title: Specific insertion and deletion of insertion sequence 1-like DNA element causes the reversible expression of the virulence capsular antigen Vi of Citrobacter freundii in Escherichia coli.
abstract: Citrobacter freundii strain WR7004 reversibly expresses the virulence capsular antigen Vi, whose production is controlled by two distinct chromosomal loci, viaA and viaB. The rate of oscillation between the Vi-producing (Vi+) state and the Vi-nonproducing (Vi-) state in strain WR7004 ranges from 2 X 10(-4) to 7 X 10(-3) transitions per bacterium per generation. A similarly high conversion rate from Vi+ to Vi- occurs in Escherichia coli HB101 harboring pWR127, a plasmid that contains the 18-kilobase-pair (kb) viaB region cloned from WR7004. However, the Vi- state in HB101 harboring pWR127 was so stable that transition to the Vi+ state was not detected (less than 10(-10) per bacterium per generation). When pWR127 DNA derived from Vi- strains of HB101 harboring pWR127 was transformed in HB101 recipient, a small number of Vi+ transformants were seen among the transformants, which were predominantly Vi-. The viaB region consists of two EcoRI digestion fragments, A (8.6 kb) and B (9.4 kb). A discrete 700- to 800-base-pair DNA element was found to be inserted in the EcoRI B fragment of the viaB region of pWR127 when derived from Vi- strains. However, no such DNA element was found in the pWR127 DNA isolated from Vi+ strains. This discrete DNA element inserts into a recombinational hot spot 1.1 kb from the end of the EcoRI B fragment and behaves as an insertion sequence 1 (IS1)-like element. The insertion of this IS1-like element in the viaB region thus disrupts expression of the Vi antigen. Restoration of Vi expression results when this element is excised.
authors.affiliation: Department of Bacterial Immunology, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
authors.forename: J T
authors.initials: JT
authors.lastname: Ou
authors.forename: L S
authors.initials: LS
authors.lastname: Baron
authors.forename: F A
authors.initials: FA
authors.lastname: Rubin
authors.forename: D J
authors.initials: DJ
authors.lastname: Kopecko
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics*; D002872:Chromosome Deletion; D002954:Citrobacter / Q000235:genetics*; D004262:DNA Restriction Enzymes; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000235:genetics*; D005796:Genes; D005798:Genes, Bacterial; D010957:Plasmids; D011135:Polysaccharides, Bacterial; D014169:Transformation, Bacterial
chemical_list: D000942:Antigens, Bacterial; D004251:DNA Transposable Elements; D011135:Polysaccharides, Bacterial; D004262:DNA Restriction Enzymes