Bacterial membrane lipids: diversity in structures and pathways

For many decades, Escherichia coli was the main model organism for the study of bacterial membrane lipids. The results obtained served as a blueprint for membrane lipid biochemistry, but it is clear now that there is no such thing as a typical bacterial membrane lipid composition. Different bacterial species display different membrane compositions and even the membrane composition of cells belonging to a single species is not constant, but depends on the environmental conditions to which the cells are exposed. Bacterial membranes present a large diversity of amphiphilic lipids, including the common phospholipids phosphatidylglycerol, phosphatidylethanolamine and cardiolipin, the less frequent phospholipids phosphatidylcholine, and phosphatidylinositol and a variety of other membrane lipids, such as for example ornithine lipids, glycolipids, sphingolipids or hopanoids among others. In this review, we give an overview about the membrane lipid structures known in bacteria, the different metabolic pathways involved in their formation, and the distribution of membrane lipids and metabolic pathways across taxonomical groups.