(472a) Examining the Partitioning Coefficients of Butanol and Other Fermentation Metabolites Produced By Clostridium Pasteurianum into a Lipid Vesicle Solvent

Continuous extractive fermentation is critical to increasing biofuel production. Extracting the fermentation products reduces product inhibition, increases the metabolic activity and drives solvent production, and can increase solvent selectivity. Liquid-liquid extraction using organic solvents has shown to be effective for extractive fermentation, but the solvents employed are often toxic to the microbes and can limit productivity. Self-assemblies such as vesicles and micelles provide an alternative to organic solvents for the extractive fermentation of biofuels. We are currently developing a process where lipid vesicles are used as the solvent phase to recover butanol from fermentation broths and remove toxic impurities present in substrate feedstocks. This approach is based on the high thermodynamic partitioning coefficients observed for butanol from water to lipid membranes, which is one of the main causes of product inhibition as butanol partitions into and fluidizes microbial membranes. This presentation will report on the partitioning behavior of butanol, as well as other metabolites produced by Clostridium pasteurianum (acetate, ethanol, 1,3-propanediol), to lipid vesicles as a function of lipid composition, pH, and temperature. We have shown that butanol partitioning increases with the amount of unsaturated lipid present within the vesicles due to an increase in the size of the â??binding pocketsâ?? for amphiphilic butanol to partition into at the vesicle/water interface.