Perhaps the most striking feature of bacterial membranes is their multifunctional nature (1 ,2 ). Bacterial cytoplasmic membranes, for example, catalyze the reactions of respiratory and photosynthetic electron transfer and associated energy transduction, and contain numerous carriers for solute transport in and out of the cell. The cytoplasmic membrane of Escherichia coli is believed to contain more than 200 protein types, of which about 60 may be involved in transport functions. In addition, there are the many highly hydrophobic protein complexes that constitute the respiratory chains, and the multicomponent BF1 and BFo ATPase complexes. Bacterial membranes are distinctive in lacking sterols, but contain hopanes, polyterpenoids that have a role in maintaining membrane rigidity. Although variable, the major lipids are phosphatidylglycerol and phosphatidylethanolamine in gram-positive bacteria, and phosphatidylethanolamine with smaller amounts of phosphatidylglycerol in gram-negative bacteria.