Autotrophic isopropanol production by Cupriavidus necator using industrial biogas and incinerator flue gases as carbon sources

Gas fermentation is a promising approach to reduce carbon emissions of production processes by using microorganisms to convert industrial gas streams into valuable carbon-based products. Here, isopropanol production by engineered Cupriavidus necator from CO₂-rich gas streams is presented. Four different engineered strains were tested first on synthetic gas mixture, and one was selected, namely Re2133/pEG7d, for further evaluation on two different industrial CO₂-rich gas streams. Up to 1.6 g L^-1 of isopropanol was obtained in autotrophic gas flasks with this strain. Then, raw biogas from landfill containing 45% methane was successfully used as a CO₂ source for isopropanol production with this strain Re2133/pEG7d producing up to 2.35 ± 0.25 g L^-1, and methane enrichment was demonstrated. Finally, flue gases from a municipal incinerator were used as a source of CO₂ and O₂ for the autotrophic cultivation of the strain Re2133/pEG7d, obtaining a final isopropanol concentration of 2.5 ± 0.3 g L^-1. This work highlighted the robustness of C. necator to potential industrial gas stream impurities and its versatility in using diverse gaseous feedstocks, promising future developments at larger scale.