title: Escherichia coli clone Sonnei (Shigella sonnei) had a chromosomal O-antigen gene cluster prior to gaining its current plasmid-borne O-antigen genes.
abstract: O antigen is part of the lipopolysaccharide present in the outer membrane of gram-negative bacteria. The surface-exposed O antigen is subject to selection by the host immune system, which may account for the maintenance of many different O-antigen forms. Characteristically, all genes specific to O-antigen synthesis are clustered in a region close to the his and gnd genes on the chromosome of Escherichia coli and related species. Shigella sonnei, essentially a clone of E. coli (E. coli clone Sonnei), is an important human pathogen and is unusual in that its O-antigen gene cluster is located on a plasmid. Our results suggest that it once had a normal chromosomal O-antigen gene cluster which has been largely deleted. We suggest that the O antigen encoded by the plasmid-borne genes offered a selective advantage in adapting to a new environment and that the chromosomal O-antigen genes were eventually inactivated. We also identified, by PCR and sequencing, a potential ancestor of E. coli Sonnei among the 166 known E. coli serotype strains.
authors.affiliation: Department of Microbiology, The University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: V
authors.initials: V
authors.lastname: Lai
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: P R
authors.initials: PR
authors.lastname: Reeves
mesh_terms: D001426:Bacterial Proteins; D002876:Chromosomes, Bacterial / Q000235:genetics*; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics* / Q000276:immunology; D005798:Genes, Bacterial / Q000235:genetics; D008359:Mannose-6-Phosphate Isomerase / Q000235:genetics; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000235:genetics; D005810:Multigene Family / Q000235:genetics*; D009713:Nucleotidyltransferases / Q000235:genetics; D019081:O Antigens / Q000096:biosynthesis*; D010957:Plasmids / Q000235:genetics*; D011134:Polysaccharides; D015183:Restriction Mapping; D017422:Sequence Analysis, DNA; D012764:Shigella sonnei / Q000235:genetics* / Q000276:immunology
chemical_list: D001426:Bacterial Proteins; D009097:Multienzyme Complexes; D019081:O Antigens; D011134:Polysaccharides; C004275:colanic acid; C093300:ManB protein, bacteria; D009713:Nucleotidyltransferases; D008359:Mannose-6-Phosphate Isomerase