Prospects for engineering Ralstonia eutropha and Zymomonas mobilis for the autotrophic production of 2,3-butanediol from CO 2 and H 2

The decarbonization of the chemical industry and a shift toward circular economies because of high global CO emissions make CO an attractive feedstock for manufacturing chemicals. Moreover, H is a low-cost and carbon-free reductant because technologies such as solar-driven electrolysis and supercritical water (scH O) gasification enable sustainable production of molecular hydrogen (H ). We review the recent advances in engineering , the representative species of "Knallgas" bacteria, for utilizing CO and H to autotrophically produce 2,3-butanediol (2,3-BDO). This assessment is focused on state-of-the-art approaches for splitting H to supply energy in the form of ATP and NADH to power cellular reactions and employing the Calvin-Benson-Bassham cycle for CO fixation. Major challenges and opportunities for application and future perspectives are discussed in the context of developing other promising CO and H -utilizing microorganisms, exemplified by .