Studies on Aspergillus Flavus: I. Biological Properties of Crude and Purified Aspergillic Acid.

In 1940 White (1940) described a strain of Aspergillus flavus which showed antibacterial activity against both gram-positive and gram-negative bacteria. A culture of this strain was obtained through the kindness of Dr. White. The following report deals with certain biological experiments carried out with this mold, with crude filtrates containing soluble products obtained from its growth, and with active crystalline aspergillic acid (White and Hill, in press), obtained from these filtrates. The culture as originally received was growing on Czapek-Dox agar and showed colonies covered with brown spores. On subculture in our laboratory on Czapek-Dox or Sabouraud' agar it proved to be a mixed culture of several distinct variants. On Sabouraud agar, which was used as the solid medium of choice, luxuriant growth occurred. All variants originally showed white hyphae but with the onset of sporulation, in those that did sporulate, the colonies took on a brown, green or yellow color. Many single colonies of these variants were picked, obtained in pure culture, grown on one or more of the better fluid media described below, and the crude filtrates tested for antibiotic activity. The variants bred true but new variants appeared in subcultures from time to time and had to be eliminated. Of the variants tested for antibiotic activity, some proved completely inactive, others gave results as good as, or better than, those of the original mixed culture, and one yellow variant proved to be particularly good. On further transfer a new and equally active variant appeared in this yellow substrain,-namely one giving greenish spores. The bulk of the work described below was carried out with the yellow substrain or with the greenish variant obtained from it. The results obtained with these latter two strains appeared identical.