LAUSR

Abstract The production of chemical and pharmaceutical substances by filamentous microorganisms is a wide and challenging field of study. The morphology of filamentous microorganisms, which can vary between loose mycelia and dense pellets, is influenced by process parameters like mechanical stress. The addition of glass particles of different sizes (0.2-2.1 mm) on the cultivation of Lentzea aerocolonigenes pellets was investigated. The glass bead-induced mechanical stress is made responsible for the increased product concentration of rebeccamycin. By coupling the discrete element method (DEM) with the computational fluid dynamics (CFD), a method for the calculation of the mechanical stress energy was developed and applied on first experimental results. As the mean stress energy was increased, the pellet diameter raised up to a maximum pellet size. This effect was explained by an increased pellet loosening and hence, a better oxygen supply. If the pellets were subject to even higher mean stress energies, the diameter decreased due to the assumed pellet fragmentation. In conclusion, to ensure high product concentrations, an optimal particle induced mechanical stress is necessary, which can be calculated with the developed method and validated with experimental cultivations. In future, this method enables the investigation of other process parameters and a process scale-up.