(682c) Butanol Partitioning At Model Bacterial Membrane/Water Interfaces

Bacteria adjust their membrane lipid composition to counteract the fluidizing effects of alcohol and to adapt to elevated alcohol concentrations during fermentation. Bacterial membranes are rich in anionic phosphatidylglycerols (PG), but little is known regarding alcohol partitioning into anionic membranes, particularly for n-butanol, which exhibits clear advantages over ethanol as an alternative biofuel. This work examines the effects of lipid charge on n-butanol partitioning into model anionic bacterial membrane vesicles composed of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylglycerol (DPPG) in the absence and presence of salt. Above a threshold n-butanol concentration (0.135 M), the membranes were interdigitated irrespective of DPPG or salt concentration, consistent with previous results for neutral membranes such as DPPC. Increasing salt concentration let to greater n-butanol partitioning in DPPC membranes and caused aggregation/fusion. However, aggregation/fusion was prevented with increasing DPPG concentration (i.e. increasing membrane charge) and small vesicles were observed. The results suggest that n-butanol partitioning, and subsequent changes in membrane and vesicle structure, was driven by a balance between the ‘salting-out’ of n-butanol, interlipid electrostatic interactions, and interfacial cation binding and hydration. This is the first study to the best of our knowledge to examine the effects of n-butanol partitioning on model bacterial membranes composed of negatively charged lipids in the presence of salts.