The effect of Al³⁺ on the physical properties of membrane lipids in Thermoplasma acidophilum

Using Electron Paramagnetic Resonance Spectroscopy, Al³⁺ was shown to produce a dramatic decrease of membrane lipid fluidity on the microorganism Thermoplasma acidophilum at a pH > 2. The ability of Al³⁺ to alter lipid fluidity was enhanced with increasing pH (from 3 to 5). At pH 4, 10^-2 M Al³⁺ increased the lower lipid phase transition by 39°C, and a detectable change was observed with AlCl₃ concentrations as low as 10^-5 M. The ability of Al³⁺ to increase the lower lipid phase transition temperature of T. acidophilum is the largest of any cation/lipid interaction yet reported.