Penicillium roqueforti

Classification

First described by the American mycologist Charles Thom in 1906, P. roqueforti was initially described as heterogeneous species of blue-green, sporulating fungi. They were grouped into different species based on phenotypic differences, but later combined into one species by Kenneth B. Raper and Thom (1949). The P. roqueforti group then got a reclassification in 1996 due to molecular analysis of ribosomal DNA sequences. Formerly divided into two varieties―cheese-making (P. roqueforti var. roqueforti) and patulin-making (P. roqueforti var. carneum)―P. roqueforti was reclassified into three species: P. roqueforti, P. carneum, and P. paneum. The complete genome sequence of P. roqueforti was published in 2014.

Description

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 on Czapek 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. Another characteristic morphological feature of this species is its production of asexual spores in phialides with a distinctive brush-shaped configuration.

Evidence for a sexual stage in P. 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 in meiosis. In 2014, researchers reported inducing the growth of sexual structures in P. roqueforti, including ascogonia, cleistothecia, and ascospores. Genetic analysis and comparison of many different strains isolated from various environments around the world indicate that it is a genetically diverse species.

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 and silage.

Uses

The chief industrial use of this species is the production of blue cheeses, such as its namesake Roquefort, Bleu de Bresse, Bleu du Vercors-Sassenage, Brebiblu, Cabrales, Cambozola (Blue Brie), Cashel Blue, Danish blue, Swedish Ädelost, Polish Rokpol made from cow's milk, Fourme d'Ambert, Fourme de Montbrison, Lanark Blue, Shropshire Blue, and Stilton, and some varieties of Bleu d'Auvergne and Gorgonzola. (Other blue cheeses, including Bleu de Gex and Rochebaron, use Penicillium glaucum.)

When placed into cream and aerated, P. roqueforti produces concentrated blue cheese flavoring, a type of enzyme-modified cheese. A similar flavoring can be produced using other sources of fat, such as coconut oil.

Strains of the microorganism are also used to produce compounds that can be employed as antibiotics, flavours, and fragrances, uses not regulated under the U.S. Toxic Substances Control Act.

Secondary metabolites

Considerable evidence indicates that most strains are capable of producing harmful secondary metabolites (alkaloids and other mycotoxins) under certain growth conditions. Aristolochene is a sesquiterpenoid compound produced by P. roqueforti, and is likely a precursor to the toxin known as PR toxin, made in large amounts by the fungus. PR-toxin has been implicated in incidents of mycotoxicoses resulting from eating contaminated grains. However, PR toxin is not stable in cheese, and breaks down to the less toxic PR imine.

Secondary metabolites of P. roqueforti, named andrastins A–D, are found in blue cheese. The andrastins inhibit proteins involved in the efflux of anticancer drugs from multidrug-resistant cancer cells, indicating potential value in cancer treatment.

P. roqueforti also produces the neurotoxin roquefortine C. 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 of proteases and specialty chemicals, such as methyl ketones, including 2-heptanone.

Recent research has shown significant differences in metabolite production between P. 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 a guanine to adenine nuceltide substitution in ORF 11 of the PR toxin biosynthetic cluster, introducing a premature stop codon. Similarly, these strains cannot produce mycophenolic acid due to a deletion in the lipase/esterase domain of the mpaC gene. While Roquefort strains show no genetic mutations in PR toxin genes, they still do not produce the toxin, suggesting downregulation of the pathway.

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 in fatty acids and terpenoids, 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.

References

References

1. (1996). "Reclassification of the ''Penicillium roqueforti'' group into three species on the basis of molecular genetic and biochemical profiles". Microbiology.
2. (August 2008). "Morphological and molecular characterisation of ''Penicillium roqueforti'' and ''P. paneum'' isolated from baled grass silage". Mycol. Res..
3. (December 1944). "Penicillin: II. Natural Variation and Penicillin Production in Penicillium notatum and Allied Species". J. Bacteriol..
4. Raper KB. (1957). "Nomenclature in ''Aspergillus'' and ''Penicillium''". Mycologia.
5. (1984). "The taxonomic situation in the hyphomycete genera Penicillium, Aspergillus and Fusarium". Antonie van Leeuwenhoek.
6. (2012). "Sex in cheese: evidence for sexuality in the fungus ''Penicillium roqueforti''". PLOS ONE.
7. (November 1976). "Enzymes of ''Penicillium roqueforti'' involved in the biosynthesis of cheese flavour". Crit Rev Food Sci Nutr.
8. (2021). "Agents of Change: Enzymes in Milk and Dairy Products".
9. (1 August 2012). "Factors Affecting the Production of Concentrated Blue Cheese Flavorings". Clemson University.
10. (Sharpell, 1985)
11. (1997). "Toxin-producin species of ''Penicillium'' and the development of mycotoxins in must and homemade wine". Nat. Toxins.
12. (February 2001). "Roquefortine C occurrence in blue cheese". [[Journal of Food Protection]].
13. (March 2004). "Mycotoxin-forming ability of two ''Penicillium roqueforti'' strains in blue moldy tulum cheese ripened at various temperatures". [[Journal of Food Protection]].
14. (November 2006). "Mycotoxins and other secondary metabolites produced in vitro by ''Penicillium paneum'' Frisvad and ''Penicillium roqueforti'' Thom isolated from baled grass silage in Ireland". [[Journal of Agricultural and Food Chemistry]].
15. (February 1993). "Aristolochene synthase. Isolation, characterization, and bacterial expression of a sesquiterpenoid biosynthetic gene (Ari1) from ''Penicillium roqueforti''". [[Journal of Biological Chemistry]].
16. (1982). "Acute toxicity of PR toxin, a mycotoxin from ''Penicillium roqueforti''". Toxicon.
17. Siemens, Zawitowski J. (1993). "Occurrence of PR imine, a metabolite of ''Penicillium roqueforti'', in blue cheese". [[Journal of Food Protection]].
18. (April 2005). "Andrastins A-D, ''Penicillium roqueforti'' Metabolites consistently produced in blue-mold-ripened cheese". [[Journal of Agricultural and Food Chemistry]].
19. SCBT. "Roquefortine - A potent neurotoxin produced most notably by ''Penicillium'' species".
20. (29 April 2015). "''Penicillium roqueforti'' Final Risk Assessment". [[United States Environmental Protection Agency]].
21. (1989). "Methyl-ketone production by Ca-alginate/Eudragit RL entrapped spores of ''Penicillium roqueforti''". [[Enzyme and Microbial Technology]].
22. Biourge P.. (1923). "Les moissisures du groupe ''Penicillium'' Link". La Cellule.
23. (2014). "Multiple recent horizontal transfers of a large genomic region in cheese making fungi". Nature Communications.
24. (2024-11-28). "Different metabolite profiles across ''Penicillium roqueforti'' populations associated with ecological niche specialisation and domestication". IMA Fungus.
25. Dattilo-Rubbo S.. (1938). "The taxonomy of fungi of blue-veined cheese". Transactions of the British Mycological Society.
26. (2014). "Induction of sexual reproduction and genetic diversity in the cheese fungus ''Penicillium roqueforti ''". Evolutionary Applications.
27. Thom C.. (1909). "Fungi in cheese ripening; Camembert and Roquefort". U.S.D.A. Bureau of Animal Industry Bulletin.
28. "GSD Species Synonymy: ''Penicillium roqueforti'' Thom". Species Fungorum. CAB International.
29. Westling R.. (1911). "Über die grünen Spezies der Gattung ''Penicillium''". Arkiv før Botanik.