PENICILLIUM ROQUEFORTI: CHARACTERISTICS, HABITAT, REPRODUCTION - BIOLOGY - 2024

Penicillium roqueforti is an Ascomycota fungus of the Trichocomaceae family that is characterized, among other aspects, by presenting brush-shaped conidiophores. In culture media it presents a great morphological diversity, but with generally well-defined colony margins.

In nature it can be found in a wide variety of substrates, including soils, plant roots and fruits. The food industry has used it for several centuries to produce blue cheeses, being responsible for its characteristic color, smell and taste.

Penicillium roqueforti spores. Taken and edited from: Arunbiel.

Due to the great morphological diversity shown by this species, some authors maintain that it is really a complex of species that includes, among others, the Penicillium glaucum, P. stilton, P. gorgonzolae and P. aromaticum species. Other researchers maintain that they are varieties of the same species.

characteristics

Since Penicillium roqueforti does not normally have sexual structures, descriptions are based on growth in culture media. In PDA culture, the colony color varies from pale yellow to dark grayish green.

The size of the colony can also vary considerably and its margins are regular, although they can be from thin to very thick. On the other hand, the texture of the colony can be velvety, floppy, fasciculate, or any texture in between.

In malt extract, the colony grows up to 50 mm in diameter, with a green coloration and margins similar to spider web fibers, while in YES or Czapek agar it only grows up to 40 mm, showing a coloration that goes from green even black, while the margins of the colony are velvety in texture.

A characteristic of this species is the production of asexual spores in phialides arranged in the form of a brush.

Habitat and distribution

Habitat

In the natural environment, Penicillium roqueforti can inhabit a wide variety of substrates, mainly in soils rich in decomposing plant material. It can also grow on the roots, trunks and even fruits of a wide variety of plants.

Distribution

Although the specific epithet of the species refers to the locality where it was found for the first time (Roquefort-sur-Soulzon, France), the species is cosmopolitan and has a wide distribution worldwide.

Taxonomy

Penicillium roqueforti is an Ascomycota fungus, belonging to the Eurotiomycetes class, Eurotiales order and Trichocomaceae family. The genus Penicillium was formerly included in the group of imperfect fungi (Deuteromycetes) because its sexual phase was unknown.

Currently, mycologists have determined that Penicillium is the asexual or anamorphic form of a group of fungi that also have a sexual form (teleomorph), which is why the genus was relocated within the Ascomycota group of fungi.

Penicillium roqueforti was first described by the North American mycologist Charles Thom in 1906. It has a high morphological diversity, which has hampered its taxonomic stability. Initially, the species was a heterogeneous group of fungi that produced blue-green spores, then the group was separated and regrouped several times.

Molecular studies allowed the separation of three species: Penicillium roqueforti, P. carneum and P. paneum. However, some of the Penicillium roqueforti morphotypes that have been described as other species, including Penicillium glaucum, P. stilton, P. gorgonzolae and P. aromaticum, are not considered valid.

Reproduction

As already noted before, Penicillium roqueforti is an anamorph, that is, an asexual reproduction phase of the species. This reproduction is achieved mainly through the production of spores in a structure called a conidiophore. These spores are capable of germinating without their fertilization having occurred.

The sexual phase of the species in nature is unknown, however, in laboratory experiences, researchers have managed to induce the formation of reproductive structures, as well as sexual reproduction in this species.

Nutrition

Penicillium roqueforti is a saprophytic species, so it requires organic matter already prepared for its food. In nature it feeds on dead plant matter. It can also spoil some foods, for example, producing the mold that attacks rye bread.

Applications

The food industry uses Penicillium roqueforti for the production of different types of blue cheese. The fungus is the main responsible for the flavor and also the color of these cheeses. Differences between different types of blue cheese may be due to manufacturing methods or the use of different strains of the fungus.

The manufacture of cheeses by man is a millenary activity, dating back to the Neolithic, about 6000 years BC. C. Blue cheeses are made using different types of milk, such as goat and cow's milk, and are consumed worldwide.

Normally, to obtain the fungus during cheese making, producers use rye bread stored in humid places, allowing the development of Penicillium roqueforti mold, which will be used as an inoculum.

Among the cheeses made based on Penicillium roqueforti are Roquefort, Bleu de Bresse, Bleu du Vercors-Sassenage, Brebiblu, Cabrales, Cambozola or also Cashel Blue and Danish blue.

Penicillum roqueforti is also used to produce bioactive compounds with antibiotic activity. Additionally, they produce aromas and fragrances, the use of which is not regulated by the FDA.

Blue cheese, made based on the Penicillium roqueforti fungus. Taken and edited from: smial.

Metabolites

The P. roqueforti fungus, under particular cultivation conditions, can produce secondary metabolites that can be harmful. One of these metabolites is for example aristoloquene, a bicyclic sesquiterpene, which is a precursor of the PR toxin.

This toxin, which can be generated in large quantities, has mycotoxic properties and has been involved in incidents due to the consumption of contaminated grains. However, the PR toxin is not stable in cheese and quickly transforms into a PR imine, which is not toxic.

Penicillium roqueforti also produces a very potent neurotoxin, called roquefortin C, which is capable of producing, at least in laboratory rats, seizures, liver damage and bleeding in the digestive tract.

However, this substance is produced in very small quantities and its concentration in cheese is too low to cause adverse effects.

Atypical wild strains of Penicillium roqueforti can also produce other toxins such as patulin, penicylic acid, citrinin, and mycophenolytic acid, however commercial strains do not produce these toxins.

On the other hand, when Penicillium roqueforti is present in mixtures of grains and silages, it seems to be responsible for abortions and retention of the placenta in cattle.

References

1. LB Bullerman (2003). Mycotoxins. Classifications, In Encyclopedia of Food Sciences and Nutrition, 2 ^nd Edition. Elsevier.
2. Penicillium roqueforti. On Wikipedia. Recovered from: en.wikipedia.org
3. V. Gómez (2019). Penicillium: characteristics, taxonomy, morphology, habitat. In lifeder. Recovered from: lifeder.com.
4. M. Boysen, P. Skouboe, J. Frisvad & L. Rossen (1996). Reclassification of the Penicillium roqueforti group into three species on the basis of molecular genetic and biochemical profiles. Microbiology.
5. J. Ropars, M. López-Villavicencio, J. Dupont, A. Snirc, G. Gillot, M. Coton, E. Coton & T. Giraud (2014). Induction of sexual reproduction and genetic diversity in the cheese fungus Penicillium roqueforti. Evolutionary Applications.
6. CM Visagie, J. Houbraken, JC Frisvad, SB Hong, CGW Klaassen, G. Perrone, KA Seifert, J. Varga, T. Yaguchi & RA Samson (2014). Identification and nomenclature of the genus Penicillium. Studies in Mycology.
7. C. Lyre. Penicillium: characteristics, morphology, habitat, reproduction. Recovered from: lifeder.com.