A continuous system for biocatalytic hydrogenation of CO₂ to formate

In this work a novel bioprocess for hydrogenation of CO₂ to formate was developed, using whole cell catalysis by a sulfate-reducing bacterium. Three Desulfovibrio species were tested (D. vulgaris Hildenborough, D. alaskensis G20, and D. desulfuricans ATCC 27774), of which D. desulfuricans showed the highest activity, producing 12�mM of formate in batch, with a production rate of 0.09�mM�h⁻¹. Gene expression analysis indicated that among the three formate dehydrogenases and five hydrogenases, the cytoplasmic FdhAB and the periplasmic [FeFe] HydAB are the main enzymes expressed in D. desulfuricans in these conditions. The new bioprocess for continuous formate production by D. desulfuricans had a maximum specific formate production rate of 14�mM�g_dcw ⁻¹ï¿½h⁻¹, and more than 45�mM of formate were obtained with a production rate of 0.40�mM�h⁻¹. This is the first report of a continuous process for biocatalytic formate production.