Efficient CO(2)-Reducing Activity of NAD-Dependent Formate Dehydrogenase from Thiobacillus sp. KNK65MA for Formate Production from CO(2) Gas

NAD-dependent formate dehydrogenase (FDH) from Candida boidinii (CbFDH) has been widely used in various CO(2)-reduction systems but its practical applications are often impeded due to low CO(2)-reducing activity. In this study, we demonstrated superior CO(2)-reducing properties of FDH from Thiobacillus sp. KNK65MA (TsFDH) for production of formate from CO(2) gas. To discover more efficient CO(2)-reducing FDHs than a reference enzyme, i.e. CbFDH, five FDHs were selected with biochemical properties and then, their CO(2)-reducing activities were evaluated. All FDHs including CbFDH showed better CO(2)-reducing activities at acidic pHs than at neutral pHs and four FDHs were more active than CbFDH in the CO(2) reduction reaction. In particular, the FDH from Thiobacillus sp. KNK65MA (TsFDH) exhibited the highest CO(2)-reducing activity and had a dramatic preference for the reduction reaction, i.e., a 84.2-fold higher ratio of CO(2) reduction to formate oxidation in catalytic efficiency (k (cat)/K (B)) compared to CbFDH. Formate was produced from CO(2) gas using TsFDH and CbFDH, and TsFDH showed a 5.8-fold higher formate production rate than CbFDH. A sequence and structural comparison showed that FDHs with relatively high CO(2)-reducing activities had elongated N- and C-terminal loops. The experimental results demonstrate that TsFDH can be an alternative to CbFDH as a biocatalyst in CO(2) reduction systems.