title: Multiple inverted DNA repeats of Bacteroides fragilis that control polysaccharide antigenic variation are similar to the hin region inverted repeats of Salmonella typhimurium.
abstract: The important opportunistic pathogen Bacteroides fragilis is a strictly anaerobic Gram-negative bacterium and a member of the normal resident human gastrointestinal microbiota. Our earlier studies indicated that there is considerable within-strain variation in polysaccharide expression, as detected by mAb labelling. Analysis of the genome sequence has revealed multiple invertible DNA regions, designated fragilis invertible (fin) regions, seven of which are upstream of polysaccharide biosynthesis loci and are approximately 226 bp in size. Using orientation-specific PCR primers and sequence analysis with populations enriched for one antigenic type, two of these invertible regions were assigned to heteropolymeric polysaccharides with different sizes of repeating units, as determined by PAGE pattern. The implication of these findings is that inversion of the fin regions switches biosynthesis of these polysaccharides off and on. The invertible regions are bound by inverted repeats of 30 or 32 bp with striking similarity to the Salmonella typhimurium H flagellar antigen inversion cross-over (hix) recombination sites of the invertible hin region. It has been demonstrated that a plasmid-encoded Hin invertase homologue (FinB), present in B. fragilis NCTC 9343, binds specifically to the invertible regions and the recombination sites have been designated as fragilis inversion cross-over (fix) sites.
authors.affiliation: Microbiology and Immunobiology, The Queen's University of Belfast, Grosvenor Road, Belfast BT12 6BN, UK.
authors.forename: Sheila
authors.initials: S
authors.lastname: Patrick
authors.affiliation: The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK.
authors.forename: Julian
authors.initials: J
authors.lastname: Parkhill
authors.affiliation: Microbiology and Immunobiology, The Queen's University of Belfast, Grosvenor Road, Belfast BT12 6BN, UK.
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: McCoy
authors.affiliation: The Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: Lennard
authors.affiliation: Biology and Biochemistry, The Queen's University of Belfast, Grosvenor Road, Belfast BT12 6BN, UK.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Larkin
authors.affiliation: Food Science, The Queen's University of Belfast, Grosvenor Road, Belfast BT12 6BN, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Collins
authors.affiliation: Institute of Cell and Molecular Biology, The University of Edinburgh, Darwin Building, King's Buildings, Edinburgh EH9 3JR, UK.
authors.forename: Matylda
authors.initials: M
authors.lastname: Sczaniecka
authors.affiliation: Institute of Cell and Molecular Biology, The University of Edinburgh, Darwin Building, King's Buildings, Edinburgh EH9 3JR, UK.
authors.forename: Garry
authors.initials: G
authors.lastname: Blakely
mesh_terms: D000940:Antigenic Variation; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001441:Bacteroides fragilis / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D004254:DNA Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D012486:Salmonella typhimurium / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D011135:Polysaccharides, Bacterial; D004254:DNA Nucleotidyltransferases; C059997:Hin recombinase