Related Experiment Videos
Characterization of two cryptic Helicobacter pylori plasmids: a putative source for horizontal gene transfer and gene
1Max von Pettenkofer Institut für Hygiene und Medizinische Mikrobiologie, Ludwig-Maximilians Universität München, Petterkoferstrasse 9A, D-80336 Munich, Germany.
Abstract:
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.
Insights
This study analyzes two Helicobacter pylori plasmids, pHel4 and pHel5, revealing their theta plasmid nature and potential mobilizability. Repeat sequences on these plasmids likely drive genetic exchange and H. pylori population diversity.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Helicobacter pylori cryptic plasmids exhibit significant size variability.
- Understanding plasmid structure and function is crucial for deciphering H. pylori genetic diversity.
Purpose of the Study:
- To analyze the genetic makeup and structural features of two H. pylori plasmids, pHel4 and pHel5.
- To investigate the potential mechanisms contributing to the high genetic variability within H. pylori populations.
Main Methods:
- Sequence analysis of H. pylori plasmids pHel4 (10,970 bp, 15 ORFs) and pHel5 (18,291 bp, 17 ORFs).
- Identification of putative open reading frames (ORFs) and conserved proteins, including RepA.
- Analysis of replication origins, repeat sequences (R2, R4), and homologous gene products.
Main Results:
- Both plasmids possess theta plasmid characteristics, including a conserved RepA protein and an iteron-containing origin of replication.
- pHel4 shows homology to mobilizable colicinogenic plasmids and genes involved in microcin C7 biosynthesis and secretion.
- pHel5 contains genes homologous to an endonuclease and H. pylori chromosomal plasticity zone elements; both plasmids have repeat sequences (R2, R4) acting as recombination sites.
Conclusions:
- H. pylori plasmids possess a modular structure, with genetic elements likely inserted/deleted at repeat sequences.
- The identified features suggest pHel4 is mobilizable and pHel5 interacts with chromosomal elements.
- Genetic exchange between plasmids and the chromosome, coupled with plasmid mobilization, contributes to H. pylori macrodiversity.