FORMATION OF THE K30 (GROUP-I) CAPSULE IN ESCHERICHIA-COLI 09-K30 DOES NOT REQUIRE ATTACHMENT TO LIPOPOLYSACCHARIDE LIPID A-CORE

Escherichia coli K antigens (capsular polysaccharides) are divided int o two broad classes, designated groups I and II, on the basis of a num ber of chemical, physical, and genetic criteria. Group I K antigens ca n be further subdivided on the basis of the absence (group IA) or pres ence (group IB) of amino sugars in the repeating unit of the K antigen . One criterion proposed for inclusion in group I is covalent linkage of the capsular polysaccharide to the lipid A-core of lipopolysacchari de (LPS). E. coli 09:K30 is a strain with a representative group IA K antigen. This organism synthesizes an LPS-associated low-molecular-wei ght form of K30 antigen which is called K-LPS. To determine the involv ement of LPS lipid A-core in expression of the K30 capsular polysaccha ride, E. coli K30/K-12 hybrid strains were constructed with mutations in the E. coli K-12 rfa locus, responsible for the biosynthesis of the LPS core oligosaccharide. These strains lack K-LPS, indicating that a full-length core is required for K-LPS expression. However, formation of a K30 capsule was unaffected by rfa defects, indicating that attac hment to lipid A-core is not an obligatory step for either export of h igh-molecular-weight capsular polysaccharide or maintenance of the cap sular structure on the cell surface. Silver-stained tricine-sodium dod ecyl sulfate-polyacrylamide gel electrophoresis profiles of lipopolysa ccharides from other E. coli K serotypes showed that all strains with group IB K antigens expressed some K-LPS. In contrast, some strains wi th group IA K antigens appear to lack K-LPS. Consequently, although as sociation of group I K antigens with lipid A-core is common, it is not a universal marker for inclusion in group I.