Changes in external trehalase activity during human serum-induced dimorphic transition in Candida albicans

Yeast-like cells (blastoconidia) of Candida albicans growing exponentially on a glucose-containing medium (YPD) exhibited low external trehalase activity and stored a negligible amount of intracellular trehalose. The addition of human serum at 37 degrees C to exponential cultures promoted a high degree of germ-tube formation with no significant changes in trehalase activity or trehalose content. In contrast, stationary cells accumulated a large amount of trehalose, while external trehalase remained at a low and practically constant level. However, resting cultures were unable to enter the dimorphic program, except when they were supplemented with fresh YPD and serum together. Only under these conditions was trehalase activated and trehalose hydrolyzed. Specific inhibition of external trehalase by validoxylamine A caused a certain delay in, and a lower level of, germ-tube formation, but did not totally block the dimorphic conversion. These results suggest that external trehalase is not involved in the serum-induced morphological transition in C. albicans.