Outer Membrane of Salmonella: Sites of Export of Newly Synthesised Lipopolysaccharide on the Bacterial Surface

Abstract

The UDP‐galactose‐4‐epimeraseless strain 1195 of Salmonella typhimurium bears incomplete lipopolysaccharide, and only after addition of galactose to the growth medium it produces wild‐type lipopolysaccharide. It was demonstrated in a double‐label experiment that already existent, incomplete lipopolysaccharide is not completed after galactose addition but that only the newly synthesised lipopolysaccharide carries the wild‐type specificity. It was thus possible to locate newly synthesised lipopolysaccharide with specific anti‐wild‐type, ferritin‐conjugated antibodies in freeze‐etch preparations and ultra‐thin sections. With the freeze‐etch technique new lipopolysaccharide was found to appear in about 220 patches per cell, 30 s after 50 mM galactose had been added to the medium. After growth for 2–3 min under these conditions new lipopolysaccharide was found to be evenly spread over the entire cell surface. In ultra‐thin sections of plasmolysed cells 86% of the ferritin patches, indicating newly synthesised lipopolysaccharide, was found located over sites where the cytoplasmic and the outer membrane adhere to one another. It is discussed that new lipopolysaccharide emerges from these sites and that lateral movement of lipopolysaccharide in the outer membrane results in an even distribution on the bacterial cell surface.