The Outer Membrane of Gram-negative Bacteria and the Cytoplasmic Membrane

Abstract

The major permeability barrier in any membrane is the lipid bilayer structure, and its barrier property is inversely correlated with its fluidity. Bacteria cannot make this membrane much less fluid or it will start to interfere with the normal functions of the membrane proteins, so some bacteria have constructed an additional structure that surrounds the cell outside the cytoplasmic membrane. An example of this are Gram-negative bacteria, such as E. coli, which surround themselves with a second outer membrane which functions as an effective barrier.