Antibiotic Effect of Steroids on Saccharomyces Fragilis and the Isolation of a Resistant Mutant.

The biosynthetic pathway leading to the steroid nucleus in both yeast and mammalian tissues has been delineated recently by a number of investigators (Ciba Foundation Symposium, 1959). With the exception of the final steps, reactions from acetate to ergosterol in yeast appear to be identical with those involved in cholesterol synthesis in mammalian systems. Certain yeasts and molds are also capable of metabolizing steroids by reactions similar to those occurring in mammalian steroid hormone biosynthesis (Eppstein et al., 1956). The physiological significance of steroids in microorganisms is not yet understood, although some recent investigations have yielded important clues as to their possible physiological role. Lester and Hechter (1958a) found that deoxycorticosterone inhibits the growth of a number of gram-positive bacteria, yeast, and molds whereas gram-negative bacteria are generally insensitive to this steroid. Jefferson and Sisco (1959) reported a similar inhibitory effect of steroids on Aspergillus niger. Lester et al. (1958), in a more detailed study of the effects of deoxycorticosterone and other steroids on Neurospora crassa, found that deoxycorticosterone markedly inhibits the uptake of carbohydrates, amino acids, and rubidium by germinated conidia. The authors suggest that the steroid exerts its inhibitory effect on growth by interfering with certain permeability processes of the cell. Further studies on rubidium uptake (Lester and Hechter, 1958b) indicated that the steroid interferes with binding and concentration of rubidium within the cell rather than with actual entry into the cell. Most recently the same authors reported (Lester and Hechter, 1959) that inhibition of growth of Penicillium puberuleum brought about by deoxycorticosterone can be prevented by the addition of estradiol to