Isolation and Some Properties of the Enzyme That Transforms Eremofortin C to PR Toxin

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.

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.

Molecular characterization of the PR-toxin gene cluster in Penicillium roqueforti and Penicillium chrysogenum: cross talk of secondary metabolite pathways

The PR-toxin is a potent mycotoxin produced by Penicillium roqueforti in moulded grains and grass silages and may contaminate blue-veined cheese. The PR-toxin derives from the 15 carbon atoms sesquiterpene aristolochene formed by the aristolochene synthase (encoded by ari1). We have cloned and sequenced a four gene cluster that includes the ari1 gene from P. roqueforti. Gene silencing of each of the four genes (named prx1 to prx4) resulted in a reduction of 65-75% in the production of PR-toxin indicating that the four genes encode enzymes involved in PR-toxin biosynthesis. Interestingly the four silenced mutants overproduce large amounts of mycophenolic acid, an antitumor compound formed by an unrelated pathway suggesting a cross-talk of PR-toxin and mycophenolic acid production. An eleven gene cluster that includes the above mentioned four prx genes and a 14-TMS drug/H(+) antiporter was found in the genome of Penicillium chrysogenum. This eleven gene cluster has been reported to be very poorly expressed in a transcriptomic study of P. chrysogenum genes under conditions of penicillin production (strongly aerated cultures). We found that this apparently silent gene cluster is able to produce PR-toxin in P. chrysogenum under static culture conditions on hydrated rice medium. Noteworthily, the production of PR-toxin was 2.6-fold higher in P. chrysogenum npe10, a strain deleted in the 56.8kb amplifiable region containing the pen gene cluster, than in the parental strain Wisconsin 54-1255 providing another example of cross-talk between secondary metabolite pathways in this fungus. A detailed PR-toxin biosynthesis pathway is proposed based on all available evidence.

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.

Secondary metabolites resulting from degradation of PR toxin by Penicillium roqueforti

PR toxin is a secondary metabolite of the fungus Penicillium roqueforti. It is lethal to rats, mice, and cats. Usually, the amount of PR toxin in the culture medium decreases from its maximum on day 15 to zero within 3 to 4 days. We found that two were secondary metabolites produced in the culture medium of this fungus while the production of PR toxin was decreasing. We isolated and purified the two compounds in pure and colorless crystalline form. On the basis of elemental analysis and mass, 1H and 13C nuclear magnetic resonance, infrared, and UV spectroscopies, the two compounds were identified as PR-imine (C17H21O5N) and PR-amide (C17H21O6N). The structures of both compounds and of PR toxin (C17H20O6) were closely related, and the peak production of PR toxin appeared earlier than those of PR-imine and PR-amide. Moreover, PR toxin was transformed to PR-imine when PR toxin was incubated with the culture medium on a given culture day. Thus, we propose that PR toxin is degraded into PR-imine and PR-amide in the culture medium of P. roqueforti.

Determination of Penicillium roqueforti toxin by reversed-phase high-performance liquid chromatography

A method for the detection and quantification of Penicillium roqueforti toxin (PRT) using reversed-phase high-performance liquid chromatography has been established. The limit of quantitation of this method was 3 ng of PRT, while the limit of detection was 2 ng of toxin. The precision of the analysis based on numerous runs was good. Retention times for PRT were highly reproducible with an average coefficient of variation of about 1.6%. Analysis of PRT in liquid and solid samples showed no interference of the sample matrix. The accuracy of the method was 98.6%, with mean PRT recoveries of 96.8%, and 100.4% for the spiked culture medium and blue cheese extracts, respectively.

Factors affecting the production of eremofortin C and PR toxin in Penicillium roqueforti

Eremofortin C (EC) and PR toxin are secondary metabolites of Penicillium roqueforti. Of 17 strains from the American Type Culture Collection that were studied for their ability to produce EC and PR toxin, 13 produced these metabolites. Toxin production by strains grown in solid media (10 cereals and 8 other agricultural products) was also investigated. Production of EC and PR toxin by fungi grown on cereals was greater than production of EC and PR toxin by fungi grown on legumes; fungi grown on corn produced the greatest amount of PR toxin. Addition of corn extracts to the culture medium greatly increased the production of EC and PR toxin in a coordinated manner, with no significant change in mycelial dry weight. The fungi produced the highest levels of EC and PR toxin at 20 to 24 degrees C depending on the strain. Toxin production was higher in stationary cultures than in cultures that were gently shaken at 120 rpm. The optimum pH for production of both EC and PR toxin was around pH 4.0. With regard to spore age, toxin levels did not change significantly when we used spores obtained from fungi that were grown at 24 degrees C for 3 up to 48 days.

Chromatographic methods as tools in the field of mycotoxins

Achievements in the applications of chromatographic techniques in mycotoxicology are reviewed. Historically, column chromatography (CC) and paper chromatography (PC) were applied first, followed by thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC) and gas chromatography (GC). Although PC techniques are no longer used in the analysis of mycotoxins, selected applications of PC are included to underline historical continuity. The most important achievements published from 1980 onwards are described. They include clean-up methods, TLC, CC, HPLC and GC of mycotoxins in environmental samples, foods, feeds, body fluids and in studies on biosynthesis and biotransformations of mycotoxins. Advantages and disadvantages of chromatographic techniques used in mycotoxicology are also evaluated.