CuInS2 quantum dots drive Clostridium ljungdahlii photosynthetic catalysis for CO2 reduction to C2 products

Clean fuels (e.g., ethanol) production by anaerobic bacteria that utilize CO 2 as the carbon source and H 2 as the electron donor constitutes a green carbon emission reduction strategy. However, the utilization of CO 2 by bacteria is severely limited due to the low water solubility and slow mass transfer rate of H 2 . In this study, a self-photosensitized CuInS 2 quantum dots (QDs)– Clostridium ljungdahlii hybrid was constructed by integrating efficient photoelectric conversion with stable biological metabolism. CuInS 2 QDs with a band gap of 1.66 eV were employed as photocatalysts to generate photogenerated electrons for replacing H 2 . The hybrid exhibited a three-fold enhancement in photoelectron absorption efficiency compared with pure Clostridium ljungdahlii . In the self-photosensitized cells, the expression level of ferredoxin oxidoreductase, carbon monoxide dehydrogenase, and phosphate acetyltransferase was upregulated by 10%, 36%, and 47%. These changes in metabolites and proteins associated with electron transfer and CO 2 reductive fixation via the Wood-Ljungdahl pathway demonstrated that the bacteria efficiently utilized the extra electrons generated by CuInS 2 QDs. These exogenous electrons strengthened the bacterial capacity to reduce CO 2 into cell-available organic matter, achieving a maximum acetic acid yield of 0.58 g/L and a maximum ethanol yield of 0.21 g/L. Moreover, the hybrid system realized a CO 2 conversion efficiency of 31.7% and a quantum yield of 1.35%. This study confirmed that the electrons generated by CuInS 2 QDs can be transported into bacterial cells and replace H 2 to supply energy for cellular carbon metabolism.