The mould that spoils your bread also gave us penicillin and Roquefort
The blue fuzz on stale bread belongs to the same genus that ripens Brie, veins Stilton and produced the first great antibiotic. Penicillium has over 300 species. One of them, long thought to reproduce without sex, was finally caught mating in 2013, more than a century after scientists first tried to make it happen.
Johann Link named the genus in 1809, after the Latin for a painter's brush, because its chains of spores sprout from branched stalks that look like tiny brooms. He described three species, and the apple-rotting Penicillium expansum later became the reference species. The fungus grows as a web of fine threads and spreads mainly by releasing clouds of green, round asexual spores. It lives in soil wherever there is organic matter, prefers cool to mild climates, and is one of the leading causes of food spoilage; several species make dangerous toxins.
Indoors it is everywhere. A British study found Aspergillus and Penicillium spores were the most common in household air, at levels above those outside. Even ceiling tiles can host it if humidity reaches 85% and the tiles hold more than 2.2% moisture. Certain species attack fuels, lubricants and even optical glass, while others infect apples, citrus and garlic.
The useful side is just as broad. Penicillium roqueforti flavours Roquefort, Stilton, Danish Blue and Gorgonzola, and P. camemberti gives Camembert and Brie their white rind. P. nalgiovense seasons sausages and hams while keeping rival microbes away. Industry uses related moulds to make citric and gluconic acids and a range of enzymes, and some species can break down pollutants.
Medicine owes it most. Alexander Fleming stumbled on penicillin, made by P. chrysogenum, in 1929 and saw that it held back certain bacteria. Howard Florey and Ernst Chain purified and concentrated it in the late 1930s, and after it saved soldiers dying of infected wounds in the Second World War, the three shared the 1945 Nobel Prize in Medicine. Another species yielded griseofulvin, an antifungal drug. P. chrysogenum was considered sexless for over 100 years until Bohm and colleagues showed otherwise in 2013, and P. roqueforti turned out to carry working mating genes too, supporting the idea that sex goes back to the common ancestor of all complex cells.
Source: Penicillium
