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 <i>Thiobacillus</i> 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⁻¹_FDH 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.