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Engineering and applications of surface displayed tyrosinase on Escherichia coli

Time: Fri 2019-11-29 14.00

Location: F3, Lindstedtsvägen 26, Stockholm (English)

Subject area: Biotechnology

Doctoral student: David Hörnström , Industriell bioteknologi

Opponent: Joachim José,

Supervisor: Professor Antonius J. A. van Maris, Industriell bioteknologi

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The rise of biotechnology has provided a toolbox to deal with major challenges related to pollution and health. Microbial enzymes constitute powerful macromolecules with applications in environmental technology, and industrial and medical production. The display of enzymes on cellular surfaces promotes external access to reactants, thereby simplifying production and cost-effectiveness of bioprocesses. To this end, a system for the surface display of the oxidative enzyme tyrosinase was developed, optimized and implemented. The first part of the thesis focused on developing tyrosinase surface-display via autotransport-based secretion in Escherichia coli. Initially, the presence of active surface-displayed tyrosinase, catalyzing the oxidation, of L-tyrosine was verified. Next, the components of the surface expression system were systematically engineered to yield an optimized tyrosinase-displaying strain with five times higher biomass-specific tyrosinase activity. The second half of the thesis applied the surface-displayed tyrosinase for wastewater treatment and biosensor development. It was found that the catalyzed oxidation of L- tyrosine resulted in the deposition of melanin at the E. coli cell surface. The resulting melanized cells were used in a membrane bioreactor for adsorption of the pharmaceutical chloroquine from an aqueous solution, with a specific binding capacity of 140 mg/g cells and allowed simple cell regeneration by lowering the pH. In a second application, the tyrosinase- display system was integrated into a genetic circuit with regulated oxidation and production of L-tyrosine in response to specific toxins. By employing the resulting cells in an electrochemical cell, the circuit generated a means to directly and selectively link biological information to an electrical output. Overall, the results in this thesis highlight the functionality of the surface expression methodology and demonstrates its versatile applicability.