The Effect of Lipopolysaccharide Composition on the Ultrastructure ofPseudomonas aeruginosa

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Abstract
SUMMARY: The surface structure of Pseudomonas aeruginosa PAC1 and PAC1R and of lipopolysaccharide-defective mutants derived from them was studied by negative-staining and thin-section electron microscopy and compared with that of a rough mutant with wild-type lipopoly-saccharide. The rough mutant and the parent strains had fairly smooth outer layers. Negatively stained preparations of all the mutants lacking polymerized O-antigenic side-chains, including a semi-rough mutant, showed numerous blebs on the surface. In thin sections of these mutants occasional extrusions from the surface were seen. They appeared to consist of material extruded from the outer membrane, but there was no evidence to suggest they were complete unit membranes. Polymerized O-antigenic side-chains in the lipopolysaccharide appear to be required to produce the wild-type appearance of the outer membrane in P. aeruginosa.