Scalable succinate biomanufacturing via in-situ Citrobacter freundii-CdS biohybrids: Light-driven redox balancing enhances reductive succinate biosynthesis

In situ biomineralized C. freundii -CdS biohybrid enabled light-driven fermentation. • Photoelectrons increased intracellular NADH/NAD + by 59%. • Succinate production increased by 26.2% in a 5 L bioreactor. • rTCA and electron transport pathways were coordinately activated. • Light-driven redox balancing enhanced reductive succinate biosynthesis. Microbial fermentation provides a sustainable route to succinic acid production, yet the reductive tricarboxylic acid (rTCA) pathway demands more NADH than anaerobic glucose catabolism can supply, thereby limiting the yield. Here, we constructed a Citrobacter freundii -CdS biohybrid in which CdS nanoparticles, biomineralized on the cell surface, harvest visible light and are proposed to supply photoelectrons to the host cell, augmenting intracellular NADH availability. Under optimized conditions, the illuminated biohybrid elevated the intracellular NADH/NAD + ratio by 59% relative to controls. In a 5 L bioreactor, the illuminated biohybrid achieved a succinate titer of 42.8 g L −1 (yield: 0.49 g g −1 glucose), a 26.2% increase over the dark control, with concurrent reductions in formate, acetate, and lactate. Transcriptomic analysis identified coordinated upregulation of electron transport, NADH synthesis, and rTCA pathway genes alongside downregulation of competing branch-point enzymes. These findings support a model in which light-driven electron supply can serve as a non-genetic approach for redirecting intracellular reducing power and carbon partitioning toward succinate biosynthesis in facultative anaerobes, although the precise electron-transfer route remains to be established. Download: Download high-res image (170KB) Download: Download full-size image