Induction of sporulation in Blastocladiella emersonii: Influence of nutritional variables

We have studied the induction of zoosporangial sporulation in Blastocladiella emersonii by determining the influence of nutritional variables on the formation of the basal septum. This is an easy-to-monitor structure that has proved to be a useful marker of initiation of this cellular differentiation process. At any time before formation of the septum, the cells returned to the growth phase when incubated in the presence of 2% casamino acids. However, after septum formation has occurred, the cells were committed to sporulation. Certain of the amino acid components of the defined growth medium, DM 2, either prevent (tyrosine, phenylalanine, tryptophan, histidine, and threonine) or delay (valine, serine, arginine, and methionine) formation of the septum when added to the cultures together with the sporulation solution (buffered 1 m M CaCl 2). Sugars do not prevent the formation of the septum, although they can interrupt sporulation at later developmental phases. Glucosamine and acetylglucosamine can prevent formation of the discharge papilla and glucose can block completion of zoospore production. Glutamine, adenosine, and guanosine also caused long delays in septum formation. Taken together, these data favor (a) the hypothesis that amino acid starvation is one of the most important variables with respect to the induction of sporulation, and (b) the use of certain environmental chemical conditions that block sporulation at different steps as developmental tools for the study of this cellular differentiation process.