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Characterization of Helicobacter pylori factors that control transformation frequency and integration length during inter-strain DNA recombination.

ABSTRACT: Helicobacter pylori is a genetically diverse bacterial species, owing in part to its natural competence for DNA uptake that facilitates recombination between strains. Inter-strain DNA recombination occurs during human infection and the H. pylori genome is in linkage equilibrium worldwide. Despite this high propensity for DNA exchange, little is known about the factors that limit the extent of recombination during natural transformation. Here, we identify restriction-modification (R-M) systems as a barrier to transformation with homeologous DNA and find that R-M systems and several components of the recombination machinery control integration length. Type II R-M systems, the nuclease nucT and resolvase ruvC reduced integration length whereas the helicase recG increased it. In addition, we characterized a new factor that promotes natural transformation in H. pylori, dprB. Although free recombination has been widely observed in H. pylori, our study suggests that this bacterium uses multiple systems to limit inter-strain recombination.

SUBMITTER: Humbert O

PROVIDER: S-EPMC3075595 | biostudies-literature | 2011 Jan

REPOSITORIES: biostudies-literature

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Characterization of Helicobacter pylori factors that control transformation frequency and integration length during inter-strain DNA recombination.

Humbert Olivier O Dorer Marion S MS Salama Nina R NR

Molecular microbiology 20101123 2

Helicobacter pylori is a genetically diverse bacterial species, owing in part to its natural competence for DNA uptake that facilitates recombination between strains. Inter-strain DNA recombination occurs during human infection and the H. pylori genome is in linkage equilibrium worldwide. Despite this high propensity for DNA exchange, little is known about the factors that limit the extent of recombination during natural transformation. Here, we identify restriction-modification (R-M) systems as ...[more]

PMID: 21219459

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Project description:Dear Sir or Madam, we report an in-depth proteogenomics study of Helicobacter pylori strain 26695 and provide the supporting MS data via ProteomExchange. The study includes 2 biological replicates with 6 different datasets: G1: in-gel digestion with trypsin, replicate 1 G2: in-gel digestion with trypsin, replicate 2 T1: SEC fractionation of low molecular weight (LMW) proteins and subsequent trypsin digestion, replicate 1 T2: SEC fractionation of LMW proteins and subsequent trypsin digestion, replicate 2 A1: SEC fractionation of LMW proteins and subsequent AspN digestion, replicate 1 A2: SEC fractionation of LMW proteins and subsequent AspN digestion, replicate 2 L1: SEC fractionation of LMW proteins and subsequent LysC digestion, replicate 1 L2: SEC fractionation of LMW proteins and subsequent LysC digestion, replicate 2 In our proteogenomics approach, we could identify four previously missing protein annotations and were able to correct sequences of six protein coding regions. Furthermore we identified signal peptidase cleavage sites for 72 different proteins. MGFs were generated by Maxquant 1.1 [1] using recalibration of peptide parent masses. For PRIDE (http://www.ebi.ac.uk/pride) submission, we made an additional database search with Mascot and X!Tandem using the SearchGUI [2]. Therefore we searched against a NCBI database of H. pylori strain 26695 complemented with the sequence corrections, signal peptide cleavage sites and missing annotations with the same configurations as described in materials and methods. For pride xml export we used the software PeptideShaker (http://code.google.com/p/peptide-shaker/). The complemented database has entries which will be submitted to the UniProtKB via SPIN. The entries have the according SPIN number as accession number. The NCBI accession numbers for the shortened sequences due to signal peptide cleavage are extended with “_1”. The fasta database is added to the submission. For additional information, please contact me: stephan.mueller@ufz.de Yours sincerely, Stephan Mueller References: [1] Cox J, Neuhauser N, Michalski A, Scheltema RA, Olsen JV, Mann M. Andromeda: a peptide search engine integrated into the MaxQuant environment. Journal of proteome research. 2011;10:1794-805. [2] Vaudel M, Barsnes H, Berven FS, Sickmann A, Martens L. SearchGUI: An open-source graphical user interface for simultaneous OMSSA and X!Tandem searches. Proteomics. 2011;11:996-9.

Project description:BackgroundHelicobacter pylori is a human stomach pathogen, naturally-competent for DNA uptake, and prone to homologous recombination. Extensive homoplasy (i.e., phylogenetically-unlinked identical variations) observed in H. pylori genes is considered a hallmark of such recombination. However, H. pylori also exhibits a high mutation rate. The relative adaptive role of homologous recombination and mutation in species diversity is a highly-debated issue in biology. Recombination results in homoplasy. While convergent mutation can also account for homoplasy, its contribution is thought to be minor. We demonstrate here that, contrary to dogma, convergent mutation is a key contributor to Helicobacter pylori homoplasy, potentially driven by adaptive evolution of proteins.ResultsOur present genome-wide analysis shows that homoplastic nonsynonymous (amino acid replacement) changes are not typically accompanied by homoplastic synonymous (silent) variations. Moreover, the majority of the codon positions with homoplastic nonsynonymous changes also contain different (i.e. non-homoplastic) nonsynonymous changes arising from mutation only. This indicates that, to a considerable extent, nonsynonymous homoplasy is due to convergent mutations. High mutation rate or limited availability of evolvable sites cannot explain this excessive convergence, as suggested by our simulation studies. Rather, the genes with convergent mutations are overrepresented in distinct functional categories, suggesting possible selective responses to conditions such as distinct micro-niches in single hosts, and to differences in host genotype, physiology, habitat and diet.ConclusionsWe propose that mutational convergence is a key player in H. pylori's adaptation and extraordinary persistence in human hosts. High frequency of mutational convergence could be due to saturation of evolvable sites capable of responding to selection pressures, while the number of mutable residues is far from saturation. We anticipate a similar scenario of mutational vs. recombinational genome dynamics or plasticity for other naturally competent microbes where strong positive selection could favor frequent convergent mutations in adaptive protein evolution.

Dataset Information

Characterization of Helicobacter pylori factors that control transformation frequency and integration length during inter-strain DNA recombination.

Publications

Characterization of Helicobacter pylori factors that control transformation frequency and integration length during inter-strain DNA recombination.

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