Screening of Microbial Metabolites Affecting Cell Membrane Function (An Attempt to Effectuation of Ineffective Inhibitors for Fungal Growth by Permeability Changes by the Metabolites)

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It has been reported that some yeasts become hypersensitive to various antibiotics and inhibitors when they are weakly exposed to cell membrane-damaging agents such as polygodial and amphotericin B. In this study we tried to search for microbial metabolites which can act specifically on the membrane barrier of yeast cells, so that impermeable inhibitors showing no effect would be able to enter the cells and show their activities.1. Yeasts for screening test were prepared : Cells of Saccharomyces cerevisiae IFO 0203 were treated with NTG to give (1) arg-p3 (arginine permease-deficient mutant) and (2) ura-p17 (uracil permease-deficient mutant) which are insensitive to the arginine analogue canavanine and the uracil analogue 5-fluorouracil, respectively. Also, (3) Candida albicans IFO 1061 was found to be deficient in uracil permease.2. About 3100 kinds of culture filtrates were subjected to the screening whether they showed anti-yeast activity against (1) - (3) only when they were tested in the presence of canavanine or 5-fluorouracil. As a result, 4 microorganisms (an unidentified filamentous fungus, Penicillium sp., an unidentified actinomycetes and Streptomyces sp.) were found to be promising producers of such activities.3. From their culture broths, 4 active principles (cell membrane-affecting metabolites) were isolated and identified as chrysodin, anhydrofulvic acid, chainin and tetramycin A, respectively.4. Besides canavanine and 5-fluorouracil, some other ineffective inhibitors for fungal growth were effectuated when combined with these cell membrane-affecting metabolites.5. Chrysodin inhibited the biosynthesis of linolenic acid and linoleic acid in yeast cells. Thus, it seems that polyenoic fatty acids play an important role in the permeability barrier of cell membrane to drugs. Further studies are needed to clarify the mode of action of other screened metabolites.