Which fungus is used to produce the antibiotic penicillin?

The fungus used industrially to produce penicillin is Penicillium chrysogenum. It is grown in large liquid fermenters, where selected high-yield strains manufacture penicillin as a secondary metabolite.

Alexander Fleming noticed antibacterial activity from a Penicillium mold in 1928, but turning that observation into a practical medicine required later work by researchers including Howard Florey, Ernst Chain, and their colleagues. Industrial strain improvement and fermentation dramatically increased antibiotic yields, helping make penicillin available on a large scale during the 1940s.

Older sources often called the production organism Penicillium notatum. Modern genetic studies have also shown that Fleming’s original strain is more accurately classified as Penicillium rubens, while P. chrysogenum has long been an important industrial producer and remains the conventional answer to this question. The penicillin-producing genes occur together in a cluster, and some industrial strains carry multiple copies of that cluster. The other listed fungi are not the standard penicillin-producing species.