Phosphatidylglycerol (PG) is found in almost all types of bacteria and represents 20-25% of phospholipids in most Gram-negative bacteria, which are present only in the inner membrane. Escherichia coli, a widely studied model organism, has up to 20% PG in its membranes . In Gram-positive bacteria, which have a single phospholipid bilayer coated with peptidoglycans, PG can constitute up to 60% of phospholipids. In many bacteria, the diacyl form of the lipids predominates, but in others, the alkylacyl and alkenylacyl forms are more abundant . The charge on the phosphate group means that it is an anionic lipid of neutral pH with a head group larger than expected due to hydration and an overall cylindrical shape.