Differential activities of bacteriophage depolymerase on bacterial polysaccharide: binding is essential but degradation is inhibitory in phage infection of K1-defective Escherichia coli

The role of the phage depolymerase in binding and degradation was investigated. Phage mutants that are specific for Escherichia coli bacteria that have a low level of K1 polysialic acid capsule were isolated. It was shown that these mutants have lost the cleaving activity of the phage endosialidase while retaining the binding activity. The results suggest that the polysaccharide-binding activity of the enzyme is necessary for phage infection, whereas the cleavage of the polysaccharide is required for penetration of the dense polysaccharide of wild-type bacteria but is inhibitory in the infection of bacteria with a sparsecapsule.