Aspergillus penicillioides is a species of fungus in the genus Aspergillus, and is among the most xerophilic fungi.
Aspergillus penicillioides is typically found in indoor air, house dust, and on substrates with low water activity, such as dried food, papers affected by foxing, and inorganic objects such as binocular lenses. The distribution of the fungus is worldwide; it has been found in bed dust from maritime temperate, Mediterranean, and tropical climates. The abundance of the fungus is influenced by outdoor climate, with highest numbers found in tropics and lowest numbers in cool climates. Cool temperature tends to decrease number of A. penicillioides in house dust.
A colony can arise from a single sexual or asexual spore under acidic conditions, and its diameter ranges from less than a milliliter to several centimeters, depending on the size and composition of the substrate. Germination of A. penicillioides was found to occur at lower water activity than growth. The lowest water activity for germination was 0.585.
Taxonomy and phylogeny
Aspergillus penicillioides is included in the genus Aspergillus, section Restricti. Presumably because of the xerophilic character, Aspergillus restrictus was recognized by Charles Thom and Kenneth B. Raper as a Series within the group of Aspergillus glaucus. Raper and Fennell later raised this Series to "A. restrictus Group". Helmut Gams et al., renamed the taxa as Aspergillus Section Restricti in agreement with the Botanical Code. Phylogenetic relationship of A. penicillioides and related teleomorph genera was inferred by 18S rDNA sequencing. A. penicillioides, A. restrictus, A. proliferans, five Eurotium teleomorphs represented by E. herbariorum and Edyuillia athecia were grouped together. All these species have Q-9 as their major ubiquinone system.
Growth and morphology
A. penicillioides has been cultivated on both Czapek yeast extract agar (CYA) plates and yeast extract sucrose agar (YES) plates. The growth morphology of the colonies can be seen in the pictures below.
History
Aspergillus penicillioides was named by Spegazzini in 1896. The species was described from moldy sugarcane in Argentina, but it was not cultivated by Spegazzini. The ex neotype strain CBS 540.65 was isolated from a human arm in Brazil that was misdiagnosed to lobomycosis. The fungus was isolated from several compounds in different places. Strain CBS 116.26 was isolated from sugar cane in Louisiana, and it was sent to Spegazzini and recognized by him to fit description of his species. Strain CBS 539.65 was isolated from a gun firing mechanism and CBS118.55 was isolated from a man in Netherlands. Several other A. penicillioides strains were isolated from Indonesian dried fish in Australia and dried chili in Papua New Guinea. ATCC 16905, extype of Aspergillus vitricola, was isolated from binocular lens in Japan by Torao Ohtsuki.
Aspergillus penicillioides was erroneously identified to be the etiologic agent in a case of aspergilloma. The conidial structure and colony appearance indicated that it was an isolate of A. fumigatus.
Description
Aspergillus penicillioides fails to grow or grows very poorly on Czapek medium at 25–26 °C with length never exceeding 2 to 3 mm. Colonies on Czapek's agar with 20% sucrose can reach length of 1–1.5 cm in 4 weeks at room temperature. However, the fungus is thin and non-sporulating. Sporulation can occur by incubation at 33 °C.
Colonies on malt extract agar grow a bit more rapidly than on standard Czapek's agar, producing microcolonies and a small number of conidial heads. Occasionally, colonies can reach 5 mm in diameter. Colonies on G25N agar can grow to 8–14 mm in diameter with wrinkled and floccose textures. There is moderate conidial production in loose columns. Color is dark green and reverse is pale to dark green. Colonies on CY20S agar have microcolonies up to 10 mm in diameter, but conidiophores are poorly formed. Color is also dull green and reverse is pale. Colonies can grow rapidly on M40Y agar, obtaining length of 5 to 6 cm in 3 weeks at room temperature. The fungus forms a "thin tough felt," sporulating in dark yellow-greenish shades. It can also grow as mycelium and have green color. Reverse is uncolored to greenish brown or dark green, with color emphasized at colony center. There is slight odor.