| Penicillium roqueforti | |
|---|---|
 | |
| Blue Stilton cheese, showing the blue-green mold veins produced byPenicillium roqueforti | |
Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Eurotiomycetes |
| Order: | Eurotiales |
| Family: | Aspergillaceae |
| Genus: | Penicillium |
| Species: | P. roqueforti |
| Binomial name | |
| Penicillium roqueforti Thom (1906) | |
| Synonyms[4] | |
Penicillium roqueforti is a commonsaprotrophicfungus in thegenusPenicillium. Widespread in nature, it can be isolated from soil, decaying organic matter, and plants.
The major industrial uses of this fungus are the production ofblue cheeses, flavouring agents, antifungals,polysaccharides,proteases, and otherenzymes. The fungus has been a constituent ofRoquefort,Stilton,Danish blue,Cabrales, and other blue cheeses. A few blue cheeses, such asGorgonzola, are made instead withPenicillium glaucum.
Firstdescribed by the American mycologistCharles Thom in 1906,[5]P. roqueforti was initially described as heterogeneous species of blue-green, sporulating fungi. They were grouped into different species based onphenotypic differences, but later combined into one species byKenneth B. Raper and Thom (1949). TheP. roqueforti group then got a reclassification in 1996 due tomolecular analysis ofribosomal DNA sequences. Formerly divided into two varieties―cheese-making (P. roqueforti var.roqueforti) andpatulin-making (P. roqueforti var.carneum)―P. roqueforti was reclassified into three species:P. roqueforti,P. carneum, andP. paneum.[6] The completegenome sequence ofP. roqueforti was published in 2014.[7]
As this fungus does not form visible fruiting bodies, descriptions are based on macromorphological characteristics of fungal colonies growing on various standard agar media, and on microscopic characteristics. When grown onCzapek yeast autolysate agar or yeast-extract sucrose (YES) agar,P. roqueforti colonies are typically 40 mm in diameter, olive brown to dull green (dark green to black on the reverse side of the agar plate), with a velutinous (velvety) texture. Grown on malt extract agar, colonies are 50 mm in diameter, dull green in color (beige to greyish green on the reverse side), with arachnoid (with many spider-web-like fibers) colony margins.[8] Another characteristic morphological feature of this species is its production of asexual spores inphialides with a distinctive brush-shaped configuration.[9][10][11]
Evidence for a sexual stage inP. roqueforti has been found, based in part on the presence of functional mating-type genes, and most of the important genes known to be involved inmeiosis.[12] In 2014, researchers reported inducing the growth of sexual structures inP. roqueforti, includingascogonia,cleistothecia, andascospores. Genetic analysis and comparison of many different strains isolated from various environments around the world indicate that it is agenetically diverse species.[13]
P. roqueforti can tolerate cold temperatures, low oxygen levels, and both alkali and weaker acid preservatives, which allows the fungi to thrive and be found in dairy environments, such as cheese. On the other hand, it also spoils refrigerated foods and meats, along with breads andsilage.
The chief industrial use of this species is the production of blue cheeses, such as its namesakeRoquefort,[14]Bleu de Bresse,Bleu du Vercors-Sassenage,Brebiblu,Cabrales,Cambozola (Blue Brie),Cashel Blue,Danish blue, SwedishÄdelost, PolishRokpol made from cow's milk,Fourme d'Ambert,Fourme de Montbrison,Lanark Blue,Shropshire Blue, andStilton, and some varieties ofBleu d'Auvergne andGorgonzola. (Other blue cheeses, includingBleu de Gex andRochebaron, usePenicillium glaucum.)
When placed into cream and aerated,P. roqueforti produces concentrated blue cheese flavoring, a type ofenzyme-modified cheese.[15] A similar flavoring can be produced using other sources of fat, such as coconut oil.[16]
Strains of the microorganism are also used to produce compounds that can be employed asantibiotics, flavours, and fragrances,[17] uses not regulated under the U.S.Toxic Substances Control Act.
Considerable evidence indicates that most strains are capable of producing harmful secondary metabolites (alkaloids and othermycotoxins) under certain growth conditions.[18][19][20][21]Aristolochene is asesquiterpenoid compound produced byP. roqueforti, and is likely a precursor to the toxin known as PR toxin, made in large amounts by the fungus.[22]PR-toxin has been implicated in incidents ofmycotoxicoses resulting from eating contaminated grains.[20][23] However, PR toxin is not stable in cheese, and breaks down to the less toxic PRimine.[24]
Secondary metabolites ofP. roqueforti, namedandrastins A–D, are found in blue cheese. The andrastins inhibit proteins involved in theefflux ofanticancer drugs from multidrug-resistantcancer cells, indicating potential value in cancer treatment.[25]
P. roqueforti also produces theneurotoxinroquefortine C.[26][27]However, the levels of roquefortine C in cheese made from it are usually too low to produce toxic effects. The organism can also be used for the production ofproteases and specialty chemicals, such asmethylketones, including2-heptanone.[28]
Recent research has shown significant differences in metabolite production betweenP. roqueforti populations. The cheese-making populations, particularly the non-Roquefort strains, produce fewer metabolites compared to non-cheese populations found in lumber and silage. The non-Roquefort populations' inability to produce PR toxin stems from aguanine toadenine nuceltide substitution inORF 11 of the PR toxin biosynthetic cluster, introducing a prematurestop codon. Similarly, these strains cannot producemycophenolic acid due to a deletion in thelipase/esterase domain of thempaC gene. While Roquefort strains show no genetic mutations in PR toxin genes, they still do not produce the toxin, suggestingdownregulation of the pathway.[29]
The Termignon cheese population shows intermediate metabolite profiles between cheese and non-cheese populations, producing low levels of PR toxin, while showing the highest production of MPA-related compounds. Non-cheese populations maintain higher metabolite diversity, particularly infatty acids andterpenoids, which may provide competitive advantages in more complex environments, where fungi must compete with other microorganisms. The reduced toxin production in cheese strains likely results from either deliberate selection for safer strains during domestication, or the degeneration of unused metabolic pathways in the cheese environment.[29]
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