The evolution of the pan-genome of Shiga-toxin (Stx) producing Escherichia coli and the Stx2 bacteriophage.

摘要

Human infections with Shiga-toxin (Stx)-producing E. coli (STEC) vary in severity of illness. The pan-genome of a bacterial species contains a shared, essential core genome, and a variably distributed accessory genome. While single nucleotide changes likely influence virulence in STEC, horizontal gene transfer (HGT) on elements such as bacteriophage are thought to be most important. My thesis objectives were to: 1) develop tools for the pangenomic analyses of bacterial genomes; 2) describe the phylogeny of STEC and; 3) determine if the evolution of the Stx2-bacteriophage parallels that of its bacterial host. For this thesis, the software program Panseq was created and used to identify pan-genomic differences among STEC. Whole-genome phylogenies showed all serotypes as discrete clusters, with 0157:H7 having three distinct lineages and grouping separately from all other STEC. Finally, the phylogenies of Stx2-bacteriophage and their bacterial hosts were largely concordant, with occasional instances of HGT having led to novel pathogen emergence.