Improved β‐Glucanase Production by a Recombinant Escherichia coli Strain using Zinc‐Ion Supplemented Medium

Abstract

AbstractIn order to investigate the suitability of different metal chelates for affinity chromatography, an expression vector was constructed. It contained a hybrid β‐glucanase as a model protein fused with a His6‐tag and a secretion cassette providing the ability to secrete β‐glucanase into the culture medium. Supplementation of zinc to the medium led to a rapidly increased expression and release of the target protein into the cultivation medium. Results in respect to the supplementation of the commonly used Terrific Broth “TB‐medium” with different metal ions are reported with special emphasis on the influence of zinc ions. A concentration of zinc ions in the order of about 0.175 mM led to optimal results. Batch cultivation under well‐controlled conditions showed that the growth behavior did not change significantly by adding zinc ions. Growth in a stirred tank bioreactor was much faster in unsupplemented TB‐medium compared to shake flask experiments leading to a much higher biomass concentration (15 g/L instead of 3 g/L). The secretion of β‐glucanase under theses conditions started at the transition into the stationary phase and increased to yield an extracellular activity of 1350 U/mL at the end of the fermentation process. An even higher yield of extracellular β‐glucanase (2800 U/mL) was reached when the fermentation was carried out with TB‐medium supplemented with 0.175 mM ZnSO4.