Controlling Aspergillus niger morphology in a low shear-force environment in a rocking-motion bioreactor

The filamentous fungus Aspergillus niger is an important production host in biotechnology. Shear force regimes are one of the key factors that affect macromorphology and product yield. While morphology changes under intensive agitation have been widely investigated, studies at a low shear force regime independently from oxygen limitation has remained a challenge. Therefore, in this study, a 2-dimensional rocking-motion bioreactor is used as an alternative platform for studying the macromorphology under a low shear force regime, but sufficient supply of dissolved oxygen. Talcum macroparticles were added at different concentrations to control the development of a certain macromorphology. Results showed that 0.25% and 1% (ww⁻¹) of talcum led to a mixture of dispersed mycelia and loose clumps, similar to what is obtained in lab-scale stirred tank reactors. At lower talcum concentrations, distinct pellet formation was observed. Quantitative analysis of pellets showed that with 0.05% of talcum, 95% of the pellets had a diameter smaller than 850 µm after 36 h. In case of 0.1% of talcum, 94% ( ± 5.0%) of the pellets had a diameter below 650 µm.The presented approach makes it possible to achieve a certain morphology as, for example, observed in large scale cultivations to study the consequences for product synthesis.