An estimate of the minimum amount of fluid lipid required for the growth of Escherichia coli.

The lipid phase transition of Escherichia coli was studied by high sensitivity differential scanning calorimetry. A temperature sensitive unsaturated fatty acid auxotroph was used to obtain lipids with subnormal unsaturated fatty acid contents. From these studies it was concluded that E. coli can grow nromally with as much as 20% of its membrane lipids in the ordered state but that if more than 55% of the lipids are ordered, growth ceases. Studies with wild-type cells show that the phase transition ends more than 10 degrees C below the growth temperature when the growth temperature is either 25 degrees C or 37 degrees C.