Pellet formation and fragmentation in submerged cultures of Penicillium chrysogenum and its relation to penicillin production.

The spores of Penicillium chrysogenum are of the noncoagulating type, and after spore germination a culture of disperse mycelia is obtained. In this study, it is shown that when the hyphal elements increase in size, they may agglomerate, and depending on the operating conditions, these agglomerates may develop into pellets with a dense core. The influence of initial spore concentration and agitation rate on agglomeration, leading to pellet formation, was studied. For a low concentration of spores in the inoculum, only a few hyphal elements agglomerate and pellets with a small diameter are obtained. At higher spore concentrations, many hyphal elements agglomerate and develop into large diameter pellets. Finally, at a very high spore concentration in the inoculum, the final hyphal element size is small and agglomerates therefore are not formed. With a high agitation rate, the agglomeration of hyphal elements is reduced. In a repeated fed-batch cultivation, where there was a shift from pellet morphology to disperse mycelia, it was found that there is no relation between macroscopic morphology and penicillin production by P. chrysogenum. The morphology was quantified throughout the repeated fed-batch cultivation, and both the pellet diameter and the concentration of pellets were affected by the agitation rate.