Model acetogens as chassis for CO2-driven bioproduction.

Microbes play a pivotal role in the Earth's carbon cycle, regulating greenhouse gas fluxes by emitting, fixing and transforming CO2. Among them, acetogens stand out for their ability to fix CO2 through the Wood-Ljungdahl pathway, an ancient, highly energy-efficient route to acetyl-CoA that operates at thermodynamic limits. By coupling hydrogen (H2) or carbon monoxide oxidation to CO2 fixation, acetogens conserve energy while generating biomass and valuable products such as ethanol and acetate. These features position them as promising microbial cell factories for sustainable bioproduction via gas fermentation. Recent advances in metabolic engineering and synthetic biology have expanded the production spectrum of acetogens, enabling production of platform chemicals at lab-to-commercial scale. Yet, CO2-only bioconversion remains energetically challenging compared to syngas-based applications, requiring innovative solutions in strain development, bioprocess optimisation and integration of renewable energy sources. This review highlights the central role of model acetogens in anaerobic CO2 conversion, covering their metabolic capabilities, strain development and emerging bioprocess strategies to unlock their potential for low-carbon biomanufacturing.