Penicillium is a genus of ascomycetous fungi of major importance in the natural environment as well as food and drug production. Members of the genus produce penicillin, a molecule that is used as an antibiotic, which kills or stops the growth of certain kinds of bacteria inside the body. According to the Dictionary of the Fungi (10th edition, 2008), the widespread genus contains over 300 species.
Taxonomy and naming
The genus was first described in the scientific literature by Johann Heinrich Friedrich Link in his 1809 work Observationes in ordines plantarum naturales. Link included three species—P. candidum, P. expansum, and P. glaucum—all of which produced a brush-like conidiophore (asexual fruiting structure). The common apple rot fungus P. expansum was selected as the type species.
Penicillium is classified as a genus of anamorphic fungi in the division Ascomycota (order Eurotiales, class Eurotiomycetes, family Trichocomaceae). The genus name is derived from the Latin root penicillium, meaning "painter's brush", and refers to the chains of conidia that resemble a broom.
The thallus (mycelium) typically consists of a highly branched network of multinucleate, septate, usually colorless hyphae. Many-branched conidiophores sprout on the mycelia, bearing individually constricted conidiospores. The conidiospores are the main dispersal route of the fungi, and often are green in color.
Sexual reproduction involves the production of ascospores, commencing with the fusion of an archegonium and an antheridium, with sharing of nuclei. The irregularly distributed asci contain eight unicellular ascospores each.
Species of Penicillium are ubiquitous soil fungi preferring cool and moderate climates, commonly present wherever organic material is available. Saprophytic species of Penicillium and Aspergillus are among the best-known representatives of the Eurotiales and live mainly on organic biodegradable substances. Commonly known as molds, they are among the main causes of food spoilage, especially species of subgenus Penicillium. Many species produce highly toxic mycotoxins. The ability of these Penicillium species to grow on seeds and other stored foods depends on their propensity to thrive in low humidity and to colonize rapidly by aerial dispersion while the seeds are sufficiently moist. Some species have a blue color, commonly growing on old bread and giving it a blue fuzzy texture.
Some Penicillium species affect the fruits and bulbs of plants, including P. expansum, apples and pears; P. digitatum, citrus fruits; and P. allii, garlic. Some species are known to be pathogenic to animals; P. corylophilum, P. fellutanum, P. implicatum, P. janthinellum, P. viridicatum, and P. waksmanii are potential pathogens of mosquitoes. P. marneffei, which causes mortality in the Vietnamese bamboo rats, has become a common opportunistic infection of HIV-infected individuals in southeast Asia.
Penicillium species are present in the air and dust of indoor environments, such as homes and public buildings. The fungus can be readily transported from the outdoors, and grow indoors using building material or accumulated soil to obtain nutrients for growth. Penicillium growth can still occur indoors even if the relative humidity is low, as long as there is sufficient moisture available on a given surface. A British study determined that Aspergillus- and Penicillium-type spores were the most prevalent in the indoor air of residential properties, and exceeded outdoor levels. Even ceiling tiles can support the growth of Penicillium—as one study demonstrated—if the relative humidity is 85% and the moisture content of the tiles is greater than 2.2%.
Some Penicillium species cause damage to machinery and the combustible materials and lubricants used to run and maintain them. For example, P. chrysogenum, P. steckii, P. notatum, P. cyclopium, and P. nalgiovensis affect fuels; P. chrysogenum, P. rubrum, and P. verrucosum cause damage to oils and lubricants; P. regulosum damages optical and protective glass.
Several species of the genus Penicillium play a central role in the production of cheese and of various meat products. To be specific, Penicillium molds are found in Blue cheese. Penicillium camemberti and Penicillium roqueforti are the molds on Camembert, Brie, Roquefort, and many other cheeses. Penicillium nalgiovense is used to improve the taste of sausages and hams, and to prevent colonization by other molds and bacteria.
In addition to their importance in the food industry, species of Penicillium and Aspergillus serve in the production of a number of biotechnologically produced enzymes and other macromolecules, such as gluconic, citric, and tartaric acids, as well as several pectinases, lipase, amylases, cellulases, and proteases. Some Penicillium species have shown potential for use in bioremediation because of their ability to break down a variety of xenobiotic compounds.
The genus is the source of major antibiotics. Penicillin, a drug produced by P. chrysogenum, was discovered by Alexander Fleming in 1929, and found to inhibit the growth of Gram positive bacteria (see beta-lactams). Its potential as an antibiotic was realized in the late 1930s, and Howard Florey and Ernest Chain purified and concentrated the compound. The drug's success in saving soldiers in World War II dying from infected wounds earned Fleming, Florey and Chain the Nobel Prize in Medicine in 1945.
Griseofulvin is an antifungal drug and a potential chemotherapeutic agent that was discovered in P. griseofulvum. Additional species that produce compounds capable of inhibiting the growth of tumor cells in vitro include: P. pinophilum, P. canescens, and P. glabrum.
- Penicillium aurantiogriseum
- Penicillium bilaiae, which is an agricultural inoculant
- Penicillium camemberti, which is used in the production of Camembert and Brie cheeses
- Penicillium candidum, which is used in making Brie and Camembert. It has been reduced to synonymy with Penicillium camemberti
- Penicillium chrysogenum (previously known as Penicillium notatum), which produces the antibiotic penicillin
- Penicillium claviforme
- Penicillium commune
- Penicillium crustosum
- Penicillium digitatum
- Penicillium echinulatum
- Penicillium expansum, a plant pathogen
- Penicillium funiculosum, a plant pathogen
- Penicillium glabrum
- Penicillium glaucum, which is used in making Gorgonzola cheese
- Penicillium italicum
- Penicillium lacussarmientei
- Penicillium marneffei, a thermally dimorphic species endemic in Southeast Asia, which presents a threat of systemic infection to AIDS patients
- Penicillium purpurogenum
- Penicillium roqueforti, which is used in making Roquefort, Danish Blue cheese, and also recently Gorgonzola
- Penicillium stoloniferum
- Penicillium ulaiense
- Penicillium verrucosum produces ochratoxin A
- Penicillium viridicatum produces ochratoxin
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