Toxicity of Rubratoxin B to Fungi

Abstract

SUMMARY: The fungi Aspergillus flavus, A. niger, Penicillium expansum, Neurospora crassa, Cladosporium herbarum, Mucor spinosus and Rhizopus nigricans were cultivated (i) in malt extract solutions with various concentrations of rubratoxin B (100, 10, 1 μg/ml) in order to study the hyphal morphology and (ii) on filter discs containing different amounts of the same toxin (100, 10, 1 μg/disc) to detect any influence on sporulation. In the presence of 100 μg toxin/ml the hyphal tips of A. niger and A. flavus were very often swollen and much septate, or were transformed into giant cells. Plasmoptysis often occurred. The germ tubes of R. nigricans were much deformed. It is assumed that all these toxic effects were caused by weakening of the hyphal tips by interference with wall synthesis. Rubratoxin B (100 μg/disc) completely inhibited the sporulation of all of the fungi. Lower concentrations diminished sporulation of most of the fungi.