Efficient hydrogen-dependent carbon dioxide reduction by Escherichia coli

Abstract

The formate hydrogenlyase (FHL) complex of Escherichia coli is normally produced under anaerobic fermentative conditions when its physiological role is to oxidise formate to carbon dioxide and couple that reaction directly to the reduction of protons to molecular hydrogen. This forward reaction is the major route of hydrogen production by E. coli and the physiology, genetics and biochemistry of this process are reasonably well understood. However, studies of the reverse reaction - hydrogen-dependent carbon dioxide reduction - have been rather less extensive. Harnessing the alternative reverse reaction has the potential to unlock FHL as a carbon dioxide cycling enzyme, or could potentially lead to the development of bio-based carbon capture technologies. In this work, it is established that FHL can operate as a highly efficient CO2 reductase. A controllable pressure system was designed with the intention of maximising substrate availability to the FHL enzyme. By placing gaseous CO2 and H2 are under pressure (up to 10 bar), and by using a compartmentalised intact whole cell approach where the produced formate is excreted, the optimised experimental system was observed to convert 100 % of gaseous CO2 to formic acid and generate >500 mM formate in solution at an initial rate of 1.2 g formate per litre per hour.