Interaction between phage P22 and phenol-water extracted lipopolysaccharides from sensitive bacteria belonging to serogroups A, B and D1 results in hydrolysis of the α--rhamnosyl linkages within the tetrasaccharide repeating unit of the O-antigenic polysaccharide chain. These O-antigens have identical structures except for the nature of the 3,6-dideoxy-hexosyl group linked to O-3 of the -mannosyl residue. Removal of the dideoxysugar, or periodate oxidation followed by borohydride reduction of the -rhamnosyl residue made the O chain resistant to the -rhamnosidase. Substitution of the -galactosyl residue at O-4, but not at O-6, with an α--glucosyl group was compatible with hydrolysis. A number of and lipo- or capsular polysaccharides containing chain -rhamnosyl residues were tested but none was sensitive to the P22 -rhamnosidase. The substrate specificity of the -rhamnosidase parallels the lytic specificity of the phage which suggests that the initial step in phage P22 infection is a P22 tail enzyme O-antigen substrate interaction. The main product of the hydrolysate was octa-, dodeca- and hexadecasaccharides. Treatment of phage FO resistant smooth strains of with P22 tails removed O polysaccharide chains and made previously ‘hidden’ FO receptors accessible to the phage.


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