Physiological effects of an antimycotic azasterol on cultures of Saccharomyces cerevisiae.

The yeast Saccharomyces cerevisiae has been studied during cultivation with a naturally occurring antimycotic azasterol. At very low concentrations (1.0 to 10.0 ng/ml), where growth retardation is not observed, an unusual sterol, ergosta-8,14-dien-3beta-ol, accumulates in high concentrations. Upon removal of the azasterol from the culture, the 8,14-diene is converted to ergosterol. Much smaller amounts of another 8,14-sterol, but with an additional unsaturation, have also been observed. Total sterol accumulation is higher in cultures containing subinhibitory levels of the antimycotic agent than the amounts of normal sterol accumulation in control cultures. With between 10 and 100 ng of azasterol per ml a transitory cessation of growth is observed from which the culture is able to recover. At much higher concentrations growth inhibition and even cell lysis results. Competitive inhibition of sterol 24(28)methylene reductase is demonstrated.