Escherichia coli membrane fluidity as detected by excimerization of dipyrenylpropane: Sensitivity to the bacterial fatty acid profile

A coordinated study of membrane fluidity and fatty acid composition has bee n carried out in Escherichia coli W3110. The lipid acyl chain profile of th e bacteria, altered by growing cells in steady state at 30, 37, 42, or 45 d egrees C, was determined by gas chromatography of the fatty acid methyl est ers. In parallel experiments, total membranes obtained from cells of the ab ove-mentioned cultures were labeled with dipyrenylpropane and their relativ e fluidity was measured on the basis of the excimer to monomer fluorescence intensity ratio of the fluorophore. It has been found that, at constant as say temperature, fluidity determined with dipyrenylpropane decreases gradua lly with the growth temperature increment, from 30 to 45 degrees C. Interes tingly, when fatty acid composition is taken into account, fluidity increas es linearly in the range under study, with the proportion of unsaturated fa tty acyl chains, both variables being highly correlated (0.924 less than or equal to r(2) less than or equal to 0.996). Our results show that dipyreny lpropane is a reliable and quantitative indicator of changes in membrane fl uidity, driven by modifications in the acyl chain composition of bacterial lipids. (C) 1999 Academic Press.