Bioconversion of C1-gases by mixotrophic co-cultures fermentation with C. carboxidivorans and C. beijerinkii

The development of newfangled bioprocess strategies for the capture of C1-gases (CO and CO₂) and their bioconversion into valuable products is currently one of the main focuses of research in order to achieve a more resilient world. This work analyses the viability of the co-culture C. carboxidivorans and C. beijerinkii to produce bioproducts (bioalcohols and organic acids) in mixotrophic conditions. In this way, the bioconversion of C1 gases (CO and CO₂), in the presence of Fe⁰, using mixotrophic co-culture fermentation by C. carboxidivorans and C. beijerinkii, was evaluated, analyzing the influence of the ratio between both microorganisms, the pH, and the presence of Fe⁰. As a result, up to 7 g/L of butanol were achieved at pH 7, 12.5 g/L Fe⁰, and using a 1:1 ratio of C. carboxidivorans: C. beijerinkii, also improving the production of ethanol, acetic acid, and butyric acid as compared to individual culture fermentations. Finally, the operation in a bioreactor, comparing discontinuous and continuous gas feeding operation modes, was also studied, with better C1-gases utilization and overall fermentation efficiency (7 vs 4.6 g/L butanol) in continuous gas operation mode.