The mold Penicillium is best known as the origin of penicillin. But it is also used in other areas, such as the production of cheese and other foods as well as in biotechnology. Because of its properties and diverse use of the individual Penicillium species, this brush mold has now been named “Microbe of the Year” 2026.
The fungus Penicillium forms filamentous structures with characteristic, often colored spores. This makes the fungal cells look like small brushes (Latin penicillus). Penicillium species are therefore also known as brush mold. The Association for General and Applied Microbiology (VAAM) has now named mold “Microbe of the Year” 2026. This title is intended to draw attention to the diversity of the microbiological world and to point out selected microbes that, thanks to their metabolism, play a particularly important role in ecology, health, nutrition and the economy. This is undoubtedly the case with Penicillium, because the mold has practical applications in several areas.
Source of penicillin
The most well-known use of the fungus is the antibiotic penicillin. The Scottish doctor Alexander Fleming discovered it in 1928 in a contaminated sample in his laboratory. Bacteria were supposed to be growing on the agar plate, but instead the mold Penicillium was spreading there. Fleming concluded that this fungus secretes a substance that kills the bacteria. He was almost right: the substance disrupts the cell wall structure of the bacteria and therefore inhibits their growth, as it later turned out.
The fungus was later identified as Penicillium notatum and the substance secreted was called penicillin. In 1941, this antibiotic was first isolated from the fungus and the first person was treated with it. Penicillin and the fungus have been continuously optimized since then, so that there are now several related synthetic forms of this molecule as well as other Penicillium strains that produce these substances in large quantities. Penicillin and its derivatives are still the most commonly used antibiotics against bacterial infections. They have saved millions of lives over the last 80 years.
Cheese enjoyment thanks to mold
Another application of this mold is the production of cheese. This is because Penicillium species produce the taste and smell of maturing cheeses such as Camembert, Brie and blue cheese. Their white, semi-solid “rind” consists predominantly of Penicillium camemberti, which is also responsible for the soft, buttery consistency of Brie and Camembert. Penicillium roqueforti is used to produce Roquefort. This type of fungus produces enzymes that break down milk proteins and form volatile compounds. These substances give the cheese taste, aroma and texture while protecting it from unwanted contamination.
For cheese production, it is important to be able to breed new Penicillium species with new properties and to rejuvenate tried and tested, exhausted species by crossing them with wild strains. This is possible because the fungus can not only reproduce asexually via its spores, but also through sexual reproduction and crossing between two sexes, as researchers surprisingly discovered in 2008.
Fruit juices, textiles, insecticides and even more medicine
In addition, the brush mold is used in biotechnology. Penicillium species also produce other enzymes and release them into their environment. Penicillium citrinum, for example, produces enzymes that break down fibers from fruit juices and textiles. This type of fungus is therefore used for the industrial clarification of cloudy fruit juices and for the pretreatment of tissues.
The fungus species Penicillium coprobium, on the other hand, produces the substance pyripyropene A for industry. This raw material is used for the production of insecticides against aphids and whiteflies. Penicillium brevicompactum, in turn, produces the substance mycophenolic acid, also a natural antibiotic. However, mycophenolic acid is used in medicine more as an immunosuppressant and is given to patients with autoimmune diseases or after a transplant to inhibit the proliferation of lymphocytes.
Source: Association of Biology, Life Sciences and Biomedicine in Germany (VBIO), Association for General and Applied Microbiology (VAAM)