Synthetic and high purity (99 %) lipids were purchased from Avanti Polar Lipids and used to prepare large unilamellar vesicles (LUVs). The vesicles all contained a mixture of 75 mol% zwitterionic phosphocholine (PC), 22.5 mol% of anionic phosphoglycerol (PG) and 2.5 mol% phosphoethanolamine (PE) conjugated to polyethylene glycol (PEG) for steric stabilization. This headgroup mixture mimics the overall membrane charge ratio of E. coli, and is consistent with previous work . While the headgroup composition was kept constant, lipids with different tail groups were used to prepare vesicles with different membrane thickness and saturation, details are given in table 1. The membrane properties are highly dependent on the phase of the membrane, which is in turn largely determined by the length and degree of saturation of the lipid tails, given the same headgroup. Hence, we in-vestigated vesicles comprised of DMPC/DMPG with a phase transition temperature, T m , of 23°C. This intermediate T m allowed the same membrane to be investigated in the gel phase at 20 °C and in the fluid phase at 37 °C. Additionally, we used DSPC/DSPG membranes with T m = 55 °C, and POPC/POPG membranes with T m = -2 °C, as they remain in the gel or fluid phase, respectively, at the experimental temperatures. The vesicles were prepared using the well established protocol previously described . Briefly, specific masses of the dry lipid powders were weighed out and transferred to a round bottom flask. The lipid powder mixture was thoroughly dissolved in a 3:1 chloroform:methanol mixture, which was subsequently evaporated using a rotory evaporator at a pressure of 40 mbar. The resulting lipid film was re-hydrated using 0.050 M Tris buffer at pH 7.4 in MilliQ water, followed by sonication and extrusion through a polycarbonate filter with a pore size of 100 nm, to a vesicle concentration of 10 mg/mL. This results in unilamellar vesicles with a narrow size distribution with an average diameter close to 100 nm.