Harnessing Escherichia coli for bio-based production of formate under pressurized H 2 and CO 2 gases.

Escherichia coli is gram-negative bacterium that is a workhorse for biotechnology. The organism naturally performs a mixed-acid fermentation under anaerobic conditions where it synthesises formate hydrogenlyase (FHL-1). The physiological role of the enzyme is the disproportionation of formate in to H 2 and CO 2 . However, the enzyme has been observed to catalyse hydrogenation of CO 2 given the correct conditions, and so has possibilities in bio-based carbon capture and storage if it can be harnessed as a hydrogen-dependent CO 2 -reductase (HDCR). In this study, an E. coli host strain was engineered for the continuous production of formic acid from H 2 and CO 2 during bacterial growth in a pressurised batch bioreactor. Incorporation of tungsten, in place of molybdenum, in FHL-1 helped to impose a degree of catalytic bias on the enzyme. This work demonstrates that it is possible to couple cell growth to simultaneous, unidirectional formate production from carbon dioxide and develops a process for growth under pressurised gases. IMPORTANCE Greenhouse gas emissions, including waste carbon dioxide, are contributing to global climate change. A basket of solutions is needed to steadily reduce emissions, and one approach is bio-based carbon capture and storage. Here we present out latest work on harnessing a novel biological solution for carbon capture. The Escherichia coli formate hydrogenlyase (FHL-1) was engineered to be constitutively expressed. Anaerobic growth under pressurised H 2 and CO 2 gases was established and aqueous formic acid was produced as a result. Incorporation of tungsten in to the enzyme in place of molybdenum proved useful in poising FHL-1 as a hydrogen-dependent CO 2 reductase (HDCR).