The Possible Involvement of Cyclic AMP and Volatile Substance (s) in the Development of a Macrocyst-Forming Strain of Dictyostelium mucoroides

A mutant MF1 previously isolated from Dictyostelium mucoroides -7 (Dm7) formed macrocysts with or without light when plated on agar at high cell dinsities. At lower cell densities, however, the MF1 cells formed only fruiting bodies. This failure to form macrocysts was shown to be due to the subthreshfold concentration of a volatile substance(s) required for macrocyst formation. Although ammonia is a volatile substance produced by both the Dm7 and MF1 cells, no evidence of its involvement in macrocyst formation was obtained. Mixing the Dm7 and MF1 in a one-to-one ratio resulted only in fruiting body formation suggesting that the Dm7 cells produced a factor which allowed MF1 cells to form fruiting bodies. This factor may be cyclic AMP (cAMP) since addition of cAMP to the medium directed development of MF1 cells to fruiting body formation. The effect of cAMP was exhibited most conspicuously when MF1 cells were exposed at the aggregation stage. Based on these results it is suggested that developmental pathway of the D. mucoroides macrocystforming strain Dm7 and its mutant MF1 may be determined by the relative concentrations of the volatile, macrocyst-inducing substance(s) and cAMP at the aggregation stage.