Penicillium chrysogenum

Penicillium chrysogenum is a fungal species of the genus Penicillium, previously known as Penicillium notatum. It belongs to the kingdom Fungi, division Ascomycota, class Eurotiomycetes, and order Eurotiales. It is a cosmopolitan saprobiont organism found in a wide variety of habitats, from soil and vegetation to indoor environments and food products. In nature, its main function is the decomposition of organic materials, where it can cause destructive rots in food crops. It is also a frequent contaminant of indoor environments, especially in buildings with moisture or water damage, and is associated with food deterioration.

The identification of this species requires caution, as it cannot be based solely on the color of the colonies. Although the conidia are typically blue to bluish-green and the fungus sometimes exudes a yellow pigment, the observation of morphological and microscopic traits is necessary to confirm its identity. Since it is part of a cryptic species complex that includes P. rubens, P. notatum, and others, DNA sequencing is essential to distinguish it from closely related species. Phylogenetic studies have established that Alexander Fleming's original strain, which produced penicillin, corresponds to P. rubens, a distinct but close species to P. chrysogenum.

The fungus reproduces asexually by forming dry chains of spores (conidia) from brush-shaped conidiophores. These conidia are transported by air currents to new colonization sites. The airborne spores of P. chrysogenum are important human allergens, and vacuolar proteases and alkaline serine proteases have been implicated as the main allergenic proteins. The species has been detected in significant concentrations in air and household dust, and its presence has been documented even in the upper atmosphere and in Antarctica.