Abstract Summary (Max 250 words)
Filamentous fungi are shear-sensitive microorganisms. Depending on the growth and flow conditions, they either grow in submerged cultures as loose mycelium or form agglomerates known as pellets. The production of natural substances can be supported depending on the growth form, and the growth form also has an important influence on the process itself. Loose mycelium increases the viscosity of the broth, which can lead to poor mixing and, consequently, oxygen and nutrient limitations. It can also lead to overgrowth of probes and other components in the bioreactor. Cultivation in pellet form does not present these problems; however, due to the dense network inside the pellets, limitations in mass transport can arise, leading to an undersupply of the core. In the case of Penicillium sp. (IBWF 040-09), the pellet form has proven suitable for producing a protease inhibitor, since this secondary metabolite is produced when the supply of substrate is limited. To specifically influence the morphology, different types of stirrer were used during cultivation, and the resulting morphology was examined. A Rushton turbine, a 3-segment blade stirrer and a modified 3-segment blade stirrer with a ring were used for this purpose. CFD simulations will be carried out in cooperation with another working group to determine the shear forces and these will be validated by mixing time experiments. This will create a simulation-based basis for further optimization of the stirrer geometry. The morphological changes caused by the different agitators have already been demonstrated and are currently being investigated with regard to important properties such as the circularity and density of the hyphal network inside the pellets.
