Relationship between bactericidal action of complement and fluidity of cellular membranes.

The mode of complement-mediated killing of Escherichia coli B cells grown at 25 and 42 degrees C and of E. coli K-12 UFAts cells grown in the presence of oleic and elaidic aicds was examined in relation to their membrane lipid compositions and the thermodynamic properties of membrane phospholipids. Phospholipids isolated from 25 degrees C-grown cells of strain B and from oleic acid-incorporated cells of strain K-12 UFAts had lower phase transition temperatures than did phospholipids from E. coli strain B grown at 42 degrees C or those from strain K-12 UFAts grown on elaidic acid. The rate of cellular susceptibility to complement action closely correlated with the liquid crystalline phase of phospholipids of cell membranes. These findings suggest that membrane fluidity is obligatory for the final expression of complement action.