Penicillium notatum

Penicillium notatum, species of fungus in the genus Penicillium (kingdom Fungi) that occurs naturally in soil and decaying organic matter. It can colonize a variety of surfaces in damp indoor environments and is especially common on fruit, bread, and other food. P. notatum is very closely related to P. chrysogenum and P. rubens and has at times been considered synonymous with both.

P. notatum was once widely thought to have been the mold behind Scottish bacteriologist Alexander Fleming’s 1928 discovery of the antibiotic penicillin. Subsequent taxonomic studies, however, identified the mold as P. rubens. Moreover, the strain Fleming identified as the source of penicillin was later found to be of limited industrial value. Thus, during World War II, to meet the medical needs of soldiers, large-scale penicillin production relied on P. chrysogenum, a strain of exceptionally high yield discovered on moldy cantaloupe.