title: Helicobacter pylori interstrain restriction-modification diversity prevents genome subversion by chromosomal DNA from competing strains.
abstract: Helicobacter pylori, bacteria that colonize the human gastric mucosa, possess a large number of genes for restriction-modification (R-M) systems, and essentially, every strain possesses a unique complement of functional and partial R-M systems. Nearly half of the H.pylori strains studied possess an active type IIs R-M system, HpyII, with the recognition sequence GAAGA. Recombination between direct repeats that flank the R-M cassette allows for its deletion whereas strains lacking hpyIIRM can acquire this cassette through natural transformation. We asked whether strains lacking HpyII R-M activity can acquire an active hpyIIRM cassette [containing a 1.4 kb kanamycin resistance (aphA) marker], whether such acquisition is DNase sensitive or resistant and whether restriction barriers limit acquisition of chromosomal DNA. Our results indicate that natural transformation and conjugation-like mechanisms may contribute to the transfer of large (4.8 kb) insertions of chromosomal DNA between H.pylori strains, that inactive or partial R-M systems can be reactivated upon recombination with a functional allele, consistent with their being contingency genes, and that H.pylori R-M diversity limits acquisition of chromosomal DNA fragments of >/=1 kb.
authors.affiliation: Department of Medicine and Microbiology, New York University School of Medicine and VA Medical Center, New York, NY, USA.
authors.forename: Rahul A
authors.initials: RA
authors.lastname: Aras
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Small
authors.forename: Takafumi
authors.initials: T
authors.lastname: Ando
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Blaser
mesh_terms: D019175:DNA Methylation; D015280:DNA Restriction-Modification Enzymes / Q000235:genetics* / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics* / Q000378:metabolism; D003850:Deoxyribonuclease I / Q000378:metabolism; D014644:Genetic Variation; D016680:Genome, Bacterial; D016480:Helicobacter pylori / Q000201:enzymology / Q000235:genetics*; D017354:Point Mutation; D013045:Species Specificity; D014169:Transformation, Bacterial
chemical_list: D015280:DNA Restriction-Modification Enzymes; D004269:DNA, Bacterial; D003850:Deoxyribonuclease I