Light-driven CO2 reduction for acetate production by coupling photocatalyst CdS with acetogenic bacteria Clostridium aceticum: An insight into the electron transfer pathway

Light-driven CO 2 reduction for acetate production by coupling photocatalyst with acetogenic bacteria has risen great interests due to the solar-to-chemical production and carbon neutrality. Although several acetogens have been employed to semi-artificial photosynthesis for acetate production, challenges remain in enhancing electron transfer efficiency and system stability. In this work, a novel hybrid of acetogenic bacteria Clostridium aceticum and photocatalyst CdS was constructed for CO 2 reduction to acetate, in which biosynthesized CdS nanoparticles on the cell surface of Clostridium aceticum served as the light harvester to provide electrons for bacterial metabolism. The CdS- C. aceticum hybrid system continuously produced acetate of 120 mg/L under irradiation of white light and summer natural light over several days of light-dark cycles. To elucidate the interfacial electron transfer and energy metabolism in this hybrid, the determination of cytochrome C and electron carriers as well as transcriptional analysis were performed. The content of cytochrome C and riboflavin in the hybrid system increased under light-exposure conditions, and H 2 was detected in the sterilized hybrid system. The genes associated with the Wood-ljungdahl pathway and energy conservation system were highly up-regulated under CdS-light irradiation along with the activation of genes encoding cytochrome C, riboflavin transporter and hydrogenase. The results indicated the CdS- C. aceticum hybrid possessed direct extracellular electron transfer via cytochrome C and indirect extracellular electron transfer via riboflavin and H 2 . This study provides a novel CdS- C. aceticum hybrid system for CO 2 reduction and insights into the electron transfer in the abiotic-biotic system for boosting the development of semi-artificial photosynthesis. • A novel CdS- C. aceticum hybrid system reduced CO 2 for acetate production. • Acetate production by the CdS- C. aceticum hybrid system was up to 120 mg/L. • This hybrid system possessed direct electron transfer via cytochrome C. • This hybrid system possessed indirect electron transfer via riboflavin and H 2 .