Scale-related process heterogeneities change properties of high-cell-density fermentation broths demonstrated with Escherichia coli B and K-12 strains

BACKGROUND The scale-up of Escherichia coli bioprocesses for production of recombinant proteins in the biopharmaceutical industry can affect process performance due to gradients occurring at production scale. The main objective of this study was to investigate the effect of scale-related process heterogeneities on properties of high-cell-density fermentation broths. Two industrially relevant Escherichia coli strains, BL21(DE3) and HMS174(DE3), were used for production of antibody fragments (Fab). To generate these heterogeneities, we used a scale-down device for cell cultivation, which mimics conditions of production scale (>1000 L) in a 20 L laboratory scale. This setup helps to evaluate the impact of process scale-up on the resulting fermentation broth properties relevant for primary recovery. RESULTS We found differences in broth viscosity between the two strains, but also between the standard laboratory-scale and the scale-down cultivations used. An increase in cell size was measured in scale-down cultivations with three orthogonal methods, using scanning electron microscopy, dynamic light scattering and a dispersion analyzer. Strong hints for an altered agglomeration tendency of the cells after scale-down cultivations were found by measurement of settling velocity and viscoelasticity of the fermentation broth. CONCLUSIONS In this work, industrially relevant fermentation broths of Escherichia coli cells producing Fab were characterized and represent a relevant basis for rational design of downstream processing operations. The findings show that scale-related process heterogeneities can alter the phenotype of Escherichia coli cells and thus alter fermentation broth properties relevant for primary recovery. Considering scale-up effects in upstream processing reflected in downstream processing will help to optimize the entire bioproduction chain in the future.