ABSTRACTThe morphological development of a glucoamylase-producing strain ofAureobasidium pullulansimmobilized in Ca-alginate was investigated during semicontinuous fermentations in a fluidized-bed reactor. A dense mycelium layer was developed by the fungus on the gel bead surface which gave the beads a“pellet-like”configuration. Varying culture conditions, such as bead, substrate and CaCl2concentrations and aeration rate, had a consistent effect on both enzyme production and morphological development of the“in situ”grown cells. Optimization of the growth conditions appeared to be necessary to prevent fungal overgrowth and to enable the immobilized inoculum to continue a sustained level of glucoamylase production over a great number of transfers.