title: Genes involved in Haemophilus influenzae type b capsule expression are frequently amplified.
abstract: The genes involved in Haemophilus influenzae type b capsule expression are present as a duplication of an approximately 18-kb DNA segment (the Cap b locus). It has been shown previously that recombination occurs between the two copies of the repeat, resulting in deletion of one copy and loss of capsule expression at frequencies of 0.1%-0.5%. The present study tested the hypothesis that the duplicated arrangement could serve as a template for further amplification of capsule gene sequences. Southern hybridization analysis of 66 type b invasive isolates showed that amplifications exist and are moderately common (23/66 were amplified). In addition to three copies of the 18-kb repeat, four copies were detected in some strains, and up to five copies in 1 isolate. By ELISA, a five-copy strain made about six times more capsular polysaccharide than did an isogenic two-copy derivative. The evolutionary significance of the duplicated arrangement may be its ability to rapidly amplify under conditions where it is advantageous to produce more capsule.
authors.affiliation: Department of Microbiology, Georgetown University School of Medicine, Washington, DC 20007.
authors.forename: P G
authors.initials: PG
authors.lastname: Corn
authors.forename: J
authors.initials: J
authors.lastname: Anders
authors.forename: A K
authors.initials: AK
authors.lastname: Takala
authors.forename: H
authors.initials: H
authors.lastname: Käyhty
authors.forename: S K
authors.initials: SK
authors.lastname: Hoiseth
mesh_terms: D016667:Bacterial Capsules / Q000235:genetics*; D001428:Bacterial Vaccines / Q000032:analysis / Q000096:biosynthesis; D015139:Blotting, Southern; D004269:DNA, Bacterial / Q000032:analysis; D004219:District of Columbia; D004797:Enzyme-Linked Immunosorbent Assay; D005387:Finland; D005784:Gene Amplification; D015964:Gene Expression Regulation, Bacterial; D006192:Haemophilus Infections / Q000382:microbiology*; D018073:Haemophilus Vaccines; D006193:Haemophilus influenzae / Q000235:genetics* / Q000472:pathogenicity; D006801:Humans; D009693:Nucleic Acid Hybridization; D011135:Polysaccharides, Bacterial / Q000032:analysis / Q000096:biosynthesis; D015183:Restriction Mapping; D014774:Virulence
chemical_list: D001428:Bacterial Vaccines; D004269:DNA, Bacterial; D018073:Haemophilus Vaccines; C044237:Haemophilus influenzae type b polysaccharide vaccine; D011135:Polysaccharides, Bacterial