High-Resolution Atomic Force Microscopy Studies of the Escherichia coli Outer Membrane:  Structural Basis for Permeability

Abstract

The structural basis of the outer membrane permeability for the bacterium Escherichia coli is studied by atomic force microscopy (AFM) in conjunction with biochemical treatment and analysis. The surface of the bacterium is visualized with unprecedented detail at 50 and 5 Å lateral and vertical resolutions, respectively. The AFM images reveal that the outer membrane of native E. coli exhibits protrusions that correspond to patches of lipopolysaccharide (LPS) containing hundreds to thousands of LPS molecules. The packing of the nearest neighbor patches is tight, and as such the LPS layer provides an effective permeability barrier for the Gram-negative bacteria. Treatment with 50 mM EDTA results in the release of LPS molecules from the boundaries of some patches. Further metal depletion produces many irregularly shaped pits at the outer membrane, which is the consequence of progressive release of LPS molecules and membrane proteins. The EDTA-treated cells were analyzed for metal content and for their reactivities toward lysozyme and antibodies specific for LPS. The experiments collectively indicate that the metal depletion procedure did not remove all the LPS molecules despite a dramatic decrease in the metal content. The remaining LPS molecules are present outside the pits, whereas the bottom of the pits is devoid of these molecules. This new structure for the outer membrane exhibits higher permeability than that for the native cells.

High-resolution imaging of pelagic bacteria by Atomic Force Microscopy and implications for carbon cycling

“…Such an increase in roughness has also been reported for E. coli 057 and the lytic phage A 157 phage-host system (Dubrovin et al, 2008). Further, AFM studies have shown that mechanical and chemical damage of cell surface results in increased roughness-including damage caused by EDTA (Amro et al, 2000), detergents (Camesano et al, 2000), proteases (F Malfatti, unpublished) (Camesano et al, 2000) and antibiotics (Braga and Ricci, 1998;Meincken et al, 2005). Marine phages lyse 10-50% of bacteria production in the upper ocean, and it would be interesting to observe if phage-infected bacteria and archaea could be identified through a surface 'signature'.…”

Extracellular synthesis of silver nanoparticles using dried leaves of pongamia pinnata (L) pierre

“…Similarly, Amro et al [35] suggested that depletion of the silver metal from the outer membrane may cause progressive release of lipopolysaccharide molecules and membrane proteins. This results in the formation of irregularly shaped pits and hence increases the membrane permeability.…”

Efficient disinfection of Escherichia coli in water by silver loaded alumina

“…It is well known that the outer membrane plays an essential role in providing a barrier of selective permeability for E. coli and other Gram-negative bacteria [23]. On the basis of the TEM investigation, after treatment with the catalysts, the cell wall and cell membrane would be destroyed, subsequently leading to a change in cell membrane permeability and leakage of intracellular substances.…”