Engineered Escherichia coli Whole Cell-Mediated Electro-Biocatalysis for Carbon Dioxide to Formic Acid Conversion

The conversion of CO2 into a valuable chemical fuel could help reduce its effect on global warming. However, the utilization of CO2 by biological transformations is challenging because of the lack of enzymes exhibiting high catalytic activity toward CO2 reduction. In this work, three NAD+/W-containing formate dehydrogenases (FDHs) were discovered, expressed, and characterized. In addition, we used PbFDH, which displays high catalytic activity toward CO2 reduction, as a biocatalyst to convert CO2 to formic acid through whole-cell biocatalysis and electro-biocatalysis. The specific activities of DaFDH, PbFDH, and CsFDH increased by 68.1, 100.0, and 18.7 times, respectively, compared with that of ClFDH reported with high catalytic efficiency. Furthermore, this paper presents a preliminary discussion of the catalytic mechanism of FDHs for CO2 reduction based on their structures. The yield of formic acid obtained from CO2 reduction using electro-biocatalysis under aerobic conditions reaches up to 4.1 mmol/L/h, without any cofactor NADH and hydrogen gas. This study also demonstrates and compares the performances of NAD+/W-containing and NAD+-dependent FDHs in whole-cell biocatalysis and electro-biocatalysis. The findings of this study provide a meaningful foundation for the conversion of CO2 into a value-added chemical fuel.