Gram-scale production of recombinant microbial enzymes in shake flasks.

Heterologous production of recombinant proteins is a cornerstone of microbiological and biochemical research as well as various biotechnological processes. Yields and quality of produced proteins have a tremendous impact on structural and enzymology studies, development of new biopharmaceuticals and establishing new biocatalytic processes. Majority of current protocols for recombinant protein expression in Escherichia coli exploit batch cultures with complex media, often providing low yields of the target protein due to oxygen transfer limitation, rapid depletion of carbon sources and pH changes during the cultivation. Recently introduced EnBase technology enables fed-batch-like cultivations in shake flasks with continuous glucose release from a soluble starch. In this study, we critically compare the yields of fourteen model enzymes in E. coli cultured in a novel semi-defined medium and in a complex medium. Significant improvements of the volumetric yields 2-31 times were observed for all tested enzymes expressed in enzymatic fed-batch-like cultures with no adverse impact on enzyme structure, stability or activity. Exceptional yields, higher than 1 g of protein per liter of culture, were obtained with six enzymes. We conclude that the novel semi-defined medium tested in this study provides a robust improvement of protein yields in shake flasks without investment into costly bioreactors.