Microbial electrosynthesis of organic chemicals from CO₂ by Clostridium scatologenes ATCC 25775^T

Background: The conversion of CO₂ into high value-added products has a very important environmental and economic significance. Microbial electrosynthesis (MES) is a promising technology, which adopts a bioelectrochemical system to transform CO₂ into organic chemicals. Results: In this study, Clostridium scatologenes ATCC 25775^T, an anaerobic acetogenic bacterium, demonstrated its utility as a biocatalyst in a MES system, for the first time. With the cathodic potential of the MES system decreased from − 0.6 to − 1.2 V (vs. Ag/AgCl), the current density of the MES, and the production of organic chemicals, increased. Combining the genetic analysis and the results of the wet lab experiments, we believe C. scatologenes may accept electrons directly from the cathode to reduce CO₂ into organic compounds at a potential of − 0.6 V. The acetic and butyric acid reached a maximum value of 0.03 and 0.01 g/L, respectively, and the maximum value of total coulombic efficiency was about 84%, at the potential of − 0.6 V. With the decrease in cathodic potentials, both direct electron transfer and exogenous electron shuttle, H₂ might be adopted for the C. scatologenes MES system. At a potential of − 1.2 V, acetic acid, butyric acid and ethanol were detected in the cathodic chamber, with their maximum values increasing to 0.44, 0.085 and 0.015 g/L, respectively. However, due to the low H₂ utilization rate by the C. scatologenes planktonic cell, the total coulombic efficiency of the MES system dropped to 37.8%. Conclusion: Clostridium scatologenes is an acetogenic bacterium which may fix CO₂ through the Wood–Ljungdahl pathway. Under H₂ fermentation, C. scatologenes may reduce CO₂ to acetic acid, butyric acid and ethanol. It can also be used as the biocatalyst in MES systems.[Figure not available: see fulltext.].