title: Acquisition and evolution of the exoU locus in Pseudomonas aeruginosa.
abstract: ExoU is a potent Pseudomonas aeruginosa cytotoxin translocated into host cells by the type III secretion system. A comparison of genomes of various P. aeruginosa strains showed that that the ExoU determinant is found in the same polymorphic region of the chromosome near a tRNA(Lys) gene, suggesting that exoU is a horizontally acquired virulence determinant. We used yeast recombinational cloning to characterize four distinct ExoU-encoding DNA segments. We then sequenced and annotated three of these four genomic regions. The sequence of the largest DNA segment, named ExoU island A, revealed many plasmid- and genomic island-associated genes, most of which have been conserved across a broad set of beta- and gamma-Proteobacteria. Comparison of the sequenced ExoU-encoding genomic islands to the corresponding PAO1 tRNA(Lys)-linked genomic island, the pathogenicity islands of strain PA14, and pKLC102 of clone C strains allowed us to propose a mechanism for the origin and transmission of the ExoU determinant. The evolutionary history very likely involved transposition of the ExoU determinant onto a transmissible plasmid, followed by transfer of the plasmid into different P. aeruginosa strains. The plasmid subsequently integrated into a tRNA(Lys) gene in the chromosome of each recipient, where it acquired insertion sequences and underwent deletions and rearrangements. We have also applied yeast recombinational cloning to facilitate a targeted mutagenesis of ExoU island A, further demonstrating the utility of the specific features of the yeast capture vector for functional analyses of genes on large horizontally acquired genetic elements.
authors.affiliation: Department of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: Bridget R
authors.initials: BR
authors.lastname: Kulasekara
authors.forename: Hemantha D
authors.initials: HD
authors.lastname: Kulasekara
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Wolfgang
authors.forename: Lisa
authors.initials: L
authors.lastname: Stevens
authors.forename: Dara W
authors.initials: DW
authors.lastname: Frank
authors.forename: Stephen
authors.initials: S
authors.lastname: Lory
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000302:isolation & purification; D001483:Base Sequence; D004251:DNA Transposable Elements; D016521:Electrophoresis, Gel, Pulsed-Field; D019143:Evolution, Molecular; D014644:Genetic Variation; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D011110:Polymorphism, Genetic; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D017384:Sequence Deletion
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; C111749:pseudomonas exoprotein A protein, Pseudomonas aeruginosa