Lowered pH eliminates the enhanced hyperthermic killing of E. coli induced by procaine or exposure to N2 gassing.

Survival of E. coli K1060 is enhanced when they are heated at 47 degrees C in pH 6 medium as compared to pH 7.4. At pH 6 nitrogen bubbling and 10 mM procaine did not increase hyperthermic killing. The membrane content of phosphatidylethanolamine is about 80 per cent of the total of phosphatidylethanolamine, phosphatidylglycerol and cardiolipin phospholipids. The polar headgroup of this lipid is highly sensitive to pH changes in this pH range. The changes in electrostatic charge with its secondary effects on membrane-protein relationships may explain resistance to hyperthermic killing. Thus, the difference in response to lowered pH of bacterial, compared to mammalian cells may be revealing membrane-related phenomena critical to hyperthermic killing. Also increased levels of cardiolipid were observed in linolenic acid grown cells which could be an 'attempt' to stabilize their membranes.