Nitrogen-doped carbon dots boost microbial electrosynthesis via efficient extracellular electron uptake of acetogens

This study investigated the molecular mechanism behind the highly efficient performance of nitrogen-doped carbon dots (NCDs)-assisted microbial electrosynthesis systems (MESs). The impact of NCDs (C:N precursor = 1:0.5-1:3) on acetogens was examined in the biocathode. The highest electrocatalytic performance was observed with NCDs_1:1. The maximum acetate production rate of 1.9 ± 0.1 mM d^-1 was achieved in NCDs_1:1-modified MESs, which was 26.7-216.7 % higher than other MESs (0.6-1.5 mM d^-1). With NCDs_1:1 modified, the biocathode exhibited a 129.3-186.8 % increase in the abundance of Sporomusa, and 38.5-104.6 % increase in cytochrome expression (cydAB, cybH). Transcriptome confirmed that cytochromes played a crucial role in the extracellular electron uptake (EEU) of NCDs_1:1-modified Sporomusa. NCDs_1:1 enhanced EEU efficiency, thereby increasing the two H⁺-pumping steps and accelerating microbial CO₂ fixation. These results provide valuable insights into increasing CO₂ fixation by maximizing EEU efficiency in acetogens.