Efficient Hydrogen-Dependent Carbon Dioxide Reduction by Escherichia coli

Hydrogen-dependent reduction of carbon dioxide to formic acid offers a promising route to greenhouse gas sequestration, carbon abatement technologies, hydrogen transport and storage, and the sustainable generation of renewable chemical feedstocks [1]. The most common approach to performing direct hydrogenation of CO2 to formate is to use chemical catalysts in homogeneous or heterogeneous reactions [2]. An alternative approach is to use the ability of living organisms to perform this reaction biologically. However, although CO2 fixation pathways are widely distributed in nature, only a few enzymes have been described that have the ability to perform the direct hydrogenation of CO2 [3–5]. The formate hydrogenlyase (FHL) enzyme from Escherichia coli normally oxidizes formic acid to carbon dioxide and couples that reaction directly to the reduction of protons to molecular hydrogen [6]. In this work, the reverse reaction of FHL is unlocked. It is established that FHL can operate as a highly efficient hydrogen-dependent carbon dioxide reductase when gaseous CO2 and H2 are placed under pressure (up to 10 bar). Using intact whole cells, the pressurized system was observed to rapidly convert 100% of gaseous CO2 to formic acid, and >500 mM formate was observed to accumulate in solution. Harnessing the reverse reaction has the potential to allow the versatile E. coli system to be employed as an exciting new carbon capture technology or as a cell factory dedicated to formic acid production, which is a commodity in itself as well as a feedstock for the synthesis of other valued chemicals. [Display omitted] •Escherichia coli produces a formate hydrogenlyase (FHL) enzyme•FHL can function in two modes dependent on the prevailing environmental conditions•Pressurized CO2 and H2 allow FHL to function as a hydrogen-dependent CO2 reductase•The produced formic acid accumulates outside of the bacterial cells Under anaerobic conditions, Escherichia coli produces a formate hydrogenlyase (FHL) enzyme. Roger et al. reveal that when H2 and CO2 gases are placed under increasing pressure, FHL operates as an efficient hydrogen-dependent carbon dioxide reductase. The product of the reaction is formic acid, which accumulates outside the bacterial cells.