Altered Clostridia response in extractive ABE fermentation with solvents of different nature

Abstract

Solvents with opposite characteristics in terms of biocompatibility towards Clostridium acetobutylicum and butanol extraction capacity: vegetable oils, 2-butyl-1-octanol and oleyl alcohol were tested in batch extractive fermentations. Concentration profiles of substrate, intermediate and final products were compared with a control (solvent-free) fermentation. By concomitantly removing the inhibitory products, the total initial substrate was completely consumed with both solvents, while about 70% of the substrate was consumed in the solvent-free batch fermentation. Overproduction of butanol attained 60% and 100% with vegetable oil and 2-butyl-1-octanol respectively. Surprisingly, in the case of 2B1O extractive fermentation, a 46% increase of butanol yield (mass of butanol per mass of glucose consumed) was also observed, as well as the doubling of the ratio for the main metabolites (butanol to acetone). However, with this solvent, a longer lag phase compared to solvent free or vegetable oil extractive fermentation was observed, although the extraction capacity of butanol improved significantly due to the higher partition coefficient. Based on these results, differences between solvents go beyond what is expected from thermodynamics (liquid-liquid extraction). Culture metabolism and/or membrane polarity related functions appear to be influenced by the presence of 2B1O. In this context, possible mechanisms for these effects are discussed.