Biocatalytic conversion of carbon dioxide to formate using a robust metal-independent <i>Thiobacillus</i> formate dehydrogenase

The capture and utilization of CO2 from industrial off-gases to produce commodity chemicals has the potential to make an important contribution to the transition to a circular economy. Formate, and its conjugate formic acid, is a potential sustainable platform chemical that can be produced from CO2. Electrochemical reduction of CO2 to formate is a promising route, but biocatalysis with formate dehydrogenase (FDH) as biocatalyst may offer advantages for industrial implementation such as mild conditions, high product selectivity, and less expensive down-stream processing. Here, we investigated the potential of a metal-independent Thiobacillus FDH (TsFDH) as a biocatalyst for the production of formate from CO2-rich industrial offgases. An excellent stability was demonstrated, also in the presence of potential off-gas impurities. A formate titer of 14 mM could be achieved at pH 6.5 and 37 °C, with an initial specific productivity of 0.37 mmol g−1FDH h−1. TsFDH compares favorably to metal-dependent FDHs with respect to stability, O2-sensitivity and activity at low pH values, but unfavorably in terms of CO2 reduction activity, hampering its potential as industrial biocatalyst. Specific rates could be significantly improved by further reaction engineering, and possibly also by enzyme engineering.