title: A linear plasmid truncation induces unidirectional flagellar phase change in H:z66 positive Salmonella Typhi.
abstract: The process by which bacteria regulate flagellar expression is known as phase variation and in Salmonella enterica this process permits the expression of one of two flagellin genes, fliC or fljB, at any one time. Salmonella Typhi (S. Typhi) is normally not capable of phase variation of flagellar antigen expression as isolates only harbour the fliC gene (H:d) and lacks an equivalent fljB locus. However, some S. Typhi isolates, exclusively from Indonesia, harbour an fljB equivalent encoded on linear plasmid, pBSSB1 that drives the expression of a novel flagellin named H:z66. H:z66+S. Typhi isolates were stimulated to change flagellar phase and genetically analysed for the mechanism of variation. The phase change was demonstrated to be unidirectional, reverting to expression from the resident chromosomal fliC gene. DNA sequencing demonstrated that pBSSB1 linear DNA was still detectable but that these derivatives had undergone deletion and were lacking fljA(z66) (encoding a flagellar repressor) and fljB(z66). The deletion end-point was found to involve one of the plasmid termini and a palindromic repeat sequence within fljB(z66), distinct to that found at the terminus of pBSSB1. These data demonstrate that, like some Streptomyces linear elements, at least one of the terminal inverted repeats of pBSSB1 is non-essential, but that a palindromic repeat sequence may be necessary for replication.
authors.affiliation: The Wellcome Trust Sanger Institute, The Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SA, UK. sgb@sanger.ac.uk
authors.forename: Stephen
authors.initials: S
authors.lastname: Baker
authors.forename: Kathryn
authors.initials: K
authors.lastname: Holt
authors.forename: Sally
authors.initials: S
authors.lastname: Whitehead
authors.forename: Ian
authors.initials: I
authors.lastname: Goodhead
authors.forename: Tim
authors.initials: T
authors.lastname: Perkins
authors.forename: Bruce
authors.initials: B
authors.lastname: Stocker
authors.forename: Jonathan
authors.initials: J
authors.lastname: Hardy
authors.forename: Gordon
authors.initials: G
authors.lastname: Dougan
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics* / Q000276:immunology*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D005407:Flagella / Q000235:genetics* / Q000276:immunology*; D005408:Flagellin / Q000096:biosynthesis / Q000235:genetics; D010957:Plasmids / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics; D012485:Salmonella typhi / Q000235:genetics* / Q000276:immunology*; D017422:Sequence Analysis, DNA; D017384:Sequence Deletion
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C079830:FljA protein, Salmonella; C094427:FljB protein, Salmonella; D012097:Repressor Proteins; D005408:Flagellin