Formation of the K30 (group I) capsule in Escherichia coli O9:K30 does not require attachment to lipopolysaccharide lipid A-core.
Escherichia coli K antigens (capsular polysaccharides) are divided into two broad classes, designated groups I and II, on the basis of a number of chemical, physical, and genetic criteria. Group I K antigens can be further subdivided on the basis of the absence (group IA) or presence (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 lipopolysaccharide (LPS). E. coli O9:K30 is a strain with a representative group IA K antigen. This organism synthesizes an LPS-associated low-molecular-weight form of K30 antigen which is called K(LPS). To determine the involvement of LPS lipid A-core in expression of the K30 capsular polysaccharide, 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 attachment to lipid A-core is not an obligatory step for either export of high-molecular-weight capsular polysaccharide or maintenance of the capsular structure on the cell surface. Silver-stained tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of lipopolysaccharides from other E. coli K serotypes showed that all strains with group IB K antigens expressed some K(LPS). In contrast, some strains with group IA K antigens appear to lack K(LPS). Consequently, although association of group 1 K antigens with lipid A-core is common, it is not a universal marker for inclusion in group I.
MacLachlan
P R
PR
Department of Microbiology, University of Guelph, Ontario, Canada.
Keenleyside
W J
WJ
Dodgson
C
C
Whitfield
C
C
D000942:Antigens, Bacterial / Q000096:biosynthesis*; D000954:Antigens, Surface / Q000096:biosynthesis*; D016667:Bacterial Capsules / Q000378:metabolism* / Q000648:ultrastructure; D002240:Carbohydrate Sequence; D004926:Escherichia coli / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D008050:Lipid A / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D012091:Repetitive Sequences, Nucleic Acid
D000942:Antigens, Bacterial; D000954:Antigens, Surface; C030659:K antigens; D008050:Lipid A; D008070:Lipopolysaccharides