Journal of Lipid Research, Vol 25, 1501-1507, Copyright © 1984 by Lipid Research, Inc.
Bacterial membranes and lipid packing theory
H Goldfine
Recent physical studies on the lipids of biological membranes have
emphasized the potential instability of the lamellar phase of mixtures of
lipids containing unsaturated species of phosphatidylethanolamine,
plasmenylethanolamine, or monoglycosyldiacylglycerols, all of which are
important constituents of the membranes of different groups of prokaryotes.
The polar lipid compositions of bacteria are examined in terms of lipid
packing theory. This survey reveals that gram-negative species with high
proportions of unsaturated fatty acids (greater than 65%), often have
phosphatidylcholine (PC), in addition to the more common
phosphatidylethanolamine (PE), phosphatidylglycerol, and cardiolipin.
Physical studies have shown that PC is capable of inducing the bilayer
phase when added to unsaturated PE. Many bacteria that are rich in
unsaturated fatty acids and contain PC, have intracytoplasmic membrane
systems (ICM), and the potential role of bilayer instability in the
formation of ICM is discussed. Two groups of bacteria that are either
natural fatty acid auxotrophs or utilize exogenous fatty acids when
endogenous synthesis is inhibited, Acholeplasma laidlawii and the butyric
acid-producing clostridia, are capable of adjusting their lipid class
compositions according to the degree of unsaturation of their lipid
aliphatic chains. Lipid class composition is also affected by growth
temperature in both groups of organisms, and by incorporation of
cholesterol in A. laidlawii. As the content of cis-unsaturated fatty acids
or temperature is increased, lipids that form an unstable lamellar phase at
physiological temperatures are replaced with lipids that have larger
effective polar head groups, and can therefore form more stable bilayers.