Effects of common defoaming agents on the growth of the endotoxin-free ClearColi® Escherichia coli host

ClearColi^® BL21(DE3) is an Escherichia coli expression system with a genetically-modified lipopolysaccharide (LPS) pathway resulting in the production of endotoxin-free material.  This feature is an economic and efficiency advantage when producing proteins intended for human therapeutic applications as downstream endotoxin removal can be avoided.  ClearColi is reported to reach similar biomass densities and produce comparable levels of protein as the commonly-used E. coli BL21(DE3) platform.  Using our standard culture conditions for batch fermentation of and expression from E. coli BL21(DE3), we observed unexpectedly low growth of ClearColi.  We conducted a series of flask and bioreactor experiments to examine the effects of common defoaming agents on the growth of ClearColi.  We found that ClearColi was particularly sensitive to the polypropylene glycol-based defoaming agent Antifoam 204, while the silicone emulsion agent Xiameter 1520 AFE supported growth equal to or greater than that without a defoamer.  Because the modified LPS of ClearColi affects properties of the cell envelope, it is possible that the modification has altered membrane integrity in such a way as to make ClearColi cells unusually sensitive to PPG-based defoaming agents.