Influence of acetate concentration on acetone production by a modified Acetobacterium woodii

Global warming is the driving force for developing production processes of chemical compounds based on CO2 reduction technologies. Bacteria can act as biological catalysts that reduce this gaseous substrate in added-value compounds. Acetobacterium woodii is one of the best-performing strains on H2-CO2 blends and naturally produces acetate. Acetone is a raw material deeply used in the chemical industry, and its global demand is increasing. Acetone-butanol-ethanol (ABE) fermentation is the oldest microbial production platform for acetone synthesis from organic substrates, and Clostridium acetobutylicum is the model strain for its production. In various wild-type acetogens and ABE-producing Clostridium species, acetate positively influences the synthesis of reduced products. In this work, a modified A. woodii strain expressing the enzymes of the acetone pathway from C. acetobutylicum was used to convert H2-CO2 streams into acetone. This study aims to assess the impact of acetate on acetone production catalyzed by such a modified A. woodii. Tests were carried out in serum bottles and a continuous stirred tank reactor up to a pressure of 10 bar, in gas-batch or in continuous gassing, providing different gas mixes. Outcomes indicated that acetone synthesis was stimulated when acetate concentration in the medium exceeded the threshold of 100-120 mM. Thus, acetic acid can affect acetone productivity in the modified A. woodii strain. This outcome should be considered in the design of fermentation processes, especially in setting up fermentations with the liquid continuous operative mode.