title: Plastic cells and populations: DNA substrate characteristics in Helicobacter pylori transformation define a flexible but conservative system for genomic variation.
abstract: Helicobacter pylori, bacteria that colonize the human gastric mucosa, are naturally competent for transformation by exogenous DNA, and show a panmictic population structure. To understand the mechanisms involved in its horizontal gene transfer, we sought to define the interval required from exposure to substrate DNA until DNA uptake and expression of a selectable phenotype, as well as the relationship of transforming fragment length, concentration, homology, symmetry, and strandedness, to the transformation frequency. We provide evidence that natural transformation in H. pylori differs in efficiency among wild-type strains but is saturable and varies with substrate DNA length, symmetry, strandedness, and species origin. We show that H. pylori cells can be transformed within one minute of contact with DNA, by DNA fragments as small as 50 bp, and as few as 5 bp on one flank of a selectable single nucleotide mutation is sufficient substrate for recombination of a transforming fragment, and that double-stranded DNA is the preferred (1000-fold >single-stranded) substrate. The high efficiency of double-stranded DNA as transformation substrate, in conjunction with strain-specific restriction endonucleases suggests a model of short-fragment recombination favoring closest relatives, consistent with the observed H. pylori population biology.
authors.affiliation: Dept. of Medicine, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Levine
authors.forename: Edward A
authors.initials: EA
authors.lastname: Lin
authors.forename: Walid
authors.initials: W
authors.lastname: Emara
authors.forename: Josephine
authors.initials: J
authors.lastname: Kang
authors.forename: Michael
authors.initials: M
authors.lastname: DiBenedetto
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ando
authors.forename: Daniel
authors.initials: D
authors.lastname: Falush
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Blaser
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics; D022761:Gene Transfer, Horizontal; D014644:Genetic Variation; D016680:Genome, Bacterial; D016480:Helicobacter pylori / Q000235:genetics / Q000502:physiology*; D017354:Point Mutation; D014169:Transformation, Bacterial
chemical_list: D004269:DNA, Bacterial