Molecular archaeology of theEscherichia coligenome

Abstract

The availability of the complete sequence ofEscherichia colistrain MG1655 provides the first opportunity to assess the overall impact of horizontal genetic transfer on the evolution of bacterial genomes. We found that 755 of 4,288 ORFs (547.8 kb) have been introduced into theE. coligenome in at least 234 lateral transfer events since this species diverged from theSalmonellalineage 100 million years (Myr) ago. The average age of introduced genes was 14.4 Myr, yielding a rate of transfer 16 kb/Myr/lineage since divergence. Although most of the acquired genes subsequently were deleted, the sequences that have persisted (≈18% of the current chromosome) have conferred properties permittingE. colito explore otherwise unreachable ecological niches.