Enhancing acetone production from H₂ and CO₂ using supplemental electron acceptors in an engineered Moorella...

Acetogens grow autotrophically and use hydrogen (H₂) as the energy source to fix carbon dioxide (CO₂). This feature can be applied to gas fermentation, contributing to a circular economy. A challenge is the gain of cellular energy from H₂ oxidation, which is substantially low, especially when acetate formation coupled with ATP production is diverted to other chemicals in engineered strains. Indeed, an engineered strain of the thermophilic acetogen Moorella thermoacetica that produces acetone lost autotrophic growth on H₂ and CO₂. We aimed to recover autotrophic growth and enhance acetone production, in which ATP production was assumed to be a limiting factor, by supplementing with electron acceptors. Among the four selected electron acceptors, thiosulfate and dimethyl sulfoxide (DMSO) enhanced both bacterial growth and acetone titers. DMSO was the most effective and was further analyzed. We showed that DMSO supplementation enhanced intracellular ATP levels, leading to increased acetone production. Although DMSO is an organic compound, it functions as an electron acceptor, not a carbon source. Thus, supplying electron acceptors is a potential strategy to complement the low ATP production caused by metabolic engineering and to improve chemical production from H₂ and CO₂.