Aspergillus flavus

A common soil and stored-crop mould with yellow-green colonies that produces aflatoxins, among the most potent natural carcinogens. It is the second most common cause of invasive aspergillosis after A. fumigatus (INSPQ). In mushroom growing, Stamets & Chilton (1983) list it with A. niger and A. fumigatus as toxic Aspergillus contaminants that occur in agar and grain culture and in compost making, and they advise growers to guard against exposure.

Photo: MedmycoCC BY-SAsource

Species profile

Edibility: Not edible

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Not edible; a contaminant. It produces aflatoxins (B1 is hepatotoxic and carcinogenic) and other mycotoxins. It causes invasive aspergillosis in immunocompromised people, as well as sinusitis, keratitis, wound infections, allergy, asthma, ABPA and hypersensitivity pneumonitis (INSPQ). Handle contaminated cultures with care (Stamets & Chilton 1983).

Mycology is an evolving science: names, classifications and safety information change as research advances. Entries are compiled from cited sources and reviewed, but may be incomplete or out of date — check the sources, and never rely on this library alone to identify or eat a mushroom.

Habitat

Soil saprobe. Grows on peanuts, maize, spices, oilseeds, cereals and stored grain. Indoors it grows on paper, wood, textiles, leather, house dust, ventilation ducts and filters (INSPQ). In mushroom farms, Aspergillus grows on almost any organic substrate and prefers near-neutral to slightly alkaline pH. It often lives on well-used wooden trays and shelves, and A. flavus attacks oily seeds stored hot and damp (Stamets & Chilton 1983).

Characteristics

Colony: fast-growing, 3-5 cm in 7 days on Czapek agar at 25 C. Dense, woolly to cottony or granular, often with radial grooves. Yellow at first, becoming bright to dark yellow-green. Sclerotia, when present, are dark brown; some isolates exude clear to pale brown droplets. On PDA it is olive to lime green with a cream reverse; the reverse is orange on AFPA. Growth range about 17-19 C to 47-48 C, optimum 25-42 C. pH optimum 7.5 for growth and 6.5 for conidia. Best water activity 0.86-0.96 (reported down to 0.78-0.80); optimum RH 80-85% (INSPQ). In mushroom culture (genus level): Aspergillus colours range from yellow (A. flavus) through green to black, vary with the medium, and often resemble Penicillium (Stamets & Chilton 1983).