The cell envelope of Gram-negative bacteria, such as the Rhizobiaceae, is built up of three distinctive layers. These layers are the inner or cytoplasmic membrane, the peptidoglycan sacculus, and the outer membrane. Both membranes contain membrane-forming lipids, mainly phospholipids, and proteins (Chapter 3). Outer membranes contain as additional component lipopolysaccharides. In this chapter ... [Show full abstract] the composition, function, and organization of phospholipids and other membrane lipids of members of the Rhizobiaceae will be discussed.