Medium-induced fragility of Schwanniomyces.

Schwanniomyces occidentalis has attracted interest because of its ability to metabolize starch and similar complex carbohydrates. Studies have been undertaken, mostly using defined media, to ascertain conditions for optimal production and secretion of hydrolytic enzymes. Here we demonstrate the fragility of Schw. occidentalis in many defined media. We especially examined viability in YNB (Yeast Nitrogen Base) plus 1% glucose. Without phosphate supplementation, viability was routinely very low at stationary phase (usually less than 37%), whereas viability of stationary-phase cultures in phosphate-supplemented YNB usually exceeded 97%. The negative implications of having many, presumably permeabilized, dead cells present in assays for secretion of enzymes by living yeast cells are discussed.