Secondary metabolites resulting from degradation of PR toxin by Penicillium roqueforti

Secondary Metabolites Produced by the Blue-Cheese Ripening Mold Penicillium roqueforti; Biosynthesis and Regulation Mechanisms

Filamentous fungi are an important source of natural products. The mold Penicillium roqueforti, which is well-known for being responsible for the characteristic texture, blue-green spots, and aroma of the so-called blue-veined cheeses (French Bleu, Roquefort, Gorgonzola, Stilton, Cabrales, and Valdeón, among others), is able to synthesize different secondary metabolites, including andrastins and mycophenolic acid, as well as several mycotoxins, such as Roquefortines C and D, PR-toxin and eremofortins, Isofumigaclavines A and B, festuclavine, and Annullatins D and F. This review provides a detailed description of the biosynthetic gene clusters and pathways of the main secondary metabolites produced by P. roqueforti, as well as an overview of the regulatory mechanisms controlling secondary metabolism in this filamentous fungus.

Germacrene A-A Central Intermediate in Sesquiterpene Biosynthesis

This review summarises known sesquiterpenes whose biosyntheses proceed through the intermediate germacrene A. First, the occurrence and biosynthesis of germacrene A in Nature and its peculiar chemistry will be highlighted, followed by a discussion of 6-6 and 5-7 bicyclic compounds and their more complex derivatives. For each compound the absolute configuration, if it is known, and the reasoning for its assignment is presented.

Cyclopiazonic acid gene expression as strategy to minimizing mycotoxin contamination in cheese

Expression of genes associated with cyclopiazonic acid (CPA) biosynthesis by Penicillium strains in a cheese-based medium has not been previously studied. To control CPA biosynthesis, it would be useful to understand the changes in gene expression during cheese production and relate them to toxin production. The objective was to evaluate the influence of pH, a_w, and temperature on expression of dmaT, which encodes the enzyme dimethylallyl tryptophan synthase involved in the biosynthesis of CPA. We assayed three Penicillium strains, Penicillium commune CBS311 and CBS341 and Penicillium camemberti CBS273, using reverse transcription real-time PCR. Our results showed that the expression patterns of the gene were influenced by strain and environmental conditions. The highest expression for the P. commune strains was observed at pH 6.0, 0.95 a_w, at 25 or 30 °C, depending on the strain. In contrast, P. camemberti CBS273 showed a lower dmaT expression with a maximum at 25 °C, pH 5.0 and 0.95 a_w. Correlation analysis indicated that the three toxigenic strains showed a strong correlation between the relative expression of the dmaT gene and concentration of CPA under conditions simulating cheese ripening. This method could be used to control CPA production in cheese by detection of dmaT expression.

Antioxidant Sesquiterpenes from Penicillium citreonigrum

A new chlorinated 11-noreremophilane-type sesquiterpene (1) together with 3-epiisopetasol, PR-amide and mycophenolic acid (2–4) were isolated from endophytic fungus Penicillium citreonigrum. The structures of 1–4 were elucidated by a combination of spectroscopic data and single-crystal X-ray diffraction analysis. Among them, compounds 1 and 4 showed moderate antioxidant capacities compared with ascorbic acid at 0.2 mM concentration.

Penicillium roqueforti PR toxin gene cluster characterization

PR toxin is a well-known isoprenoid mycotoxin almost solely produced by Penicillium roqueforti after growth on food or animal feed. This mycotoxin has been described as the most toxic produced by this species. In this study, an in silico analysis allowed identifying for the first time a 22.4-kb biosynthetic gene cluster involved in PR toxin biosynthesis in P. roqueforti. The pathway contains 11 open reading frames encoding for ten putative proteins including the major fungal terpene cyclase, aristolochene synthase, involved in the first farnesyl-diphosphate cyclization step as well as an oxidoreductase, an oxidase, two P450 monooxygenases, a transferase, and two dehydrogenase enzymes. Gene silencing was used to study three genes (ORF5, ORF6, and ORF8 encoding for an acetyltransferase and two P450 monooxygenases, respectively) and resulted in 20 to 40% PR toxin production reductions in all transformants proving the involvement of these genes and the corresponding enzyme activities in PR toxin biosynthesis. According to the considered silenced gene target, eremofortin A and B productions were also affected suggesting their involvement as biosynthetic intermediates in this pathway. A PR toxin biosynthesis pathway is proposed based on the most recent and available data.

Biosynthetic gene clusters for relevant secondary metabolites produced by Penicillium roqueforti in blue cheeses

Ripening of blue-veined cheeses, such as the French Bleu and Roquefort, the Italian Gorgonzola, the English Stilton, the Danish Danablu or the Spanish Cabrales, Picón Bejes-Tresviso, and Valdeón, requires the growth and enzymatic activity of the mold Penicillium roqueforti, which is responsible for the characteristic texture, blue-green spots, and aroma of these types of cheeses. This filamentous fungus is able to synthesize different secondary metabolites, including andrastins, mycophenolic acid, and several mycotoxins, such as roquefortines C and D, PR-toxin and eremofortins, isofumigaclavines A and B, and festuclavine. This review provides a detailed description of the main secondary metabolites produced by P. roqueforti in blue cheese, giving a special emphasis to roquefortine, PR-toxin and mycophenolic acid, and their biosynthetic gene clusters and pathways. The knowledge of these clusters and secondary metabolism pathways, together with the ability of P. roqueforti to produce beneficial secondary metabolites, is of interest for commercial purposes.

Examination of the taxonomic position of Penicillium strains used in blue cheese production based on the partial sequence of β-tubulin

Penicillium roqueforti is a well known starter used for blue cheese production. Two closely related species, P. carneum and P. paneum, were previously classified as varieties of P. roqueforti. Penicillium roqueforti does not produce patulin, a mycotoxin harmful for human health, whereas both P. carneum and P. paneum actively produce this toxin. From the viewpoint of food safety, it is thus important to confirm that P. carneum and P. paneum are not used for cheese production. In the present study, the taxonomic position of Penicillium strains used for blue cheese production was examined on the basis of the partial sequence of β-tubulin. Twenty-eight Penicillium strains isolated from blue cheeses were investigated. All the examined strains belonged to P. roqueforti. Therefore, the Penicillium strains used for production of the blue cheese samples examined here do not negatively impact on human health.

Filamentous Fungi and Mycotoxins in Cheese: A Review

Important fungi growing on cheese include Penicillium, Aspergillus, Cladosporium, Geotrichum, Mucor, and Trichoderma. For some cheeses, such as Camembert, Roquefort, molds are intentionally added. However, some contaminating or technological fungal species have the potential to produce undesirable metabolites such as mycotoxins. The most hazardous mycotoxins found in cheese, ochratoxin A and aflatoxin M1, are produced by unwanted fungal species either via direct cheese contamination or indirect milk contamination (animal feed contamination), respectively. To date, no human food poisoning cases have been associated with contaminated cheese consumption. However, although some studies state that cheese is an unfavorable matrix for mycotoxin production; these metabolites are actually detected in cheeses at various concentrations. In this context, questions can be raised concerning mycotoxin production in cheese, the biotic and abiotic factors influencing their production, mycotoxin relative toxicity as well as the methods used for detection and quantification. This review emphasizes future challenges that need to be addressed by the scientific community, fungal culture manufacturers, and artisanal and industrial cheese producers.

Chemical constituents of the fermentation broth of the marine-derived fungus Penicillium roqueforti

BACKGROUND

The filamentous fungus Penicillium roqueforti is a well-known multifunctional cell factory of high added-value biomolecules.

AIMS

The objective of this work was to carry out a detailed analysis of the metabolites present in the culture broth of a new marine-derived Penicillium roqueforti strain isolated in the Canary Islands, Spain.

METHODS

The fungal biomass production was carried out in liquid-state fermentation, and after 10-12 days of incubation at 22-25°C, the supernatant mycelia was separated by filtration, and the culture broth (12l) was stored in a refrigerator at 4°C for a subsequent liquid-liquid extraction with dichloromethane (3×), in accordance with the modified Kupchan method. The volatile and semi-volatile organic compounds were separated by chromatography and analyzed using GC-MS and NMR spectroscopy analyses.

RESULTS

Several volatile organic compounds involved in the fatty acid pathway were identified: a terpenoid, a cyclic dipeptide, phthalates, and an alkyl adipate. In addition, three categories of non-volatile compounds (alkanes, fatty acids and 1-alkanols) were identified by spectroscopy. The results show that the fermented broth of this fungal strain has no mycotoxins under the culture conditions applied.

CONCLUSIONS

It is hoped that this chemo-specific information will offer critical input for improving the biotechnological applications of this filamentous fungus.

Mycotoxin-forming ability of two Penicillium roqueforti strains in blue moldy tulum cheese ripened at various temperatures

Isolated and identified toxigenic and nontoxigenic Penicillium roqueforti (PR) strains from moldy tulum cheeses were inoculated into tulum cheeses made in the laboratory and ripened at 5 and 12 degrees C. Mycotoxin (patulin, penicillic acid, PR toxin, and roquefortine) formation in the control and mold-inoculated cheeses were detected by thin-layer chromatography on the first through fourth months of ripening. Patulin, penicillic acid, and PR toxin were not detected in the experimental cheeses. Only roquefortine was detected in cheese inoculated with the toxigenic strain of the mold and ripened at 5 and 12 degrees C on the third and first months of ripening, respectively. Toxin in cheeses ripened at 5 and 12 degrees C was 2.1 to 2.4 and 2.1 to 3.8 mg/kg cheese, respectively.

Influence of octanoic acid addition to medium on some volatile compounds and PR-toxin biosynthesis by Penicillium roqueforti

AIMS

The effect of wheat kernel medium supplementation with octanoic acid on the formation of PR toxin and some volatiles by Penicillium roqueforti was investigated.

METHODS AND RESULTS

Octanoic acid was added to the medium once, prior to inoculation (4.55 mg g-1), or periodically (total 27.3 mg g-1) during the 10 day course of incubation. No octanoic acid was added to the reference sample. Levels of 2-heptanone, 2-heptanol and aristolochene, a volatile intermediate in PR toxin biosynthesis, were monitored using a solid phase microextraction (SPME) technique. The contents of PR toxin and ergosterol were determined after incubation. Aristolochene was observed in the reference sample, and 10.4 mg kg-1 of PR toxin was detected after 10 days. In cultures periodically supplemented with octanoic acid, no aristolochene or PR toxin were observed. However, in samples supplemented with octanoic acid only prior to incubation, the aristolochene level was 25% that in the reference sample, and PR toxin content was 3.4 mg kg-1.

SIGNIFICANCE AND IMPACT OF THE STUDY

These data suggest that a high level of octanoic acid in the medium prevents PR toxin formation by P. roqueforti.

Biological detoxification of fungal toxins and its use in plant breeding, feed and food production

Enzymatic inactivation of fungal toxins is an attractive strategy for the decontamination of agricultural commodities and for the protection of crops from phytotoxic effects of fungal metabolites. This review summarizes research on the biological detoxification of fungal toxins by microorganisms and plants and its practical applications. Some mycotoxins are detoxified during ensiling and other fermentation processes (aflatoxins, alternariol, mycophenolic acid, patulin, PR toxin) while others are transformed into toxic products or survive fermentation unchanged. Plants can detoxify fomannoxin, fusaric acid, HC-toxin, ochratoxin A and oxalate but the degradation of deoxynivalenol has yet to be proven. Microflora of the digestive tract of vertebrates and invertebrates exhibit detoxification activities towards aflatoxins, ochratoxin A, oxalate and trichothecenes. Some toxin-producing fungi are able to degrade or transform their own products under suitable conditions. Pure cultures of bacteria and fungi which detoxify mycotoxins have been isolated from complex microbial populations by screening and enrichment culture techniques. Genes responsible for some of the detoxification activities have been cloned and expressed in heterologous hosts. The detoxification of aflatoxins, cercosporin, fumonisins, fusaric acid, ochratoxin A, oxalic acid, patulin, trichothecenes and zearalenone by pure cultures is reviewed. Finally, current application of these results in food and feed production and plant breeding is summarized and expected future developments are outlined.

Isolation, purification, and characterization of the PR oxidase from penicillium roqueforti

The PR oxidase, an extracellular enzyme, involved in the conversion of PR toxin into PR acid, was purified from the culture broth of Penicillium roqueforti ATCC 48936. The enzyme has a pI of 4.5 and a molecular mass of approximately 88 kDa, and it is a monomer. The optimum pH for this enzyme is ca. 4.0, and the optimum temperature is 50 degreesC.

Reclassification of the Penicillium roqueforti group into three species on the basis of molecular genetic and biochemical profiles

Penicillium roqueforti is currently divided into two varieties, one used for cheese starter cultures, P. roqueforti var. roqueforti, and one ubiquitous patulin-producing variety, P. roqueforti var. carneum. The ribosomal regions comprising the 5.8S gene and the internal transcribed spacers, ITS I and ITS II, have been analysed from 10 isolates belonging to each variety. The 10 P. roqueforti var. carneum isolates were separated into two groups of five on the basis of 12 base-pair differences in the ITS regions. One of the groups of P. roqueforti var. carneum, in the following designated P. carneum, differed from P. roqueforti var. roqueforti, here designated P. roqueforti, in just two positions, while the other group, here called P. paneum, differed from P. roqueforti in 12 positions. Random Amplified Polymorphic DNA (RAPD) analysis substantiated these findings, and a comparison of secondary metabolites produced by the three groups showed that the P. roqueforti isolates all produce Penicillium Roqueforti (PR) toxin, marcfortines and fumigaclavine A, while the P. carneum isolates produce patulin, penitrem A and mycophenolic acid, as well as unidentified metabolites. P. paneum produces secondary metabolites in five chromophore families including the known mycotoxins patulin and botryodiploidin. On the basis of these findings it is proposed that P. roqueforti is reclassified into three species named P. roqueforti, P. carneum and P. paneum.