Scale-down studies of Corynebacterium glutamicum to oscillating substrate and oxygen avalilability in multi-compartment bioreactor sytems

At the example of a cadaverin process with Corynebacterium glutamicum we studied the possible impact of substrate and oxygen gradients in scale-down bioreactors that mimic different zones of an industrial scale bioreactor. Recently developed multiposition sensors are presented that allow the determination of gradients during operation. They can be used for improved scale-down bioreactor design aside CFD and hybrid models. Beside well-established two-compartment-reactor systems, consisting of a stirred-tank reactor (STR) coupled to a plug-flow reactor (PFR), a novel three-compartment scale-down reactor (3CR) is introduced, consisting of an STR and two PFRs. Experimental conditions with a zone of high substrate and low oxygen in one PFR and a zone of oxygen and substrate limitation in the second PFR were selected based on a CFD study of an industrial-scale lysine process. Cells were exposed cyclically to these zones, while the STR was characterized by moderate substrate limitation and sufficient oxygen supply.

The results of cultivations performed in either complex or mineral salt medium reveal the robustness of C.glutamicum against oscillatory conditions. Exposure to substrate excess does not lead to accumulation of pyruvate, but of lactate in the 3CR, if mineral salt medium is used. Lysine, a precursor of cadaverine, is reduced under heterogeneous conditions by 30%.

For the first time the particle-size distribution on a single-cell basis was followed using the laser-based in-situ BioCell-Analyzer (Sequip) to study the impact of oscillatory conditions on the cell morphology in-line. Such data could be the basis in the future to design realistic scale-down experiments.