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Journal of Bacteriology, May 2002, p. 2755-2766, Vol. 184, No. 10
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.10.2755-2766.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Characterization of Two Cryptic Helicobacter pylori Plasmids: a Putative Source for Horizontal Gene Transfer and Gene Shuffling

Dirk Hofreuter,{dagger} and Rainer Haas*

Max von Pettenkofer Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians Universität München, D-80336 Munich, Germany

Received 29 November 2001/ Accepted 20 February 2002

Many Helicobacter pylori isolates carry cryptic plasmids of extremely variable size. In this study we analyzed two H. pylori plasmids, pHel4 and pHel5, from H. pylori strains P8 and P29, respectively. Plasmid pHel4 consists of 10,970 bp, constituting 15 putative open reading frames (ORFs), whereas pHel5 consists of 18,291 bp, constituting 17 ORFs. The findings that both plasmids encode a conserved RepA protein and that both have an origin of replication containing an iteron place them in the group of theta plasmids. In pHel4, the products of the overlapping orf4C, orf4D, orf4E, and orf4F sequences are homologous to MobA, MobB, MobC, and MobD, encoded by colicinogenic plasmids, suggesting that pHel4 might be mobilizable. A further putative operon consists of orf4B and orf4A, the products of which are homologous to microcin C7 (MccC7) biosynthesis and secretion proteins MccB and MccC, respectively. Plasmid pHel5 carries putative genes encoding proteins with homology to an endonuclease and gene products of an H. pylori chromosomal plasticity zone. Both plasmids contain repeat sequences, such as the previously identified R2 repeat, which are considered preferred recombination sites. In pHel4, a new repeat sequence (R4 repeat), which seems to act as a hot spot for site-specific recombination, was identified. All H. pylori plasmids characterized so far have a modular structure. We suggest a model that explains the existing plasmids by insertions and deletions of genetic elements at the repeat sequences. A genetic exchange between plasmids and the bacterial chromosome, combined with plasmid mobilization, might add a novel mechanism to explain the high genetic macrodiversity within the H. pylori population.

* Corresponding author. Mailing address: Max von Pettenkofer Institut, LMU Munich, Pettenkoferstr. 9A, D-80336 Munich, Germany. Phone: (0049)-89-5160 5255. Fax: (0049)-89-5160 5223. E-mail: haas{at}m3401.mpk.med.uni-muenchen.de.

{dagger} Present address: Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, CT 06536-0812.

Journal of Bacteriology, May 2002, p. 2755-2766, Vol. 184, No. 10
0021-9193/02/$04.00+0     DOI: 10.1128/JB.184.10.2755-2766.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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