Acetogens beyond gas fermentation: Enhancing bioconversion of lignocellulosic biomass.

As the demand for sustainable and cost-effective bioprocesses intensifies, acetogenic bacteria have gained renewed attention for their unique metabolic capabilities. Traditionally recognised for their role in gas fermentation, these anaerobes fix CO2 and other C1 substrates via the Wood-Ljungdahl pathway, enabling carbon-neutral production of platform chemicals and biofuels. However, recent research has expanded their potential well beyond gaseous substrates. Acetogens exhibit remarkable metabolic flexibility, utilising a wide array of organic compounds, including saccharides, alcohols, organic acids, and complex hydrolysates derived from lignocellulose and industrial waste streams. Here, their simultaneous hydrolysate, and CO2 fixing ability could enable superior carbon conversion efficiency compared to conventional production hosts by achieving near 100% carbon valorisation into value-added products. Their tolerance to typical fermentation inhibitors and operational resilience under harsh industrial conditions further enhance their appeal. This review examines the emerging roles of acetogenic bacteria beyond gas fermentation, focusing on their integration into mixotrophic systems and co-culture strategies with hydrolytic enzymes and organisms. These developments offer new opportunities for consolidated bioprocessing, improved carbon conversion efficiency, and the valorisation of underutilised feedstocks, positioning acetogens as key players in next-generation circular bioeconomy applications.