Capsular sialyl chains ofEscherichia coli K1 mutants resistant to K1 phage

Capsular polysialyl chains of wild-typeEscherichia coli K1 consist of about 200 sialyl units. Factors associated with the degree of polymerization of the K1 polysaccharide were studied by isolation of mutant bacteria resistant to K1 phage. The mutants (n=55) were characterized with respect to the length of their capsular sialyl chains by gel electrophoresis and reactivity with anti-K1 antibodies. No mutants with short sialyl chains were found, although the mutants displayed different phenotypic properties and produced different amounts of sialic acid. Ultrastructural examination revealed phenotypes with accumulations of apparent polysialic acid in the periplasm or cytosol. This observation provides direct support for the previously proposed translocation of the K1 polysaccharide via the periplasmic space during its biosynthesis.