Reinventing shake flask fermentation: The breathable flask.

ABSTRACT

Cultivating cells in shake flasks is a routine operation that is largely unchanged since its inception. A glass or plastic Erlenmeyer vessel with the primary gas exchange taking place across various porous plugs is used with media volumes typically ranging from 100 mL to 2 L. Oxygen limitation and carbon dioxide accumulation in the vessel is a major concern for studies involving shake flask cultures. In this study, we enhance mass transfer in a conventional shake flask by replacing the body wall with a permeable membrane. Naturally occurring concentration gradient across the permeable membrane walls facilitates the movement of oxygen and carbon dioxide between the flask and the external environment. The modified flask called the breathable flask, has shown a 40% improvement in mass transfer coefficient (kLa) determined using the static diffusion method. The prokaryotic cell culture studies performed with Escherichia coli showed an improvement of 28%-66% in biomass and 41%-56% in recombinant product yield. The eukaryotic cell culture study performed with Pichia pastoris expressing proinsulin exhibited a 40% improvement in biomass and 115% improvement in protein yield. The study demonstrates a novel approach to addressing the mass transfer limitations in conventional shake flask cultures. The proposed flask amplifies its value by providing a membrane-diffusion-based sensing platform for the integration of low-cost, noninvasive sensing capabilities for real-time monitoring of critical cell culture parameters like dissolved oxygen and dissolved carbon dioxide.