Effect of nutrition on pellet formation by <i>Rhizopus arrhizus</i>

Abstract

Many fungi can grow in submerged culture in different forms ranging from dispersed filaments to pellets. Factors which affect growth morphology include level and type of inoculum, medium shear, medium constitutents, and pH.'.' Various fungal fermentations require different growth morphologies for optimum product yield. Pelleted growth is preferred for itaconic acid production by Aspergillus terr e ~s . ~ Pelleted and filamentous growth have been used for pencillin p r o d ~c t i o n . ~. ~ Filamentous growth is preferred for pectic enzyme production by Aspergillus niger6 and for fumaric acid production by Rhizopus arrhizus. 7.8 Growth morphology affects nutrient and oxygen uptake rate in submerged culture.' Filamentous growth increases the viscosity of the medium, thereby requiring a higher power input to maintain adequate mixing and aeration." Viscosity of media containing pellets is substantially lower and less power is required for aeration and agitation.*'.'2 Higher specific growth rates are achieved with filamentous growth. I3.l4 Pellet interiors often become anaerobic and fungal growth is confined to the external region of the pellet. l5,I6