EVIDENCE FOR A CONJUGATION-LIKE MECHANISM OF DNA TRANSFER IN HELICOBACTER-PYLORI

Many strains of Helicobacter pylori are naturally competent for transf ormation in vitro. Since there is a high degree of genetic variation a mong H. pylori strains, we sought to determine whether mechanisms of D NA exchange other than transformation exist in these organisms. Studie s were done with H. pylori cells that each were resistant to two diffe rent antibiotics; the procedure used involved mating of cells on plate s or in broth, in the absence or presence of DNase. In each experiment , such matings produced progeny with the markers of both parents. Exam ination of the full resistance profile and random arbitrarily primed D NA PCR (RAPD-PCR) profiles of the progeny indicated that DNA transfer was bidirectional. DNase treatment reduced but did not eliminate trans fer; only the presence of both DNase and a membrane separating the cel ls did so. For progeny derived from matings in the presence of DNase, antibiotic resistance and RAPD profiles indicated that transfer was un idirectional. DNase-treated cell free supernatants also did not transf orm, ruling out transduction. These experiments indicate that both a D Nase-sensitive mechanism (transformation) and a DNase-resistant conjug ation-like mechanism involving cell-to-cell contact may contribute to DNA transfer between H. pylori cells.