Investigations on the thermotropic phase behaviour of lipids A from Brucella and other Gram-negative bacteria

Abstract The phase behaviour of the lipopolysaccharide lipid moiety, free lipid A, of Salmonella typhimurium, S. minnesota, Shigella flexneri, Escherichia coli and, especially, Brucella melitensis and B. abortus has been investigated by applying differential scanning calorimetry. Working with samples in the solid state and a N 2 atmosphere, we have obtained results that could lead to a redefinition of the main temperature of the gel ⇐ liquid crystalline transition of the hydrocarbon chains to between 30 and 41°C (instead of around 45°C). The fluidity of the acyl chains and the lyotropic behaviour in the β ⇐ α melting transition, which are important parameters with respect to the expression of biological activities, are also discussed for the lipids A from the different bacterial species.