Effect of the Biocontrol Yeast Rhodotorula glutinis Strain LS11 on Patulin Accumulation in Stored Apples

Natural feed additives and bioactive supplements versus chemical additives as a safe and practical approach to combat foodborne mycotoxicoses

This review highlights the possible hazard of mycotoxins occurrence in foods and feeds in regards to foodborne diseases. The possible management of the risk of contamination of foods and feeds with mycotoxins by using natural feed additives, protecting against deleterious effects of mycotoxins or inhibiting the growth of fungi and mycotoxin production, is deeply investigated in the available literature and some effective measures for safe utilization of mycotoxin contaminated feed/food are proposed. The biological methods of decontamination, degradation or biotransformation of mycotoxins are deeply analyzed and discussed. Some natural antagonists against target fungi are also reviewed and a comparison is made with conventional fungicides for ensuring a safe prevention of mycotoxin contamination. The most common and useful chemical methods of mycotoxins decontamination of agricultural commodities or raw materials are also investigated, e.g., chemical additives inactivating or destroying and/or adsorbing mycotoxins as well as chemical additives inhibiting the growth of fungi and mycotoxin production. The practical use and safety of various kind of feed/food additives or herbal/biological supplements as possible approach for ameliorating the adverse effects of some dangerous mycotoxins is deeply investigated and some suggestions are given. Various possibilities for decreasing mycotoxins toxicity, e.g., by clarifying the mechanisms of their toxicity and using some target antidotes and vitamins as supplements to the diet, are also studied in the literature and appropriate discussions or suggestions are made in this regard. Some studies on animal diets such as low carbohydrate intake, increased protein content, calorie restriction or the importance of dietary fats are also investigated in the available literature for possible amelioration of the ailments associated with mycotoxins exposure. It could be concluded that natural feed additives and bioactive supplements would be more safe and practical approach to combat foodborne mycotoxicoses as compared to chemical additives.

Isolation and characterization of filamentous fungi capable of degrading the mycotoxin patulin

Patulin is a toxic secondary metabolite synthesized by various fungal strains. This mycotoxin is generally toxic to microorganisms as well as mammals due to its reactivity with the important cellular antioxidant glutathione. In this study, we explored the presence of microorganisms capable of degrading patulin. Microorganisms were screened for the ability to both grow in culture medium containing patulin and reduce its concentration. Screening of 510 soil samples resulted in the isolation of two filamentous fungal strains, one of which, Acremonium sp. TUS-MM1 was characterized in detail. Liquid chromatography-mass spectrometry and nuclear magnetic resonance analyses revealed that TUS-MM1 cells degraded patulin to desoxypatulinic acid. In addition, extracellular components of strain TUS-MM1 also exhibited patulin-transforming activity. High-performance liquid chromatography analysis revealed that the extracellular components generated several products from patulin. Disc diffusion assay using Escherichia coli cells revealed that the patulin-transformation products by the extracellular components are less toxic than patulin. We also demonstrated that a thermostable, low-molecular-weight compound within the extracellular components was responsible for the patulin-transforming activity. These results suggest that strain TUS-MM1 transforms patulin into less-toxic molecules by secreting a highly reactive compound. In addition, once patulin enters the cells, strain TUS-MM1 can transform it into desoxypatulinic acid to reduce its toxicity.

Perfume Guns: Potential of Yeast Volatile Organic Compounds in the Biological Control of Mycotoxin-Producing Fungi

Pathogenic fungi in the genera Alternaria, Aspergillus, Botrytis, Fusarium, Geotrichum, Gloeosporium, Monilinia, Mucor, Penicillium, and Rhizopus are the most common cause of pre- and postharvest diseases of fruit, vegetable, root and grain commodities. Some species are also able to produce mycotoxins, secondary metabolites having toxic effects on human and non-human animals upon ingestion of contaminated food and feed. Synthetic fungicides still represent the most common tool to control these pathogens. However, long-term application of fungicides has led to unacceptable pollution and may favour the selection of fungicide-resistant mutants. Microbial biocontrol agents may reduce the incidence of toxigenic fungi through a wide array of mechanisms, including competition for the ecological niche, antibiosis, mycoparasitism, and the induction of resistance in the host plant tissues. In recent years, the emission of volatile organic compounds (VOCs) has been proposed as a key mechanism of biocontrol. Their bioactivity and the absence of residues make the use of microbial VOCs a sustainable and effective alternative to synthetic fungicides in the management of postharvest pathogens, particularly in airtight environments. In this review, we will focus on the possibility of applying yeast VOCs in the biocontrol of mycotoxigenic fungi affecting stored food and feed.

"An apple a day keeps the doctor away": The potentials of apple bioactive constituents for chronic disease prevention

Apples are rich sources of selected micronutrients (e.g., iron, zinc, vitamins C and E) and polyphenols (e.g., procyanidins, phloridzin, 5′‐caffeoylquinic acid) that can help in mitigating micronutrient deficiencies (MNDs) and chronic diseases. This review provides an up‐to‐date overview of the significant bioactive compounds in apples together with their reported pharmacological actions against chronic diseases such as diabetes, cancer, and cardiovascular diseases. For consumers to fully gain these health benefits, it is important to ensure an all‐year‐round supply of highly nutritious and good‐quality apples. Therefore, after harvest, the physicochemical and nutritional quality attributes of apples are maintained by applying various postharvest treatments and hurdle techniques. The impact of these postharvest practices on the safety of apples during storage is also highlighted. This review emphasizes that advancements in postharvest management strategies that extend the storage life of apples should be optimized to better preserve the bioactive components crucial to daily dietary needs and this can help improve the overall health of consumers.

Analysis of Stored Wheat Grain-Associated Microbiota Reveals Biocontrol Activity among Microorganisms against Mycotoxigenic Fungi

Wheat grains are colonized by complex microbial communities that have the potential to affect seed quality and susceptibility to disease. Some of the beneficial microbes in these communities have been shown to protect plants against pathogens through antagonism. We evaluated the role of the microbiome in seed health: in particular, against mycotoxin-producing fungi. Amplicon sequencing was used to characterize the seed microbiome and determine if epiphytes and endophytes differ in their fungal and bacterial diversity and community composition. We then isolated culturable fungal and bacterial species and evaluated their antagonistic activity against mycotoxigenic fungi. The most prevalent taxa were found to be shared between the epiphytic and endophytic microbiota of stored wheat seeds. Among the isolated bacteria, Bacillus strains exhibited strong antagonistic properties against fungal pathogens with noteworthy fungal load reduction in wheat grain samples of up to a 3.59 log₁₀ CFU/g compared to untreated controls. We also found that a strain of the yeast, Rhodotorula glutinis, isolated from wheat grains, degrades and/or metabolizes aflatoxin B₁, one of the most dangerous mycotoxins that negatively affects physiological processes in animals and humans. The mycotoxin level in grain samples was significantly reduced up to 65% in the presence of the yeast strain, compared to the untreated control. Our study demonstrates that stored wheat grains are a rich source of bacterial and yeast antagonists with strong inhibitory and biodegradation potential against mycotoxigenic fungi and the mycotoxins they produce, respectively. Utilization of these antagonistic microorganisms may help reduce fungal and mycotoxin contamination, and potentially replace traditionally used synthetic chemicals.

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.

Kosakonia radicincitans and Cryptococcus laurentii controlled Penicillium expansum rot and decreased patulin production at 4 and 25 °C

In the present work, we evaluated the effects of a mixture of biocontrol agents against two toxigenic strains of Penicillium expansum isolated in Argentine Patagonia from pome fruits. The two strains, INTA-5 and INTA-10, were previusly selected among ten strains coming from the Alto Valle (Rio Negro-Argentina) for their high production of patulin. For the biocontrol, Kosakonia radicincitans, Cryptococcus laurentii, and Rhodosporidium fluviale were tested in vitro experiments on Potato Dextrose Agar (PDA) dishes against the INTA-5 and INTA-10 strains. The bacterium K. radicincitans and the yeast C. laurentii were selected to be used in a mixture due to their capacity to control the fungus and reduce the mycotoxin severely. In vitro assays with the mixture showed a high antagonism against P. expansum INTA-5 and INTA-10, at 21 d of incubation at 25 °C and a patulin reduction of 98%. The mixture of microorganisms was also effective in apples stored at 25 °C for 10 d and 4 °C for 30 d. At cold storage, the mixture controlled moderately the development of rot and decreased patulin concentration. At 25 °C, the pathogen's optimal growth temperature, the mixture of Biological Control Agent (BCAs) assured both the control of rot and decrease of patulin concentration. The combination of two microorganisms, with different requirements and abilities, resulted in a mix with a strong antagonism against P. expansum with the capability to decrease the patulin concentration. Treatment with the selected mixture could be a good option for controlling strains with different behaviours and in different environmental conditions.

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.

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.

Genomics- and Metabolomics-Based Investigation of the Deep-Sea Sediment-Derived Yeast, Rhodotorula mucilaginosa 50-3-19/20B

Red yeasts of the genus Rhodotorula are of great interest to the biotechnological industry due to their ability to produce valuable natural products, such as lipids and carotenoids with potential applications as surfactants, food additives, and pharmaceuticals. Herein, we explored the biosynthetic potential of R. mucilaginosa 50-3-19/20B collected from the Mid-Atlantic Ridge using modern genomics and untargeted metabolomics tools. R. mucilaginosa 50-3-19/20B exhibited anticancer activity when grown on PDA medium, while antimicrobial activity was observed when cultured on WSP-30 medium. Applying the bioactive molecular networking approach, the anticancer activity was linked to glycolipids, namely polyol esters of fatty acid (PEFA) derivatives. We purified four PEFAs (1–4) and the known methyl-2-hydroxy-3-(1H-indol-2-yl)propanoate (5). Their structures were deduced from NMR and HR-MS/MS spectra, but 1–5 showed no anticancer activity in their pure form. Illumina-based genome sequencing, de novo assembly and standard biosynthetic gene cluster (BGC) analyses were used to illustrate key components of the PEFA biosynthetic pathway. The fatty acid producing BGC3 was identified to be capable of producing precursors of PEFAs. Some Rhodotorula strains are able to convert inulin into high-yielding PEFA and cell lipid using a native exo-inulinase enzyme. The genomic locus for an exo-inulinase enzyme (g1629.t1), which plays an instrumental role in the PEFA production via the mannitol biosynthesis pathway, was identified. This is the first untargeted metabolomics study on R. mucilaginosa providing new genomic insights into PEFA biosynthesis.

Wheat phyllosphere yeasts degrade propiconazole

BACKGROUND

Yeasts, which are ubiquitous in agroecosystems, are known to degrade various xenobiotics. The aim of this study was to analyze the effect of fungicides on the abundance of natural yeast communities colonizing winter wheat leaves, to evaluate the sensitivity of yeast isolates to fungicides in vivo, and to select yeasts that degrade propiconazole.

RESULTS

Fungicides applied during the growing season generally did not affect the counts of endophytic yeasts colonizing wheat leaves. Propiconazole and a commercial mixture of flusilazole and carbendazim decreased the counts of epiphytic yeasts, but the size of the yeast community was restored after 10 days. Epoxiconazole and a commercial mixture of fluoxastrobin and prothioconazole clearly stimulated epiphyte growth. The predominant species isolated from leaves were Aureobasidium pullulans and Rhodotorula glutinis. In the disk diffusion test, 14 out of 75 yeast isolates were not sensitive to any of the tested fungicides. After 48 h of incubation in an aqueous solution of propiconazole, the Rhodotorula glutinis Rg 55 isolate degraded the fungicide in 75%. Isolates Rh. glutinis Rg 92 and Rg 55 minimized the phytotoxic effects of propiconazole under greenhouse conditions. The first isolate contributed to an increase in the dry matter content of wheat seedlings, whereas the other reduced the severity of chlorosis.

CONCLUSION

Not sensitivity of many yeast colonizing wheat leaves on the fungicides and the potential of isolate Rhodotorula glutinis Rg 55 to degrade of propiconazole was established. Yeast may partially eliminate the ecologically negative effect of fungicides.

Recent trends in detecting, controlling, and detoxifying of patulin mycotoxin using biotechnology methods

Patulin (PAT) is a mycotoxin that can contaminate many foods and especially fruits and fruit-based products. Therefore, accurate and effective testing is necessary to enable producers to comply with regulations and promote food safety. Traditional approaches involving the use of chemical compounds or physical treatments in food have provided practical methods that have been used to date. However, growing concerns about environmental and health problems associated with these approaches call for new alternatives. In contrast, recent advances in biotechnology have revolutionized the understanding of living organisms and brought more effective biological tools. This review, therefore, focuses on the study of biotechnology approaches for the detection, control, and mitigation of PAT in food. Future aspects of biotechnology development to overcome the food safety problem posed by PAT were also examined. We find that biotechnology advances offer novel, more effective, and environmental friendly approaches for the control and elimination of PAT in food compared to traditional methods. Biosensors represent the future of PAT detection and use biological tools such as aptamer, enzyme, and antibody. PAT prevention strategies include microbial biocontrol, the use of antifungal biomolecules, and the use of microorganisms in combination with antifungal molecules. PAT detoxification aims at the breakdown and removal of PAT in food by using enzymes, microorganisms, and various adsorbent biopolymers. Finally, biotechnology advances will be dependent on the understanding of fundamental biology of living organisms regarding PAT synthesis and resistance mechanisms.

Biocontrol ability and volatile organic compounds production as a putative mode of action of yeast strains isolated from organic grapes and rye grains

The inhibiting activity of three yeast strains belonging to Pichia kudriavzevii, Pichia occidentalis, and Meyerozyma quilliermondii/Meyerozyma caribbica genera against common plant pathogens representing Mucor spp., Penicillium chrysogenum, Penicillium expansum, Aspergillus flavus, Fusarium cereals, Fusarium poae, as well as Botrytis cinerea genera was investigated. The yeast strains tested had a positive impact on growth inhibition of all target plant pathogens. The degree of inhibition was more than 50% and varied depending on both the yeast antagonist and the mold. Ethyl esters of medium-chain fatty acids, phenylethyl alcohol, and its acetate ester prevailed among the analyzed volatile organic compounds (VOCs) emitted by yeasts in the presence of the target plant pathogens. Due to the method used, assuming no contact between the antagonist and the pathogen, the antagonistic activity of the yeast strains studied resulted mainly from the production of biologically active VOCs. Moreover, the antagonistic activity was not only restricted to a single plant pathogen but effective towards molds of different genera, making the yeast strains studied very useful for potential application in biological control.

S-Adenosylmethionine-Dependent Methyltransferase Helps Pichia caribbica Degrade Patulin

Patulin contamination not only is a menace to human health but also causes serious environmental problems worldwide due to the synthetic fungicides that are used to control it. This study focused on investigating the patulin degradation mechanism in Pichia caribbica at the molecular level. According to the results, P. caribbica (2 × 10⁶ cells/mL) was able to degrade patulin from 20 μg/mL to an undetectable level in 72 h. The RNA-seq data showed patulin-induced oxidative stress and responses in P. caribbica. The deletion of PcCRG1 led to a significant decrease in patulin degradation by P. caribbica, whereas the overexpression of PcCRG1 accelerated the degradation of patulin. The study identified that PcCRG1 protein had the ability to degrade patulin in vitro. Overall, we demonstrated that the patulin degradation process in P. caribbica was more than one way; PcCRG1 was an S-adenosylmethionine-dependent methyltransferase and played an important role in the patulin degradation process in P. caribbica.

An analysis of codon bias in six red yeast species

Red yeasts, primarily species of Rhodotorula, Sporobolomyces, and other genera of Pucciniomycotina, are traditionally considered proficient systems for lipid and terpene production, and only recently have also gained consideration for the production of a wider range of molecules of biotechnological potential. Improvements of transgene delivery protocols and regulated gene expression systems have been proposed, but a dearth of information on compositional and/or structural features of genes has prevented transgene sequence optimization efforts for high expression levels. Here, the codon compositional features of genes in six red yeast species were characterized, and the impact that evolutionary forces may have played in shaping this compositional bias was dissected by using several computational approaches. Results obtained are compatible with the hypothesis that mutational bias, although playing a significant role, cannot alone explain synonymous codon usage bias of genes. Nevertheless, several lines of evidences indicated a role for translational selection in driving the synonymous codons that allow high expression efficiency. These optimal synonymous codons are identified for each of the six species analyzed. Moreover, the presence of intragenic patterns of codon usage, which are thought to facilitate polyribosome formation, was highlighted. The information presented should be taken into consideration for transgene design for optimal expression in red yeast species.

Effective Biodegradation of Mycotoxin Patulin by Porcine Pancreatic Lipase

Patulin is a common contaminant in fruits and vegetables, which is difficult to remove. In this study, the biodegradation of patulin using porcine pancreatic lipase (PPL) was investigated. The method of HPLC was used to analyze the concentration of patulin. Batch degradation experiments were performed to illustrate the effect of PPL amount, pH, temperature, contact time, and initial concentration. Besides, the degradation product of patulin was characterized by full wavelength scanning and MS technologies. The results showed that the optimum degradation conditions of PPL for patulin was observed at pH 7.5, 40°C for 48 h. The percentage of degradation could reach above 90%. The structure of degradable product of patulin was inferred by the molecular weight 159.0594, named C7H11O4+. It indicated that PPL was effective for the degradation of patulin in fruits and vegetables juice.

Complete Genome Sequence of the Biocontrol Agent Yeast Rhodotorula kratochvilovae Strain LS11

Rhodotorula kratochvilovae strain LS11 is a biocontrol agent (BCA) selected for its antagonistic activity against several plant pathogens both in the field and postharvest. Genome assembly includes 62 contigs for a total of 22.56 Mbp and a G+C content of 66.6%. Genome annotation predicts 7,642 protein-encoding genes.

Mosquitoes can harbour yeasts of clinical significance and contribute to their environmental dissemination

There is still a lack of studies on fungal microbiota in mosquitoes, compared with the number available on bacterial microbiota. This study reports the identification of yeasts of clinical significance in laboratory mosquito species: Anopheles gambiae, Anopheles stephensi, Culex quinquefasciatus, Aedes albopictus and Aedes aegypti. Among the yeasts isolated, they focused on the opportunistic pathogen Candida parapsilosis, since there is a need to better understand breakthrough candidaemia with resistance to the usual antifungals, which requires careful consideration in the broad-spectrum therapy, as documented in many clinical reports. C. parapsilosis occurs widely and has been isolated from diverse sources, including insects, which may contribute to its dissemination. In this study, it was isolated from the gut of An. gambiae and its presence in developmental stages and organs of different mosquito species was studied. Our results indicated that there was a stable association between C. parapsilosis and reared mosquitoes during the entire life cycle, and in adult male and female gut and gonads. A wide occurrence of C. parapsilosis was also documented in several populations of wild mosquitoes. Based on these findings, it can be said that mosquitoes might participate in the spreading of this opportunistic pathogen, not only as a carrier.

Biocontrol Agents Increase the Specific Rate of Patulin Production by Penicillium expansum but Decrease the Disease and Total Patulin Contamination of Apples

Synthetic fungicides are commonly employed for the control of postharvest diseases of fruits. However, due to health concerns about the use of these chemicals, alternative control methods including biocontrol based on antagonistic yeasts are gaining in popularity. In this study, we investigated the effects of two biocontrol yeasts, Rhodotorula mucilaginosa strain 3617 and Rhodotorula kratochvilovae strain LS11, on blue mold and patulin (PAT) contamination caused by Penicillium expansum strains PY and FS7 in artificially inoculated Fuji apples stored at 20°C for 9 days. To correlate the development of the P. expansum strains in yeast-treated and untreated apples with PAT production, we quantified their biomass in the infected fruits using a recently published quantitative real-time polymerase chain reaction method based on specific primers for patF, a gene from P. expansum that is involved in PAT biosynthesis. Both yeasts significantly reduced the disease incidence caused by the two strains of P. expansum up to 5–7 days of incubation, and lowered their biomass and the progression of symptoms up to 9 days. Interestingly, both yeasts strains increased the rate of PAT production (expressed as ng patulin/μg fungal DNA) by the two pathogenic strains. Nevertheless, both biocontrol agents reduced the total PAT contamination, especially in the case of P. expansum strain FS7, the higher PAT producer of the two tested P. expansum strains. Comparing between the yeast strains, R. kratochvilovae LS11 was more effective than R. mucilaginosa 3617 for the control of P. expansum.

Patulin Degradation by the Biocontrol Yeast Sporobolomyces sp. Is an Inducible Process

Patulin is a mycotoxin produced by Penicillium expansum and a common contaminant of pome fruits and their derived products worldwide. It is considered to be mutagenic, genotoxic, immunotoxic, teratogenic and cytotoxic, and the development of strategies to reduce this contamination is an active field of research. We previously reported that Sporobolomyces sp. is able to degrade patulin and convert it into the breakdown products desoxypatulinic acid and ascladiol, both of which were found to be less toxic than patulin. The specific aim of this study was the evaluation of the triggering of the mechanisms involved in patulin resistance and degradation by Sporobolomyces sp. Cells pre-incubated in the presence of a low patulin concentration showed a higher resistance to patulin toxicity and a faster kinetics of degradation. Similarly, patulin degradation was faster when crude intracellular protein extracts of Sporobolomyces sp. were prepared from cells pre-treated with the mycotoxin, indicating the induction of the mechanisms involved in the resistance and degradation of the mycotoxin by Sporobolomyces sp. This study contributes to the understanding of the mechanisms of patulin resistance and degradation by Sporobolomyces sp., which is an essential prerequisite for developing an industrial approach aiming at the production of patulin-free products.

Biodegradation Mechanisms of Patulin in Candida guilliermondii: An iTRAQ-Based Proteomic Analysis

Patulin, a potent mycotoxin, contaminates fruits and derived products worldwide, and is a serious health concern. Several yeast strains have shown the ability to effectively degrade patulin. However, the mechanisms of its biodegradation still remain unclear at this time. In the present study, biodegradation and involved mechanisms of patulin by an antagonistic yeast Candida guilliermondii were investigated. The results indicated that C. guilliermondii was capable of not only multiplying to a high population in medium containing patulin, but also effectively reducing patulin content in culture medium. Degradation of patulin by C. guilliermondii was dependent on the yeast cell viability, and mainly occurred inside cells. E-ascladiol was the main degradation product of patulin. An iTRAQ-based proteomic analysis revealed that the responses of C. guilliermondii to patulin were complex. A total of 30 differential proteins involved in 10 biological processes were identified, and more than two-thirds of the differential proteins were down-accumulated. Notably, a short-chain dehydrogenase (gi|190348612) was markedly induced by patulin at both the protein and mRNA levels. Our findings will provide a foundation to help enable the commercial development of an enzyme formulation for the detoxification of patulin in fruit-derived products.

The Possible Mechanisms Involved in Degradation of Patulin by Pichia caribbica

In this work, we examined the mechanisms involved in the degradation of patulin by Pichia caribbica. Our results indicate that cell-free filtrate of P. caribbica reduced patutlin content. The heat-killed cells could not degrade patulin. However, the live cells significantly reduced the concentration of the patulin. In furtherance to this, it was observed that patulin was not detected in the broken yeast cells and cell wall. The addition of cycloheximide to the P. caribbica cells decreased the capacity of degradation of patulin. Proteomics analyses revealed that patulin treatment resulted in an upregulated protein which was involved in metabolism and stress response processes. Our results suggested that the mechanism of degradation of patulin by P. caribbica was not absorption; the presence of patulin can induce P. caribbica to produce associated intracellular and extracellular enzymes, both of which have the ability to degrade patulin. The result provides a new possible method that used the enzymes produced by yeast to detoxify patulin in food and feed.

Transcriptomic responses of the basidiomycete yeast Sporobolomyces sp. to the mycotoxin patulin

BACKGROUND

Patulin is a mycotoxin produced by Penicillium expansum, the causal agent of blue mold of stored pome fruits, and several other species of filamentous fungi. This mycotoxin has genotoxic, teratogenic and immunotoxic effects in mammals, and its presence in pome fruits and derived products represents a serious health hazard. Biocontrol agents in the Pucciniomycotina, such as the yeasts Sporobolomyces sp. strain IAM 13481 and Rhodosporidium kratochvilovae strain LS11, are able to resist patulin and degrade it into the less toxic compounds desoxypatulinic acid and ascladiol.

RESULTS

In this investigation we applied a transcriptomic approach based on RNAseq to annotate the genome of Sporobolomyces sp. IAM 13481 and then study the changes of gene expression in Sporobolomyces sp. exposed to patulin. Patulin treatment leads to ROS production and oxidative stress that result in the activation of stress response mechanisms controlled by transcription factors. Upregulated Sporobolomyces genes were those involved in oxidation-reduction and transport processes, suggesting the activation of defense mechanisms to resist patulin toxicity and expel the mycotoxin out of the cells. Other upregulated genes encoded proteins involved in metabolic processes such as those of the glutathione and thioredoxin systems, which are essential to restore the cellular redox homeostasis. Conversely, patulin treatment decreased the expression of genes involved in the processes of protein synthesis and modification, such as transcription, RNA processing, translation, protein phosphorylation and biosynthesis of amino acids. Also, genes encoding proteins involved in transport of ions, cell division and cell cycle were downregulated. This indicates a reduction of metabolic activity, probably due to the high energy requirement by the cells or metabolic arrest while recovering from the insult caused by patulin toxicity.

CONCLUSIONS

Complex mechanisms are activated in a biocontrol yeast in response to patulin. The genes identified in this study can pave the way to develop i) a biodetoxification process of patulin in juices and ii) a biosensor for the rapid and cost-effective detection of this mycotoxin.

Evaluation of yeasts from Tibetan fermented products as agents for biocontrol of blue mold of Nashi pear fruits

A total of 20 strains of yeast isolated from Tibetan fermented products were screened for antagonism against blue mold of pear caused by Penicillium expansum. Six isolates that inhibited incidence of postharvest decay by 35% or more were selected for further screening. Among them, the most effective was Rhodotorula mucilaginosa. The results showed that washed cell suspensions of R. mucilaginosa yielded better antagonistic efficacy than unwashed cell-culture mixtures, cell-free culture filtrates, and autoclaved cell cultures. Biocontrol activity improved with increasing concentrations of incubated cells. The best concentration was 1×10(8) cells/ml, at which the incidence of decay was only 16.7% after 6 d of incubation. The germination of conidia of P. expansum in vitro was significantly inhibited by both washed cell-suspensions and unwashed cell-culture mixtures. Rapid colonization by yeast at different concentrations showed a relationship between yeast-cell concentration and biocontrol activity. Although the titratable acidity of pear fruits increased after treatment, R. mucilaginosa did not affect the total soluble solids or ascorbic acid content. This is the first study to report that the yeast R. mucilaginosa from Tibet Autonomous Region of China may have potential as an antagonist to control the postharvest decay of pear fruits.

Effect of the yeast Rhodosporidium paludigenum on postharvest decay and patulin accumulation in apples and pears

The effect of a strain of marine yeast Rhodosporidium paludigenum on postharvest blue mold and patulin accumulation in apples and pears stored at 23°C was evaluated. The occurrence and severity of apple and pear decay caused by Penicillium expansum were significantly inhibited by R. paludigenum. However, the application of the yeast at a high concentration (10(8) cells per ml) enhanced patulin accumulation after 7 days of storage; the amount of patulin increased 24.2 times and 12.6 times compared to the controls in infected apples and pears, respectively. However, R. paludigenum reduced the patulin concentration in the growth medium by both biological degradation and physical adsorption. Optimal in vitro patulin reduction was observed at 30°C and at pH 6.0. R. paludigenum incubated at 28°C was tolerant to patulin at concentrations up to 100 mg/liter. In conclusion, R. paludigenum was able to control postharvest decay in apples and pears and to remove patulin in vitro effectively. However, because the yeast induced patulin accumulation in fruit, the assessment of mycotoxin content after biological treatments in postharvest decay control is important. R. paludigenum may also be a promising source of gene(s) and enzyme(s) for patulin degradation and may be a tool to decrease patulin contamination in commercial fruit-derived products.

Natural occurrence, analysis, and prevention of mycotoxins in fruits and their processed products

Mycotoxins are small toxic chemical products formed as the secondary metabolites by fungi that readily contaminate foods with toxins in the field or after harvest. The presence of mycotoxins, such as aflatoxins, ochratoxin A, and patulin, in fruits and their processed products is of high concern for human health due to their properties to induce severe acute and chronic toxicity at low-dose levels. Currently, a broad range of detection techniques used for practical analysis and detection of a wide spectrum of mycotoxins are available. Many analytical methods have been developed for the determination of each group of these mycotoxins in different food matrices, but new methods are still required to achieve higher sensitivity and address other challenges that are posed by these mycotoxins. Effective technologies are needed to reduce or even eliminate the presence of the mycotoxins in fruits and their processed products. Preventive measures aimed at the inhibition of mycotoxin formation in fruits and their processed products are the most effective approach. Detoxification of mycotoxins by different physical, chemical, and biological methods are less effective and sometimes restricted because of concerns of safety, possible losses in nutritional quality of the treated commodities and cost implications. This article reviewed the available information on the major mycotoxins found in foods and feeds, with an emphasis of fruits and their processed products, and the analytical methods used for their determination. Based on the current knowledge, the major strategies to prevent or even eliminate the presence of the mycotoxins in fruits and their processed products were proposed.

Alternative methods for the control of postharvest citrus diseases

The postharvest diseases of citrus fruit cause considerable losses during storage and transportation. These diseases are managed principally by the application of synthetic fungicides. However, the increasing concern for health hazards and environmental pollution due to chemical use has required the development of alternative strategies for the control of postharvest citrus diseases. Management of postharvest diseases using microbial antagonists, natural plant-derived products and Generally Recognized As Safe compounds has been demonstrated to be most suitable to replace the synthetic fungicides, which are either being banned or recommended for limited use. However, application of these alternatives by themselves may not always provide a commercially acceptable level of control of postharvest citrus diseases comparable to that obtained with synthetic fungicides. To provide more effective disease control, a multifaceted approach based on the combination of different postharvest treatments has been adopted. Actually, despite the distinctive features of these alternative methods, several reasons hinder the commercial use of such treatments. Consequently, research should emphasize the development of appropriate tools to effectively implement these alternative methods to commercial citrus production.

Searching for genes responsible for patulin degradation in a biocontrol yeast provides insight into the basis for resistance to this mycotoxin

Patulin is a mycotoxin that contaminates pome fruits and derived products worldwide. Basidiomycete yeasts belonging to the subphylum Pucciniomycotina have been identified to have the ability to degrade this molecule efficiently and have been explored through different approaches to understand this degradation process. In this study, Sporobolomyces sp. strain IAM 13481 was found to be able to degrade patulin to form two different breakdown products, desoxypatulinic acid and (Z)-ascladiol. To gain insight into the genetic basis of tolerance and degradation of patulin, more than 3,000 transfer DNA (T-DNA) insertional mutants were generated in strain IAM 13481 and screened for the inability to degrade patulin using a bioassay based on the sensitivity of Escherichia coli to patulin. Thirteen mutants showing reduced growth in the presence of patulin were isolated and further characterized. Genes disrupted in patulin-sensitive mutants included homologs of Saccharomyces cerevisiae YCK2, PAC2, DAL5, and VPS8. The patulin-sensitive mutants also exhibited hypersensitivity to reactive oxygen species as well as genotoxic and cell wall-destabilizing agents, suggesting that the inactivated genes are essential for tolerating and overcoming the initial toxicity of patulin. These results support a model whereby patulin degradation occurs through a multistep process that includes an initial tolerance to patulin that utilizes processes common to other external stresses, followed by two separate pathways for degradation.

Overcoming recalcitrant transformation and gene manipulation in Pucciniomycotina yeasts

The red yeasts of the Pucciniomycotina have rarely been transformed with DNA molecules. Transformation methods were recently developed for a species of Sporobolomyces, based on selection using uracil auxotrophs and plasmids carrying the wild-type copies of the URA3 and URA5 genes. However, these plasmids were ineffective in the transformation of closely related species. Using the genome-sequenced strain of Rhodotorula graminis as a starting point, the URA3 and URA5 genes were cloned and tested for the transformation ability into different Pucciniomycotina species by biolistic and Agrobacterium-mediated transformations. Transformation success depended on the red yeast species and the origin of the URA3 or URA5 genes, which may be related to the high G + C DNA content found in several species. A new vector was generated to confer resistance to nourseothricin, using a native promoter from R. graminis and the naturally high G + C nourseothricin acetyltransferease gene. This provides a second selectable marker in these species. Targeted gene disruption was tested in Sporobolomyces sp. IAM 13481 using different lengths of homologous DNA with biolistic and Agrobacterium transformation methods. Both DNA delivery methods were effective for targeted replacement of a gene required for carotenoid pigment biosynthesis. The constructs also triggered transgene silencing. These developments open the way to identify and manipulate gene functions in a large group of basidiomycete fungi.

Conversion of the mycotoxin patulin to the less toxic desoxypatulinic acid by the biocontrol yeast Rhodosporidium kratochvilovae strain LS11

The infection of stored apples by the fungus Penicillium expansum causes the contamination of fruits and fruit-derived products with the mycotoxin patulin, which is a major issue in food safety. Fungal attack can be prevented by beneficial microorganisms, so-called biocontrol agents. Previous time-course thin layer chromatography analyses showed that the aerobic incubation of patulin with the biocontrol yeast Rhodosporidium kratochvilovae strain LS11 leads to the disappearance of the mycotoxin spot and the parallel emergence of two new spots, one of which disappears over time. In this work, we analyzed the biodegradation of patulin effected by LS11 through HPLC. The more stable of the two compounds was purified and characterized by nuclear magnetic resonance as desoxypatulinic acid, whose formation was also quantitated in patulin degradation experiments. After R. kratochvilovae LS11 had been incubated in the presence of (13)C-labeled patulin, label was traced to desoxypatulinic acid, thus proving that this compound derives from the metabolization of patulin by the yeast. Desoxypatulinic acid was much less toxic than patulin to human lymphocytes and, in contrast to patulin, did not react in vitro with the thiol-bearing tripeptide glutathione. The lower toxicity of desoxypatulinic acid is proposed to be a consequence of the hydrolysis of the lactone ring and the loss of functional groups that react with thiol groups. The formation of desoxypatulinic acid from patulin represents a novel biodegradation pathway that is also a detoxification process.

Development of resources for the analysis of gene function in Pucciniomycotina red yeasts

The Pucciniomycotina is an important subphylum of basidiomycete fungi but with limited tools to analyze gene functions. Transformation protocols were established for a Sporobolomyces species (strain IAM 13481), the first Pucciniomycotina species with a completed draft genome sequence, to enable assessment of gene function through phenotypic characterization of mutant strains. Transformation markers were the URA3 and URA5 genes that enable selection and counter-selection based on uracil auxotrophy and resistance to 5-fluoroorotic acid. The wild type copies of these genes were cloned into plasmids that were used for transformation of Sporobolomyces sp. by both biolistic and Agrobacterium-mediated approaches. These resources have been deposited to be available from the Fungal Genetics Stock Center. To show that these techniques could be used to elucidate gene functions, the LEU1 gene was targeted for specific homologous replacement, and also demonstrating that this gene is required for the biosynthesis of leucine in basidiomycete fungi. T-DNA insertional mutants were isolated and further characterized, revealing insertions in genes that encode the homologs of Chs7, Erg3, Kre6, Kex1, Pik1, Sad1, Ssu1 and Tlg1. Phenotypic analysis of these mutants reveals both conserved and divergent functions compared with other fungi. Some of these strains exhibit reduced resistance to detergents, the antifungal agent fluconazole or sodium sulfite, or lower recovery from heat stress. While there are current experimental limitations for Sporobolomyces sp. such as the lack of Mendelian genetics for conventional mating, these findings demonstrate the facile nature of at least one Pucciniomycotina species for genetic manipulation and the potential to develop these organisms into new models for understanding gene function and evolution in the fungi.

Strains of Aureobasidium pullulans can lower ochratoxin A contamination in wine grapes

Wine contamination with ochratoxin A (OTA) is due to the attack of wine grapes by ochratoxigenic Aspergillus carbonarius and Aspergillus spp. section Nigri. Four A. pullulans strains, AU14-3-1, AU18-3B, AU34-2, and LS30, are resistant to and actively degrade ochratoxin A in vitro. The less toxic ochratoxin alpha and the aminoacid L-beta-phenylalanine were the major degradation products, deriving from the cleavage of the amide bond linking these two moieties of OTA. The same strains were studied further as biocontrol agents of A. carbonarius on wine grapes in laboratory experiments. Three of the four strains significantly prevented infections by A. carbonarius. Berries pretreated with the biocontrol agents and infected with A. carbonarius contained lower amounts of OTA as compared to the untreated infected control berries. Two of these strains were shown to degrade OTA to ochratoxin alpha in fresh grape must, but the mechanisms of the decrease of OTA accumulation in infected berries pretreated with the biocontrol agents remain to be elucidated. Assessment of one strain carried out in the vineyard during the growing season of 2006 showed that the tested strain was an effective biocontrol agent, reducing both severity of Aspergillus rots and OTA accumulation in wine grapes. To our knowledge this is the first report describing the positive influence of biocontrol agents on OTA accumulation in this crop species.

Mouldy fruits and vegetables as a source of mycotoxins: part 2

Although chemical control is still the main way to reduce the preharvest and postharvest incidence of mycotoxigenic fungi, the worldwide tendency to reduce chemical use, and the emergence of resistant strains, have accelerated the search for non-chemical strategies. Those applied at the postharvest stage include heat treatments, biological control, and modified-or controlled-atmosphere storage. It is now evident that combinations of treatments are more efficient than individual treatments applied alone. Most of the studies on mycotoxins in fruits are focused on patulin (produced mainly by Penicillium expansum) in apple products, and ochratoxin A (produced mainly by Aspergillus carbonarius) in grapes and in wines. Patulin levels can be significantly reduced by washing and sorting apples, and trimming away rotten tissues. Other treatments for patulin reduction have been associated with its ability to react readily with compounds containing sulphydryl groups. Other additives that reduce patulin levels are ascorbic acid and B-complex vitamins. The rate of ochratoxin A reduction during fermentation depends, among others, on the yeast used for fermentation and the type of wine produced. During vinification, ochratoxin A is also reduced by binding to the solid residues of grapes. Alternaria mycotoxins may be produced naturally in a variety of fruits and vegetables and their processed products. At least two of these mycotoxins, alternariol and alternariol monomethyl, were shown to be stable in heated apple juice. In some apple cultivars, Alternaria occurs in the core and the damage is hidden. Contamination with mycotoxins is recognized as an unavoidable risk, but three major components are involved in the attempt to minimize the risk: Good Agricultural Practices, Good Manufacturing Practices, and Hazard Analysis Critical Control Points. In many countries, regulatory measures have been taken to limit the presence of mycotoxins in fruits and vegetables. Several factors may influence the establishment of national and regional mycotoxin limits and regulations.

Synergistic effect of chitosan and Cryptococcus laurentii on inhibition of Penicillium expansum infections

This study was conducted to determine the efficacy of chitosan at different concentrations with various intrinsic viscosities alone, and in its combination with a yeast antagonist Cryptococcus laurentii in reducing the blue mold rot caused by Penicillium expansum in apple fruit. The results indicated that application of chitosan alone was effective in inhibiting the blue mold rot in apple fruit wounds, especially with the high concentrations and low viscosities. But its efficacy was declining with the incubation time so that chitosan alone could not provide enduring protection of apple fruit from P. expansum infections. When applied at the concentration range from 0.001 to 0.1% (wt/vol), chitosan did not influence the population growth of C. laurentii in vivo, whereas it markedly repressed the yeast growth as its concentrations were increased up to 0.25% (wt/vol) or higher. Moreover, combination of chitosan and C. laurentii resulted in a synergistic inhibition of the blue mold rot, being the most effective at the optimal concentration of 0.1% of chitosan with the lowest viscosity (12 cP). The possible mode of action of the combination of chitosan and C. laurentii was discussed.