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, Cladapt, exhibits a 2.5-fold increase in growth rate and a 120-fold enhancement in C2 production compared to the wild type (Clwt). Isotopic labeling confirmed Cladapt'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 Cladapt, 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 Cladapt 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.
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