The Site of LPS Synthesis

The demonstration of adhesions between the outer and inner membranes suggested the possibility that these zones may be involved in the intercalation of newly synthesized LPS into the outer membrane. 

On the basis of these results, we propose that S. anatum produces Eg antigens at a limited number of sites located over some of the adhesion zones. The synthesis of the new O-polysaccharides is not restricted to the equatorial or polar regions, but rather occurs over the entire cell. The spreading of the new EPS in the layer of preexisting antigens is relatively slow—patches of ferritin are still observed after 15 min of growth in nutrient medium. After 20 min, however, the ferritin label is seen to be distributed in a relatively even layer over the entire cell surface. 

The synthesis of EPS has recently also been studied by MUhlradt et ai in a Salmonella strain lacking UDP-galactose-4-epimerase. Their results also point to the involvement of adhesion sites in the insertion of O-antigen into the outer membrane. In the mutant, however, larger numbers (220) of sites of EPS production were found. This observation might be interpreted as suggesting that the mutant lacking the enzyme(s) necessary for completion of the EPS molecule has a less restricted mechanism of EPS 

Our studies on the adhesion zones of E. coli and S. anatum indicate that these specialized areas are intimately connected with a number of important functions of the bacterial-cell envelope. Bacteriophage infection, F-pilus production, insertion of newly synthesized LPS, and possibly killing by phage ghosts appear to take place at a limited number of sites which correspond to the zones of adhesion between the outer and inner membranes seen in plasmolyzed cells. 

That other important cellular processes and events may be associated with these structures as well, is supported by our recent finding that capsular polysaccharides also seem to be produced over the adhesion zones, and by the observation of other laboratories that bacterial DNA adheres to those portions of envelope isolates that show connections between the inner and outer membrane. 

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