A singular state of membrane lipids at cell growth temperatures

Cells adjust their membrane lipid composition when they adapt to grow at di fferent temperatures. The consequences of this adjustment for membrane prop erties and functions are not well understood. Our report shows that the tem perature dependence of the diffusion of a probe molecule in multilayers for med from total lipid extracts of E. coli has an anomalous maximum at a temp erature corresponding to the growth temperature of each bacterial preparati on (25, 29, and 32 degrees C). This increase in the lateral diffusion coeff icient, D, is characteristic of membrane lipids in a critical state, for wh ich large fluctuations of molecular area in the plane of the bilayer are ex pected. Therefore, changes in lipid composition may be due to a requirement that cells maintain their membranes in a state where molecular interaction s and reaction rates are readily modulated by small, local perturbations of membrane organization.