Enhanced CO2 Reduction by Electron Shuttle Molecules via Coupling Different Electron Transport Processes in Microbial Electrosynthesis

Electron shuttling molecules (ESMs) have been proven to accelerate the electron transfer from the electrode to the electroactive microorganism in microbial electrosynthesis (MES) for higher CO2 reduction or chemical production rate. However, the microbial electron acceptors of electroactive microorganisms and their responses to different electron shuttling molecules in MES were still unknown. In this study, three kinds of ESMs, e.g., riboflavin (B2), methyl viologen (MV) and neutral red (NR) were applied in the MES for acetate production to explore the mechanism of different ESMs on microbial interactions. The acetate concentrations were 41% and 51% higher than that of the control in B2 and NR addition. The acetogens relative abundances of control, B2, MV and NR were 0.29%, 5.68%, 22.78% and 42.89%, respectively. The microbial function profile of the microbial community on the biocathodes indicated that the performance of acetate production was more closely related to the expression of electron transport. The B2 was coupled with the NADH complex and hydrogenase, while MV and NR were coupled with the Rnf complex to support electron transfer and energy conversion via various electron transfer pathways. The study revealed that the ESMs coupled with different electron transport complexes of microorganisms to achieve electron transfer, resulting in product changes.