A knowledge of the factors concerned in the growth of yeasts is of value for theoretical plant science and biochemistry, and provides information for practical application in the field of microbiological assays, the production of yeast for fodder and food, and the development of fermentative industrial processes. In this paper some data are presented on the vitamin requirements of 163 strains of yeasts belonging in 110 named species and varieties. Dosage response curves of a yeast which is deficient for 6 B vitamins and an illustration of the-application of such information to the assay of vitamins are given. No attempt is made here to review the literature in this field; some valuable references may be found in the citations given in our earlier papers (Burkholder, 1943;Burkholder and Moyer, 1943).Grateful acknowledgment is made to the following persons who supplied cultures for this work: L. J. Wickerham,
The production by an organism of organic substances inimical to the life processes of other organisms and inhibiting their growth is known as antibiosis. The phenomenon of antibiosis has attracted wide-spread attention in recent years chiefly because of the remarkable chemotherapeutic effects of penicillin, a product of the mold Penicillium. The anabolic products of many kinds of bacteria,' molds,2 and algae,3 and substances elaborated by certain species of flowering plants4 can be readily demonstrated to have antibiotic properties when small amounts of the active materials are tested on microorganisms with suitable assay procedures. In view of the reported antibacterial activity of the green alga Chlorekla and the many antagonistic substances now known to be produced by numerous kinds of fungi, the lichens seemed to offer favorable material for antibiotic investigations, inasmuch as the bodies of these plants are comprised of mixtures of algae and fungi. Accordingly we have tested a considerable number of lichens for antagonistic action against some common species of bacteria, and offer herewith a preliminary report concerning some of our observations.Methods.-The lichens were brought in fresh condition to the laboratory, placed in shallow pans, and moistened with water for the purpose of allowing them to become physiologically more active. After a few hours of exposure to sunlight, samples of the moist lichens were separated from the substrata with a razor blade and forceps. Extracts were made by grinding, with a glass mortar and pestle, 100 mg. of lichen in 1 ml. of phosphate buffer solution adjusted to pH 7.4. The final aqueous extract was approximately pH 7.0. Extractions were carried out at room temperature and the samples were stored at 1°C. for a short time until the materials could be assayed. No attempt was made to clarify the extracts in these preliminary tests. The aqueous suspensions were assayed against Staphylococcus aureus, Escherichia co/i, Bacillus subtilis or other bacteria by means 250 PROC. N. A. S.
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