The development of genetic tools to study Helicobacter pylori pathogenesis and persistence

In the model organism E. coli, recombination mediated by the related XerC and XerD recombinases complexed with the FtsK translocase at specialized dif sites, resolves dimeric chromosomes into free monomers to allow efficient chromosome segregation at cell division. Computational genome analysis of Helicobacter pylori, a slow growing gastric pathogen, identified just one chromosomal xer gene (xerH) and its cognate dif site (difH). Here we show that recombination between directly repeated difH sites requires XerH, FtsK but not XerT, the TnPZ transposon associated recombinase. xerH inactivation was not lethal, but resulted in increased DNA per cell, suggesting defective chromosome segregation. The xerH mutant also failed to colonize mice, and was more susceptible to UV and ciprofloxacin, which induce DNA breakage, and thereby recombination and chromosome dimer formation. xerH inactivation and overexpression each led to a DNA segregation defect, suggesting a role for Xer recombination in regulation of replication. In addition to chromosome dimer resolution and based on the absence of genes for topoisomerase IV (parC, parE) in H. pylori, we speculate that XerH may contribute to chromosome decatenation, although possible involvement of H. pylori’s DNA gyrase and topoisomerase III homologue are also considered. Further analyses of this system should contribute to general understanding of and possibly therapy development for H. pylori, which causes peptic ulcers and gastric cancer; for the closely related, diarrheagenic Campylobacter species; and for unrelated slow growing pathogens that lack topoisomerase IV, such as Mycobacterium tuberculosis. Citation: Debowski AW, Carnoy C, Verbrugghe P, Nilsson H-O, Gauntlett JC, et al. (2012) Xer Recombinase and Genome Integrity in Helicobacter pylori, a Pathogen without Topoisomerase IV. PLoS ONE 7(4): e33310. doi:10.1371/journal.pone. 0033310 Editor: Niyaz Ahmed, University of Hyderabad, India Received December 15, 2011; Accepted February 7, 2012; Published April 12, 2012 Copyright: 2012 Debowski et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: The study was supported by Ondek Pty Ltd, by research grants to DEB from the US National Institutes of Health R21 AI078237, R21 AI088337 and by a PhD scholarship from NSERC (Natural Sciences and Engineering Research Council of Canada) and the Australian Government to AWD and by a grant to MB from the University of Western Australia Research Grants Scheme RA/1/485/802. HN, JCG, AF, TC, BJM and MB are Employees of Ondek Pty Ltd and participated in the study design, data collection and analysis, and preparation of the manuscript. The other funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscripts. Competing Interests: The authors have read the journal’s policy and have the following conflicts: Hans-Olof Nilsson, Jonathan C. Gauntlett, Alma Fulurija, Tania Camilleri, Barry J. Marshall and Mohammed Benghezal are Employees of Ondek Pty Ltd and participated in the study design, data collection and analysis, and preparation of the manuscript. This does not alter the authors’ adherence to all the PLoS ONE policies on sharing data and materials. * E-mail: mbenghezal@ondek.com