Culture medium density as a simple monitoring tool for cell integrity of Escherichia coli

During the expression of recombinant proteins in the periplasm of Escherichia coli, the integrity of the outer membrane can change, so that product leaks to the medium. Additional stress can induce lysis, the complete disintegration of both inner and outer membrane, leading to release of both product and host cell proteins. Whether leakiness is unwanted or intentional, appropriate monitoring of leakiness and its distinction from lysis is necessary to ensure product quality and process performance. Here, we investigated a novel monitoring tool for leakiness and lysis based on the measurement of the culture supernatant density. The method benefits from short analysis time and low analytical error, simple result output, relatively low cost, low risk of operator errors and the option of easy on-line implementation. Although limitations exist regarding selectivity, we could show that the method is capable of detecting changes in cell integrity. This tool is therefore an interesting addition to the monitoring toolbox for industrial E. coli bioprocesses.