Engineering cyanobacterial carbonic anhydrase surface mutations for fast CO2 hydration and capture

Equilibration between CO2 and the other forms of dissolved inorganic carbon (DIC) is slow under ambient conditions, bottle-necked by the hydration of dissolved CO2 to form bicarbonate and a proton. This step is often rate-limiting for aqueous CO2 capture processes under ambient temperature and pressure, and is precisely the chemistry catalyzed by the family of carbonic anhydrase enzymes. As a result, incorporation of carbonic anhydrases (CAs) into various CO2 capture schemes may be used to accelerate CO2 hydration, increasing the rates of downstream processes coupled to this DIC equilibrium. While this potential use for CA has been long-studied, extending these basic chemical principles to real applications have been hampered by practical questions of how to economically source carbonic anhydrase enzymes at mass scale. This work explores the use of modified cyanobacterial expression hosts as a potential resolution to that problem. Specifically, engineering the surface display of carbonic anhydrases in fast-growing, marine cyanobacteria would yield a self-sustaining CO2 hydration catalyst that requires only sunlight, CO2 itself, and nutrients freely available in seawater, as inputs for passively generating carbonic anhydrases on the cell envelope during cell growth. These possibilities motivated the development of such constructs; their potential for enhancing CO2 hydration rates are reported here.