Phylogeographic evidence of cognate recognition site patterns and transformation efficiency differences in H. pylori: theory of strain dominanceReport as inadecuate




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BMC Microbiology

, 13:211

Ecological and evolutionary microbiology

Abstract

BackgroundHelicobacter pylori has diverged in parallel to its human host, leading to distinct phylogeographic populations. Recent evidence suggests that in the current human mixing in Latin America, European H. pylori hpEurope are increasingly dominant at the expense of Amerindian haplotypes hspAmerind. This phenomenon might occur via DNA recombination, modulated by restriction-modification systems RMS, in which differences in cognate recognition sites CRS and in active methylases will determine direction and frequency of gene flow. We hypothesized that genomes from hspAmerind strains that evolved from a small founder population have lost CRS for RMS and active methylases, promoting hpEurope’s DNA invasion. We determined the observed and expected frequencies of CRS for RMS in DNA from 7 H. pylori whole genomes and 110 multilocus sequences. We also measured the number of active methylases by resistance to in vitro digestion by 16 restriction enzymes of genomic DNA from 9 hpEurope and 9 hspAmerind strains, and determined the direction of DNA uptake in co-culture experiments of hspAmerind and hpEurope strains.

ResultsMost of the CRS were underrepresented with consistency between whole genomes and multilocus sequences. Although neither the frequency of CRS nor the number of active methylases differ among the bacterial populations average 8.6 ± 2.6, hspAmerind strains had a restriction profile distinct from that in hpEurope strains, with 15 recognition sites accounting for the differences. Amerindians strains also exhibited higher transformation rates than European strains, and were more susceptible to be subverted by larger DNA hpEurope-fragments than vice versa.

ConclusionsThe geographical variation in the pattern of CRS provides evidence for ancestral differences in RMS representation and function, and the transformation findings support the hypothesis of Europeanization of the Amerindian strains in Latin America via DNA recombination.

KeywordsH. pylori Haplotypes Restriction-Modification system Recombination Electronic supplementary materialThe online version of this article doi:10.1186-1471-2180-13-211 contains supplementary material, which is available to authorized users.

Shrinivasrao P Mane, Xue-Song Zhang contributed equally to this work.

An erratum to this article is available at http:-dx.doi.org-10.1186-1471-2180-14-122.

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