Adapting gas fermenting bacteria for light-driven domino valorization of CO2

Abstract

The solar-driven valorization of CO₂ to fuels and chemicals provides an exciting opportunity to develop a circular chemical industry, but the controlled production of multicarbon organics remains a major challenge. Here, we present an abiotic–biotic domino strategy that integrates a photocatalytic CO₂-to-syngas conversion system with evolved syngas-fermenting bacteria to enable the upcycling of CO₂ into valuable C₂ products, including acetate and ethanol. To optimize microbial syngas fermentation through an accessible and chemist-friendly platform, we employ adaptive laboratory evolution (ALE) of Clostridium ljungdahlii (Cl). The adapted strain, Cl_adapt, exhibits a 2.5-fold increase in growth rate and a 120-fold enhancement in C₂ production compared to the wild type (Cl_wt). Isotopic labeling confirmed Cl_adapt's high conversion efficiency, yielding 6 : 1 and 9 : 1 ratios of ¹³C : ¹²C in acetate and ethanol, respectively. Whole genome sequencing revealed mutations in Cl_adapt, offering initial clues to its enhanced metabolism. A scaled-up semiconductor-molecule hybrid photocatalyst, TiO₂|phosphonated Co(terpyridine)₂, was employed to generate sufficient syngas (CO/H₂ ratio: ∼30 : 70 with 1.3 mmol of CO after 6 days) for Cl_adapt to demonstrate photocatalytic CO₂ → syngas → C₂ conversion (yielding 0.46 ± 0.07 mM, or 3.2 μmol, of acetate). This study offers a streamlined approach to improving syngas fermentation in Cl, insights into microbial adaptability, and an ALE-guided pathway for solar-powered CO₂ upcycling using an inorganic-microbial domino strategy.