(371b) Use of Flocculation to Improve Clarification Efficiency in a Microbial Feedstream

E. coli is one of the fastest growing, least expensive, and highest product-to-volume systems available for the production of therapeutic proteins. Despite these advantages, efficient clarification of the product stream can be challenging due to its high solids content, propensity for cell lysis, as well as high concentrations of impurities such as DNA and host cell protein.  While centrifugation can be used to remove larger particles, such as whole cells, many small particles, such as cell debris and protein DNA complexes, are difficult to sediment.  Depth filtration can be used to remove fine particulates but capacities of the depth filters can be limited, especially by high DNA concentration.   In this presentation, polycation and divalent cation precipitation are explored as methods to enhance the removal of cells, cell debris and DNA during centrifugation processes. Screening is performed using a combination of high throughput methods and bench scale experimentation. We examined the impact of several polycations and divalent salts, as well as changes to the pH and conductivity of the fermentation broth on the overall clarification process.  Subsequent scale-up work has demonstrated a minimum four-fold increase in depth filter capacity using optimized flocculation conditions.