 apples (organically and conventionally grown), destined to produce compotes, of the variety "Golden Delicious" were sampled at multiple postharvest steps. The apple samples were analyzed for their patulin content and P. expansum was quantified using real-time PCR. The patulin results showed no significant differences between the two cultivation techniques; however, two critical control points were identified: the long-term storage and the deck storage of apples at ambient temperature before transport. Additionally, alterations in the epiphytic microbiota of both fungi and bacteria throughout various steps were investigated through the application of a metabarcoding approach. The alpha and beta diversity analysis highlighted the effect of long-term storage, causing an increase in the bacterial and fungal diversity on apples, and showed significant differences in the microbial communities during the different postharvest steps. The different network analyses demonstrated intra-species relationships. Multiple pairs of fungal and bacterial competitive relationships were observed. Positive interactions were also observed between P. expansum and multiple fungal and bacterial species. These network analyses provide a basis for further fungal and bacterial interaction analyses for fruit disease biocontrol.

New insights into searching patulin degrading enzymes in Saccharomyces cerevisiae through proteomic and molecular docking analysis

Global warming has increased the contamination of mycotoxins. Patulin (PAT) is a harmful contaminant that poses a serious threat to food safety and human health. Saccharomyces cerevisiae biodegrades PAT by its enzymes during fermentation, which is a safe and efficient method of detoxification. However, the key degradation enzymes remain unclear. In this study, the proteomic differences of Saccharomyces cerevisiae under PAT stress were investigated. The results showed that the proteins involved in redox reactions and defense mechanisms were significantly up-regulated to resist PAT stress. Subsequently, molecular docking was used to virtual screen for degrading enzymes. Among 18 proteins, YKL069W showed the highest binding affinity to PAT and was then expressed in Escherichia coli, where the purified YKL069W completely degraded 10 μg/mL PAT at 48 h. YKL069W was demonstrated to be able to degrade PAT into E-ascladiol. Molecular dynamics simulations confirmed that YKL069W was stable in catalyzing PAT degradation with a binding free energy of - 7.5 kcal/mol. Furthermore, it was hypothesized that CYS125 and CYS101 were the key amino acid residues for degradation. This study offers new insights for the rapid screening and development of PAT degrading enzymes and provides a theoretical basis for the detoxification of mycotoxins.

WSC1 Regulates the Growth, Development, Patulin Production, and Pathogenicity of Penicillium expansum Infecting Pear Fruits

In this study, the role of WSC1 in the infection of pear fruit by Penicillium expansum was investigated. The WSC1 gene was knocked out and complemented by Agrobacterium-mediated homologous recombination technology. Then, the changes in growth, development, and pathogenic processes of the knockout mutant and the complement mutant were analyzed. The results indicated that deletion of WSC1 slowed the growth rate, reduced the mycelial and spore yield, and reduced the ability to produce toxins and pathogenicity of P. expansum in pear fruits. At the same time, the deletion of WSC1 reduced the tolerance of P. expansum to cell wall stress factors, enhanced antioxidant capacity, decreased hypertonic sensitivity, decreased salt stress resistance, and was more sensitive to most metal ions. Our results confirmed that WSC1 plays an important role in maintaining cell wall integrity and responding to stress, toxin production, and the pathogenicity of P. expansum.

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.

Modulation of extracellular Penicillium expansum-driven acidification by Papiliotrema terrestris affects biosynthesis of patulin and has a possible role in biocontrol activity

The active regulation of extracellular pH is critical for the virulence of fungal pathogens. Penicillium expansum is the causal agent of green-blue mold on stored pome fruits and during its infection process acidifies the host tissues by secreting organic acids. P. expansum is also the main producer of patulin (PAT), a mycotoxin found in pome fruit-based products and that represents a serious health hazard for its potential carcinogenicity. While it is known that PAT biosynthesis in P. expansum is regulated by nutritional factors such as carbon and nitrogen and by the pH, the mechanistic effects of biocontrol on PAT production by P. expansum are not known. In this work, we assessed how optimal and suboptimal concentrations of the biocontrol agent (BCA) Papiliotrema terrestris LS28 affect both extracellular pH and PAT biosynthesis in P. expansum. In wounded apples, the optimal and suboptimal concentrations of the BCA provided almost complete and partial protection from P. expansum infection, respectively, and reduced PAT contamination in both cases. However, the suboptimal concentration of the BCA increased the specific mycotoxigenic activity by P. expansum. In vitro, the rate of PAT biosynthesis was strictly related to the extracellular pH, with the highest amount of PAT detected in the pH range 4–7, whereas only traces were detectable at pH 3. Moreover, both in vitro and in apple wounds the BCA counteracted the extracellular P. expansum-driven acidification maintaining extracellular pH around 4, which is within the pH range that is optimal for PAT biosynthesis. Conversely, in the absence of LS28 the pathogen-driven acidification led to rapidly achieving acidic pH values (<3) that lie outside of the optimal pH range for PAT biosynthesis. Taken together, these results suggest that pH modulation by LS28 is important to counteract the host tissue acidification and, therefore, the virulence of P. expansum. On the other hand, the buffering of P. expansum-driven acidification provided by the BCA increases the specific rate of PAT biosynthesis through the extension of the time interval at which the pH value lies within the optimal range for PAT biosynthesis. Nevertheless, the antagonistic effect provided by the BCA greatly reduced the total amount of PAT.

Epigenetic Modification: A Key Tool for Secondary Metabolite Production in Microorganisms

Microorganisms are stupendous source of secondary metabolites, having significant pharmaceutical and industrial importance. Genome mining has led to the detection of several cryptic metabolic pathways in the natural producer of secondary metabolites (SMs) such as actinobacteria and fungi. Production of these bioactive compounds in considerable amount is, however, somewhat challenging. This led to the search of using epigenetics as a key mechanism to alter the expression of genes that encode the SMs toward higher production in microorganisms. Epigenetics is defined as any heritable change without involving the changes in the underlying DNA sequences. Epigenetic modifications include chromatin remodeling by histone posttranslational modifications, DNA methylation, and RNA interference. Biosynthetic gene cluster for SMs remains in heterochromatin state in which the transcription of constitutive gene is regulated by epigenetic modification. Therefore, small-molecule epigenetic modifiers, which promote changes in the structure of chromatin, could control the expression of silent genes and may be rationally employed for discovery of novel bioactive compounds. This review article focuses on the types of epigenetic modifications and their impact on gene expression for enhancement of SM production in microorganisms.

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.

Involvement of caspase in patulin-induced hepatotoxicity in vitro and in vivo

Patulin (PAT) a kind of mycotoxin, is a widely disseminated mycotoxin found in agricultural products and could cause liver damage. However, evidence on the underlying mechanisms of patulin is still lacking. In the present study, Human liver cancer cells (HepG2) together with a mouse model were used to explore the possible effect and mechanism. The results demonstrated that PAT treatment inhibited cell proliferation and caused liver toxicity in mice. In vitro, PAT inhibited the growth of HepG2 cells in a dose-dependent manner and a time-dependent manner; lipid peroxidation, malondialdehyde (MDA) production increased and the level of SOD and GSH in cells changed significantly. In vivo, Kunming mice were treated with PAT(2.5-15 μM), We indicated that liver damage are observed. The activity of serum alanine transaminase (ALT) and aspartate transaminase (AST) were increased significantly, the hepatocyte nucleus stained with Hematoxylin and Eosin (HE) was blurred and deformed. we also explored the lipid peroxidation and enzymes related to redox and found that the activities of SOD in animals do not change significantly, not like that in cells, while GSHpx played a major role. In addition, we measured the caspase activity of cells and the expression of caspase in mice. PAT-induced the caspase cascade was confirmed with the elevation of the activity and expression of caspase. These data suggest that PAT treatment altered both the redox systems in cells and animals. involvement of caspase in patulin-induced hepatotoxicity.

Control of Penicillium expansum by an Epiphytic Basidiomycetous Yeast

Postharvest biocontrol agents are considered a viable alternative to the use of synthetic chemicals as demonstrated by extensive research conducted by scientists and companies worldwide. In the present investigation, the biocontrol potential of a carotenoid-producing basidiomycetous yeast isolated from table grape flowers was analyzed. The strain RY1 proved to be Sporobolomyces roseus. In vitro and in vivo tests were conducted to assess its efficacy against Penicillium expansum, one of the most important postharvest pathogens and producer of the mycotoxin patulin. The yeast proved to control both fungal growth and patulin production, and, in addition, to greatly affect disease incidence and severity on apples. Its mode of action is presumably related both to the competition for nutrients and the production of antifungal volatiles. As such, although further large-scale trials are needed, our S. roseus strain represents a potential interesting biocontrol agent to be applied after harvest.

Recent advances in Penicillium expansum infection mechanisms and current methods in controlling P. expansum in postharvest apples

One of the most significant challenges associated with postharvest apple deterioration is the blue mold caused by Penicillium expansum, which leads to considerable economic losses to apple production industries. Apple fruits are susceptible to mold infection owing to their high nutrient and water content, and current physical control methods can delay but cannot completely inhibit P. expansum growth. Biological control methods present promising alternatives; however, they are not always cost effective and have application restrictions. P. expansum infection not only enhances disease pathogenicity, but also inhibits the expression of host-related defense genes. The implementation of new ways to investigate and control P. expansum are expected with the advent of omics technology. Advances in these techniques, together with molecular biology approaches such as targeted gene deletion and whole genome sequencing, will lead to a better understanding of the P. expansum infectious machinery. Here, we review the progress of research on the blue mold disease caused by P. expansum in apples, including physiological and molecular infection mechanisms, as well as various methods to control this common plant pathogen.

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.

Pichia anomala Induced With Chitosan Triggers Defense Response of Table Grapes Against Post-harvest Blue Mold Disease

To study the mechanism by which Pichia anomala induced with chitosan (1% w/v) controls blue mold disease in table grapes caused by Penicillium expansum, this study evaluated alterations in three yeast enzymatic activities. The changes in the five primary disease defense-related enzymes and two non-enzyme activities of table grapes were assayed. The results of the study showed that chitosan (1% w/v) significantly increased the yeast β-1,3-glucanase, catalase (CAT), and malondialdehyde (MDA) activities. Furthermore, P. anomala alone or induced with chitosan (1% w/v) significantly increased the table grapes enzymatic activities of Polyphenol oxidase (PPO), phenylalanine (PAL), peroxidase (POD), and catalase (CAT) compared to the control. The RT-qPCR results also confirmed that the genes of these major disease defense enzymes were up-regulated when the table grapes were treated with P. anomala. The highest results were recorded when the fruit was treated by yeast induced with chitosan (1% w/v). The phenolic compounds, in addition to their nutritional value, can also increase the antimicrobial properties of table grapes. The current experiment determined that the total phenol and flavonoid contents of table grapes showed the highest results for fruits treated by P. anomala induced with chitosan compared with the control. Generally, the increment of these fruit enzymatic and non-enzymatic activities shows improved table grape defense against the pathogenic fungus. The induction of the yeast with chitosan also increases its bio-control efficacy against the pathogen. This study will enable future detailed investigation in the yeast pathogen control mechanisms and the use of yeasts as bio-pesticides.

New Isolated Metschnikowia pulcherrima Strains from Apples for Postharvest Biocontrol of Penicillium expansum and Patulin Accumulation

Wild yeasts isolated from the surface of apples were screened for antagonistic activity against Penicillium expansum, the main producer of the mycotoxin patulin. Three antagonistic yeasts (Y33, Y29 and Y24) from a total of 90 were found to inhibit P. expansum growth. Identification by ITS region sequence and characterization showed that three selected isolates of yeast should be different strains of Metschnikowia pulcherrima. Several concentrations of the selected yeasts were used to study their in vitro antifungal effectivity against P. expansum on Petri dishes (plates with 63.6 cm² surface) whereas their potential activity on patulin reduction was studied in liquid medium. Finally, the BCA that had the best in vitro antifungal capacity against P. and the best patulin degradation capacity was selected to be assessed directly on apples. All the selected strains demonstrated antifungal activity in vitro but the most efficient was the strain Y29. Isolated strains were able to reduce patulin content in liquid medium, Y29 being the only strain that completely reduced patulin levels within 120 h. The application of Y29 as biocontrol agent on the surface of apples inoculated with P. expansum, inhibited fungal growth and patulin production during storage. Therefore, the results shown that this yeast strain could be used for the reduction of P. expansum and its mycotoxin in apples or apple-based products by adapting the procedure application.

Phenotypic features and molecular study of airborne Penicillium species isolated in the northern part of the Persian Gulf, Bushehr, Iran

BACKGROUND AND PURPOSE

The main environmental saprobes, such as Penicillium, play an essential role in natural ecosystems as economically, ecologically, and medically important microorganisms. Biodiversity of this genus has not been described in Bushehr city, Iran. The present study is based on air biodiversity of Penicillium species on culture-dependent approach and culture-independent technique using partial b-tubulin sequences.

MATERIALS AND METHODS

By using active sampling with a high volume air sampler, a total of 157 Penicillium isolates were selected and screened for phenotypic characters. For the purposes of the study, 46 strains representative of 11 morphological species were selected and identified by molecular analysis.

RESULTS

Based on the findings, P. crustosum (18 isolates, 39.1%) and P. chrysogenum (15 isolates, 32.6%) were the most common isolated species, followed by P. brevicompactum, P. rubens, P. citrinum, P. italicum (each 2 isolates, 4.3%), P. olsonii, P. expansum, P. griseofulvum, P. palitans, and P. polonicum (each 1 isolate, 2.1%). Except for P. chrysogenum and P. expansum with floccose colony texture, the rest of the isolated species had velutinous texture.

CONCLUSION

This is the first report in southern Iran to identify a large number of Penicillium strains isolated from air samples, showing P. crustosum and P. chrysogenum as the most common isolated species.

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.

Microbiome Status of Cider-Apples, from Orchard to Processing, with a Special Focus on Penicillium expansum Occurrence and Patulin Contamination

Patulin is a secondary metabolite produced primarily by the fungus Penicillium expansum, responsible for the blue mold disease on apples. It is found in apple products including apple cider when apple juice is added after fermentation. In the present study, two hundred and twenty-five cider-apples of the variety “Bedan”, cultivated in Brittany in France, were sampled from the orchard during harvesting until the storage step, right before processing. The patulin analysis on these samples reported a low contamination at the orchard and a significantly higher-level of contamination in the cider-apples starting from the transporting bin. The percentage of positive samples increased from 6% to 47% after 12 h in the harvesting bin before transporting and reached 95% after 24 h of transporting, decreasing then to 69% at the end of the storage. Penicillium expansum was quantified on the surface of apples using real-time PCR and was observed to be mostly consistent between the harvest and post-harvest steps. It was detected on average, on the surface of 85% of all sampled apples with a mean value around 2.35 × 10⁶Penicillium expansum DNA/g of apple. Moreover, the changes in the fungal and bacterial epiphytic microbiota in the different steps were studied using a metabarcoding approach. The alpha and beta diversity analysis revealed the presence of unique and more diverse bacterial and fungal communities on the surface of apples picked from the orchard compared to the rest of the sampling steps. Potential indigenous biological control agents were identified on the surface of sampled apples. Future perspective includes developing actions of prevention and control of the contamination by Penicillium expansum during the harvest and along the various critical post-harvest stages before transformation in a sustainable development concern.

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.

Cinnamon Oil Inhibits Penicillium expansum Growth by Disturbing the Carbohydrate Metabolic Process

Penicillium expansum is a major postharvest pathogen that mainly threatens the global pome fruit industry and causes great economic losses annually. In the present study, the antifungal effects and potential mechanism of cinnamon oil against P. expansum were investigated. Results indicated that 0.25 mg L⁻¹ cinnamon oil could efficiently inhibit the spore germination, conidial production, mycelial accumulation, and expansion of P. expansum. In addition, it could effectively control blue mold rots induced by P. expansum in apples. Cinnamon oil could also reduce the expression of genes involved in patulin biosynthesis. Through a proteomic quantitative analysis, a total of 146 differentially expressed proteins (DEPs) involved in the carbohydrate metabolic process, most of which were down-regulated, were noticed for their large number and functional significance. Meanwhile, the expressions of 14 candidate genes corresponding to DEPs and the activities of six key regulatory enzymes (involving in cellulose hydrolyzation, Krebs circle, glycolysis, and pentose phosphate pathway) showed a similar trend in protein levels. In addition, extracellular carbohydrate consumption, intracellular carbohydrate accumulation, and ATP production of P. expansum under cinnamon oil stress were significantly decreased. Basing on the correlated and mutually authenticated results, we speculated that disturbing the fungal carbohydrate metabolic process would be partly responsible for the inhibitory effects of cinnamon oil on P. expansum growth. The findings would provide new insights into the antimicrobial mode of cinnamon oil.

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.

Penicillium expansum: biology, omics, and management tools for a global postharvest pathogen causing blue mould of pome fruit

Blue mould, caused primarily by Penicillium expansum, is a major threat to the global pome fruit industry, causing multimillion-dollar losses annually. The blue mould fungus negatively affects fruit quality, thereby reducing fresh fruit consumption, and significantly contributes to food loss. P. expansum also produces an array of mycotoxins that are detrimental to human health. Management options are limited and the emergence of fungicide-resistant Penicillium spp. makes disease management difficult, therefore new approaches and tools are needed to combat blue mould in storage. This species profile comprises a comprehensive literature review of this aggressive pathogen associated with pomes (apple, pear, quince), focusing on biology, mechanisms of disease, control, genomics, and the newest developments in disease management.

TAXONOMY

Penicillium expansum Link 1809. Domain Eukaryota, Kingdom Fungi, Phylum Ascomycota, Subphylum Pezizomycotina, Class Eurotiomycetes, Subclass: Eurotiomycetidae, Order Eurotiales; Family Trichocomaceae, Genus Penicillium, Species expansum.

BIOLOGY

A wide host range necrotrophic postharvest pathogen that requires a wound (e.g., stem pull, punctures, bruises, shoulder cracks) or natural openings (e.g., lenticel, stem end, calyx sinus) to gain ingress and infect.

TOXINS

Patulin, citrinin, chaetoglobosins, communesins, roquefortine C, expansolides A and B, ochratoxin A, penitrem A, rubratoxin B, and penicillic acid.

HOST RANGE

Primarily apples, European pear, Asian pear, medlar, and quince. Blue mould has also been reported on stone fruits (cherry, plum, peach), small fruits (grape, strawberry, kiwi), and hazel nut.

DISEASE SYMPTOMS

Blue mould initially appears as light tan to dark brown circular lesions with a defined margin between the decayed and healthy tissues. The decayed tissue is soft and watery, and blue-green spore masses appear on the decayed area, starting at the infection site and radiating outward as the decayed area ages.

DISEASE CONTROL

Preharvest fungicides with postharvest activity and postharvest fungicides are primarily used to control decay. Orchard and packinghouse sanitation methods are also critical components of an integrated pest management strategy.

USEFUL WEBSITES

Penn State Tree Fruit Production Guide (https://extension.psu.edu/forage-and-food-crops/fruit), Washington State Comprehensive Tree Fruit (http://treefruit.wsu.edu/crop-protection/disease-management/blue-mold/), The Apple Rot Doctor (https://waynejurick.wixsite.com/applerotdr), penicillium expansum genome sequences and resources (https://www.ncbi.nlm.nih.gov/genome/browse/#!/eukaryotes/11336/).

The brlA Gene Deletion Reveals That Patulin Biosynthesis Is Not Related to Conidiation in Penicillium expansum

Dissemination and survival of ascomycetes is through asexual spores. The brlA gene encodes a C2H2-type zinc-finger transcription factor, which is essential for asexual development. Penicillium expansum causes blue mold disease and is the main source of patulin, a mycotoxin that contaminates apple-based food. A P. expansum PeΔbrlA deficient strain was generated by homologous recombination. In vivo, suppression of brlA completely blocked the development of conidiophores that takes place after the formation of coremia/synnemata, a required step for the perforation of the apple epicarp. Metabolome analysis displayed that patulin production was enhanced by brlA suppression, explaining a higher in vivo aggressiveness compared to the wild type (WT) strain. No patulin was detected in the synnemata, suggesting that patulin biosynthesis stopped when the fungus exited the apple. In vitro transcriptome analysis of PeΔbrlA unveiled an up-regulated biosynthetic gene cluster (PEXP_073960-PEXP_074060) that shares high similarity with the chaetoglobosin gene cluster of Chaetomium globosum. Metabolome analysis of PeΔbrlA confirmed these observations by unveiling a greater diversity of chaetoglobosin derivatives. We observed that chaetoglobosins A and C were found only in the synnemata, located outside of the apple, whereas other chaetoglobosins were detected in apple flesh, suggesting a spatial-temporal organization of the chaetoglobosin biosynthesis pathway.

Elaborated regulation of griseofulvin biosynthesis in Penicillium griseofulvum and its role on conidiation and virulence

Penicilium griseofulvum, the causal agent of apple blue mold, is able to produce in vitro and on apple a broad spectrum of secondary metabolites (SM), including patulin, roquefortine C and griseofulvin. Among them, griseofulvin is known for its antifungal and antiproliferative activity, and has received interest in many sectors, from medicine to agriculture. The biosynthesis of SM is finely regulated by filamentous fungi and can involve global regulators and pathway specific regulators, which are usually encoded by genes present in the same gene cluster as the backbone gene and tailoring enzymes. In the griseofulvin gene cluster, two putative transcription factors were previously identified, encoded by genes gsfR1 and gsfR2, and their role has been investigated in the present work. Analysis of P. griseofulvum knockout mutants lacking either gene suggest that gsfR2 forms part of a different pathway and gsfR1 exhibits many spectra of action, acting as regulator of griseofulvin and patulin biosynthesis and influencing conidia production and virulence on apple. The analysis of gsfR1 promoter revealed that the regulation of griseofulvin biosynthesis is also controlled by global regulators in response to many environmental stimuli, such as carbon and nitrogen. The influence of carbon and nitrogen on griseofulvin production was further investigated and verified, revealing a complex network of response and confirming the central role of gsfR1 in many processes in P. griseofulvum.

Citrus Postharvest Green Mold: Recent Advances in Fungal Pathogenicity and Fruit Resistance

As the major postharvest disease of citrus fruit, postharvest green mold is caused by the necrotrophic fungus Penicillium digitatum (Pd), which leads to huge economic losses worldwide. Fungicides are still the main method currently used to control postharvest green mold in citrus fruit storage. Investigating molecular mechanisms of plant-pathogen interactions, including pathogenicity and plant resistance, is crucial for developing novel and safer strategies for effectively controlling plant diseases. Despite fruit-pathogen interactions remaining relatively unexplored compared with well-studied leaf-pathogen interactions, progress has occurred in the citrus fruit-Pd interaction in recent years, mainly due to their genome sequencing and establishment or optimization of their genetic transformation systems. Recent advances in Pd pathogenicity on citrus fruit and fruit resistance against Pd infection are summarized in this review.

Protein Expression Profile and Transcriptome Characterization of Penicillium expansum Induced by Meyerozyma guilliermondii

Antagonistic yeasts can inhibit fungal growth. In our previous research, Meyerozyma guilliermondii, one of the antagonistic yeasts, exhibited antagonistic activity against Penicillium expansum. However, the mechanisms, especially the molecular mechanisms of inhibiting activity of M. guilliermondii, are not clear. In this study, the protein expression profile and transcriptome characterization of P. expansum induced by M. guilliermondii were investigated. In P. expansum induced by M. guilliermondii, 66 proteins were identified as differentially expressed, among them six proteins were upregulated and 60 proteins were downregulated, which were associated with oxidative phosphorylation, ATP synthesis, basal metabolism, and response regulation. Simultaneously, a transcriptomic approach based on RNA-Seq was applied to annotate the genome of P. expansum and then studied the changes of gene expression in P. expansum treated with M. guilliermondii. The results showed that differentially expressed genes such as HEAT, Phosphoesterase, Polyketide synthase, ATPase, and Ras-association were significantly downregulated, in contrast to Cytochromes P450, Phosphatidate cytidylyltransferase, and Glutathione S-transferase, which were significantly upregulated. Interestingly, the downregulated differentially expressed proteins and genes have a corresponding relationship; these results revealed that these proteins and genes were important in the growth of P. expansum treated with M. guilliermondii.

Blistering1 Modulates Penicillium expansum Virulence Via Vesicle-mediated Protein Secretion

The blue mold fungus, Penicillium expansum, is a postharvest apple pathogen that contributes to food waste by rotting fruit and by producing harmful mycotoxins (e.g. patulin). To identify genes controlling pathogen virulence, a random T-DNA insertional library was created from wild-type P. expansum strain R19. One transformant, T625, had reduced virulence in apples, blistered mycelial hyphae, and a T-DNA insertion that abolished transcription of the single copy locus in which it was inserted. The gene, Blistering1, encodes a protein with a DnaJ domain, but otherwise has little homology outside the Aspergillaceae, a family of fungi known for producing antibiotics, mycotoxins, and cheese. Because protein secretion is critical for these processes and for host infection, mass spectrometry was used to monitor proteins secreted into liquid media during fungal growth. T625 failed to secrete a set of enzymes that degrade plant cell walls, along with ones that synthesize the three final biosynthetic steps of patulin. Consequently, the culture broth of T625 had significantly reduced capacity to degrade apple tissue and contained 30 times less patulin. Quantitative mass spectrometry of 3,282 mycelial proteins revealed that T625 had altered cellular networks controlling protein processing in the endoplasmic reticulum, protein export, vesicle-mediated transport, and endocytosis. T625 also had reduced proteins controlling mRNA surveillance and RNA processing. Transmission electron microscopy of hyphal cross sections confirmed that T625 formed abnormally enlarged endosomes or vacuoles. These data reveal that Blistering1 affects internal and external protein processing involving vesicle-mediated transport in a family of fungi with medical, commercial, and agricultural importance.

Identification and Functional Analysis of NLP-Encoding Genes from the Postharvest Pathogen Penicillium expansum

Penicillium expansum is a major postharvest pathogen that infects different fruits, mainly through injuries inflicted during harvest or subsequent handling after harvest. Several effectors were suggested to mediate pathogenicity of P. expansum in fruit tissue. Among these effectors Nep1-like proteins (NLPs), produced by various microorganisms with different lifestyles, are known for their ability to induce necrosis in dicot plants and were shown to be involved in virulence of several plant-related pathogens. This study was aimed at the identification and functional characterization of two NLP genes found in the genome of P. expansum. The genes were designated Penlp1 and Penlp2 and were found to code type1 and type3 NLP respectively. Necrosis-inducing activity of the two proteins was demonstrated by transient expression in Nicotiana benthamiana leaves. While Penlp1 expression was induced during apple infection and in liquid culture, the highest level of Penlp2 expression was found in ungerminated spores. Deletion of Penlp1, but not Penlp2, resulted in reduced virulence on apples manifested by reduced rate of lesion development (disease severity).

Effects of ascorbic acid on patulin in aqueous solution and in cloudy apple juice

Degradation of the mycotoxin patulin (PAT) and the generation of (less toxic) breakdown products, such as (E/Z)-ascladiol (ASC-E/Z) and desoxypatulinic acid (D-PAT), can occur due to chemical, physical and biological treatments. Our study focused on the chemical degradation of PAT in the presence of ascorbic acid (AA) both for pure PAT standard in acidified aqueous solution and for PAT-contaminated cloudy apple juice (CAJ) (obtained via addition of apple mash produced from apples inoculated with Penicillium expansum). Within this framework, different concentrations of AA were evaluated, as well as the presence/absence of oxygen and different storage temperatures. In order to do so, an in-house methodology allowing a good separation of PAT from its reaction and breakdown products was optimized first. The highest PAT reduction (60%) in CAJ with an initial PAT concentration of 100 μg/kg and 0.25% (w/v) AA was achieved after 6 days of incubation at 22 °C in the presence of oxygen. It was also found that the treatment by AA resulted in the generation of degradation products less toxic than PAT (such as (E/Z)-ASC). In conclusion, AA used to improve numerous product quality aspects (e.g. colour (less browning), nutritional value, etc.) and considered as a safe food additive (Food and Drug Administration (FDA) (1999)) has an effect on PAT degradation. It was shown that such degradation generated less toxic compounds in the presence of oxygen. In view of consumers' safety, fortification of apple juice (and possibly apple-based products) with AA could be helpful within an integrated system to ensure products with low levels of patulin. The optimum conditions for such an approach within a legal and practical point of view need to be further explored.

Volatile 1-octen-3-ol increases patulin production by Penicillium expansum on a patulin-suppressing medium

1-Octen-3-ol is one of the most abundant volatile compounds associated with fungi and functions as a germination and growth inhibitor in several species. By investigating its effect on the biosynthesis of patulin, a mycotoxin made by Penicillium expansum, it was found that a sub-inhibitory level of volatile 1-octen-3-ol increased accumulation of patulin on a medium that normally suppresses the mycotoxin. Transcriptomic sequencing and comparisons of control and treated P. expansum grown on potato dextrose agar (PDA; patulin permissive) or secondary medium agar (SMA; patulin suppressive) revealed that the expression of gox2, a gene encoding a glucose oxidase, was significantly affected, decreasing 10-fold on PDA and increasing 85-fold on SMA. Thirty other genes, mostly involved in transmembrane transport, oxidation-reduction, and carbohydrate metabolism were also differently expressed on the two media. Transcription factors previously found to be involved in regulation of patulin biosynthesis were not significantly affected despite 1-octen-3-ol increasing patulin production on SMA. Further study is needed to determine the relationship between the upregulation of patulin biosynthesis genes and gox2 on SMA, and to identify the molecular mechanism by which 1-octen-3-ol induced this effect.

Contamination of fresh and dried tomato by Alternaria toxins in southern Italy

In the present investigation, fresh and dried tomato samples from markets and packinghouses located in Apulia region (southern Italy) were analysed for Alternaria toxins. All samples proved to be contaminated by tenuazonic acid (TeA); in particular, dried tomatoes were contaminated in the range 425-81,592 µg/kg, while fresh tomatoes were in the range 11-4560 µg/kg. The second most abundant toxin was alternariol monomethyl ether (AME), followed by tentoxin (TEN) and alternariol (AOH). Overall dried tomatoes were more contaminated than fresh ones, although this seemed not directly related to the presence of sodium chloride, utilized in the drying process. Five representative Alternaria isolates within those collected from samples proved to be one Alternaria arborescens (A215) and four Alternaria alternata. Within the latter species, one strain belonged to morphotype tenuissima (A216), and three to alternata (A214, A217 and A218). They were confirmed to produce TeA, AOH, and AME in vitro. This study demonstrates the possible risk for consumers' health related to the consumption of contaminated fresh and dried tomatoes, and thus the need for suitable control strategies.

Low dose exposure of patulin and protective effect of epicatechin on blood cells in vitro

In the present study, we aimed to assess antioxidant status in erythrocytes in vitro after patulin (PAT) and epicatechin exposure by measuring antioxidant enzymes (superoxide-dismutase - SOD, glutathione peroxidase - GPx and catalase - CAT) and parameters associated with oxidative stress (malondialdehyde - MDA and ROS). We also investigated the effect of PAT on viability and count of lymphocytes and lymphocyte subpopulations in rabbit blood in vitro. Whole blood of rabbits was used for analysis of antioxidant changes in rabbit erythrocytes after epicatechin and PAT treatment (separately or in combination, at concentrations of 0.2; 2; 20; 200 µg mL^-1 of epicatechin and 0.5; 5; 10 µg mL^-1 of PAT). Whole blood of rabbits was also used for analysis of count and viability of lymphocytes after PAT treatment at concentrations of 10; 25 and 50 µg mL^-1. Results from our experiment confirmed the ability of epicatechin to protect cells against oxidative stress and lipoperoxidation. Our findings indicate that mycotoxin PAT in low concentrations did not affect the activity of antioxidant enzymes in erythrocytes of rabbits significantly. Only slight non-significant changes in lymphocytes count after treatment with low doses of PAT in rabbit blood were observed.

Molecular heterogeneity in the 18s DNA gene of Alternaria sp. and Fusarium sp. producing mycotoxins in rice and maize grains

BACKGROUND

Food contaminated with fungi and their toxins is a problem that threatens many developing countries. Kingdom of Saudi Arabia depends on the exported grain and legume seeds.

MATERIALS AND METHODS

The study involved examination of 160 samples of rice and maize seeds collected from different locations in the Kingdom of Saudi Arabia. Heterogeneity in the 18s rRNA gene of toxigenic Alternaria sp. and Fusarium sp. was unraveled. The seeds were disinfected and cultured on Potato Dextrose Agar (PDA), Yeast Extract Sucrose (YES) media and incubated at 25 °C/7 days. The isolated fungi were subjected to 18s rRNA gene sequencing. Five toxins were extracted from maize and rice grains infected with isolated fungi.

RESULTS

The isolated fungi were identified based on morphological and spores characters as Fusarium sp. and Alternaria sp. Molecular identification based on18s rDNA barcode' was performed due to its high degree of inter specific variability, conserved primer sites and multi-copy nature in the genome. Fusarium sp. produced the highest detected (2070 μg/kg) fumonisin especially in cereal production season 2011. The collected grain from Dammam recorded the highest percentage (5485.2 g/kg) of toxins.

CONCLUSION

This work highlights that 50% of samples were found contaminated with toxins in various concentrations which impose a threat for public health and necessitate rapid identification methods for toxigenic fungi such as 18s rDNA sequencing.

Effect of the Nature and Relative Concentration of Substrate, Water Mineralization, and Storage Temperature on the Oxidants Produced by Lactoperoxidase and on Their Antifungal Activity against Penicillium expansum and Botrytis cinerea

Lactoperoxidase is an enzyme that generates oxidants with antimicrobial activity in presence of a (pseudo)halogen and hydrogen peroxide, but various factors can drastically reduce the antimicrobial activity of the lactoperoxidase system. Spectroscopic, ionic chromatography, and 13C-NMR methods showed that the oxidants generated by lactoperoxidase are OSCN− in the presence of SCN− and I2 in the presence of I−. Neither of them, however, inhibited Penicillium expansum, one of the causal agents of fruit mold. When a mixture of SCN− and I− was used, no OSCN−, OCN−, I2, or interhalogen I2SCN− was produced. However, its long-term stability, NH2-oxidizing capacity, and antifungal activity against P. expansum argue in favor of an I−-derived oxidant. Strongly mineralized water optimized enzyme-catalyzed reactions with higher oxidant production. Storage at 4 °C resulted in long-term stability and extended antifungal activity against P. expansum. The relative iodide/thiocyanate concentrations turned out to be important, as better in vitro inhibition of Botrytis cinerea, the causal agent of apples’s grey mold, was obtained with a high KI + KSCN concentration, a KI/KSCN ratio of 4.5, and a (KI + KSCN)/H2O2 ratio of 1. The nature of the substrates, their relative concentrations, the medium, and the storage temperature modifed the antifungal activity of lactoperoxidase.

Paecilomyces niveus: Pathogenicity in the Orchard and Sensitivity to Three Fungicides

Paecilomyces rot of apples is a postharvest disease caused by the thermotolerant fungus Paecilomyces niveus (Byssochlamys nivea). The etiology of disease and the activity of fungicides against P. niveus are not yet well understood. This study evaluated the ability of P. niveus to infect 'Gala' apples growing in a conventionally managed orchard. In addition, the sensitivity of P. niveus isolates to postharvest fungicides difenoconazole, fludioxonil, and pyrimethanil was characterized for isolates from both agricultural and nonagricultural environments. Apples were wounded and mock-inoculated or inoculated with P. niveus in early July. At the time of harvest, 8 weeks after wounding, the inoculated apples had significantly larger lesions than mock-inoculated apples (P < 0.005). The average diameter of lesions on wound-inoculated apples was 11.17 mm ± 6.82 SD, while the average diameter of mock-inoculated lesions was 3.34 mm ± 1.85 SD. Disease symptoms in the orchard were similar to postharvest symptoms of Paecilomyces rot. Symptoms included a brown, flattened, circular lesion with faint concentric rings. The necrosis of mesocarp was firm and roughly U-shaped. Baseline isolates of P. niveus, from nonagricultural environments, were used to determine the effective fungicide dose at which growth was inhibited by 50% (EC₅₀). Furthermore, fungicide sensitivity of P. niveus isolates was examined using relative growth assays at the mean baseline EC₅₀ values to compare baseline isolates with isolates obtained from commercial apple orchards where they were likely exposed to fungicides. Among the exposed isolates, reduced sensitivity to all fungicides was observed, but significant differences between baseline and exposed isolates were only observed with fludioxonil (P < 0.0001). This is the first report demonstrating that P. niveus can infect apples that are wound-inoculated in the orchard and that isolates from agricultural environments are less sensitive to common fungicides, especially fludioxonil. This finding may have implications for the control of this postharvest diseases. Whether natural infections of apples by P. niveus is initiated in the orchard or during postharvest has yet to be determined.

Patulin in Apples and Apple-Based Food Products: The Burdens and the Mitigation Strategies

Apples and apple-based products are among the most popular foods around the world for their delightful flavors and health benefits. However, the commonly found mold, Penicillium expansum invades wounded apples, causing the blue mold decay and ensuing the production of patulin, a mycotoxin that negatively affects human health. Patulin contamination in apple products has been a worldwide problem without a satisfactory solution yet. A comprehensive understanding of the factors and challenges associated with patulin accumulation in apples is essential for finding such a solution. This review will discuss the effects of the pathogenicity of Penicillium species, quality traits of apple cultivars, and environmental conditions on the severity of apple blue mold and patulin contamination. Moreover, beyond the complicated interactions of the three aforementioned factors, patulin control is also challenged by the lack of reliable detection methods in food matrices, as well as unclear degradation mechanisms and limited knowledge about the toxicities of the metabolites resulting from the degradations. As apple-based products are mainly produced with stored apples, pre- and post-harvest strategies are equally important for patulin mitigation. Before storage, disease-resistance breeding, orchard-management, and elicitor(s) application help control the patulin level by improving the storage qualities of apples and lowering fruit rot severity. From storage to processing, patulin mitigation strategies could benefit from the optimization of apple storage conditions, the elimination of rotten apples, and the safe and effective detoxification or biodegradation 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.

Patulin removal from apple juice using a novel cysteine-functionalized metal-organic framework adsorbent

Patulin (PAT) is one of the most common toxic contaminants of apple juice, which causes severe food safety issues throughout the apple industry. In order to remove PAT efficiently, a metal-organic framework-based adsorbent (UiO-66(NH₂)@Au-Cys) was successfully synthesized and used for PAT removal from juice-pH simulation solution and real apple juice. Batch adsorption experiments were systematically performed to study the adsorption behavior for PAT. The results showed that adsorption process could be well described by the Pseudo-second order model and Freundlich isotherm model. The maximum adsorption capacity (4.38 µg/mg) was 10 times higher than the microbe-based biosorbents. Thermodynamic investigation demonstrated that adsorption process was spontaneous and endothermic. Furthermore, no marked cytotoxicity on NIH 3T3 cell lines was observed when the concentration of the adsorbent was lower than 10 μg/mL. Therefore, UiO-66(NH₂)@Au-Cys is a potential adsorbent for PAT removal from apple juice with little quality changes.

Mycoflora assessment, growth and toxigenic features of patulin-producers in kiwifruit in China

BACKGROUND

Fungal development in agricultural products may cause mycotoxin contamination, which is a significant threat to food safety. Patulin (PAT) and PAT-producer contamination has been established as a worldwide problem. The present study aimed to investigate the mycoflora and PAT-producers present in kiwifruits and environmental samples collected from orchards and processing plants in Shaanxi Province, China.

RESULTS

Variations in mycoflora were observed in different samples, with penicillia and aspergilli as the predominant genera. Approximately 42.86% of dropped fruits were contaminated with PAT-producers, which harbored the 6-methylsalicylic acid synthase and the isoepoxydon dehydrogenase genes that are involved in PAT biosynthesis. The growth of Penicillium expansum, Penicillium griseofulvum and Penicillium paneum in kiwi puree agar (KPA) medium and kiwi juice well fitted the modified Gompertz and Baranyi and Roberts models (R² ≥ 0.95). A significant positive correlation between colony diameter and PAT content in KPA medium of P. expansum and P. griseofulvum was observed (P < 0.05).

CONCLUSIONS

The present study analyzed the mycofloral composition and the potential risk for PAT and PAT-producer contamination in kiwifruit, which may be utilized in the establishment of proper management practices in the kiwifruit industry. © 2017 Society of Chemical Industry.

Impact of veA on the development, aggressiveness, dissemination and secondary metabolism of Penicillium expansum

Penicillium expansum, the causal agent of blue mould disease, produces the mycotoxins patulin and citrinin amongst other secondary metabolites. Secondary metabolism is associated with fungal development, which responds to numerous biotic and abiotic external triggers. The global transcription factor VeA plays a key role in the coordination of secondary metabolism and differentiation processes in many fungal species. The specific role of VeA in P. expansum remains unknown. A null mutant PeΔveA strain and a complemented PeΔveA:veA strain were generated in P. expansum and their pathogenicity on apples was studied. Like the wild-type and the complemented strains, the null mutant PeΔveA strain was still able to sporulate and to colonize apples, but at a lower rate. However, it could not form coremia either in vitro or in vivo, thus limiting its dissemination from natural substrates. The impact of veA on the expression of genes encoding proteins involved in the production of patulin, citrinin and other secondary metabolites was evaluated. The disruption of veA drastically reduced the production of patulin and citrinin on synthetic media, associated with a marked down-regulation of all genes involved in the biosynthesis of the two mycotoxins. Moreover, the null mutant PeΔveA strain was unable to produce patulin on apples. The analysis of gene expression revealed a global impact on secondary metabolism, as 15 of 35 backbone genes showed differential regulation on two different media. These findings support the hypothesis that VeA contributes to the pathogenicity of P. expansum and modulates its secondary metabolism.

Reaction Product Variability and Biological Activity of the Lactoperoxidase System Depending on Medium Ionic Strength and pH, and on Substrate Relative Concentration

The potential of ions produced in water by the lactoperoxidase system against plant pests has shown promising results. We tested the bioactivity of ions produced by the lactoperoxidase oxidation of I^- and SCN^- in several buffers or in tap water and characterized the ions produced. In vitro biological activity was tested against Penicillium expansum, the causal agent of mold in fruits, and the major cause of patulin contamination of fruit juices and compotes. In buffers, the ionic concentration was increased 3-fold, and pathogen inhibition was obtained down to the 1:15 dilution. In tap water, the ionic concentration was weaker, and pathogen inhibition was obtained only down to the 1:3 dilution. Acidic buffer increased ion concentrations as compared to less acidic (pH 5.6 or 6.2) or neutral buffers, as do increased ionic strength. ¹³ C-labelled SCN^- and MS showed that different ions were produced in water and in buffers. In specific conditions the ion solution turned yellow and a product was formed, probably diiodothiocyanate (I₂ SCN^- ), giving an intense signal at 49.7 ppm in ¹³ C-NMR. The formation of the signal was unambiguously favored in acidic media and disadvantaged or inhibited in neutral or basic conditions. It was enhanced at a specific SCN^- : I^- ratio of 1:4.5, but decreased when the ratio was 1:2, and was inhibited at ratio SCN^- >I^- . We demonstrated that the formation of the signal required the interaction between I₂ and SCN^- , and MS showed the presence of I₂ SCN^- .