Detecting cell lysis using viscosity monitoring in E. coli fermentation to prevent product loss

Monitoring the physical or chemical properties of cell broths to infer cell status is often challenging due to the complex nature of the broth. Key factors indicative of cell status include cell density, cell viability, product leakage and DNA release to the fermentation broth. The rapid and accurate prediction of cell status for hosts with intracellular protein products can minimise product loss due to leakage at the onset of cell lysis in fermentation. This paper reports the rheological examination of an industrially relevant E. coli fermentation system producing antibody fragments (Fab'). Viscosity monitoring showed an increase in viscosity during the exponential phase in relation to the cell density increase; this is a relatively flat profile in the stationary phase, followed by a rapid increase which correlated well with product loss, DNA release and loss of cell viability. This phenomenon was observed over several fermentations that a 25% increase in broth viscosity (using induction-point viscosity as a reference) indicated 10% product loss. Our results suggest that viscosity can accurately detect cell lysis and product leakage in post-induction cell cultures, and can identify cell lysis earlier than several other common fermentation monitoring techniques. This work demonstrates the utility of rapidly monitoring the physical properties of fermentation broths, and that viscosity monitoring has the potential to be a tool for process development to determine the optimal harvest time and minimise product los

Investigating and modelling the effects of cell lysis on the rheological properties of fermentation broths

This article examines the rheology of an industrially relevant E. coli fermentation system producing antibody fragments (Fab′), to gain a deeper understanding of the physical properties of fermentation broths. Viscosity monitoring has been shown to be a useful tool to detect cell lysis and product leakage in late stage fermentation, and here we add to this work by characterising the rheological properties of an E. coli cell broth and its individual components, such as cell paste, supernatant, DNA and protein. Viscoelastic measurements have been carried out to provide novel insight into properties such as changes in cell strength, stability and robustness during fermentation, with ramifications for alternative process monitoring and control strategies. Additionally, an empirical model has been created to determine the extent of cell lysis using viscosity measurements, based on DNA leakage in late stage fermentation. The model directly indicates product loss to extracellular space, as intracellular content (product, DNA and host cell protein) is released simultaneously during cell lysis in late stage fermentation