Acetogenic bacteria utilize light-driven electrons as an energy source for autotrophic growth.

Abstract

Acetogenic bacteria use cellular redox energy to convert CO₂ to acetate using the Wood-Ljungdahl (WL) pathway. Such redox energy can be derived from electrons generated from H₂ as well as from inorganic materials, such as photoresponsive semiconductors. We have developed a nanoparticle-microbe hybrid system in which chemically synthesized cadmium sulfide nanoparticles (CdS-NPs) are displayed on the cell surface of the industrial acetogen <i>Clostridium autoethanogenum</i> The hybrid system converts CO₂ into acetate without the need for additional energy sources, such as H₂, and uses only light-induced electrons from CdS-NPs. To elucidate the underlying mechanism by which <i>C. autoethanogenum</i> uses electrons generated from external energy sources to reduce CO₂, we performed transcriptional analysis. Our results indicate that genes encoding the metal ion or flavin-binding proteins were highly up-regulated under CdS-driven autotrophic conditions along with the activation of genes associated with the WL pathway and energy conservation system. Furthermore, the addition of these cofactors increased the CO₂ fixation rate under light-exposure conditions. Our results demonstrate the potential to improve the efficiency of artificial photosynthesis systems based on acetogenic bacteria integrated with photoresponsive nanoparticles.