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A Fork Trap in the Chromosomal Termination Area Is Highly Conserved across All Escherichia coli Phylogenetic Groups.

ABSTRACT: Termination of DNA replication, the final stage of genome duplication, is surprisingly complex, and failures to bring DNA synthesis to an accurate conclusion can impact genome stability and cell viability. In Escherichia coli, termination takes place in a specialised termination area opposite the origin. A 'replication fork trap' is formed by unidirectional fork barriers via the binding of Tus protein to genomic ter sites. Such a fork trap system is found in some bacterial species, but it appears not to be a general feature of bacterial chromosomes. The biochemical properties of fork trap systems have been extensively characterised, but little is known about their precise physiological roles. In this study, we compare locations and distributions of ter terminator sites in E. coli genomes across all phylogenetic groups, including Shigella. Our analysis shows that all ter sites are highly conserved in E. coli, with slightly more variability in the Shigella genomes. Our sequence analysis of ter sites and Tus proteins shows that the fork trap is likely to be active in all strains investigated. In addition, our analysis shows that the dif chromosome dimer resolution site is consistently located between the innermost ter sites, even if rearrangements have changed the location of the innermost termination area. Our data further support the idea that the replication fork trap has an important physiological role that provides an evolutionary advantage.

SUBMITTER: Goodall DJ

PROVIDER: S-EPMC8347550 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The characterization of population structures plays a main role for understanding outbreaks and the dynamics of bacterial spreading. In Escherichia coli, the widely used combination of multiplex-PCR scheme together with goeBURST has some limitations. The purpose of this study is to show that the combination of different phylogenetic approaches based on concatenated sequences of MLST genes results in a more precise assignment of E. coli phylogenetic groups, complete understanding of population structure and reconstruction of ancestral clones. A collection of 80 Escherichia coli strains of different origins was analyzed following the Clermont and Doumith's multiplex-PCR schemes. Doumith's multiplex-PCR showed only 1.7% of misassignment, whereas Clermont's-2000 protocol reached 14.0%, although the discrepancies reached 30% and 38.7% respectively when recombinant C, F and E phylogroups were considered. Therefore, correct phylogroup attribution is highly variable and depends on the clonal composition of the sample. As far as population structure of these E. coli strains, including 48 E. coli genomes from GenBank, goeBURST provides a quite dispersed population structure; whereas NeighborNet approach reveals a complex population structure. MLST-based eBURST can infer different founder genotypes, for instance ST23/ST88 could be detected as the founder genotypes for STC23; however, phylogenetic reconstructions might suggest ST410 as the ancestor clone and several evolutionary trajectories with different founders. To improve our routine understanding of E. coli molecular epidemiology, we propose a strategy based on three successive steps; first, to discriminate three main groups A/B1/C, D/F/E and B2 following Doumith's protocol; second, visualization of population structure based on MLST genes according to goeBURST, using NeighborNet to establish more complex relationships among STs; and third, to perform, a cost-free characterization of evolutionary trajectories in variants emerging along the clonal expansion using parsimony methods of phylogenetic analysis.

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A Fork Trap in the Chromosomal Termination Area Is Highly Conserved across All Escherichia coli Phylogenetic Groups.

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