Homeoviscous Response of Clostridium Pasteurianum to Butanol

          Clostridium pasteurianum has been shown to ferment pure and partially purified biodiesel-derived crude glycerol into butanol at higher yields than obtained when sugars are used as the carbon source. n-Butanol is an attractive biofuel with favorable physicochemical properties. However, n-butanol is lipophilic and, when produced by fermentation, fluidizes biological membranes and leads to cellular inhibition. This study was focused on investigating the homeoviscous response of C. pasteurianum during n-butanol challenge experiments.  Membrane lipid composition was analyzed by GC-MS and NMR, and membrane structure was analyzed by fluorescence anisotropy.  C. pasteurianum was found to display two different homeoviscous responses that altered membrane lipid composition in an attempt to counteract the n-butanol toxicity.  Addition of exogenous n-butanol to a fermentation, when C. pasteurianum produced endogenous n-butanol, led to an increase in the ratio of saturated to unsaturated fatty acids.  On the other hand, addition of exogenous n-butanol to fermentation, when C. pasteurianum did not produce endogenous n-butanol, led to a decrease in the ratio of saturated to unsaturated fatty acids.  This differential response for exogenous n-butanol during the presence and absence of n-butanol production indicates that C. pasteurianum is a versatile micro-organism that has the potential to be engineered as an industrial n-butanol producer using crude glycerol, a promising low cost feedstock for n-butanol production.