Polymannose O-antigens of Escherichia coli, the binding sites for the reversible adsorption of bacteriophage T5+ via the L-shaped tail fibers.

A study of the adsorption kinetics of T5+ and the tail fiber-less mutant hd-2 to lipopolysaccharides of various Escherichia coli strains demonstrated T5+ binding to the O-antigen of th O8 and O9 types. Incorporation of radioactive mannose into the phosphomannose isomerase-deficient strain E. coli F860 O9 pmi allowed the derivation of the number of O-antigens per cell required to increase T5 adsorption. With more than 500 O-antigen molecules, acceleration of T5+ adsorption was observed. The highest adsorption rate was obtained when nearly all lipopolysaccharide molecules were substituted with a polymannose O-antigen. Inhibition studies with purified components of an enzymatically degraded lipopolysaccharide of the O8 type showed that among the mannosides tested the smallest unit, the trimannoside, was the strongest inhibitor of T5+ binding. We conclude that the reversible preadsorption to the O8 and O9 polymannose antigens increases the rate of infection via the cellular receptor protein encoded by the fhuA (formerly tonA) gene.