In biotechnological production processes performed with filamentous fungi the monitoring and control of morphological development is difficult to obtain due to the highly complex relation between morphology and productivity. Product formation by filamentous fungi, like Aspergillus niger is closely linked to their morphology. The morphological characteristics can vary between freely dispersed mycelia and distinct pellets of aggregated biomass with strong impact on rheology, mass transfer, mass transport and biochemical reaction. Mycelial growth has procedural disadvantages, for instance a high viscosity of the cultivation broth and therefore a low nutrient supply due to insufficient mixing. In comparison, cultivation broths with distinct pellets show Newtonian flow behaviour, but disadvantages related to a limited nutrient availability within the inner part of the biopellets. Hence, in every biotechnological process, the optimal morphology varies due to specific product properties and cannot be generalized. The morphogenese of A. niger cultivation can be controlled effectively by adjusting the pH-value and the volumetric power input. In the early phase of cultivation the aggregation of A. niger conidia is dominantly affected by the pH-value, while the morphology of fungal pellets is mainly influenced by volumetric power input. The comparison of the volumetric power input caused by agitation and aeration revealed that the aeration has a higher impact to counteract the aggregation process, which leads to pellets with smaller diameter and an open structure, and also to a higher pellet concentration. Due to higher agitation induced power input denser pellets occur with a compact pellet surface. Based on intracellular reactions up to physico-chemical and fluid dynamic phenomena at a macroscopic level, which determine the fungal morphology, the morphogenesis of mycelial growth and pellet formation via distinct aggregation steps ought to be completely covered by population balancing and verified by different particle size analysis techniques. The methods of population balancing will help to model and characterize morphologic developments and to connect fluiddynamic dependencies, the transport gradients, intracellular biological reactions and productivity in a comprehensive model for rational, target-oriented design of cultivation processes with filamentous fungi.
Full conference title:
Society of General Microbiology Meeting
- SGM 164th (2009)