Aspergillus nidulans. Petri dishes containing dark cultures of the fungus Aspergillus nidulans. These are cultures of a mutant form of the fungus with an abnormal metabolic pathway, and are being used in research to understand gene regulation. A. nidulans produces the toxin "sterigmatocysin" which may lead to food contamination. It also causes allergic aspergillosis, a hypersensitive lung reaction in asthmatics and those with lowered resistance, provoked by repeated inhalation of the spores. Mycetoma (Madura foot) may result when this fungus infects subcutaneous tissue, bone and skin.